gas kick simulation study for horizontal wells

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IADC/SPE 27498 Gas Kick Simulation Study for Horizontal Wells Zhihua Wang, J.M. Peden, and R.Z. Lemanczyk, Heriot-Watt U. SPE Members Copyright 1994, IADC/SPE Drilling Conference, This paper was prepared for presentation at the 1994 IADC/SPE Drilling Conference held in Dallas, Texas, 15-18 February 1994. This paper was selected for presentation by an IADC/SPE Program Committee following review of informati?n contai.ned in an abstract submitted by the author(s). Contents of the as presented have not been reviewed by the Society of Petroleum Engineers or the International ASSOCIation of Drilling Contractors and are subject to correction by ,he material, as presented, does not necessarily reflect any position of the IADC or SPE, their officers, or members. Papers presented at IADC/SPE meetings are subject to pu Icatlon review by Editorial Committees of the IADC and SPE. Permission to copy is restricted to an abstract of not more than 300 words. lUustratlons may not contain conspicuous acknowledgment of where and by whom the paper Is presented. Write Libra"an, SPE, P.O. Box 833836, Richardson, TX 75083-3836, ... e ex, . ABSTRACT Ibis paper presents a gas kick simulation model for horizontal and conventional wells. The model is based on the solution of the appropriate mass and pressure balance equations. The unique aspect of this model is the coupling of the fluid flow in the horizontal section with the gas influx from the formation. Two particular kick control scenarios are presented. The simulation results demonstrate that the actual horizontal drilling situation. actions taken immediately upon kick detection, and operations during kick development, all have an effect on the development of the kick profile along the wellbore. which in turn has significant impact on the pressure build-up during the shut-in period and the subsequent kick circulation operations. INTRODUCTION During the past several years. horizontal wells have found increasing applications to address a wide variety of technical challenges in improving hydrocarbon production. as well as providing a new technique for developing reservoirs which would otherwise not be economical to attempt with conventional wells. Evidence of this is demonstrated by the increase in the number of horizontal wells drilled world-wide and the increased volume of literature published in the area of horizontal well technology. Parallel to the increase in horizontal well activity. many aspects of horizontal well technology have become the subject of thorough research and investigation. However the aspect of well control has only recently begun to attract a high level of research interest. References and figures at end of paper Loss of well control during drilling operations constitutes one of the major hazards faced by rig personnel. and can lead to loss of life and major destruction of a drilling installation. Extensive studies have been conducted to address this safety concern and to improve the understanding of the kick development and control mechanisms for conventional or non-horizontal wells. These studies include full scale experlments(l). development of computer kick simulation models(2-6). and the related physics. e.g. gas rise velocity(7- 9). However. published studies on kick control in horizontal wells so far have been relatively few(lo-13). Ibis may be due to the fact that up until now. most horizontal wells have been drilled for development rather than for exploration reasons. Well control in these situations where reservoir behaviour is well characterised might not be regarded as a critical problem. Nevertheless as horizontal well technology becomes increasingly mature. the instances where it may be employed in exploration and appraisal drilling are also increasing. Well control will then become a critical issue in the execution of a horizontal well programme. well control could conceivably become a constraint in extending horizontal well applications. Santos(lO,ll) has performed computer simulation studies of the kick displacement in a horizontal well. He assumes that the horizontal section is true 90° and the entire kick volume remains in the horizontal section and is distributed as a uniform gas-mud mixture extending from the drill bit back to a point in the annulus defIned by the pit gain and gas void fraction (user-specified) and the .annular capacity defIned by the well geometry. From his simulation studies. he argues that for horizontal wells. shut-in drill pipe pressure (SIOPP) and shut-in casing pressure (SICP) are roughly equal. The 625

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Page 1: Gas Kick Simulation Study for Horizontal Wells

IADC/SPE 27498

Gas Kick Simulation Study for Horizontal WellsZhihua Wang, J.M. Peden, and R.Z. Lemanczyk, Heriot-Watt U.

SPE Members

Copyright 1994, IADC/SPE Drilling Conference,

This paper was prepared for presentation at the 1994 IADC/SPE Drilling Conference held in Dallas, Texas, 15-18 February 1994.

This paper was selected for presentation by an IADC/SPE Program Committee following review of informati?n contai.ned in an abstract submitted by the author(s). Contents of the pa~r,as presented have not been reviewed by the Society of Petroleum Engineers or the International ASSOCIation of Drilling Contractors and are subject to correction by ~he autho~~). ,hematerial, as presented, does not necessarily reflect any position of the IADC or SPE, their officers, or members. Papers presented at IADC/SPE meetings are subject to pu Icatlonreview by Editorial Committees of the IADC and SPE. Permission to copy is restricted to an abstract of not more than 300 words. lUustratlons may not b~c~~e~. ~he 1a:;~~"t~~';,"~~contain conspicuous acknowledgment of where and by whom the paper Is presented. Write Libra"an, SPE, P.O. Box 833836, Richardson, TX 75083-3836, . . . e ex, .

ABSTRACT

Ibis paper presents a gas kick simulation model forhorizontal and conventional wells. The model is based on thesolution of the appropriate mass and pressure balanceequations. The unique aspect of this model is the coupling ofthe fluid flow in the horizontal section with the gas influxfrom the formation. Two particular kick control scenarios arepresented. The simulation results demonstrate that the actualhorizontal drilling situation. actions taken immediately uponkick detection, and operations during kick development, allhave an effect on the development of the kick profile alongthe wellbore. which in turn has significant impact on thepressure build-up during the shut-in period and thesubsequent kick circulation operations.

INTRODUCTION

During the past several years. horizontal wells have foundincreasing applications to address a wide variety of technicalchallenges in improving hydrocarbon production. as well asproviding a new technique for developing reservoirs whichwould otherwise not be economical to attempt withconventional wells. Evidence of this is demonstrated by theincrease in the number of horizontal wells drilled world-wideand the increased volume of literature published in the areaof horizontal well technology. Parallel to the increase inhorizontal well activity. many aspects of horizontal welltechnology have become the subject of thorough research andinvestigation. However the aspect of well control has onlyrecently begun to attract a high level of research interest.

References and figures at end of paper

Loss of well control during drilling operations constitutes oneof the major hazards faced by rig personnel. and can lead toloss of life and major destruction of a drilling installation.Extensive studies have been conducted to address this safetyconcern and to improve the understanding of the kickdevelopment and control mechanisms for conventional ornon-horizontal wells. These studies include full scaleexperlments(l). development of computer kick simulationmodels(2-6). and the related physics. e.g. gas rise velocity(7­9).

However. published studies on kick control in horizontalwells so far have been relatively few(lo-13). Ibis may bedue to the fact that up until now. most horizontal wells havebeen drilled for development rather than for explorationreasons. Well control in these situations where reservoirbehaviour is well characterised might not be regarded as acritical problem. Nevertheless as horizontal well technologybecomes increasingly mature. the instances where it may beemployed in exploration and appraisal drilling are alsoincreasing. Well control will then become a critical issue inthe execution of a horizontal well programme. Furtherm.~.

well control could conceivably become a constraint inextending horizontal well applications.

