Directional survey hand book

1. Upstream Technology Group

2. ISSUE 1 SEPTEMBER 1999

3. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 i Contents Authorisation for Issue Preface Amendment Summary Section 1 Introduction 1.1 About this Handbook 1.2 Directional Survey and Value Addition 1.3 The Design-Execute Principle Section 2 Policy and Standards 2.1 Drilling and Well Operations Policy 2.2 Policy Expectations 2.3 Standard Practices Section 3 Theory 3.1 Surface Positioning 3.2 The Earth’s Magnetic Field 3.3 Position Uncertainty 3.4 Position Uncertainty Calculations Section 4 Methods 4.1 Multi-Well Development Planning 4.2 Survey Program Design 4.3 Anti-Collision – Recommended Practice 4.4 Anti-Collision – Selected Topics 4.5 Target Analysis 4.6 Survey Calculation 4.7 In-Hole Referencing 4.8 In-Field Referencing 4.9 Drill-String Magnetic Interference 4.10 Survey Data Comparison

4. BP Amoco BPA-D-004 Directional Survey Handbook ii Introduction September 1999 Issue 1 Contents (cont’d) Section 5 Survey Tools 5.1 Inclination Only Tools 5.2 Measurement While Drilling (MWD) 5.3 Electronic Magnetic Multishots 5.4 North-Seeking and Inertial Gyros 5.5 Camera-Based Magnetic Tools 5.6 Surface Read-Out Gyros 5.7 Dipmeters 5.8 Obsolete and Seldom Used Tools 5.9 Depth Measurement 5.10 JORPs Section 6 Technical Integrity 6.1 What is Technical Integrity ? 6.2 Risk Assessment 6.3 Surface Positioning 6.4 The Directional Design 6.5 Executing the Design 6.6 Survey Data Management 6.7 Performance Review Appendix A Mathematical Reference Appendix B Approved Tool Error Models Appendix C Data and Work Sheets

5. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-i Appendix A +* Contents Page 5 '' A-1 5 4 ' % - A-3 5 ' A-8 5 ! 5 ' A-9 5

6. 5#' ' A-17 5 ) A-22 Figure A.1 Reverse survey calculation A-2 A.2 Geometrical construction of the pedal curve A-7 A.3 The pedal curve and uncertainties in the north and east directions A-7 A.4 Naming convention for sensor axes A-8 A.5 A ‘bit’s-eye-view’ of the target: the basis of the BP Amoco target analysis method A-10 A.6 Graphical method of target analysis A-16 A.7 Calculating a no-go area on the travelling cylinder diagram A-18

7. BP Amoco BPA-D-004 Directional Survey Handbook A-ii Mathematical Reference September 1999 Issue 1 Appendix A +* Contents (cont’d) A.8 Derivation of the risk-based separation rule A-20 A.9 Behaviour of the risk-based separation rule at low positional uncertainty A-21 A.10 Behaviour of the risk-based separation rule at intermediate positional uncertainty A-21 A.11 Behaviour of the risk-based separation rule at high positional uncertainty A-22

8. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-1 5--%A 5 +* Some of the equations and formulae underlying the methods described in the main part of the Handbook. ( ( 5 ' ' 7 [ ]∆ ∆ N MD I A I A RF= + 2 1 1 2 2sin cos sin cos . [ ]∆ ∆ E MD I A I A RF= + 2 1 1 2 2sin sin sin sin . [ ]∆ ∆ V MD I I RF= + 2 1 2cos cos . C 9

9. RF DL DL =       2 2 tan $

10. DL@+I I . I I S6+A A .T

11. BP Amoco BPA-D-004 Directional Survey Handbook A-2 Mathematical Reference September 1999 Issue 1 RF@6 DL ( X ( DL ( Y7 RF DL DL DL = + + +1 12 120 17 20160 2 4 6 (

12. XN446° YN6°

13. 6 64 5 68++ ; + 0+; ='57'075 1

15. P0 P2 P1 u1 u2 u0 r01 r02 r12 u12 u01 α12 C u02 ' ' ' + .

16. ' (

17. 7 u u u1 12 02 01 01 02 12= + r r r r A similar method, also based on interpolating the hole direction, can be found in

18. World Oil, April 1986 Figure A.1 Reverse survey calculation

19. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-3 '

20. 7 ( ) ( )u u u u u u u0 1 01 0 1 01 0 2 1 01 12 022 1 2 2 2+ = ∠       = ∠ =cos cos .P CP P P P ( )u u u u u0 01 12 02 12= −. O' ( )u u u u u2 12 01 02 12= −.

21. + .

23. ∆D r12 12 12 12 2 2 =       α α csc α12 1 1 2= ×− sin u u 5 4 ' % - ' $ ( (7 (@Cnev @ σ σ σ σ σ σ σ σ σ n ne nv ne e ev nv ev v 2 2 2           A

25. BP Amoco BPA-D-004 Directional Survey Handbook A-4 Mathematical Reference September 1999 Issue 1 * ( #+*%5A $ ( + .

26. $ (+ $T

27. $ $

28. (7 C T C Thla h hl ha hl l la ha la a hla nev hla T =           = σ σ σ σ σ σ σ σ σ 2 2 2 Thla I A I A I A A I A I A I = − −           cos cos cos sin sin sin cos sin cos sin sin cos 0 # IA

29. ! 6 E 4 0

30. ! 7+ . ! $ +

31. . + .

33. . 0' +5=8546 77

35. - (7 Cne @ σ σ σ σ n ne ne e 2 2        

36. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-5 0' +5=55; ; +'57 46

37. $ $ (

38. (7 C T C Tne n ne ne e ne nev ne T* * * * * * * =         = σ σ σ σ 2 2 Tne I A I A * tan cos tan sin = − −       1 0 0 1 '57'07586+F57 +++ 774 ! 7 1$ (@σmax @ ( )σ σ σ σ σn e n e ne 2 2 2 2 2 2 4 2 + + − + 1$ (@σmin @ ( )σ σ σ σ σn e n e ne 2 2 2 2 2 2 4 2 + − − + ! (ψ ψ

39. 7 tan2 2 2 2 ψ σ σ σ = − ne n e

40. $:4° P:4° 7 σ σn e 2 2 $,3°Nψmaj NP,3° σ σn e 2 2 $,3°Nψmin NP,3° ( Cne * (

41. BP Amoco BPA-D-004 Directional Survey Handbook A-6 Mathematical Reference September 1999 Issue 1 ' *%7 * -% - %

43. +- .

