A guide to relief well planning. Allow for multiple surface location changes. Minimise surface location PU. Long baseline acoustic positioning : Differential GPS : Ensure Magnetic Ranging is within range 100’ to take over from MWD survey acquisition. Magnetic Ranging – relates to proximity measurements from the drilling well to the target well Magnetic ranging is a general term which is used to describe a variety of techniques which use

magnetic measurements to determine the relative position (i.e., relative orientation and/or separation distance) of a borehole being drilled relative to a target such as another borehole Magnetic ranging techniques include both “passive” techniques and “active” techniques. In both cases, the position of a borehole being drilled is compared with the position of the target borehole Passive Magnetic Ranging refers to the measurement of remnant magnetization of the target well's casing or BHA Active Magnetic Ranging refers to the measurement of magnetization that is induced from a source We had no involvement in the ranging runs because of the absence of Baker Hughes service offerings of the required technology Dual Inclination– relates to TVD uncertainty With use of the Near Bit Inclination, that is available in our AutoTrak drilling systems together with the survey inclination, we produce an averaged inclination that is of a higher accuracy than the single survey inclination This procedure results in a nominally surveyed position with a smaller position uncertainty (smaller TVD uncertainty) and higher accuracy Tool Setup for This Job: Scaling for Near Bit inclination has historically been defaulted to 11 bit transmitted which gives an effective inclination resolution of +/- 0.043945° 11 bit scaling could lead to "spiral effect", "noise" or "steps" When running the Dual Inclination Service we recommend setting up the Near Bit inclination with 13 bit resolution With the change to 13 bit we got an effective inclination resolution of +/- 0.010986° The Dual Inclination service was run at the rig-site with the offline use of an Excel workbook The workbook facilitated the comparison between the OnTrak survey inclination and the AutoTrak Near Bit inclinations The workbook also provided for calculating the final posted inclination and for QA / QC of the data Continuous Inclination– relates to TVD uncertainty This service was initially requested by xx but was not used With the use of the Near Bit Inclination available in the AutoTrak system we offer a service to post-correct the directional survey data to more accurately reflect any vertical inflections in the wellbore The tool setup for the Continuous Inclination Service is the same as for Dual Inclination This service was not used because the enhanced survey as a result of this procedure would have been “offline” and not realtime – this was seen as a potential source of confusion and not critical to well placement for this profile Magcorr – relates to drillstring interference & Azimuthal uncertainity.

This is a common correction and is standard for many BHAs for well profiles outside of a critical “no-go” region (high angle, due magnetic East or West) Magcorr was applied for all BHA runs on this well The directional sensor is subject to long-axial magnetic interference. At the rig-site a correction is applied to the survey data based on the data collected at that station (single survey magnetic correction - Magcorr) The application of a Magcorr correction is automated in our rig-site surface software A weakness of Magcorr correction is that it treats each survey independently, thereby discarding useful information which might be obtained from the relationship between measurements at successive surveys Multi Station Analysis – survey quality control & quality assurance The basis for multiple-survey corrections (MSA) is the assumption that the interference effects are the same for all surveys This assumption is reasonable provided that all surveys processed as a group are taken with the same BHA, and without jarring or excessive time intervals between surveys Each survey provides three magnetic measurements, but azimuth is the only independent magnetic variable calculated for each survey, since the total field and dip angle are assumed either constant for all surveys or known from in-field referencing Thus the use of data from several surveys provides sufficient information to solve for additional parameters Multi Station Analysis (MSA) is a technique widely used in MWD directional surveying to provide additional quality control and to correct for systematic errors On this well we used MSA and thus benefitted by having more confidence in the quality of the magnetic azimuths which was critical for geometric well placement BHA Misalignment Misalignment of the directional survey tool with the wellbore at the measure point causes a systematic error in survey inclinations. BHA SAG correction rectifies this SAG correction was applied where we had inclination above 1° Depth Correction Drillpipe stretch represents a systematic error for drillpipe conveyed survey tools such as with MWD surveys. A robust method for estimating and correcting for this stretch is offered We were asked to calculate the casing stretch on the target well, but BP declined realtime depth correction on the drilling well. The reason for this was to eliminate possible sources of confusion/misinformation IFR corrected surveys have a smaller lateral position uncertainty when compared with standard surveys The Instantaneous Magnetic Field = Main Field + Crustal Field ( Local geology ) + Disturbance Field ( Elect currents in upper atmosphere) The Crustal Field would be mapped by an external provider, for example Fugro The Crustal data acquired would then be processed by an external provider, for example the BGS Necessary advanced survey corrections can be applied (post drill) to aid in reducing positional uncertainty It is important to minimize positional uncertainty. The survey program identified survey frequency, tool type and applicability of advanced survey corrections. Increased survey frequency as the relief well approaches intersection point. A continuous gyro was run to back fill surveys every 10’. Wild Well and Boots & Coots. Initially created scenarios around 2 surface locations to determine which one was preferred. Scenario 1- An S type well heading directly to the planned point of intersect. In this scenario the build started after KOP 10000’TVD reaching a maximum inclination of 45 deg. Inclination then dropped to 15 deg. When the relief well is approximately 100’ distance from the target well a tangent of 100’ was planned keeping 15 deg inclination. Inclination is then reduced to 3-4 deg (highside tool face above 3-4 degs, Vector needs angle in the hole also …..confirm reason) . After which intersection is planned (Target well is vertical in this case). Note: Vector Magnetics ranging tool has a maximum range 100’ Scenario 2 (BH preferred) - The second scenario incorporates a “flyby point” into the design. In this scenario the relief well will start KOP @ 10000’ TVD build to ~ 35 deg then drop to 15 deg. Inc. We

expect to pass the xx well, above the planned intersection point, to determine the position of the well and facilitate refinement of the well plan. This will allow us to drop angle and track the Macondo well until reaching the planned intersection point. During the initial crossing (of the offset well) our MWD tools will experience magnetic interference, rendering MWD surveys unusable for this reason a gyro while drilling (GWD) tool will be included in the BHA to ensure there are no survey gaps. Usable surveys may have been obtainable for several hundred feet after the initial crossing however the plan as previously stated is to track the offset well closely (with 30’ center to center distance) which would mean increasing magnetic interference. To ensure consistent survey integrity during and after the planned flyby an MWD Gyro was planned for use in this section including the crossing of the target well (flyby). From this point onwards Magnetic Ranging will be used to determine the position of the Macondo well relative to the relief well being drilled. Planned well intersection with 3-4 deg. Inc. Dogleg severity restricted to no more than 2 deg/100’. Due to planned wireline runs. Continuous collision avoidance monitoring during the drilling phase – two relief wells drilled simultaneously. Dispensation signed by client allowing well intersection. The Planned intersection: The relief well trajectory is designed such that prior to any intersection attempt the relief well tracks the target well for some predetermined distance During this time numerous Magnetic Ranging shots are taken to help determine the relative location of the target well as best as possible. When the desired intersection point is reached, the relief well builds or drops to attempt to intersect Bit selection is important, sometimes a concave mill will be used to help maintain physical contact between relief and target wells during intersection attempts.

Impact of welpath turn on rotation of semi major axis of ellipsoid of positional uncertainty. Not all the above thoughts are originally mine. But I have accepted all of them. I have used several existing resources from many experienced persons in the field. If this subject could be of use to any practioner & help our industry in return – My objectives shall be fullfilled. Any help on my part – punam.kapoor@gmail.com. +91 7738338877.