Santos(lO,ll) has performed computer simulation studies ofthe kick displacement in a horizontal well. He assumes thatthe horizontal section is true 90° and the entire kick volumeremains in the horizontal section and is distributed as auniform gas-mud mixture extending from the drill bit back toa point in the annulus defIned by the pit gain and gas voidfraction (user-specified) and the .annular capacity defIned bythe well geometry. From his simulation studies. he arguesthat for horizontal wells. shut-in drill pipe pressure (SIOPP)and shut-in casing pressure (SICP) are roughly equal. The

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Page 2: Gas Kick Simulation Study for Horizontal Wells

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IADC/SPE 27498

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Horizontal Well Representation. In this study, thehorizontal well in the simulation model is represented by abasic profile (Fig 1). It consists of a vertical section fromsurface to the kick off point (KOP), a single build curve (truecircular arc) from vertical to a specified angle and a straightsection.

Gas Bearing Formation. Two types of reservoir areconsidered in this paper. One is a heterogeneous (i.e.compartmentalised) reservoir and the other is a flathomogeneous reservoir. Accordingly, two kick controlscenarios have been studied. The first is the case of ahorizontal well being drilled into a compartmentalisedreservoir where gas influx occurs at the bit when a highpressure zone is encountered (Fig 2). The second (Fig 3) isthat of a horizontal section drilled along a homogeneousreservoir where minor changes in drilling conditions (e.g.circulation rate) may provoke gas influx. In this case, gasinflux can enter the wellbore both at the bit and at anylocation in the wellbore exposed to the gas-bearingformation.

Solution Procedure. To solve the set of equations, pressure,mixture velocity, and block masses of gas and liquid areselected as primary variables. The technique adopted in thisstudy is similar to that used by Ekrann and Rommetveit(2).However, modifications are required for its application tohorizontal wells. A typical block in a horizontal well isillustrated in Fig 4. Liquid can only enter and leave the blockat the ends whereas gas may enter the block both at theupstream end and, more importantly, in the radial directionalong the block from the formation, and leaves the block atthe down-stream end of the block. The discretised massbalance equation should include this gas influx term.

IdentifICation of Influx Type. Since most of the kick or theentire kick remains in the horizontal section, the differencebetween SICP and SIDPP is small. This makes it difficult to

The annulus and drillstring may have as many sections ofdifferent cross-sectional area as desired. For simulation, eachmain section of drill string and annulus is divided into gridblocks. The inclination of blocks in the curved section(s) istaken to be the average of those at the two ends. The holeinclination, measured depth, and true vertical depth at thetwo ends of the block are calculated using the appropriateequations.

Eqs. (1) and (2) are the mass balance equations for the mudand gas respectively. Eq. (3) is the pressure balanceequation, and Eq. ,(4) is an empirical correlation relating gasvelocity to the average mixture plus the relative slip velocity.Eqs. (5) and (6) are equations of state for gas and mudrespectively. To solve the system of equations, additionalphysical models are required. These models are discussed inAppendix A.

(3)

(1)

(2)

i.[A(I- A)P,]+~[A(I- A)p,V,] = 0dt dZ

;t[AAP,]+ ;JAAP,V,]=o

~ +(~l +[p,(I-A)+p,A]gcos8 = 0

For water-based mud, gas solubility in the drilling mud maybe neglected. If the temperature gradients in the wellbore areassumed known and constant throughout the transient, sixvariables are required: gas and mud densities, gas and mudvelocities, gas void (volume) fraction, pressure to describethe gas/liquid system completely. The independent variablesare time and position along the wellbore. Six equationsrelating the six· variables are required to obtain a closedsolution. They are given as follows.

FORMULATION OF THE KICKSIMULATION MODEL

In this paper, the development and application of a computersimulation model is presented for horizontal wells whenwater-based mud is used. This model differs from othersimulation models in that it c<>uples the fluid flow along thehorizontal section with the gas influx from the formationduring the kick development and shut-in phases. The modelcan be used to simulate the whole cycle of kick development,determination of formation pressure and identification ofinflux type, and kick displacement Two particular scenariosbased on this model are presented below.

2 Gas Kick Simulation Study in Horizontal Wells

choke pressure in horizontal wells remains constant and at a v, = Co[(l-A)v, +AV,]+V,value close to the SICP for a longer period than it does in avertical well during kick circulation. The effects of ( T)P, =P, p,horizontal section length and angle build rate are small on thepressure behaviour in horizontal wells. However, well controloperations are harder to implement for horizontal wells if theWait-and-Weight method of kick circulation is used becauseof the complex development of drill pipe pressure as afunction of time. In addition, horizontal wells have greatertolerance than vertical wells to take a kick without fracturingthe weakest formation at the moment of well closure.Nevertheless, the kick development and other importantaspects, i.e., determination of formation pressure andidentification of influx type (gas or liquid), have not beenaddressed due to the limitations of the computer simulationmodel developed.

In field situations a horizontal well would actually be aslightly inclined hole either upwards or downwards, slightlyundulating in some cases. In these cases, the buoyancy of thegas may cause it to become trapped in certain parts of thehorizontal well. Aas et al(12) recently conducted laboratoryscale experiments to simulate the circulation out of a gas kickin such cases. In particular, the experiments were designedfor simulating the process of removing a gas pocket for threetypes of gas traps, namely, upward inclined end-of-wellsections, high lying parts of an undulating well trajectory,and washouts.

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IADC/SPE 27498 Wang. Z.• Peden. J. M.• Lemanczyk. Z. R. 3

identify the influx type (gas or liquid) by the conventionaltechnique which relies on this pressure difference todetermine the influx density and hence the influx type. Forthis study. a recently. published Rressure analysis techniquedescribed by Billingham et az(l ) and Jardine et az(l5) isimplemented for the identification of influx type in horizontalwells.

SIMULAnON RESULTS

The above described kick simulation model for horizontalwells and the pressure analysis technique have beenprogrammed in FORTRAN.. Some typical simulation resultsare presented in this section. The data used in thesecalculations for horizontal wells is listed in Tables 1 and 2.To enable comparison with conventional wells. one verticalwell having the same TVD of 7000 ft at bottomhole. has beenconsidered. The casing shoe is set at 4000 ft. The other datarequired is the same as that used in horizontal wells.

Scenario 1 - Application to ComparlmenklUsed Reservoir

We fIrst discuss the scenario of a horizontal well beingdrilled into a compartmentalised reservoir where a highpressure "zone" is encountered (Fig 2). This scenario isreferred to as Scenario 1 and for illustrative purposes. thereference horizontal well will be the medium radius well.

In the following discussions. we frrst compare the typicalkick behaviours between the vertical and horizontal wells.We then examine the effects of the horizontal well types, thegas rise velocity. and the non-horizontal lateral sections.