45. /G0 1) /G0 *8) 2( %

46. G$1

47. 7 χ νp, 2

50. ν χ νp, 2 $ +ν @-. +ν @. p. Example. Find the number of standard deviations at which a 3D error ellipsoid must be drawn to represent a 95% confidence region, assuming the well position errors follow a trivariate normal distribution. Setting p = 0.95 and ν = 3, we find from tables that χ0 95 2 . ,3 = 7.81. The 95% confidence region is therefore represented by a 2.79-sigma error ellipsoid. 4% ' 98 -: ! !#7 [ ]σ σ σ σ σ σ σ σA n ne ne e n ne eA A A A A A A=               = + +cos sin cos sin cos sin sin 2 2 2 2 2 2 # ( / )

52. 9#-

53. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-7 pedal curve standard error ellipse 9 # + .

54. standard error ellipse North East pedal curve or “footprint” σnorth σeast Figure A.2 Geometrical construction of the pedal curve Figure A.3 The pedal curve and uncertainties in the north and east directions

55. BP Amoco BPA-D-004 Directional Survey Handbook A-8 Mathematical Reference September 1999 Issue 1 5 ' * %

59. 7 Y-axis X-axis Z-axis (down hole) Gravity Highside τ τ = instrument toolface angle Gx, Gy, Gz Bx, By, Bz

60. + . ! 7 Inclination = I =cos− + +           1 2 2 2 G G G G z x y z sin− + + +           1 2 2 2 2 2 G G G G G x y x y z Magnetic Azimuth = Am = ( ) ( ) ( ) tan− − + + + − +           1 2 2 2 2 2 G B G B G G G B G G G G B G B x y y x x y z z x y z x x y y Instrument toolface = τ =tan−         1 G G x y Figure A.4 Naming convention for sensor axes

61. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-9 7 G G Ix = − sin sinτ G G Iy = − sin cosτ Gz@GI B B I A B I B Ax m m= − +cos cos cos sin sin sin sin cos sin cosΘ Θ Θτ τ τ B B I A B I B Ay m m= − −cos cos cos cos sin sin cos cos sin sinΘ Θ Θτ τ τ B B I A B Iz m= +cos sin cos sin cosΘ Θ G, B Θ

62. 7 Gravity Field Intensity@ G G Gx y z 2 2 2 + + Magnetic Field Intensity@ B B Bx y z 2 2 2 + + Magnetic Dip Angle@sin . − + +     1 G B G B G B G B x x y y z z 5 ! 5 ' ) '#

64. BP Amoco BPA-D-004 Directional Survey Handbook A-10 Mathematical Reference September 1999 Issue 1 (45 % A

66. + .

70. Vi Ui Xi Yiσh σl lij hij φij φi+1 φi+1− φi Ns PX PY b Exclusion probability is integrated over the part of each sector lying outside the target... …then summed over all sectors geological target reference point geological target boundary standard error ellipse φi as-surveyed point of penetration 1 +! .δ !+ ! $ .α K$ ( ! ! α − °90 M$ ( $ Figure A.5 A ‘bit’s-eye-view’ of the target: the basis of the BP Amoco target analysis method

71. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-11 1

72. Nv $ Xi Yi xi i i X Y =       1 $

73. p =       P P X Y

74. $ (

75. + .

76. $ b 9(:# = ; :86 5+ (05+= (

77. x pi − $ +*28.$

78. ( Ttp = − − − −           sin cos cos cos sin cos sin α α δ α α δ δ0 #

79. ( (

80. ( )T x p btp i − + 9

81. ( Ttc I A A I A A I = − −      cos cos sin cos sin cos sin 0 ( ( $ 7 ( )[ ] U V highside lateral i i tc tp i       =       = − +T T x p b

82. BP Amoco BPA-D-004 Directional Survey Handbook A-12 Mathematical Reference September 1999 Issue 1 4886 +0 (4 (

84. + .

85. $ (

87. $ 7 C T C Ttc h hl hl l tc nev tc T =       = σ σ σ σ 2 2

89. ( ) ( ) pdf tc T tc t C t C t= −      −1 2 1 2 1 π det exp ( ) = − − + − −         1 2 2 22 2 2 2 2 2 2 2 2 2 π σ σ σ σ σ σ σ σ σh l hl l hl h h l hl h hl l exp t =       h l '704+(5(7=

91. h l r r       →       cos sin φ φ ( ) ( )( ) ( ) ( ) pdf r r f h l r h l hl , exp det , , φ π σ σ σ φ ∂ ∂ φ = − −       1 2 2 2 2 2 ( )( )= − − r r f h l hl2 2 2 2 2 π σ σ σ φexp ( ) ( ) f l hl h h l hl φ σ φ σ φ σ φ σ σ σ = − + − 2 2 2 2 2 2 2 2 2 cos sin sin

92. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-13

93. Ns (

94. 7 ( ) ( ) I pdf r d drij j N j N r h l r i i i s i i i s ij ij ≈                = + − − = + − = + =∞ + + ∫∫ ,φ φ φ φ φ φ φ φ φ φ 1 1 1 2 2 h l ij ij       $

95. ( $ φi i i U V =       − tan 1 (

96. ( $ ( (

97. $ ( )I N pdf r drij i i s ij r h l r ij ij ≈ −+ = + =∞ ∫ φ φ φ1 2 2 , φ φ φ φ ij i i i s j N = + −      −+1 2 1

98. ( 7 ( )( )I N r r f drij i i s h l hl ij r h l r ij ij = − − − + = + =∞ ∫ φ φ π σ σ σ φ1 2 2 2 21 2 2 2 exp

