azimuthal gamma,

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GEOSTEERING WITH ADVANCEDLWD TECHNOLOGIES PLACEMENTOF MAXIMUM RESERVOIR CONTACTWELLS IN A THINLY LAYERED

CARBONATE RESERVOIR

Shouxiang Mark Ma

Mohammed A. Al-Mudhhi

Abdalrasool A. Al-Hajari

Ken L. Lewis

Garo M. Berberian

Parvez Butt

Mohammed A. Al-Mudhhi is a senior engineer with the

Southern Area Petrophysics Unit of the Reservoir

Description Division in Dhahran, Saudi Arabia. He holds a

BS (1987) in Petroleum Engineering from Tulsa University,

Oklahoma, USA. Mohammed joined Saudi Aramco in

1978. He has 27 years of experience in various petroleum

disciplines including production engineering, reservoir

management and reservoir description.

Shouxiang Mark Ma is a petrophysicist with the

Reservoir Description Division of Saudi Aramco. He has a

BS, an MS and a PhD in Petroleum Engineering. He has

worked as a research associate at the New Mexico

Petroleum Recovery Research Center, a post-doctoral

fellow at the Western Research Institute, was an adjunct

assistant professor at the University of Wyoming, and was

a senior research engineer with the Exxon Production

Research Company. Shouxiang has published more than 30

technical papers in laboratory and field petrophysics.

Abdalrasool A. Al-Hajari is a supervisor with the

Reservoir Description Division of Saudi Aramco. He has a

BS degree in petroleum engineering from King Fahd

University of Petroleum and Minerals, in Saudi Arabia.

Abdalrasool has worked in different areas of petroleumengineering, drilling, production and reservoir management.

He has co-authored several papers in petrophysics and well-

monitoring logging. He has 18 years of experience in

sand-shale and carbonate petrophysics.

Ken L. Lewis is a geologist with the Southern Fields

Characterization Division of the Reservoir


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SAUDI ARAMCO JOURNAL OF TECHNOLOGY WINTER 2005 3

Characterization Department and has been with Saudi

Aramco since 2001. Ken has been involved in reservoir

development activities in the North Ghawar region and

Abqaiq field areas. He worked 20 years with Kuwait Santa

Fe in the Neutral Zone between Kuwait and Saudi Arabia,

with Pinnacle Resources in Western Canada and with

Husky Oil International in Indonesia on a variety of oil and

gas development opportunities. He received his BS inGeology and MBA in Finance from the University of

Calgary, Canada.

Garo M. Berberian is the supervisor of the Abqaiq

Reservoir Management Division in Dhahran, Saudi Arabia

and has been with Saudi Aramco since 1998. He holds BS

(1979) and MS (1982) degrees, both in Petroleum

Engineering from Louisiana Tech University, USA, and an

MBA (1988) from Louisiana State University, USA. He is a

registered Professional Engineer in Texas and a member of

the Society of Petroleum Engineers (SPE). Garo has 27

years of industry experience; he previously worked as a

special technical adviser in Production and Reservoir

Engineering for the Ministry of Oil in Yemen, was a

reservoir engineering consultant for Sonatrach in Algeria,

and was a senior production/analytical engineer for Arco.

Parvez Butt is currently the manager of the Schlumberger

Logging While Drilling formation evaluation in Saudi

Arabia, responsible for LWD log interpretation. Butt has an

MS in geophysics (1981) from the University of Islamabad,

Pakistan. His primary focus is the interpretation and

development of new real-time answer products from LWD

services, with his areas of technical expertise including

advanced formation evaluation with LWD services,geosteering, horizontal well placement and drain hole length

optimization using real-time images and real-time LWD

services.

ABSTRACT

Placing a maximum reservoir contact well in a thinly

layered reservoir has always been a challenge. Experiences

showed that the well trajectory could easily be steered out

of the target, necessitating expensive plug-back and

redrilling operations to ensure that the well is drilled asplanned. With the deployment of advanced LWD

technologies, such as density image (DI), resistivity image

(RI) and directional deep resistivity (DDR) logging tools,

and high-speed real-time satellite data transmission, well

paths can be geosteered from anywhere and kept in a thinly

layered reservoir.