Typical Kick Behaviour

To present a typical kick behaviour in a horizontal well, wedivide the whole cycle into three stages. (1) kickdevelopment or taking a kick. (2) closing in the well forpressure to build up. and (3) kill of the kick or kickdisplacement Responses from the surface observableparameters are compared between the horizontal and verticalwells. It is assumed that the horizontal and vertical wells aredrilled to a reservoir at the same TVD. which will lead todifferent frictional pressure losses while the well is flowingeither during drilling or kick control due to the differentmeasured depths of the two wells. In the followingexamples. the friction pressure loss at 400 gal/min in thehorizontal well is about 18 psi higher than that in the verticalwell. This difference depends upon many parameters: thewell geometry, depth. mud properties and flow rate, forexample.

The sequence of events leading to the shut-in of the well arethe same for the horizontal and the vertical wells: drillinginto the high pressure reservoir. taking a (drilled) kick until itis detected at 10 bbl of pit gain. stopping both drilling andcirculation for 12 seconds. and closing in the well forpressure to build up. Kick displacement commences once thebottomhole pressure has built up to the formation pressure. Astatic pressure underbalance of 300 psi is assumed for the

typical kick behaviour unless otherwise specifIed. The gasrise velocity model is the Air-Water model (see Appendix A).

Kick detection - Delta flow. It is well established that thedelta flow (flow-out Dlinus flow-in at surface) is the mostsensitive kick detection parameter in conventional wells inmost cases. This is also observed here for the horizontal wellin question. Fig 5 shows the delta flow responses for thehorizontal and the vertical wells during the kick developmentstage at two different initial pressure underbalances. Onecase is assumed to have an equal static underbalance of 300psi and the other to have an initially equal dynamicunderbalance of 50 psi. The corresponding pit gain responsesare shown in Fig 6. For a threshold of 40 gal/min for thedelta flow and 10 bbl for the pit gain, the kicks in both casescan be detected much earlier using the delta flow criteria.

It is interesting to note the different delta flow responses forthe horizontal and vertical wells. The delta flow increases ata decreasing rate in the case of horizontal well whereas itincreases almost linearly in the case of vertical well. Thepresence of gas influx in the vertical section and the gasexpansion. even if small. increase the pressure underbalance.hence causing the delta flow in the vertical well to increasealmost linearly with time. Le.• bit penetration. On the otherhand. in the horizontal well. the influx remains in thehorizontal section. the bottomhole pressure increases slightlycaused by higher friction pressure drop due to gas influx.However. as the gas influx is circulated into the build sectionduring the later stage. the delta flow starts to increase at anincreasing rate as illustrated by the case of APd = 50 psi (Fig5).

It can be observed that delta flow in horizontal wells remainsthe most sensitive conventional kick detection parameter.However. it may not necessarily be as sensitive as in verticalwells (compare APd = 50 psi in Fig 5) and in some horizontalwell cases (long horizontal section. small pressureunderbalance) it may fail to detect the kick completely.whereas it could detect a kick under similar conditions in thevertical well. Pit gain therefore remains a more robustbackup means for kick detection.

Effect of gas migration, SICP versus SIDPP. Upon kickdetection. the well is shut-in to allow pressure stabilisation.Pressure increases during the shut in period due to twofactors: continuing influx from the formation and gasmigration up the wellbore. Gas migration is a concern inconventional wells if extended shut-in is required. Fig 7shows the SICP for the vertical and the horizontal wells.Two obvious features are observed immediately: Firstly. thegas migration effect is clearly seen in the vertical wellwhereas it is practically not observed in the horizontal wellbecause the majority of influx remains in the horizontalsection. Secondly. the "stabilised" SICP in the horizontalwell is lower than that in the vertical well due to the lessergas presence in the verticallbuild section.

The above two observations are advantageous in horizontalwells with respect to kick control since the well can sustain a

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4 Gas Kick Simulation Study in Horizontal Wells IADC/SPE 27498

larger volume kick and can be shut in longer if necessarywithout fear of fracturing the weakest zone as a result of gasmigration. In other words. a horizontal well can have largerkick tolerance at the initial moment of well closure.However. this does not imply that the larger kick can becirculated out without endangering the well and surfaceequipment as in conventional wells.

Determination of influx type and formation pressure.Traditionally. the influx type has been estimated bycalculating its density from the difference between thestabilised SICP and SIDPP. The formation pressure iscalculated from the stabilised SIDPP. Fig 8 shows the shut-incasing and drillpipe pressure responses for the horizontalwell. It is clearly seen that the difference between SICP andSIDPP is very small. Indeed. the difference is only about 18psi at a pit gain of about 12 bbl compared with 139 psi in thevertical well. Such a small difference may be completelymasked by the pressure gauge resolution. However. thedetermination of formation pressure is easier in the horizontalwell since the stabilised SIDPP can be readily obtained.

For estimating the influx type. a new technique(l4.15) isimplemented in this study. As shown in Fig 8. a curve fit ofEq. 3 in reference 14 to the drillpipe pressure is obtained andplotted in the figure. From the curve fit. Cs2 is 0.1482 s-l.The formation producibility. F. is estimated by taking thedelta flow and pressure underbalance just before shut-in as0.03572 (bbl/min)/psi. The volume of mud in the well is 506bbl and the mud compressibility is 2xlO-6 psi-I. The pit gainat shut-in is 11.87 bbl. The compressibility of influx is thencalculated as: 2.532xlO-4 pst1. This is at least an order ofmagnitude higher than that of oil. The actual gascompressibility at bottomhole pressure and temperature is 1.8xlO-4 psi-I. The estimated time when formation ceases to

flow is 348 s compared with the actual time of 354 s from theinitial penetration of the formation.

Kick displacement. Kick displacement is an important andcritical part of kick control. Santos(lO·ll) has studied thekick displacement in a horizontal well. Although herecognised the complexity of implementing the' Wait-and­Weight method due to the resulting complex drillpipepressure schedule. the effect of Wait-and-Weight method onthe choke pressure has not been discussed. In addition. theassumptions that the kick is a uniform gas/mud mixture andthat it remains in the horizontal section at the moment of wellclosure may not be valid in many cases (this will beaddressed below). In this section. the choke pressureresponses from the vertical well and the medium radius wellare briefly discussed and the effect of the Wait-and-Weightmethod on choke pressure is also examined.

Fig 9 shows the choke pressure during kick displacement forthe vertical well using the Driller's method and chokepressures for the horizontal well using both Driller's methodand Wait-and-Weight method. First. we compare the chokepressure responses from the vertical and horizontal wellsusing the Driller's method. The choke pressure for thevertical well shows a typical behaviour where pressureincreases slightly initially lID.d then at an increasing rate as

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the gas/mud mixture is displaced further up the hole withconcurrent gas expansion. However. for the horizontal well.the choke pressure starts to increase more rapidly ascirculation begins because of the added effect of reduction inthe hydrostatic pressure as the gas/mud mixture is displacedfrom the horizontal section into the build section. Thisobservation is different from what Santos(l0,11) has obtainedsince in our case. some of the gas influx has been allowed toenter the build section during the actual kick developmentstage. This also reveals that a realistic assumption of theinitial kick profile is important in deriving the more realistickick behaviour from either computer simulation orexperimental studies. When the entire volume of mixture hasentered the vertical section. a behaviour similar to that in avertical well is observed.

