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DESCRIPTIONSPE Aberdeen S implified S eries 2014 Demystifying Petroleum Engineering. Sponsored by Shell UK Limited. Ross Lowdon June 4 th 2014. SPE Aberdeen S implified S eries 2014 Demystifying Petroleum Engineering. WELLBORE SURVEY S IMPLIFIED. Kindly Sponsored by - PowerPoint PPT Presentation
Ross Lowdon June 4th 2014 SPE Aberdeen Simplified Series 2014Demystifying Petroleum EngineeringSponsored by Shell UK Limited
Ross Lowdon June 4th 2014
SPE Aberdeen Simplified Series 2014Demystifying Petroleum EngineeringWELLBORE SURVEY SIMPLIFIED
Kindly Sponsored by Shell UK LimitedAgendaDefining a survey
History of Wellbore surveying
Why do surveys matter?
Future of surveying3What is a Survey?4
WellboreMD = lengthOf wellboreAlong pathTVD = Vertical depthIndependentOf pathD-66Existing wellCurrently drillingSurface well locationWellbore trajectoriesThere are many types of survey, but effectively for a wellbore we need to know a start location, normally the wellhead position, a measured depth from a known datum to derive TVD, and an inclination and azimuth measured from vertical and a North reference respectively.
The emphasis here is on the level of detail required, every measurement has errors, and all are open to gross errors, depth can have pipe tally errors, leading to TVD issues, Inclination and azimuth are open to errors, with misalignment calculation being applied incorrectly or the azimuth North reference being incorrect.
On the surface all of this seems trivial, there appears to be very little to a borehole survey, MD. Incl and Azi. However you need to know your start point or origin, you need to know how that was derived, what error there is in it, and also understand all the other possible errors before you can make an assessment about you actual well position.6/24/20144History of Wellbore surveyingTexas 1890s
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Simple slide read the reasons for surveying, final point is you spend possibly $100s of millions on a wellbore, surveying is a very small incremental costs, but getting it wrong will have major impacts on project costs.6/24/20145
History of Wellbore surveying1930 Photo Magnetic single shot
1930 Photo Gyroscopic survey
1980 Measurement While Drilling
1999 Gyro While Drilling6
Simple slide read the reasons for surveying, final point is you spend possibly $100s of millions on a wellbore, surveying is a very small incremental costs, but getting it wrong will have major impacts on project costs.6/24/20146Survey TechnologiesMagneticRobust and RT 5 second surveysPoor referenceAffected by offset casing
GyroscopicExcellent ReferenceSensitive RT 2-7minsNot affected by offset casing7
Simple slide read the reasons for surveying, final point is you spend possibly $100s of millions on a wellbore, surveying is a very small incremental costs, but getting it wrong will have major impacts on project costs.6/24/20147Why Does a Wellbore Survey MatterAvoiding wells collisionsAvoiding well control issuesRelief wells
Ensure you hit the your targetsLWD to reservoir model tie inReserves estimatesLegal requirements8
Simple slide read the reasons for surveying, final point is you spend possibly $100s of millions on a wellbore, surveying is a very small incremental costs, but getting it wrong will have major impacts on project costs.6/24/20148The Value of Good Surveying PracticeShorter gyro run $15KSaved casing survey $125KProduction shut in $700KTarget sidetrack $23MDry well$25MMajor collision blowout $$$??9Simple slide, defining the benefits of good survey practice in order of cost.
A shorter gyro run optimising how far you need a gyro to go and still hit a target not just running to casing TDA saved casing survey optimising your MWD survey accuracyA production shut in reducing the EOUs in your offset wells improving your survey accuracy in the well you are drillingA target sidetrack understanding your reservoir and trajectory uncertainty as simple as having a consisten vertical datumA dry well as above, but having the data and ability to understand what went wrong with your well positioning
A blow-out not understanding your offset well positions survey management.6/24/20149Avoiding other WellsWell avoidanceComplex and contradictory dataManaging the survey dataPoor data quality/missing data
Survey ManagementEnsuring data accuracyEnsuring reserves estimatesEnsuring HSE
There are large number of surveying challenges in drilling, well avoidance, relief well planning and target interception.