The first Saudi Aramco field examples of utilizing RI and

DDR are shown to demonstrate the added values of new

technologies in geosteering difficult-to-drill wells. In some

of the examples, images of density and resistivity are

consistent, and all could be used for geosteering. In other

examples, wrong geosteering decisions would have been

made had the DI been the only available tool. With the help

of RI, reservoir contact of multi-lateral wells is increased.

Examples also show that using DDR can prevent the well

trajectory from being too close to the zero porosity rock

layer or the underlying water.

INTRODUCTION

The main oil-producing reservoir in the XA field is a

massive carbonate reservoir. At the top of this good quality

reservoir there is a thin heterogeneous reservoir interval

(named L1Z1) with rock porosity ranging from less than 10

porosity unit (pu) to more than 20 pu (Fig. 1). This L1Z1 is

sandwiched between an 8 ft. thick overlaying zero porosity

anhydrite unit and an underlying 2 ft. thick zero porosity

anhydrite or close to zero porosity anhydritic dolomite unit.

The thickness of L1Z1 ranges from less than a few feet tomore than 20 ft., with a typical thickness from 4-8 ft.

Because of the rock quality, this thin layer has been

difficult to target through traditional vertical producers. To

improve oil recovery, maximum reservoir contact (MRC)

multi-lateral (ML) horizontal wells have been drilled in the

last few years; some drilled in new locations and others

side-tracked from existing vertical wells.1

Conventional Geosteering Tools

It is impossible to place a horizontal well in a thinly layered

reservoir such as L1Z1 without the help of logging-while-drilling (LWD). Traditionally, LWD tools consist of gamma

ray (GR), density, neutron, and resistivity (triple combo)

measurements. Geosteering a horizontal well with only

conventional LWD triple combo and GR is difficult

because it does not provide direction of the measurement.

For example, if drilling rate of penetration (ROP) is low

Fig. 1. Well cross-section of the targeted top thin reservoir interval, sandwiched

by a top zero porosity anhydrite and a bottom zero porosity anhydrite or very

low porosity anhydritic dolomite.


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4 SAUDI ARAMCO JOURNAL OF TECHNOLOGY WINTER 2005

and porosity log shows that the hole is cutting zero porosity

rock (i.e., anhydrite), there is no way to tell if this zero

porosity rock is above or below the target reservoir.

Therefore, more advanced directional geosteering

technologies are needed.

Advanced LWD Geosteering Technologies

With continuous development of LWD technologies,

azimuthal measurement became a reality. The first azimuthal

measurement for 6-1/8 in. hole size was density,2 then GR.3

Azimuthal density has proved to be a useful tool for well

placement in thinly bedded carbonates,4 as well as in shaly

sands.5 But azimuthal GR has limited application in carbonate

reservoirs due to the inconclusive GR responses in carbonates.

Since density is a relatively shallow measurement, it is

more sensitive to hole rugosity. Our experience has shown

that wrong geosteering decisions may be made if only

azimuthal density is available.

LWD resistivity image6-10 and the new extra deepdirectional resistivity11-13 are more robust measurements (less

sensitive to hole conditions) and have been used to improve

the placement of ML wells in thinly bedded reservoirs.

Objectives of This Paper

The main objectives of this paper are to demonstrate the

benefits of using advanced LWD technologies in geosteering

MRC ML wells in thinly layered carbonate reservoirs. A

historical trail of LWD geosteering technology is reviewed

from conventional LWD triple combo, images of density

and resistivity, to the newly developed directional deepresistivity measurements.

ADVANCEMENT IN GEOSTEERING

A REVIEW

Rotary Steerable System (RSS) Technology

An advanced log can only provide the driller real-time

guidance regarding the direction of the borehole to be drilled.