99. BP Amoco BPA-D-004 Directional Survey Handbook A-14 Mathematical Reference September 1999 Issue 1 ( )( ) ( ) = − − − −          + = + =∞ φ φ π σ σ σ φ φ i i s h l hl ij ij r h l r N r f f ij ij 1 2 2 2 2 1 2 2 2 2 exp ( ) ( ){ } ( ) = − − + − +φ φ φ π φ σ σ σ i i s ij ij ij ij h l hl N h l f f 1 2 2 2 2 2 4 exp h lij ij 2 2 + h l ij ij       7 + . $ 7 h l ij= tanφ +

100. . i 7 l V h U V V U U i i i i i i − − = − − + + 1 1 1 l ( ) ( ) ( ) ( ) l V U U U V V U U V V ij i i i i i i i i i i ij = − − − − − − + + + + 1 1 1 1 tanφ ( ) ( ) ( ) ( ) h l l l l V U U U V V U U V V ij ij ij ij ij ij ij i i i i i i i i ij i i ij 2 2 2 2 2 2 2 1 1 1 1 2 + = + = = − − − − − −         + + + + tan cos cos sin φ φ φ φ

102. (

104. 7

106. p @ ( )1 11 − == ∑∑ Iij j N i N sv p

107. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-15 - % ) ! ( :;Q+

109. )

110. :;Q. 9

111. (

112. 4 G $

113. +bH σH .

114. +bL σL .1 ! A 4

115. 4 *

116. ! ( )2σH Hb Inc− cos ! A Inc 4! ! ( )2σH Hb Inc+ cos !AP6;4F 4

117. ! 2σL Lb− !AP:4F 4) ! 2σL Lb+ !A$:4F

118. BP Amoco BPA-D-004 Directional Survey Handbook A-16 Mathematical Reference September 1999 Issue 1 4, ) 9#H ( planned well azimuth, A 2σH - bH 2σL - bL2σH + bH 2σL + bL geological targetdriller’s target step 3 step 5 step 4 step 6 cos Inc cos Inc Figure A.6 Graphical method of target analysis

119. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-17 5

120. 5#' ' - ' 0+85' 40' +5= 7 σ σ σ2 2 2 = +surf hole σsurf @ C

121. 6 σhole @ + . 6 5775' 8+0+; =(5

122. # ( + . =

123. =+

124. .

125. (

126. 7 Sb @MaxU4+$.V @ @

127. BP Amoco BPA-D-004 Directional Survey Handbook A-18 Mathematical Reference September 1999 Issue 1 * + $ .

128. + .

129. ' * # 5 $ β + 6- ) .

130. 7 . $ 7 @ ( ) ( ) ( ) ( ) ( ) cos cos cos sin sin cos sin cos cos sin sin cos I A A A A I A A A A I A β β β β β − − − − + − − −           7 I @ G A@ #! G β u interfering well no-go area 0 minimum allowable separation Figure A.7 Calculating a no-go area on the travelling cylinder diagram

131. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-19 . 7 σ1@ u C uT 1 σ2 @ u C uT surf2 2 +σ 7 C1 @ ' ( C2 @ ( σsurf @ C

132. 6 .

133. +,. +$#(%- + $

134. S d d P d d = +      + + σ σ π 2 2 2 1 2 1 2 ln

136. G 9 #; OS

137. $$ σ

138. R +

139. . %

141. z

142. 7 ( ) f z z S ( ) exp= − −      1 2 2 2 2 σ π σ

143. BP Amoco BPA-D-004 Directional Survey Handbook A-20 Mathematical Reference September 1999 Issue 1 #

145. ( )P f z dz d d d d = − + + ∫ 1 2 1 2 2 2 + #;. % ( + $ .1

146. ( ) ( )[ ]P d d f d d d d S d d ≈ + +      = + − − +          1 2 1 2 1 2 1 2 2 22 2 2 2σ π σ exp / S

147. ( S z = 0 z = d1d2 d1 d2+ 2 d1 d2+ 2 z =_ z = S σ f(z) interfering well planned well (

148. # (

149. Figure A.8 Derivation of the risk-based separation rule

150. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-21 % + 6. Collision Risk (low position uncertainty) Collision Risk (higher position uncertainty) σaσb SaSb Tolerable Collision Risk Actual Collision Risk Minimum Separation increases as Combined Position Uncertainty increases Case 1 d + d 1 2 P σ 0.242

151. #

154. + -.

155. ab σaσb SS Tolerable Collision Risk Minimum Separation decreases as Combined Position Uncertainty increases Case 2 d + d 1 2 P σ 0.242 d + d 1 2 P 0.399 2

156. (

157. + . Figure A.9 Behaviour of the risk-based separation rule at low positional uncertainty Figure A.10 Behaviour of the risk-based separation rule at intermediate positional uncertainty

158. BP Amoco BPA-D-004 Directional Survey Handbook A-22 Mathematical Reference September 1999 Issue 1 σaσb Sa Tolerable Collision Risk Tolerable Collision Risk is never exceeded - no Minimum Separation exists Case 3 d + d 1 2 P σ 0.399 5 )

159. DA the average excess dogleg severity over plan #

160. DTD +

161. D0 . !

162. 7 [ ]D I A i MP i P i P i 0 ≤ ≤ $

163. [ ]D I A j NS j S j S j 0 ≤ ≤ Figure A.11 Behaviour of the risk-based separation rule at high positional uncertainty

164. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Mathematical Reference A-23/24 9 +#6. 7 ( ) ( )[ ]{ }DL I I I I A AP i P i P i P i P i P i P i = − − − −− − − − cos cos sin sin cos1 1 1 1 1 7 DLS D D DLP TD P i i M = − = ∑ 1 0 1 O $ 7 DLS D D DLS TD S j j N = − = ∑ 1 0 1 ( ) ( )[ ]{ }DL I I I I A AS j S j S j S j S j S j S j = − − − −− − − − cos cos sin sin cos1 1 1 1 1 7 Wellbore Tortuosity = DLS DLSS P−

165. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Approved Tool Error Models B-i/ii Appendix B

166. Contents Page

167. !