Well avoidance the issues are that we have multiple surveys from different times in a wells life, how do you understand their relative accuracy and quality so you know your well position accurately?How do you manage your surveys, database security and auditingHow do you know if wells are missing? If they are how do you avoid them, how accurate are the surveys you already have, what is your confidence in them?
Relief well planning if the target well is poorly surveyed how do you prevent an accidental intercept, how long will it take to find the well?, how do you manage your survey accuracy to optimise well intercept but minimise time to intercept? Your survey accuracy is going to define your ranging technology and have a direct impact on you time to kill the well.
Target interception How do you define your geological targets, do you understand the accuracy values from the survey tools run? What are the well positioning objectives, if geo-steering how do you tie the LWD data into the reservoir model and make allowances for their accuracy? This has a direct impact on your reservoir model interpretation, i.e. do you really have compartmentalisation, or is it a lack of understanding around survey accuracy?
6/24/201410Lateral MWD Survey Errors
Main = Bm
Crustal = Bc
Disturbance = BdDS interference = Bds
Total Magnetic Field = Bm + Bc + Bd Bds 11An MWD is essentially a downhole compass with inclinometers. It can be extremely accurate but that is reliant on the reference values you feed the azimuth calculation ands the amount of drillstring interference affecting the MWD tool down hole.
The reference field is made of the main, the crustal and disturbance fields. The main field is well known and maps the change in position of magnetic North over the space of a year between updates, the BGGM model is the best know of these and includes estimates of the crustal field.
The crustal field is formed when igneous/magnetised rocks are extruded close to the surface of the earth and significantly distort the Earths magnetic field, these are commonly known as magnetic anomalies as there resulting change in the local magnetic field is not captures in the mail field models such as the BGGM.
The disturbance field is cause by solar activity, and can have a significant impact on MWD tools, quite specifically at higher latitudes such as Alaska and to some extent the North Sea. The effects are generally short in duration, but can be very disruptive to the drilling process as the tool swings in and out of FAC, and the azimuth becomes erratic.
Drillstring interference is another issue that affects an MWD tools accuracy, this is less of an issue at lower latitudes, but it still has an effect as if a tool fails FAC then it becomes difficult to decide if the MWD tool itself has failed, or if there is a reference problem or finally if there is drillstring interference. DS interference can be mitigated against with the use of Non-Mag collars, and LWD and modern RSS tools are generally non-mag anyway this for SLB this is becoming less of an issue. It should be noted however that even small amounts of magnetic interference will have a large impact on azimuth when drilling east West, and this is checked in the design phase of SLBs DD service to control these effects.
Thus the total magnetic field the tool sees is the equation at the bottom6/24/201411Improving DefinitionBGGM 54 degreeHDGM 720 degreeMagVar 5,400 degree
12Improving definition, here we have 3 maps the BGGM, another global model the HDGM and then an aeromagnetic derived local magnetic field. You can see the increase in definition as we go from left to right, and the associated spherical harmonic increase from 54 to 5400 degree, denoting the improved definition.
It is in reducing the uncertainty of the magnetic model you use that improves the azimuthal accuracy of MWD surveys6/24/201412Capturing the Crustal FieldAeromag or Marine
3D mag cube13There are two ways on water to capture the local magnetic field, (on land this can be done with a theodolite and accurate GPS co-ordinates) one is a direct vector method using a towed magnetic package and the other is Aeromag, where a plane takes magnetic field intensity surveys which are inverted into vector measurements.
All of these techniques produce Dip Total field and declination values for a given area, which are more accurate than those to be found in global magnetic models. The use of aeromag (shown in the diagram on the left) allows the production of a 3D cube that can be interrogated for a given wellpath to give precise numbers of the reference field as shown in the diagram on the right6/24/201413Optimising Lateral Survey AccuracyAdvanced survey QCLocal magnetic mapMulti-station correctionIFR = 65% Lateral EOU reduction14In order to optimise lateral survey accuracy with an MWD you need to get the most accurate reference possible including accounting for variations in the local magnetic field, reduce the effect of drillstring interference and employ a more rigorous survey QA/QC.
There are some restrictions on the application of multi-station correction (which is use to reduce the effects of drillstring interference) at High an