To follow the guidance closely, the driller also needs an

advanced steerable drilling assembly, and the newly developed

rotary steerable system (RSS) is one such system.14-15

The RSS assembly, (also referred to as point-the-bit

technology), used for ML well drilling in this study has a

steering assembly that continuously orients the tilted bit

shaft to control the drilling direction and the dogleg severity

of the borehole (Fig. 2). The tool does not push against the

borehole to build angle, and is therefore more effective for

steering. It is a fully rotating tool with no stationary external

parts, which reduces the risk of sticking pipe assembly. It

looks and acts like a conventional drilling motor although it

has the ability to adjust azimuth and inclination of the bit.ROP is improved because there are no stationary

components to create friction (which reduces efficiency) to

anchor the bottom hole assembly (BHA) in the hole.

The tool is comprised of a slick collar with two spiral

stabilizers positioned 12 ft. behind the bit. The bit shaft is

deflected internally with hydraulics allowing only the bit

box to be offset.

Density Image (DI)

The tool used for density measurement described in this

paper has an OD of 4.75 in., which is suitable for drilling6-1/8 in. hole (Fig. 3). It utilizes a 1.7 Curie Cesium-137

density source and two scintillating NaI crystal detectors.

High-energy gamma rays are emitted from the source into

the formation. They undergo interaction with the formation

and return at reduced energies to the long and short spacing

detectors. The quantity that returns to the detectors is

inversely proportional to the formation electron density.

Using an empirically determined and laboratory-calibrated

relationship between electron density and bulk density, the

formation bulk density can be estimated.

Azimuthal density image (DI) is made from color-coding

density measurements around the borehole. Density

measurements are circumferentially binned into 16 sectors

(Fig. 3), and these measurements are color coded on a

graduated scale to bring out the heterogeneity of the

borehole as a stabilized tool traverses the formation.

Azimuthal measurements are established by placing

Fig. 2. Rotary steerable system (RSS) tool schematics.

Fig. 3. Schematics of density/neutron LWD tool and 16 sector density image.

Tool OD is 4.75 in., suitable for 6-1/8 in. hole size.


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fluxgate magnetometers in the tool. When the tool is

rotating, these magnetometers measure the Earths magnetic

field strength along their axis. The result of these

measurements can be used to analyze the relative position

of the tools measurement in relation to the earths magnetic

field. This relationship converts the north, south, east and

west measurements to up, down, left and right, thereby

establishing the quadrant measurements. Each quadrant isfurther subdivided into four sectors, giving a total of 16

sector measurements (Fig. 3).

Resistivity Image (RI)

The azimuthal resistivity image (RI) tool is a bigger tool

with an OD of 6.75 in., only suitable for 8-1/2 in. hole size

drilling. It provides a laterolog type resistivity-at-the-bit, a

high-resolution ring resistivity and three azimuthally

focused buttons resistivities (Fig. 4). The three button

electrodes are approximately 1 in. in diameter and are

longitudinally spaced along the axis of the tool. The spacingprovides shallow (1 in.), medium (3 in.), and deep (5 in.)

depths of investigation for quantifying invasion profiles.

These azimuthally acquired button measurements are also

displayed as 56-sector resistivity images, which is essential

for better structural interpretation while drilling.

An integral, cylindrical electrode is used to provide a

high-resolution lateral resistivity referred to as ring

resistivity. The ring resistivity has a 7 in. depth of

investigation. In addition to these four resistivity

measurements, the tool also acquires a bit resistivity,

azimuthal gamma ray, radial and lateral shock records, and

temperature measurements.

Images and Formation Dip Calculation

As discussed above, the circumferential measurements of

azimuthal densities are binned into 16 sectors to obtain DI,

while the RI is obtained by binning the measurements into 56

sectors. As shown in Fig. 5, the resolution of DI is about 6 in.

while the RI resolution is about 1.2 in., five times better than

that of DI. Although this is a considerable improvement, it

still does not meet the standard of wireline resistivity images,

which are about 10-fold better in resolution.

The interpretation of real-time image logs requires both

an understanding of the geology and how the tool respondsto different lithologies and borehole environment. The DI

and RI tools are proven to be useful for advanced

interpretation of geologic structures, such as calculating

dips from up and down measurements.