Also shown in Fig 9 is the comparison between the Driller'sand Wait-and-Weight circulation m,ethods for the horizontalwell. At t = 34.1 min from start of kick displacement, killmud arrives at the bit and its effect on the choke pressure ispractically not felt until it reaches the target in the annulus att = 46.0 min. Even when its effect is observed. the reductionin the choke pressure compared with that in a conveentionalwell occurs at a much slower rate since this reduction is alinear function of vertical elevation gained by the kill mud.which for a given volume pumped will have moved higher inthe vertical well annulus than in that for the horizontal well.For the horizontal well. this gain in vertical elevation isstrongly affected by the build rate of the build section. Thiscan be illustrated by a simple calculation.

Assuming that the build curve of a horizontal well is a singlecircular arc and the density difference is 1 ppg. thehydrostatic pressure difference caused by a 500 ft MD of killmud would be 26 psi in a vertical well. 10.6 psi for a 10°/100ft build curve. and only 2.25 psi for a 2.5°/100 ft build curve.In other words. to achieve 26 psi pressure difference or 500 ftvertical elevation gain. the required measured depth for the10°/100 ft build curve would be 827 ft and 1543 ft for the 2.5°/100 ft build curve in addition to the length of horizontalsection. This suggests that the use of the Wait-and-Weightmethod in the horizontal well would not assist in the pressurereduction compared with the Driller's method in general. andin particular for long- and medium-radius wells with smallangle build rate. Indeed. in this particular case. the effect ofkill mud on the choke pressure is small. and moreimportantly. its effect is only observed when the peak chokepressure has already been experienced.

In summary. the reduction in choke pressure when using theWait-and-Weight method in conventional wells becomesnegligible in the horizontal wells. In addition. it is morecomplicated to practically implement the Wait-and-Weightmethod as shown in the drillpipe pressure schedule illustratedin Fig 10. However. the Driller's method can beimplemented in the same way regardless of the well profIles.

Effect of Horizontal Well Types

A medium radius well was selected above to highlight thesimilarities and differences of a kick taken in the horizontal

Page 5: Gas Kick Simulation Study for Horizontal Wells

The simulation is run using the same well geometry and mudproperties data as the horizontal well in the typical kickbehaviour scenario above. The static underbalance is 300psi. and the sequence of events is the same. The effect on thedelta flow and pit gain responses is not observed until at thelater stage of the kick development when the gas influx hasentered the build section. But the effect is small. Fig 13compares the SICPs during the shut-in stage. The gasmigration effect is clearly observed and the SICP is higher inthe case of the Air-Mud model because more gas influx hasentered the build section due to the larger value of bubbledistribution and velocity coefficient The rate at which theSICP increases due to gas migration is considerably higher inthe case of the Air-Mud model because of the higher gasmigration velocity assumed.

The choke pressure and pit gain responses during the kickdisplacement are shown in Figs 14 and 15. The kickdisplacement using the Driller's method begins once thebottomhole presSure builds up to the formation pressure. Thechoke pressure and pit gain responses for both gas risevelocity models show similar behaviour. The gas reaches thesurface much earlier assuming the Air-Mud model with alower peak choke pressure which may be caused by thephysical dispersion due to higher distribution and velocityproftle coefficient and higher gas slip velocity. The pit gaindemonstrates a similar behaviour to the choke pressure.However. the surface gas flow rate from the well assumingthe Air-Mud model is higher than that assuming the Air­Water model (Fig 16).

In fIeld operations. gas rise velocity is not a parameter thatcan be manipulated for good well control Higher gas risevelocity will normally yield a higher surface flow rate fromthe well. which has implications for sizing mud/gas separatorfacilities. However. the choke pressure and pit gainresponses assuming both models exhibit a similar behaviouralthough their absolute value may be different

Indeed. for the wells shown in Fig 11. the percentage of totalgas influx masses remaining in the horizontal section are46%. 76% and 99% for the short-. medium- and long-radiuswells. respectively although the total gas influx masses areabout the same: 758. 746. and 741 Ibm for the short-.medium- and long-radius wells. respectively. In other words.the kick proftles are different for all three types of well at themoment of well closure.

The kick proftle and the build rate have signifIcant effects onthe choke pressure responses during the kick displacementstage as shown in Fig 12. Compared with the medium radiuswell. the initial choke pressure increase is even more rapid inthe short-radius well because of a more rapid gain in thevertical elevation by the gas/mud mixture. However. in thecase of the long radius well. the choke pressure remainsconstant for some time and then increases at a slower ratecompared with the medium radius well. This choke pressureresponse is mainly due to two effects: (1) at the time of wellshut-in. 99% of the gas influx remains in the horizontalsection, furthermore. about 94% is in the furthest 1500 ft ofthe horizontal section; (2) even when the influx is displacedinto the build section, the small build rate in the long radiuswell only results in slight loss of hydrostatic pressure due tosmall vertical elevation gain.

One common feature is that when the entire mixture entersthe vertical section. the choke pressure behaves in a similarway to what it would in a vertical well. The peak chokepressure is highest in the short radius well and lowest in thelong radius well. This is attributed to the larger frictionalpressure loss encountered in longer wells.

Effect of horizontal well profile. Simulations have alsobeen run assuming a well proftle with two build curves(which can have different build rates) connected by a tangentsection. No significant effects have been observed.

Effect of Gas Rise Velocity

Fig 11 compares the casing pressure during the shut-in periodfor short-. medium- and long-radius wells. It is clear that thehighest SICP is observed in the short radius well whilst thelowest. in the long radius well. In addition, an apparent gasmigration effect is observed in the short radius well. Thismay be attributed to the length and the volume of horizontalsection and to a lesser extent. the build rate. For longerhorizontal sections. most of the gas influx would be expectedto remain in the horizontal section. If there was to be anyinflux in the section(s) beyond the horizontal section. thebuild rate would affect the SICP since it would affect thevertical elevation for a given length of build section.

IADC/SPE 27498 Wang, Z., Peden. J. M.• Lemanczyk. Z. R. 5

and conventional wells. In this section, the effects of The rate at which the free gas rises up the wellbore is a verydifferent horizontal well types are discussed. The data used important parameter in the development of a gas kick. In thefor this purpose is given in Tables 1 and 2. It is assumed that context of taking a kick in a drilling environment. the gasthe static pressure underbalance is 300 psi for all three wells. migration characteristics will be governed by the wellThe Air-Water gas rise velocity model is again assumed. The trajectory (deviation). geometry (annulus). and the nature ofsequence of events leading to the well closure for all three thenon-Newtonianfluid. While some studies(7-9) have beenwells is the same as that for the earlier discussions. and are being conducted. a comprehensive model which

describes all these effects still remains to be developed. Toexamine the sensitivity of this parameter. two gas risevelocity models. referred to as Air-Water and Air-Mudmodels. have been compiled based on data from thepublished literature (Appendix A). An important aspectbetween the two models is the effect of the well deviation onthe gas slip velocity. In the Air-Water model. the deviationeffect is considered by the gravity effect only whereas in theAir-Mud model. a correlation presented by Hasan andKabir(16) is employed in which the gas slip velocityincreases as the hole deviates from the vertical. The gas slipvelocity reaches a maximum when the deviation angle isabout 45° and then starts to decrease. The gas slip velocitybecomes zero when in horizontal flow.