168. #$ %

169. $ ' (

170. ' ) *

171. '

172. + (

173. ,

174. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Approved Tool Error Models B-1

175. An inventory of the survey tool error models approved for use in BP Amoco.

176. ! #$% • ' ( • ( ) # • ( ) * # + The standard format for survey tool error models is described in

177. BPAmoco BPA-D-004DirectionalSurveyHandbook B-2ApprovedToolErrorModelsSeptember1999Issue1

178. MWD - Standard MWD MWD MWD with no (or no known) special corrections The model allows for the fact that axial interference may marginally exceed the upper limit specified in Section 4.9 when the well is near to horizontal east/west MWD + Sag correction MWD+SAG MWD+SG MWD with a BHA deformation correction applied Covers all BHA corrections, from simple 2D to finite-element 3D models MWD + Short Collar correction MWD+SCC MWD+SC MWD with single station axial interference correction applied (4.9) “Short Collar” is the name of Sperry-Sun’s correction, but the error model covers all such MWD + Sag + SC corrections MWD+SAG+SC MWD+SS MWD with both BHA sag correction and single station axial interference correction applied MWD + IHR correction MWD+IHR MWDIHR In-hole referenced MWD (4.8). Assumes a BHA sag correction is applied to enhance inclination accuracy MWD + IFR correction MWD+IFR MWDIFR In-field referenced MWD (4.7), with time-varying field applied. Model is applicable whether or not Short Collar type correction is applied. Assumes a BHA sag correction is applied to enhance inclination accuracy. Table B.1 Approved Survey Tool Error Models – MWD (Part 1 of 2)

179. BPAmoco DirectionalSurveyHandbookBPA-D-004 September1999Issue1ApprovedToolErrorModelsB-3

180. MWD + IFR [Alaska] MWD+IFR:AK MWDIAK In-field referenced MWD in Alaska Model takes account of increased violence of magnetic field disturbances in Alaska. Assumes a BHA sag correction is applied to enhance inclination accuracy MWD + IFR [Wytch Farm] MWD+IFR:WF MWDIWF In-field referenced MWD at Wytch Farm Model takes account of observed low levels of axial low level interference using Anadrill BHA components and design. Assumes a sag correction is applied to enhance inclination accuracy MWD + IFR + Multi-station MWD+IFR+MS MWDIMS In-field referenced MWD with multi- station analysis and correction (4.9) applied in post-processing Assumes a BHA sag correction is applied to enhance inclination accuracy MWD + Crustal Anomaly corrn MWD+crust MWD+CA MWD where local magnetic field has been measured (or derived from aero-magnetic data) and corrected for, but short-term time variations are not applied. Assumes a BHA sag correction is applied to enhance inclination accuracy MWD + Crustal + SC corrections MWD+CA+SC MWD+CS Same as MWD + Crustal Anomaly correction but with single station axial interference correction applied Assumes a BHA sag correction is applied to enhance inclination accuracy Table B.1 Approved Survey Tool Error Models – MWD (Part 2 of 2)

182. EMS - Standard EMS EMS Electronic multishot with no (or no known) special corrections Includes ex-BP “Electronic Single Shots” model. Assumes large axial interference errors have been corrected. EMS + Sag correction EMS+SAG EMS+SG Electronic multishot with a BHA deformation correction applied Covers all BHA corrections, from simple 2D to finite-element 3D models. Assumes large axial interference errors have been corrected. EMS + IHR correction EMS+IHR EMSIHR In-hole referenced electronic multishot (4.8). Assumes a BHA sag correction is applied to enhance inclination accuracy. EMS + IFR correction EMS+IFR EMSIFR In-field referenced electronic multishot (4.7), with time-varying field applied. Model is applicable whether or not Short Collar type correction is applied. Assumes a BHA sag correction is applied to enhance inclination accuracy. EMS + IFR [Alaska] EMS+IFR:AK EMSIAK In-field referenced electronic in Alaska Model takes account of increased violence of magnetic field disturbances in Alaska. Assumes a BHA sag correction is applied to enhance inclination accuracy EMS + Crustal Anomaly corrn EMS+crust EMS+CA Electronic multishot where local magnetic field has been measured (or derived from aero-magnetic data) and corrected for, but short-term time variations are not applied. Assumes large axial interference errors have been corrected. Table B.2 Approved Survey Tool Error Models - Electronic Magnetic Multishots

184. BHI RIGS multishot RIGS RIGS INTEQ RIGS multishot surveys BHI Seeker multishot Seeker MS SKR MS All INTEQ Seeker (5.8) multishot surveys Ferranti FINDS multishot FINDS FINDS All Ferranti FINDS (5.8) surveys Gyrodata - gyrocompassing m/s GYD GC MS GYD GC Older Gyrodata gyro multishots, plus all battery/memory tool surveys (RGS-BT) Replaces ex-BP “Gyrodata multishot into open hole” model. Gyrodata - cont. casing m/s GYD CT CMS GYD CC Gyrodata multishot surveys with continuous tool (RGS-CT) in casing. OD 13-3/8” or less. Gyrodata - cont. drillpipe m/s GYD CT DMS GYD CD Gyrodata pump-down multishot surveys with continuous tool (RGS- CT) in drill-pipe. Gyrodata - large ID casing m/s GYD LID MS GYD LC Gyrodata multishot surveys (gyrocompassing or continuous tool) in larger size casing strings (greater than 13-3/8” OD). Includes an increased misalignment term Gyrodata – bat/mem drop m/s GYD BM MS GYD BM Gyrodata multishot using Battery/Memory tool in any configuration. Table B.3 Approved Survey Tool Error Models - North Seeking and Inertial Gyro Multishots (Part 1 of 2)

186. Schlumberger GCT multishot GCT MS GCT GCT surveys in casing or open hole. GCT = “Gyro Continuous Tool” (5.8) SDC Finder - multishot Finder MS FDR MS Finder multishots in casing or drill pipe Replaces ex-BP “Inrun” and “Outrun” models SDC Keeper - casing m/s KPR csg MS KPR CM Keeper multishot surveys in casing. OD 13-3/8” or less. SDC Keeper - drillpipe m/s KPR d/p MS KPR DP Keeper pump-down multishot surveys in drill-pipe. SDC Keeper - large ID csg m/s KPR LID MS KPR LC Keeper multishot surveys in larger size casing strings (greater than 13-3/8” OD). Includes an increased misalignment term Sperry-Sun G2 multishot G2 gyro MS G2 MS G2 (5.8) multishots in casing, drill pipe or open hole Replaces ex-BP “Static” and “Dynamic” models Table B.3 Approved Survey Tool Error Models - North Seeking and Inertial Gyro Multishots (Part 2 of 2)