The method of calculating dips relies on measuring the

offset between the top and bottom measurements.16-20 When

the borehole intersects a bed at a high incident angle from

above, the bottom log is the first to see the formation,

followed by the right and left, and finally by the top

measurement. The logs will appear as if the top and bottom

measurements are depth offset. The offset between the top

and bottom measurements is used to calculate the apparent

dip of the formation ().

(1)

(2)

(3)Fig. 4. Azimuthal near-bit latero resistivity tool configuration. The tool

outputs a bit resistivity, a ring resistivity with a DOI of 7 in., and three button

resistivities of depth of investigations of 1 in., 3 in. and 5 in. Tool OD is 6.75

in., suitable for 8-1/2 in. hole size.

Fig. 5. Resolution comparison between LWD images and that of wireline. The

resolution of LWD RI is about 5 times better than that of LWD DI, but is still

much worse (about 10 times) than the wireline RI.


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Where is the intersection angle between the borehole

and the formation, I the borehole inclination, D the depth

offset between the top and bottom measurements, DE the

effective wellbore diameter, DBHthe borehole diameter, and

DOIdepth of investigation of the measurement.

For LWD DI, DOI is about 1 in. while for LWD RI, DOI

is about 1.5 in. Use of DOI in Eq. 3 is to account for the

apparent increase in wellbore diameter created by the depthof investigation of the measurement.2 Fig. 6 provides a

diagrammatic explanation of Eqs. 1-3.

Directional Deep Resistivity (DDR)

A new LWD technology, which introduces directional deep

electromagnetic (EM) measurements that uses tilted and

transverse current-loop antennas, was developed recently.

The directional deep resistivity (DDR) determines the


Fig. 6. (a) Dip calculation from azimuthal measurements and (b) examples of

image and the calculated dip angles.

Fig. 7. Directional deep resistivity (DDR) tool layout with axial (T5, T3, T1,

T2, and T4) and transverse (T6) transmitter antennas and axial (R1 and R2)

and tilted (R3 and R4) receiver antennas. Tool spacings are 22 in., 34 in., 84

in., and 96 in., frequencies are 100 kHz, 400 kHz, and 2 MHz. Tool OD is

4.75 in., suitable for 6-1/8 in. hole size.

Fig. 8. Pre-job modeling of DDR tool response to conductive boundaries.

Fig. 9. BHAs used to drill the three wells.


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distance to approaching formation boundaries and their

orientation to help in proactive geosteering. It can be

combined with conventional LWD resistivity to improve

formation resistivity modeling and interpretation around

the wellbore. By monitoring in real time, distance to

formation boundary up to 15 ft. around the wellbore can

be detected allowing for sufficient time to make trajectory

adjustments to stay within the reservoir.A schematic representation of the antenna configuration

is shown in Fig. 7. The array offers directional phase shift

and attenuation measurements at four different spacings (22

in., 34 in., 84 in. and 96 in.) with three different frequencies

(100 kHz, 400 kHz and 2 MHz). The tool has an OD of

4.75 in.; thus it is suitable for a hole size of 6-1/8 in.

The azimuthal orientation of the tool is provided by a

magnetometer system. The downhole resistivity and EM

direction are sent to the surface through mud pulse telemetry,

with a speed of six bits per second, and then streamed into

automatic inversion software. The inversion produces the best

solution distance to resistivity boundaries and the resistivity of

layers close to wellbore. No prior knowledge of the bedding

structure is assumed, making the process fully automated. The

inversion software is also used for pre-job planning of the tool

responses. An example of pre-job modeling of tool response in

a thin reservoir is shown in Fig. 8.