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Discnssion. One practical concern during the kickcirculation phase is that the lateral section will not be entirelylevel. H the slow circulation during kick displacement doesnot remove the gas trapped in the undulations. normalcirculation may force the gas into the vertical section of thewell. The well could go to under-balance again with a newkick generated as a result. An estimation for the minimumvelocity required to remove the trapped gas has beenpresented by Currans et al (13). Essentially. it states that themud velocity should exceed the gas slip velocity in order toremove the gas in the high spots. For this method to work. agood estimation of the gas slip velocity is critical.

Scenario 2: Long Horizontal Section in aFlat Homogeneous Reservoir

The second scenario studied in this paper is· that of a longhorizontal section drilled in a flat homOgeneous reservoir(Fig 3). Since current horizontal wells are used mostly forreservoir development, reservoir pressure is normally known.and therefore. drilled kicks are very unlikely. One mightargue that a kick could only occur through swabbing.However. one still cannot role out the possibility of drillinginto a high pressure or an undepleted formation which has notbeen encountered previously. Nevertheless. this scenario isoutside the scope of this paper and requires further study.

However. the formation producibility may be high and slightchanges in annular pressure can result in a gas influx. Oneparticular situation that is presented in this paper is that whenthe well is dynamically overbalanced and is only 30 psiunderbalanced under static conditions. The formationpressure is 3800 psi. The medium radius well is used as theexample well. The Air-Water gas rise velocity model isassumed.

Two cases have been simulated for different casing settingdepths. The first case is to set the casing to the target. whichonly enables influx into the horizontal section. and the secondto 100 ft MD above the target. The sequence of events is (1)drilling for 15 s for the system to stabilise; (2) stop bothdrilling and circulation for 2 minutes; (3) shut-in and pressurebuild-up; and (4) circulating the kick out.

The pit gain responses during the kick development stagefollows the expected trends with a larger gain for case 2 at

Kick detection. It was found that the lateral section angledoes not affect the kick detection either by delta flow or pitgain in this case. The kick detection criteria was assumed tobe 10 bbl pit gain threshold and the kick was detected at 4.63.4.57. and 4.73 min for the horizontal. the high angle. and theinverted high angle wells respectively. The correspondingdelta flow rates at the moment of kick detection are 143. 150.and 136 gal/min.

Gas migration and SICP. Gas migration during the shut-inperiod is characterised by the rising SICP. In the case of thehorizontal and the inverted high angle wells. if the entire gasinflux remains in the lateral section just before the wellclosure, free gas will not migrate upwards along the wellbore.However. as discussed earlier. some gas may enter the buildsection and hence gas migration will be observed. Fig 17compares the SICPs for three wells in a somewhat extendedshut-in period to illustrate the effects of changing the lateralsection angles. In all three wells. the gas migration effect isobserved as characterised by the linear increase in the SICP.But the rate at which the SICP increases differs slightly withthe high angle well showing the highest rate and the invertedhigh angle well the lowest rate. This difference may becaused by the amount of free gas mass involved in the gasmigration. In the case of the high angle well, the entire gasinflux migrates upwards along the wellbore. In the case ofthe horizontal and the inverted high angle wells. only the freegas that has entered the build section migrates. Some gas hasentered the build section in both wells in this particular caseand therefore gas migration is observed. The interestingpoint in the case of the inverted high angle well is that thefree gas in the lateral section migrates towards the bit endwhose position is higher than that at target. This effect isclearly seen in the choke pressure response during kickdisplacement. especially if the extended shut-in is required.

A true horizontal section has been assumed in the abovecalculations. In practice. the lateral section may not be trulyhorizontal and in many cases. it may be undulating. In thissection. attempts are made to examine the effects of thelateral section angles with respect to kick detection and thecasing/choke pressures during shut-in and kick displacement.The medium radius well is selected for the illustrativepurpose. Two particular angles. i.e. 87.5° and 92.5° havebeen studied and compared with that of a true horizontalsection. The relevant well data is presented in Table 3.These three wells are referred to as horizontal well (90°).high angle well (87.5°). and inverted high angle well (92.5°)according to the angle of the lateral section.

The sequence of events is the same as for the typical kickbehaviour used above. The static pressure underbalance isassumed to be 300 psi for the horizontal well which yields aninitial dynamic underbalance of 184 psi. Since the TVD atthe bottomhole varies for the three wells. the formationpressure is adjusted to obtain the same initial dynamicunderbalance of 184 psi for the high angle and the invertedhigh angle wells. The Air-Mud gas rise velocity model isassumed.

6 Gas Kick Sim~tionStudy in Horizontal Wells IADC/SPE 27498

Effect of the Lateral Section Angle Kick displacement. The choke pressure and pit gainresponses for three wells during kick displacement areillustrated in Figs 18 and 19. The kick displacement usingthe Driller's method commences immediately once thebottomhole pressure builds up to tht; formation pressure. Inall three wells. choke pressure starts to increase immediately.The high angle well experiences the highest choke pressure.In the inverted high angle well. the lowest choke pressure isobserved but the peak choke pressure sustains a longerperiod. This is also reflected in the pit gain responses (Fig19). The distinct transition point when the entire gas influxenters the vertical section disappears in the inverted highangle well due to the spread of gas influx. The· pit gainresponses show the same trend as observed in the chokepressure.

630

Page 7: Gas Kick Simulation Study for Horizontal Wells

cross-sectional area (ft2)bubble distribution and velocity prof1le coefficientconstant in drillpipepressure curve fIt, Eq 3(14)outside diameter o! inner pipe (in)inside diameter of outer pipe (in)formation producibility (bbllminlpsi)acceleration of gravity (cm/s2)permeability (md)pressure (psi)gas flow rate (Mscflday)radius of wellbore (in)time (s)temperature (oF)

velocity (ftls)gas slip velocity (ftls)gas slip velocity in bubble flow regime (cm/s)gas slip velocity in slug flow regime (cm/s)position along flo",.line (£1)real gas compressibility factorporositygas SpecifIC gravity (air = 1.0)gas void (volume) fractionviscosity (cp)density (PPG)

surface tension (dyne/cm)

NOMENCLATURE

vVsvsbVsszZell'YgA.J.l.p

o

Swabbed kicks. Due to the high producibility of a horizontalwell, extra care should be taken when tripping so as to .avoidthe possibility of a swabbed kick. If swabbing occurs, aswabbed kick could occur anywhere in the horizontal section.depending upon the bit position. If it is detected when mostof the influx still remains in the horizontal section, theresponse during the its displacement should be similar to thatdiscussed above for Scenario 2.