188. Inclinometer (Totco/Teledrift) INC INC Inclination only surveys in near- vertical hole, including TOTCO, Teledrift and Anderdrift. Inclinometer + known azi trend INC+trend INC+TR Inclination only surveys in near- vertical hole, where formation dip and experience enables direction of drift to be predicted. Replaces ex-BP “Inclinometer (azimuth in known quadrant)” model Table B.4 Approved Survey Tool Error Models - Inclination Only Surveys

190. Camera-based mag single shot CB mag SS CBM SS Traditional (mechanical) magnetic single shot (5.5) Assumes tandem probes are run and that both are adequately magnetically spaced. Replaces ex-BP “PMSS”. Conventional SRG single shots SRG SRG Optically-referenced gyro single shots (5.6) Includes SDC Keeper when used in “siteline reference mode”. Tool types include SRG and MSRG (scientific Drilling), Sigma (INTEQ) and SRO (Sperry-Sun). Camera-based gyro single shots CB gyro SS CBG SS Traditional surface referenced gyro tool run on wireline, including “level rotor” gyros and Sperry-Sun SU3. Replaces ex-BP “PGSS” model. Gyrodata - gyro single shots GYD SS GYD SS Gyrodata gyro orientation surveys SDC Keeper - gyro single shots KPR SS KPR SS Keeper gyro orientation surveys Excludes siteline (ie. surface) referenced surveys SDC Keeper – surface ref s/s KPR SR SS KPR SR Keeper gyro orientation surveys, where azimuth alignment is achieved by optical referencing at surface. SDC Finder - gyro single shots Finder SS FDR SS Finder gyro orientation surveys NS Gyro single shots NS gyro SS NSG SS North seeking gyro orientation surveys taken with unspecified tool. Note Gyrodata, SDC Keeper and SDC Finder have their own models, which should be used if the tool type is known to be one of these. Table B.5 Approved Survey Tool Error Models - Other Single Shot Types

192. Camera-based gyro multishot CB gyro MS CBG MS Traditional optically referenced gyro surveys run on wireline, including “level rotor” gyros and Sperry-Sun SU3 (5.8). Replaces ex-BP “PGMS” model. Camera-based magnetic multishot CB mag MS CBM MS Traditional (mechanical) magnetic multishot (5.5) Assumes adequate magnetic spacing. Replaces ex-BP “PMMS”. Dipmeter or other wireline log Dipmeter DIPMTR Wireline conveyed logging tools with directional survey capability (5.7). Schlumberger OBDT, BGT are examples Sperry-Sun BOSS gyro multishot BOSS gyro BOSS Sperry-Sun BOSS multishot surveys (5.8). Table B.6 Approved Survey Tool Error Models - Other Multishot Types

194. Blind drilling Blind n/a Hole intervals where no surveys are taken Model assumes well direction deviates from last known survey at a constant rate. Errors grow with square of distance drilled. Unknown survey Unknown n/a Any survey data of unknown or dubious type Replaces ex-BP “unknown multishot” model. Zero Error model Zero Error n/a Used to set position uncertainty to zero down to a given depth (eg. sidetrack point). Table B.7 Approved Survey Tool Error Models - Special Models

195. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-i/ii Appendix C

196. Contents Page C-5 C-8 C-9

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284. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-5 WELL LOCATION MEMORANDUM LOCATION DESIGNATION This WLM supersedes the following previous locations: (NB: Any change in shotpoint location must have a new location designation) Country: Prospect/Field: Region/State: Lease/PSC/Block: 1. WELL LOCATION DEFINITION (To be completed by Buisiness Unit subsurface and/or reservoir team) SURFACE LOCATION: PRIMARY DEFINITION: 3D, 2D, HR Seismic Survey or OTHER* (* Circle appropriate definition) Survey name: Survey mnemonic: 3D Inline bin, or Database type name: 2D/HR line number: 3D Xline bin, or Acquisition contractor year: 2D/HR shot number: 3D bin size (Inline x Xline): Processing contractor year: or 2D/HR shotpoint interval: OTHER DEFINITION (eg: template slot No.): SECONDARY DEFINITION: 3D, 2D or HR* Seismic Survey (* Circle appropriate definition) Survey name: Survey mnemonic: 3D Inline bin, or Database type name: 2D/HR line number: 3D Xline bin, or Acquisition contractor year: 2D/HR shot number: 3D bin size (Inline x Xline): Processing contractor year: or 2D/HR shotpoint interval: PRIMARY DRILLING TARGET LOCATION (for non-vertical wells): PRIMARY DEFINITION: 3D, 2D or HR* Seismic Survey (* Circle appropriate definition) Survey name: Survey mnemonic: 3D Inline bin, or Database type name: 2D/HR line number: 3D Xline bin, or Acquisition contractor year: 2D/HR shot number: 3D bin size (Inline x Xline): Processing contractor year: or 2D/HR shotpoint interval: Section 1 completed by: Section 1 approved by: Signature: Signature: Date: Date: Name: Name: Position/Job Title: Position/Job Title:

285. BP Amoco BPA-D-004 Directional Survey Handbook C-6 Data and Work Sheets September 1999 Issue 1 Well Location Memorandum - Page 2 LOCATION DESIGNATION 2. SUBSURFACE DATA(To be completed by Business Unit Subsurface Team) Attach a separate map sheet to this WLMshowing seismic lines and geological structure around target location Describe below in words and diagramatically the surface location and it's constraints (give dimensions): Proposed Location TOLERANCE Define Surface Location Tolerance(s) Surface Location Area Diagram Illustrate shape and size of the zone within which a surface location would be acceptable and indicate constraints which limit rig anchoring or manoevring (eg: shallowgas, obstructions, pipelines). For location(s) derived fromworkstation provide: Coordinates of surface and primary target locations and two other bins remote fromthe primary target (one bin with same Inline and one with same Xline bin number as primary target) Location 3DSurvey Name Bin Size Inline Xline Eastings Northings Surface: PrimaryTarget: Same Inline: Same Xline: For surface and target locations based on 2Dor HRseismic provide: Location 2D/HR Survey Name Point* Line No. Shotpoint Eastings Northings Surface: PrimaryTarget: *Mapped point type (SP, CDP, etc) Attach extract of relevant 2D and/or HRline fromdatabase listing shotpoint coordinates values for 2kmeither side of proposed location

286. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-7 Well Location Memorandum - Page 3 LOCATION DESIGNATION 3. WELL LOCATION COORDINATES (To be completed by UTG SURVEY GROUP) LOCATION COORDINATES SURFACE LOCATION (Vertical or Deviated well) PRIMARY TARGET LOCATION (Deviated well) Latitude: Latitude: Longitude: Longitude: Eastings: Eastings: Northings: Northings: Surface Positioning Tolerance: True azimuth from surface location: degrees Water depth: Horizontal offset distance: m ft Ground Elevation: Geodetic Information: Datum name: Datum mnemonic: Ellipsoid name: Ellipsoid mnemonic: Projection name: Projection mnemonic: Zone: Data source of coordinates (eg: database name, report, etc): Surface Location: Primary Target Location: Seismic survey positioning systems and horizontal accuracy estimates: Surface Location Primary Target Location Positioning System Accuracy Positioning System Accuracy 3D Seismic: 2D Seismic: HR Seismic: Other positioning information: Section 3 completed by: Section 3 approved by: Signature: Signature: Date: Date: Name: Name: Position/Job Title: Position/Job Title: Circulation: D.S. / S.D.E. / D.E. Site Investigation Specialist Subsurface Team Leader Data Administrator (load to database) Asset Geoscientists Head of Survey

287. BP Amoco BPA-D-004 Directional Survey Handbook C-8 Data and Work Sheets September 1999 Issue 1 )*$*)*)-)

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304. BPAmoco DirectionalSurveyHandbookBPA-D-004 September1999Issue1DataandWorkSheetsC-9 Country: Area:

305. Well Number: Prospect/Field:

306. Submit to BP Amoco Survey for checking/approval Location designation: Date Completed: Accepted Surface Position Secondary Positioning System Contractors report no. (Geogs: 2 dec places, Grid: 1 dp (m) 0 dp (ft)) (Geogs: 3 dec places, Grid: 2 dec places) Geodetic Parameters Lat: ° Long: ° Geodetic Datum Projection and zone: ! Ref.Stn.1: Name/Country: Associated Ellipsoid !#

307. !#$ !% Easting: Northing: Lat. Long. Semi-major axis ' Radius of error: ( ' Primary Positioning System Easting Northing Semi-minor axis (Geogs: 3 dec places, Grid: 2 dec places) Dist to Ref.Stn. km Reciprocal flattening 1/ System/method for Names of Reference Station(s) used for Ref.Stn.2: Name/Country: Datum Shift accepted position )*+$, -. Primary Position Lat. Long. From WGS84 to Local Datum Easting Northing dX: ' dY: ' dZ: ( ' Secondary positioning Dist to Ref.Stn. km rX: rY: rZ: ( system: %#+$, -. Antenna Position: WGS84 Datum Ref.Stn.3: Name/Country: Scale Factor: //' Lat: ° Lat. Long. Useful Information / Notes Rig positioning contractor: 0112 Long: ° Easting Northing Job number: Sph. Ht. Dist to Ref.Stn. km 3$4 +

308. ' '/$%5 6* 7 83 9$%%$'4 ! 4 ! Site survey date: Antenna Coords: Network Solution $%% 4#

309. #$ ! +

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312. :* Contractor: Offset: Antenna to rotary WGS84 Datum 7!56 ) # %%

313. 5$!#4 43 ;!

314. Report number: (Relative range/bearing) Lat. ° correct. Rig name: ! 0 3 ' °

315. Long ° Sph.Ht. Coords of rotary: Local Datum Type of rig: Lat: ° S.D. X: Y: Z: Vertical datum: Long: ° Offset: Antenna to rotary (Rel. range/bearing) ! 2:% Ellip. Ht. ' °

316. B.M.S.L. Easting: Coords of rotary: Local Datum Water or stated ' Northing: Lat. ° depth Vert Datum Long ° B.L.A.T. ' S.D. X: Y: Z: Easting: S.D. RTE A.M.S.L ' Northing S.D. Diagram Diagram Rig Hdg 309.7 deg T R/T 1.0m 56.3 m GPS Antenna Rig Hdg 309.7 deg T R/T 17.4m 42.55 m GPS Antenna Completed by: (block caps) 17 Checked by: (block caps) =

317. BP Amoco BPA-D-004 Directional Survey Handbook C-10 Data and Work Sheets September 1999 Issue 1 WELL PLAN DATA SHEET * delete as appropriate Rig / Platform / Drill Site* Well Sheet completed by Date SURFACE LOCATION planned / actual* Datum/Ellipsoid Projection Structure reference Description Lat. N / S* Easting Long. E / W* Northing Well reference point Description Lat. N / S* Easting Long. E / W* Northing Offset from structure ref. N / S* E / W* Elevation (land rig) Elevation (offshore) Drill datum RT / KB* Drill datum RT / KB* Drill datum to well ref. pt. Drill datum to MSL Well ref. pt. to MSL Drill datum to well ref. pt. TARGET #1 TARGET #2 TARGET #3 Name Name Name Easting Easting Easting Northing Northing Northing Depth TVDss Depth TVDss Depth TVDss Tolerance Tolerance Tolerance Survey reference True / Grid* North arrows (diag.) Grid convergence (T to G) E / W* Magnetic declination (T to M) E / W* Magnetic model Date Correction (magnetic to survey ref.) Correction (true to survey ref.) Curved conductors Drill datum to well reference point MD TVD North East N / S* E / W* Incl. at w.r.p. Azim at w.r.p.

318. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-11 WELL PLAN DATA SHEET * delete as appropriate Rig / Platform / Drill Site* Well

319. Sheet completed by Date SURFACE LOCATION planned / actual* Datum/Ellipsoid Projection !# $%% ' ()* Structure reference Description + Lat. $°,-%$. N / S* Easting / 0 ,$1 Long. $$°%-. E / W* Northing 0 ,$%1$

320. 1 Well reference point Description + $ (+! 23* Lat. $°,-%. N / S* Easting / 0 ,$$

321. Long. $$°%-%

322. . E / W* Northing 0 ,$%1%

323. Offset from structure ref. %- N / S* 1%- E / W* Elevation (land rig) Elevation (offshore) Drill datum RT / KB* Drill datum RT / KB* Drill datum to well ref. pt. Drill datum to MSL 1- Well ref. pt. to MSL Drill datum to well ref. pt. $%- TARGET #1 TARGET #2 TARGET #3 Name Name Name Easting / 0 ,$$ Easting / 0 ,

324. Easting Northing 0 ,

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326. ,$ Northing Depth TVDss %%- Depth TVDss - Depth TVDss Tolerance Tolerance Tolerance - ,

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335. , Survey reference True / Grid* North arrows (diag.) Grid convergence (T to G) Magnetic declination (T to M) Magnetic model 77' Correction (magnetic to survey ref.) Correction (true to survey ref.) ,1° E / W* ° E / W* Date 8 ,° ,1° Curved conductors Drill datum to well reference point MD TVD North East $- $%- %1- N / S* - E / W* G M decl. = +0.11 conv. = +2.34 Incl. at w.r.p. 1° Azim at w.r.p. %$$°

336. BP Amoco BPA-D-004 Directional Survey Handbook C-12 Data and Work Sheets September 1999 Issue 1 DIRECTIONAL DESIGN CHECK LIST Rig / Platform / Drill Site Well Date Sheet completed by Checked by / Comment Well Objectives Document from BU sub-surface team Updates to well objectives Well Location Memorandum Planning File Well Plan Data Sheet Survey Program Data Sheet Proposed well trajectory BU sub-surface approval of trajectory Target analysis (1 per target) Offset well data (surveys, completion diags. etc.) Initial clearance scan (global scan) Tolerable Collision Risk Worksheet(s) Minimum separation calculations Anti-Collision Instruction Sheet Magnetic interference prediction Relief well contingency calculation Dispensations from Recommended Practice Wellsite Drawings Plan view drawings Vertical section drawings Structure (spider) plots Travelling cylinder - global clearance scan Travelling cylinder - working drawing(s) Travelling cylinder - wellsite plots

337. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-13 DIRECTIONAL DESIGN CHECK LIST Rig / Platform / Drill Site Well

338. Date Sheet completed by , Checked by +9: / Comment Well Objectives Document from BU sub-surface team 5 !! !#; =; , Updates to well objectives ! != = 9!: Well Location Memorandum 5::!9;

339. Planning File Well Plan Data Sheet Survey Program Data Sheet Proposed well trajectory 8:= % BU sub-surface approval of trajectory = 9!: Target analysis (1 per target) Offset well data (surveys, completion diags. etc.) 9:= 3:!!9 !!3 Initial clearance scan (global scan) Tolerable Collision Risk Worksheet(s) Minimum separation calculations + + :=6 Anti-Collision Instruction Sheet Magnetic interference prediction + + :=6 Relief well contingency calculation Recommended Practice Dispensation Form(s) ! =):3= 8 Wellsite Drawings Plan view drawings Vertical section drawings ? Structure (spider) plots @6:3 Travelling cylinder - global clearance scan Travelling cylinder - working drawing(s) Travelling cylinder - wellsite plots ?

340. BPAmoco BPA-D-004DirectionalSurveyHandbook C-14DataandWorkSheetsSeptember1999Issue1 SURVEY PROGRAM DATA SHEET Rig / Platform / Drill Site Well Program version Sheet completed by Date Survey Tool / Error Model Hole Casing Depth interval Comments / Contingency Size Size from to

341. BPAmoco DirectionalSurveyHandbookBPA-D-004 September1999Issue1DataandWorkSheetsC-15 SURVEY PROGRAM DATA SHEET Rig / Platform / Drill Site Well

342. Program version Sheet completed by Date Survey Tool / Error Model Hole Casing Depth interval Comments / Contingency Size Size from to ! # $ %%' ' ! # % $ ' ' ( () * * !+, * , -. !! % $ ' ' ! / ), , ()# ! #, * )) #+) / ( -. 0 1 !+ , $ ' ' 2 !! !#+ -()#

343. $ %%' ' -. 0 1 !+ , $ ' ' ! / ), , ()# ! #, * )) #+) / (

344. BP Amoco BPA-D-004 Directional Survey Handbook C-16 Data and Work Sheets September 1999 Issue 1 ANTI-COLLISION INSTRUCTION SHEET Rig / Platform / Drill Site Well Date Sheet completed by BU authorisation The instructions given in this sheet are based on: 999 Well plan no. Date Survey program no. Date and are not otherwise valid. Wells to be Shut In Minimum Shut-in Interval Well name Slot MD from MD to Comment Minor Risk Wells Well name TCR* Key Assumptions *Tolerable Collision Risk Travelling Cylinder Plots Plot no. Depth from Depth to Date Comment Contingency Plans / Special Instructions

345. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-17 ANTI-COLLISION INSTRUCTION SHEET Rig / Platform / Drill Site Well

346. Date Sheet completed by BU authorisation A:9 2 , The instructions given in this sheet are based on: Well plan version no. Date 1

347. Survey program version no. Date 1 , and are not otherwise valid. Well Shut-ins Minimum Shut-in Interval Well name Slot no. MD from MD to Comment % $- - # ?! !6 :) . !:= , $- ,- : !B Minor Risk Wells Well name TCR* Key Assumptions

349. *Tolerable Collision Risk Travelling Cylinder Plots Plot no. Depth from Depth to Date Comment $- ,1- 1 ,1- 1 Contingency Plans / Special Instructions 5 ! 2= !==3 !B B ( * 9!:= )B:= ::= ) =:== 6 := 2 !#= 2C ::= !9 = !38: ) ::=! : B: := . !:= !! (-* D B ! ,- ' :! !6:= !8:3!= 9!6 =!C ::=! : 9!# : !9 !B! ) 9! 2!2::C ) ::=