Bottomhole Assemblies Used in This Study

Three different BHAs were used in this study, as shown in

Fig. 9. BHA-A consists of normal LWD triple combo with

azimuthal density and DI. This BHA was used in drilling

well XA-A in 2003. In BHA-B, conventional resistivity was

replaced with RI to provide real-time RI for geosteering as

well as shallow formation resistivity for formation

evaluation. This BHA was used for drilling/geosteering the

8-1/2 in. hole sections of wells XA-B and XY-A. With DDR,

BHA-C was used to drill/geosteer laterals 1 and 2 of wellXY-A. Drilling/geosteering wells XA-A, XA-B and XY-A are

discussed in more detail below.

DRILLING ML WELLS IN THINLY LAYERED

RESERVOIRS

Geosteering with DI An Example

XA-A, a L1Z1 ML well, was drilled in 2003 with

conventional LWD triple combo and density image (DI). In

general, the well was drilled and geosteered successfully,

except at depth x400 where the well trajectory intersected

the zero porosity anhydrite (Fig. 10a); both azimuthal

density and DI indicated that the anhydrite was at the top

of the reservoir. Therefore, the well was geosteered

downward to get back to the reservoir.

DI, being a shallower measurement, was not able to

detect the approaching boundary in advance. Consequently,

when it detects an anhydrite above or below, the drill bit

has already entered into it and coming back to the reservoir

could be difficult.

Fig. 10. Raw LWD logs and calculated volumetrics for well XA-A (a) and well

XA-B (b).

Fig. 11. Real time LWD RI, deep, medium, shallow, and bit resistivity. The real

time logs were transmitted to surface by mud pulse telemetry at a speed of six

bits per second, and then to office via satellite.


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Formation Resistivity

In conventional formation evaluation, deeper measurement

is always preferred since it is less affected by borehole

rugosity and borehole fluids.21 Deep measurements inhorizontal wells, especially in thinly layered reservoir

intervals such as L1Z1, may be severely affected by adjacent

bed, rock anisotropy, and other factors.

From Fig. 10a, it is seen that the conventional triple

combo deep (30+ in.), medium (20 in.), and shallow (10 in.)

resistivity measurements are very lazy from the top to the

bottom of the hole, even though reservoir porosity changed

from 15 pu to zero pu. In this case, shallower measurement

may be more representative of the reservoir, provided that

the mud filtrate invasion is minimized.

Geosteering with RI An Example

XA-B, another L1Z1 ML well in the same field as well XA-

A, was drilled in 2004. This well was geosteered with LWD

RI tool, the first RI job in Saudi Arabia (Fig. 10b). Examples

of static and dynamic real-time RI are shown in Fig. 11.

There were two main objectives for using RI in well XA-

B. One was that, due to the higher resolution of RI

compared to DI (Fig. 5), it can be used for better reservoir

characterization, thus better geosteering of the well. The

other was that RI may be able to provide more

representative reservoir resistivity, as discussed above, than

the normal LWD deeper resistivity measurement if mud

filtrate invasion can be minimized by optimizing the designof drilling fluid. After completing this well, we believe we

achieved both objectives.

Fig. 12 shows a comparison between RI and DI. It is

evident from this figure that the quality of the RI is much

better than that of the DI, and it is much easier for

geoscientists to characterize reservoir features along the well

path with RI. Azimuthal densities are also plotted in the

figure for the purpose of comparison.

Fig. 13 shows a similar plot as Fig. 12, but in this figure

the well trajectory with respect to the boundary formation

is also shown based on the real-time RI interpretation. Real-

time LWD RI provides clear guidance to the geoscientists as

to whether the wellbore is close to the bottom or the top

zero porosity anhydrite. Based on this information, real-

time geosteering decisions can be made and appropriate

actions can be taken in order to have a more successful

MRC well.

Effect of Borehole Rugosity on Shallow Measurements

Fig. 14 demonstrates the benefits of the higher resolution

and deeper measurement of RI. In this example, due to the

effect of borehole rugosity on shallow density

measurements, the azimuthal density indicated that the well

path was approaching the bottom anhydrite (bottom

density is heavier than the top density). Had this been the

Fig. 12. In this example, both DI and RI can be used successfully for

geosteering, even though the RI has better resolution.