A more detailed study on the kick behaviour and the relevantcontrol aspect will be presented in a forthcoming paper(17).

CONCLUSIONS

A dynamic computer model has been· developed forsimulating kick behaviour in horizontal wells. Twoparticular scenarios have been studied in detail. Based onthis study. it is concluded that:

For a horizontal well drilled into a high pressurecompartmentalised reselVoir:

(1) Delta flow as a kick detection parameter remains themost sensitive kick detection parameter. It may not

The kick can be circulated out by using the Driller's method.One should note that maintaining the constant bottomholepressure does not necessarily mean the pressure in thewellbore everywhere in the exposed section is greater thanthe formation pressure. Therefore, a sufficient pressuresafety factor has to be added to avoid secondary kicks duringcirculation out of the initial kick.

This example demonstrates that in horizontal wells. if thewell for some reason becomes pressure-underbalanced byeven a small amount. the well can take an "explosive" kick ina very short time. particularly if the build section within thereselVoir is not entirely cased off. Nevertheless. this does notnecessarily mean that the well cannot be brought back undercontrol in a suitable manner.

IADC/SPE 27498 Wang, Z., Peden, J. M., Lemanczyk, Z. R. 7

the end of the 2 minute flowing intelVal due to the extra 100 however be as sensitive as in a conventional well inft MD in the build section open to flow and more importantly similar circumstances.the larger dynamic pressure underbalance in this build (2) The effect of gas migration is considerably smaller, insection. The total pit gains for this 2 minutes flowing are 3.5 particular for wells with long horizontal sections.bbl for case 1 and 4.5 bbl for case 2. respectively. (3) The difference between shut-in casing pressure (SICP)

and shut-in drillpipe pressure (SIDPP) is much smallerthan that in a comparable conventional well.

(4) A horizontal well demonstrates a larger kick tolerance atthe moment of well closure and can be shut in longer ifnecessary without fear of fracturing the weakest zone.

(5) The influx type (gas or liquid) can be identified by itscompressibility derived from analysis of SIDPP.

(6) The lateral section angle has a signifIcant effect on thekick profile during the kick development phase and thepressure and pit gain responses during kick circulation.

For a well drilled in a flat homogeneous reselVoir fordevelopment purposes:

(7) Swabbed kicks are a major concern and a small amountof pressure underbalance may cause an "explosive" kick.

For kick control in horizontal wells in general:

(8) The use of the Wait-and-Weight method may not yieldlower peak choke pressure as it may in a conventionalwell. Also. the pump pressure schedule becomes morecomplicated. On the other hand. the Driller's method canbe implemented without any modifIcation from. aconventional well application.

(9) There is a requirement to develop a more rigorouscorrelation for the gas rise velocity in a drillingenvironment covering the whole range of the deviationangle from the vertical to the horizontal.

It is more interesting to examine the gas influx rate into thewellbore. Fig 20 shows influx rates versus horizontal

. distance from the bottomhole (bit end) at t = 35 s from thebeginning of simulation for both Cases. In both cases theinflux rate increases along the horizontal section from thebottomhole back to the target due to the increased drawdowncaused by the friction pressure loss in the wellbore. But. incase 2. the influx rate increases "explosively" in the 100 ftbuild section. The flow rates along the horizontal section incase 2 are smaller than those in case 1 because the larger totalinflux rate in case 2 results in a larger friction pressure drop.Indeed. the average dynamic pressure underbalances are 0.5psi in case 1 and 0.2 psi in case 2 in the horizontal section.and 2.5 psi in the 100ft build section in case 2 for a givenoverall 30 psi hydrostatic pressure underbalance in bothcases.

631

Page 8: Gas Kick Simulation Study for Horizontal Wells

(A1) .

Viscosity. The mud viscosity, ~l' is assumed to remainconstant and equal to the input values at surface conditions.Kill mud may have properties different from the initial mud.The gas viscosi~ is calculated from the correlation given byDranchuk et ai< 8).

Gas Slip Velocity. Correlations for gas-liquid two phaseflow in the deviated and horizontal annular geometry for non­Newtonian fluid are virtually non-existent. Recently,studies(7-9) have been conducted which have contributed tothe better understanding of the gas migration in a deviated

Single- and Two-Phase Friction. For a single phase mud,both the Power Law and Bingham Plastic models have beenused. For the gas-mud two phase flow, the friction pressuregradient is calculated from the Beggs-Brill correlation(19).This correlation is for steady-state conditions where the voidfraction is determined by gas and liquid flow and inclinationangle of the pipe. In the present study, the void fraction, andthe mixture velocity used in the correlation are thosecalculated from Eqs. (1) through (6).

Density. The mud density is calculated by adjusting thedensity at measurement pressure and temperature to accountfor the pressure and temperature effects. The free gas densityis calculated from:

28.96y.pp. ZKf

8 Gas Kick Simulation Study in Horizontal Wells IADC/SPE 27498

e hole inclination angle (0 for vertical) European Well Control Conference, Paris, France, 2-4. Subscript June 1993

g gas 14.Billingham, J., Thompson, M. and White, D. B.:1 liquid "Advanced Influx Analysis Gives More Information

Following a Kick", paper SPE/IADC 25710 presented atREFERENCES the 1993 SPE/IADC Drilling Conference, Amsterdam, 23-1. Rommetveit, R and Olsen, T. L.: "Gas Kick Experiments 25 February 1993

in Oil Based Drilling Muds in a -Full-Scale Inclined 15.Jardine, S. I., White, D. B., and Billingham.. J.:Research Well", paper SPE 19561 presented at the 64th "Computer-Aided Real-Time Analysis and Control",Annual Tech. Conf. and Ex. of the SPE, San Antonio, TX. paper SPE/IADC 25711 presented at the 1993 SPE/IADCOct. 8-11,1989 Drilling Conference, Amsterdam, 23-25 February 1993

2. Ekrann, S. and Rommetveit, R: "A Simulator for Gas 16.Hasan, A R and Kabir, C. S.: ''Two-Phase Flow inKicks in Oil-Based Drilling Muds", paper SPE 14182 Vertical and Inclined Annuli", Int. J. Multiphase Flow,presented at the 60th Annual Tech. Conf. and Ex. of the Vol. 18, No.2, pp. 279-293 (1992)SPE, Las Vegas, NY, Sept 22 - 25,1985 17.Lemanczyk, R Z., Wang, Z., and Peden, J. M.:

3. Nickens, H. V.: "A Dynamic Computer Model of a "Parametric Analysis of Gas Kick Behaviour DuringKicking Well", SPE Drilling Engineering, (June 1987) Drilling of Horizontal Sections in a Homogeneous159-73 Reservoir", to be presented at the Canadian

4. Podio, A L. and Yang A. P.: ''Well Control Simulator for SPE/CIM/CANMET International Conf. on RecentIBM Personal Computer", paper IADC/SPE 14737 Advances in Horizontal Well Applications", March 20-23,presented at the IADC/SPE 1983 Drilling Conf., Dallas, Calgary, Alberta, CanadaTX. Feb. 10-12, 1986 18.Dranchuk, P. M., Islam, M. R and Bentsen, R G.: "A

5. White, D. B. and Walton, I. c.: "A Computer Model for Mathematical Representation of the Carr, Kobayashi andKick in Water- and Oil-Based Muds", paper IADC/SPE Burrows Natural Gas Viscosity Correlations",!. Canadian19975 presented at the IADC/SPE 1990 Drilling Conf., Pet. Tech. (Jan. - Feb. 1986)Houston, TX, Feb. 27 - Mar. 2,1990 19.Beggs, H. D. and Brill, 1. P.: "A Study of Two-Phase Flow

6. Bamford, A. S. and Wang, Z.: ''Well Control Simulation in Inclined Pipes", 1. Pet Tech. (May 1973)Integrated With Real Rig Equipment to Improve Training 20 Harmathy, T. Z.: "Velocity of Large Drops and Bubbles inand Skills Validation", paper SPE 27269 to be presented Media of Infinite or Restricted Extent", AI.Ch.E. 1. Vol.at the Intl. Conf. on Health, Safety & Environment, 6, No.2, (June 1960)Jakarta, 25-27 Jan. 1994

7. Johnson, A B. and White, D. B.: "Gas Rise Velocities APPENDIX A PHYSICAL MODELSDuring Kicks", paper SPE 20431 presented at the 65thAnnual Technical Conf and Ex. of SPE, New Orleans,LA,Sept.23-26,199O

8. Hovland, F. and Rommetveit, R: "Analysis of Gas-RiseVelocities From Full-Scale Kick Experiments", paper SPE24580 presented at the 67th Annual Tech. Conf. andExhibition of the SPE, Washington, DC, October 4-7,1992

9. Johnson, A B. and Cooper, S.: "Gas Migration VelocitiesDuring Gas Kicks in Deviated Wells", paper SPE 26331presented at the 68th Annual Tech. Conf. of SPE,Houston, Texas, 3-6 Oct. 1993

1O.Santos, O. L. A: "Important Aspects of Well Control forHorizontal Drilling Including Deepwater Situation", paperSPE/IADC 21993 presented at the 1991 SPE/IADCDrilling Conf.. Amsterdam, 11-14 March, 1991

l1.Santos, O. L. A: "Well Control Operations in HorizontalWells", SPEDrilling Engineering (June 1991) 111-117

12.Aas, B., Bach, G., Hauge, H. C. and Sterri, N.:''Experimental Modelling of Gas Kicks in HorizontalWells", paper SPE/IADC 25709 presented at 1993SPE/IADC Drilling Conference, Amsterdam, 23-25February, 1993

13.Currans, D., Brandt, W., Lindsay, G. and Tarvin, 1.: 'TheImplications of High Angle and Horizontal Wells. forSuccessful Well Control", paper presented at 1993 IADC

632

Page 9: Gas Kick Simulation Study for Horizontal Wells

aD 5"Drillpipe II) 4.28"

Lenszth variable

Heavy weightaD 5"II) 3"

drillpipeLenlrth 900ft

aD 6.33"Collars II) 2.62"

Lenlrth 200ftDiameter 8.5"

Bit Nozzles 3Nozzle size 15/32"

CasingII) 8.55"

Lene:th to Tarjtet

Long radius 2.5°/100 ft

Build rate Medium radius 10°/100 ft

Short radius 150°/100 ft

Length of horizontalLong radius 2000ft

sectionMedium radius 1000 ft

Short radius 200ftTVD at tare:et for 3 tvnes 7000ft

Long radius 4708.17 ftKick-off Point Medium radius 6427.04 ft

Short radill$ 6961.80 ftLong radius 10308.17ft

Total Measured Medium radius 8327.04 ftDepth Short radius 7221.80 ft

Ooenhole size 8.5"

(A.3)

(A.4)

(A.2)

v. (8) = v. (0)oos8

(D) 2.54gD.(p,-p,)

v.. = 0.345+0.1 D: PI

Transition flow: The slip velocity in the transition flow (Ab <A < As) is assumed to vary linearly with void fractionbetween bubble flow and slug flow.

Effect of the deviation angle:

IADC/SPE 27498 Wang. Z.• Peden. J. M.• Lemanczyk. Z. R. 9

annular geometry filled with non-Newtonian fluid. Table 1: Wellbore Geometry for Kick SimulationNevertheless. controversy remains. especially on the effect ofthe deviation angle on the slip velocity. In this study. twogas rise velocity models are simulated. one is referred to asthe Air-Water model. the other. the Air-Mud model. For bothmodels. Eq. (4) is used to model the gas velocity.

Air-Water gas rise velocity model. Co is assumed to take avalue of 1.2. For the purpose of calculating the slip velocity.the flow regime is divided into bubble flow (A ~ Ab = 0.2).slug flow (A ~ As = 0.4) and a transition (At, < A < As) frombubble flow to slug flow. The effect of hole inclination onthe slip velocity is considered by a simple correction. Theslip velocities for the three regimes are calculated as follows:

Bubble flow(20);

[

8.3447gcr(PI _p,)]O.2Sv•• = 1.53 •

PI

Slug flow(16);

(A.6)

Air-Mud gas rise velocity model. In this model. Co takes avalue of 1.39. The slip velocity is assumed to be independentof the gas void fraction and to have a value given by Eq.(A.3). The effect of the deviation angle is calculated (16) by;

v. (8) = v.(0),Jcos8(I+sin8)L2 (A.5)

Gas Influx Rate. A simple equation from the solution of theradial diffusivity equation for a homogeneous. gas-saturatedan4 infinite reservoir is used to calculate the gas flow ratefrom the formation into the wellbore:

Q = k",h(p;-p:)

, 71IJJZT ln[i O.OOO264k",t]y cIl(J.lC\r:

Table 2: Physical Properties for Kick Simulation

Density 10.5 ppgMud Yield point 10.5 1bf/100 f~

Plastic viscositv 20.0 coGas Soecific Irravitv 0.65 (air=l)

Formation Vertical 100mdPermeabilitv Horizontal 100mdTemperature

2 °F/1oo ftJUadient

Rap 100 ft/hr if applicable

Pump rate 400 gal/min

Kill rate 150 gal/min

Table 3 Well Profile Data - Effect of the LateralSecti A Ion n~le

Hori- ffigh Invertedzontal an2Ie Hamde

Anale of lateral section 90° 87.5° 92.5°TVD at tarlIet (ft) 7000 7000 7000

TVD at bottomhole (ft) 7000 7043.62 6956.38KOP (ft) 6427.04 6427.59 6427.59

:MD at tarltet (ft) 7327.04 7302.59 7352.59Total:MD (ft) 8327.04 8302.59 8352.59

where t is flowing time (hour); (J.lCJi is evaluated at pressure.PI' and y is a constant equal to 1.781. The reservoir ''height''open to flow is assumed to be equal to the block length plusany drilled portion for the block at the bottomhole and equalto the block length for any other blocks. The effectivepermeability is used to account for the presence of vertical

permeability: keff =~khkv

633

Page 10: Gas Kick Simulation Study for Horizontal Wells

10 Gas Kick Simulation Study in Horizontal Wells IADC/SPE 27498

h~

--- Vertic.1 SectionKick-off point

(KOp)..