Fig. 13. This example shows that the well was avoided to hit the overlaying

and underneath anhydrite with the help of RI.

Fig. 14. In this example, azimuthal density (DI) indicates that the well is

approaching the bottom anhydrite (see top and bottom density) while the RI

shows otherwise. Further investigation reveals that hole rugosity affects the

shallow DI measurement and the well was geosteered down to get back to the

reservoir.


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only information available, it would have been necessary to

geosteer the well upward.

Since RI was also run in real time, it clearly showed that

the approaching anhydrite was at the top of the reservoir,

thus indicating the need to geosteer the well downward.With more confidence in RI, a real-time decision was made

and the well was geosteered downward to stay away from

the top anhydrite. As a result, a better well was achieved

(Fig. 10b).

The difference between DI and RI in this interval is

attributed to the effect of borehole rugosity. These borehole

rugosity effects on the shallower DI measurement, but not

much on the deeper RI measurement, are clearly shown in

Fig. 15.

Geosteering with DDR An Example

Directional Deep Resistivity (DDR) data was acquired in

well XY-A, the first well geosteered with DDR in Saudi

Arabia (Fig. 16). The objective was to drill a ML well to

improve well productivity and enhance reservoir sweep by

providing maximum reservoir contact. To ensure the well

objectives are delivered, DDR was run to provide real-time

measurements of distance to conductive boundary (DTCB).

The capability to detect boundaries away from the borehole

provides the means to maximize the net horizontal length

drilled in the reservoir, and reduces the risk of exiting to

non-pay zones.

Around-the-clock coverage of well placement operations

was conducted from Saudi Aramcos office by both the

Saudi Aramco and service company geoscientists. InterACT

and satellite data transmission services were used to provide

communication and data connectivity from the rig site to

Saudi Aramcos Geosteering Operation Center (GOC),

enabling real-time interpretation, which was the key in

delivering DTCB for effective decision-making.

Pre-Job Modeling

Pre-job planning is essential for a successful delivery of the

well objectives. Data from nearby wells was used to model

the expected LWD resistivity and DDR responses for the

laterals, as shown in Fig. 8. This pre-job modeling helped

the well placement team to understand the expected tool

measurements along the planned well path and distance to

boundary response from the inversion software. This

approach enhances the teams capability to act before the

wellpath exits any reservoir.

Added Value of DDR

It was decided by the asset team that the 1st and 2nd

laterals of well XY-A would be logged by the DDR. The

Fig. 15. Effect of borehole rugosity on shallow, but not deep measurement. Fig. 16. BHA used for drilling well XY-A and real geosteering using DDR.


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objective for the 1st lateral was to drill half of the planned

well length in lobe 1 (L1) and then cut through the

anhydrite stringer and drill the remaining half in lobe 2 (L2,

a thicker reservoir interval below L1). While in L1, DDR

and log correlation indicated that the interval thickness in

this well is about half of that expected from nearby wells.

Consequently, a decision was made to drop the hole

inclination to enter and drill in L2.

While in L2, a low porosity dolomitic zone was

encountered. It was decided to drop the well trajectory

further in TVD until the well was in good reservoir rock,

and then the well was kept 3 ft. TVD below the dolomitic

layer. As planned, the well was placed in the good reservoir,

and drilling continued in this zone until DDR detected that

the oil-water contact (OWC, Fig. 17) was approaching. Thewell was called TD based on the DTCB information

provided by DDR in real time.

The 2nd lateral was planned to be drilled in L1 only, but

based on L1 thickness in the 1st lateral, it was decided to

drill the 2nd lateral in both L1 and L2, with 1/3 of the

length in L1 and 2/3 in L2. With the aid of DDR, the well

was drilled longer than planned in L1 in a tight 3 ft.

window (Fig. 18).

Drilling through the anhydrite stringer into L2 proved to

be more challenging than anticipated as the formation

started dipping downward at a relatively steep angle

(relative dip of about 1.5 degrees), and as a result about

200 ft. was drilled in the anhydrite before the well

eventually got into L2. After drilling into L2, DDR

indicated that the well was approaching the OWC, and it

was decided to stop drilling and TD the well.