- R.diu. of Curv.ture

Build up section Horizont.l Section

~Target

Fig 1 Typical Horizontal Well Profile and Terminology Fig 2 A Horizontal Well Drilled Into aCompartmentalised Reservoir

Gas Mass in

.----~\\'0-----::-,....-,...."....-:-------.~.:::::====Hon=.zon=~t.-lSect=ion

Gas Mass out

Liquid M••• out

Gas Mass in

LiquidM... in

Flat Homogeneous Reservoir Gas Mass in

Fig 3 A Horizontal Well Drilled in a FlatHomogeneous Reservoir

Fig 4 Mass Balance for a Typical Block in aHorizontal Well

10

Ver~cal, 4PSa300psiHorizoDlaI. M'sz3OO psi

Ver~cal. M'c1>oSO psi-- Horizonlal. APd=50 psi

4 6

Time (min)

Fig 6 Pit Gain: Vertical vs Horizontal Well.

0 ....~~.......~-........-"'"'C"......,.......~~-r--~-1o104 6

Time (min)

Fig 5 Delta Flow: Vertical v. Horizontal Wen.

O.J!=:;......,~.....,..~~.........~~- .........~~........~----lo

12

Vertical. &Ps=300 psi200

HorizoDta1. M'sz3OO psi

Vertical, M'd=5O psi 10

Horizoolal. M'd=50 psi

i160.. :E

SE- e~ 120 c

11 6.. ". i:::i:!l 80

600..-------------------, 4oo-r-------------------,

-- Vertical well

Horizoolal well

3SO

7 300 r! F~ 2SO

!It 200

ISO------

S1CP

Cum: Filla SIDW

SIDPI'

Time from .tart of shut-in (min)

Fig 8 SICP vs SIDPP and Curve Fit to SIDPPin the Horizontal wen

100~-~-r__--__r-~-_r_-~.....,r__--_1o2 4 6

Time From Starl of Shut-in (min)

Fig 7 SICP: Vertical VI Horizontal wen.

loo.J--~-.....,r__---......-~--.._-~-_to

634

Page 11: Gas Kick Simulation Study for Horizontal Wells

IADC/SPE 27498 Wang, Z., Peden, 1. M., Lemanczyk, Z. R. 11

Tlm.e FrOID Start or Kick Displacemcat (m.Ia)

Fig 10 Pump Pressure Using Wait-and-Weight Method

so40

IGJI mud at [email protected]

Vcrtical well

Horimntal well

302010

700

600

i'A

SOO

i..400...a

.e300

200100 0

Vertical: Drinc.sHorizontal: Driller'sHorizooraI: Wait & Weight

Kill mud at target in the [email protected].

20 40 60 80

Time From Start of Kkk Displacement (min)

Fig 9 Choke Pressure: Vertical vs Horizoutal Wells

700

600

i' 500~~

400~~

0';300

~...0...U 200

100

00

soo 700Shortradiua

600i'~ 400

S~

A SOO~=~

~0';400.. 300

= 0';i

~u -- Short radius.5 ... 300

; Medium radius U200...., Long radius

2 4 6

Time From. Sblrt of Shut-In (min)

12010080604020

Time From Start of Kkk Displacement (min)

100 +---....,...-~__r--__.-~-..._--"T""""--_lo

100.f-~~~----.-~~_...,-~~~----.~~~~o

Fig 11 SICP: Effect of Horizontal Well Types Fig 12 Choke Pressures: Errect of Horizontal Well Types

4OO-r------------------,

Air-W_ModeI

Air-Mud Model

6OO-r-----------------,Air-Water Model

Air-Mud Model

soo

200

100 +--~,........,c__"-~_,_~~~...,_--~..__,........,-__lo 20 40 60 80 ~

Time From Start of Kk:1I: Dlsplacemeat (mla)

Fig 14 Effect of Gas RIse Velocity on Choke PressureDuring Kick Displacement

102 4 6Time From Statt of Shut-In (mlo)

Fig 13 Errect of Gas Rise Velocity on SICPIn Horizontal Wells

lOO+--~-_._-~-......-~-___r-~-__r---_lo

635

Page 12: Gas Kick Simulation Study for Horizontal Wells

Gas Kick Simulation Study in Horizontal Wells IADC/SPE 27498

A...W_ModoI

A"·MudModel14

0~--4-..--'-~~- __-.-::~--~o w ~ 00 W ~

Time F...... SllU't or KIck D..plllC.....' (..III)

Fig 16 Surface Gas Flow Rate During Kick Displacement:Effect of Gas RIae Velocity

16 .,--------------------,

100

Air·W..., Model

Air·Mud Model

o+---~--.---..,.--~-_-~_---io ::0 ~ 00 W

Time Fn>.. SllU't or KIck DIop........t (..III)

Fig 15 Effect of Gas RIae Velocity on Pit Gain

12

3~

30

~

~~. ::0

~;: I~

10

~OO.,...-------------------.., High anglo: 87.5"

Horizcaal well: so­Inv..-...! higll onglc: 92-\"

WO+-------r-----.-------..---.---4o ::0 ~ 00 W

T... Fro. Slain of Kkk Dllplacemca' (....)

Fig 18 Choke Preuure: Effect of the Lateral Section Angle

300

6OO..----------------~

:i m.;··!4000:·....8'"

Higll '"'lIto: 87.5"

_well: 90"

Inv..-...! higll onglc: 92-\"

2 4 6TIlDe Fro. Start or Shut-Ill (...tal

Fig 17 SICP: Effect of Lateral Section Angle

100+-~-~"""'---~""--~-"""_----1o

.i~ 300..~'-'.; ZOO...'"

30..-------------------,

1200WO 400 600 SOO 1000HorizODlal D....ce Fro.. Bit Ead t tt)

Fig 20 101IuJ: Rate Along Horizontal Secllon " • .,= B;::omhole

hollomhole

C.iIl8 oboe 10 1oIF'Cuing aboc 10 100 ft above tlr'gCt

1600.,--------------------,

IWO

IIigll qlc: 87.5"

Homc,"al well: 90"

In..ncd higll angle: 92.5"

o+--~~--.--.-~-....,....~..-~----__lo ~ ~ 00 W

Time FrOID Start of Kkk DilpiKemeDt (mla)

Fig 19 Pit Gain: Effect of the Lateral Section Angle

~

10

.5~ IS

.:::- 20...~

636