SUMMARY AND CONCLUSIONS

To recover oil from thinly layered reservoirs, MRC ML

wells must be drilled with advanced LWD geosteering

technologies to maximize net reservoir contact.

LWD provides different levels of service: conventional

triple combo for simple formation evaluation as well as

geosteering simple-to-drill wells. For more difficult-to-drill

wells, azimuthal measurement and image are required.

DI is commonly used because of its slim tool OD. RI, with

more than five times of resolution, has a deeper depth ofinvestigation, thus is less affected by near wellbore effects. High

resolution measurements are needed for accurate formation dip

analysis and geosteering. However, the RI tool OD is bigger,

which limits its application to 8-1/2 in. holes only.

Both DI and RI are shallower measurements. When a

boundary shows on the image, it means the wellpath is

already close to it. DDR provides a much deeper

measurement and thus can be used in geosteering a well

away from a boundary before getting too close to it.

The three case studies presented in this paper have

showed that it is possible to develop thin targets through

enhanced geosteering and reservoir planning. Well XA-A,

geosteered with LWD triple combo and DI, was a successful

well except the well penetrated the zero porosity anhydrite

at one interval.

For well XA-B, LWD RI provided extra added value by

keeping the well path in the reservoir. LWD azimuthal

density and DI were affected by borehole rugosity and

could not have been effective in keeping the borehole in the

thin reservoir.

For well XY-A, though the formation was initially

assumed to be almost flat based on pre-spud maps, RI

confirmed that the formation was actually dipping. L1thickness was initially assumed to be between 5 ft. and 7 ft.

TVD but both RI in the 8-1/2 in. section and DDR in the 6-

1/8 in. section confirmed that the thickness of L1 is about 3

ft. With the aid of DDR, it was possible to drill a rather

long horizontal lateral in L1 despite the tight window. In

addition, drilling plans for both laterals of well XY-A were

optimized in real time based on DDRs response to WOC.

Fig. 17. DDR inversion processing using memory data confirmed the real time

results of the presence of OWC about 13 ft. TVD below the XY-A lateral 1

path. Well TD is shorter than planned because of this real-time monitoring.

Fig. 18. DDR was used to geosteer well XY-A lateral 2. The thickness of L1Z1

in this area was found very thin, about 3 ft. TVD. In addition, an advancing

WOC was detected by DDR during drilling. Consequently, the well was called

TD to avoid being too close to the WOC.


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RECOMMENDATIONS

Apart from the drilling performance benefits that the RSS

delivers, it is important to utilize it in difficult-to-drill wells

where active geosteering is required.

Running high-resolution LWD RI will not only improve

geosteering but also enhance reservoir characterization. It has

the potential to replace some of the pipe-conveyed image logsfor geological feature characterization, thus saving rig time.

It is recommended that DDR be run in wells where distance

to formation boundary is crucial, provided that the

conductivity contrast is large enough to be detected by the tool.

ACKNOWLEDGEMENTS

The authors would like to thank Saudi Aramco

management for granting permission to publish this paper.

Special thanks are also extended to colleagues from both

Saudi Aramco and Schlumberger for their support.

REFERENCES

1. Ma, S.M., Al-Hajari, A.A., Berberian, G. and

Rammamorthy, R.: Cased-Hole Reservoir Saturation

Monitoring in Mixed Salinity Environments A New

Integrated Approach, paper SPE 92426, 2005.

2. Akinsanmi, O., et al.: Application of Azimuthal

Density While Drilling Images for Dips, Facies and

Reservoir Characterization Niger/Delta Experience,

paper SPE 65460, 2000.

3. Greiss, R.M., et al.: Real Time Density and Gamma

Ray Images Acquired While Drilling Help to Position

Horizontal Wells in a Structurally Complex North Sea

Field, SPWLA, 2003.

4. Ballay, G., et al.: In the Drivers Seat with LWD

Azimuthal Density Images, paper SPE 72282, 2001.

5. Al-Fawwaz, A., Al-Yosef, O., Al-Qudaihy, A., Al-

Shobaili, Y., Al-Faraj, H., Maeso, C. and Roberts, I.:

Increased Net to Gross Ratio as the Result of an

Advanced Well Placement Process Utilizing Real-Time

Density Images, paper SPE 87979, APDTCE, 2004.

6. Bonner, S., et al.: Resistivity While Drilling Images from

the String, Oilfield Review, Spring 1996, 8, No. 1, 4.

7. G. Ford, J. et al.: Dip Interpretation from Resistivity at

Bit Images (RAB) Provides a New and Efficient Method

for Evaluating Structurally Complex Areas in the Cook

Inlet, Alaska, paper SPE 54611, WRM, 1999.

8. Bratton, T. et al.: Logging-While-Drilling Images for

Geomechanical, Geological, and Petrophysical

Applications, SPWLA, paper JJJ, 1999.

9. Li, Q., Bornemann, T., Rasmus, J., Wang, H., Hodenfield,

K. and Lovell, J.: Real-Time LWD Image: Techniques

and Applications, SPWLA, paper WW, 2001.

10. Rohler, H., Bornemann, T., Darquin, A., Rasmus, J.:

The Use of Real-Time and Time-Lapse Logging-

While-Drilling Images for Geosteering and Formation

Evaluation in the Breitbrunn Field, Bavaria, Germany,

paper SPE 71331, ATCE, 2001.

11. Li, Q., Liu, C. B., Maeso, C., Wu, P., Smits, J.,

Prabawa, H. and Bradford, J.: Automated

Interpretation for LWD Propagation Resistivity Tools

Through Integrated Model Selection, Petrophysics,

54, pp1-12, 2004.

12. Daveridge, S., et al.: An Innovative Business Model to

Leverage Innovative Well-Placement Technology,

paper OTC-17591-PP, OTC, 2005.

13. Li, Q., Omeragic, D., Chou, L., Yang, L., Duong, K.,

Smits, J. and Yang, J.: New Directional

Electromagnetic Tool for Proactive Geosteering and

Accurate Formation Evaluation While Drilling,

SPWLA, 2005.

14. Tribe, I.R., Burns, L., Howell, P.D., Dickson, R.: Precise

Well Placement Using Rotary Steerable Systems and

LWD Measurements, paper SPE 71396, ATCE, 2001.

15. Oguntona, J., Kelsch, K., Osman, K., Ingebrigsten, E., Butt,

P. and Saha, S.: Thin Sand Development Made Possible

Through Enhanced Geosteering and Reservoir Planning

with While-Drilling Resistivity and NMR Logs: Example

from Niger Delta, paper SPE 88889, ITCE, 2004.

16. Carpenter, W.W., et al.: Applications and Interpretation

of Azimuthally Sensitive Density Measurements

Acquired While Drilling, SPWLA, 1996.

17. Garrity, J., Onyirioha, R., Logan, J., Ingebrigsten, E.

and Butt, P.: Real-Time Dip Applications for

Geosteering in Swamp Fields of Nigeria, paper SPE

85660, 2002.

18. Labat, C.P., Doghmi, M. and Tomlinson, J.C.: Image-

Dip Calculation Using New-Generation LWD

Density-Porosity Tools, paper SPE 74370, IPCE, 2002.

19. Luthy, S., et al.: Precise Dip Determination in RealTime to Improve Well Placement Using LWD Azimuthal

Density Images, paper SPE 79172, ITCE, 2002.

20. Ingebrigsten, E., et al.: Real Time Dip Applications

for Geosteering Horizontal Wells, Onshore Nigeria,

paper SPE, ITCE, 2003.

21. Al-Sunbul, A., Ma, S., Al-Hajari, A., Scrivaslava, A.,

Ramamoorthy, R.: Quantifying Remaining Oil by Use of

Slimhole Resistivity Log in Mixed Salinity Environments

A Pilot Field Test, paper SPE 97489, 2005.


azimuthal gamma,

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