350. BP Amoco BPA-D-004 Directional Survey Handbook C-18 Data and Work Sheets September 1999 Issue 1 DISPENSATION FROM RECOMMENDED PRACTICE To be used for recording planned violations of standard directional and survey procedures and recommended practices Rig / Platform / Drill Site Well Date Sheet prepared by Recommended Practice Document Procedure / Standard to be violated Details of Dispensation Requested Justification Attachments Technical Assessment / Recommendation Signature / Date / Comment BU Authorisation

351. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-19 DISPENSATION FROM RECOMMENDED PRACTICE To be used for recording planned violations of standard directional and survey procedures and recommended practices Rig / Platform / Drill Site Well

352. Date Sheet prepared by =3C +9: Recommended Practice Document :C 89= ::=! !: ) := Procedure / Standard to be violated ! !=!C: =):3= 8 (

353. E* Details of Dispensation Requested :- ! ) ! 2 !6!3 ! $E =):3= Justification !:! 9:=:969 :F ) 3:- ! !#= ! - ! )):8 := ) 62!=:!C 36:= ::= 6=!:=C =!:= :! ! 363 =):3= 8 !3 B: = = Attachments * ! !=!C: := 6 !

354. E; $E !=3 $E =):3= * = 9!:; Technical Assessment / Recommendation Signature / Date / Comment A =:3 := ):3 )=:= ) )66 B !C; 7 5; % BU Authorisation 83 =; :C 5 ; $

355. BP Amoco BPA-D-004 Directional Survey Handbook C-20 Data and Work Sheets September 1999 Issue 1 NON-COMPLIANCE / NON-CONFORMANCE REPORT To be used for reporting unplanned violations of standard directional and survey procedures or unplanned deviations from directional plan or survey program Rig / Platform / Drill Site Well Date Sheet prepared by Procedure / Standard / Plan / Program document Procedure / Standard / Plan / Program violated What happened Most serious likely consequence Contributory causes Action Responsible Date

356. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-21 NON-COMPLIANCE / NON-CONFORMANCE REPORT To be used for reporting unplanned violations of standard directional and survey procedures or unplanned deviations from directional plan or survey program Rig / Platform / Drill Site Well

357. Date Sheet prepared by =3C +9: % % Procedure / Standard / Plan / Program document ::= !9 := % +68C:= !9 Procedure / Standard / Plan / Program violated 1. := '5G +! := +68C What happened '5 68C := 1. := B = 3 ) ! := ! :9 ::=! : (7 B=* 6 + )B! !:3 := !69!:!C '5 =:= (+ 7=* !3 = = 68C !9 Most serious likely consequence = : B; 63 !8 @6:3 ?! 3::=! B# := $ . := = :C B; B

358. $. C : = 6=; ! 63 !8 2= 9:3 ::2 :=! := !=: ::= :# Contributory causes ::=! : B! 6=)!9::! B: + )B!; !=3 63 : B= '4 )B! ) 68C !6!:= '5 9!=C !3 = 2= 3 ) @6:9= ) ! := Action Responsible Date 3 ) ! := 2 =3 = +68C !9 !! + B !:! +9: H66 B ::=! 9!=C !9=3 @6!:C 36 I 4=6 ! - !:=3 = + 3!! =C +=3 C ) +68C !9 !! + ! 68C 9!=C !:= +68: : 63 +9: %

359. BP Amoco BPA-D-004 Directional Survey Handbook C-22 Data and Work Sheets September 1999 Issue 1 List all the consequences of collision and the necessary remedial action STOP Use Conventional rule - Major risk Are the consequences of collision predictable ? Do the consequences of collision include a risk to personnel or the environment ? Estimate the total cost of collision Estimate the value of the planned well to the BU Is there a practical way to substantially reduce either the probability of collision or the severity of the consequences ? no yes no no yes yes Prepared by: Authorised by: How could the probability of collision or the severity of the consequences be reduced ? How might this impact the drilling operation ? Accepting a finite risk of collision will reduce the value of the planned well. What reduction, as a fraction of the total value, are you prepared to tolerate ? (guideline = 0.05) Tolerable Collision Risk = Estimate the total cost of substantially reducing the risk Given the uncertainty in the above estimates, by how many times must the savings made from not reducing the risk outweigh the risk itself ? (guideline = 20) M = Tolerable Collision Risk Worksheet = 1 in = 1 : close approach tolerances need not be set 1 : Tolerable Collision Risk = 1 in Use this sheet to justify classifying a well as Minor risk and to establish the Tolerable Collision Risk for use in risk-based well separation rule. Ref. BPA-D-004 (Dir. Svy. H’book) Sections 4.2, 4.3 V = C = F = VF C VF C VF C C VF F M = = 1 V = H.Williamson, UTG Well Integrity Key Assumptions (Elements of the drilling program which are critical to the above analysis) Scenario Name: (Be specific. Include all factors which affect either the cost of collision or the cost of reducing the risk) Description:

360. BP Amoco Directional Survey Handbook BPA-D-004 September 1999 Issue 1 Data and Work Sheets C-23 List all the consequences of collision and the necessary remedial action STOP Use Conventional rule - Major risk Are the consequences of collision predictable ? Do the consequences of collision include a risk to personnel or the environment ? Estimate the total cost of collision Estimate the value of the planned well to the BU Is there a practical way to substantially reduce either the probability of collision or the severity of the consequences ? no yes no no yes yes Prepared by: Stuart Telfer (Directional Engineer) Authorised by: Richard Harland (Ops Superintendant) How could the probability of collision or the severity of the consequences be reduced ? How might this impact the drilling operation ? Accepting a finite risk of collision will reduce the value of the planned well. What reduction, as a fraction of the total value, are you prepared to tolerate ? (guideline = 0.05) Tolerable Collision Risk = Estimate the total cost of substantially reducing the risk Given the uncertainty in the above estimates, by how many times must the savings made from not reducing the risk outweigh the risk itself ? (guideline = 20) M = Tolerable Collision Risk Worksheet = 1 in = 1 : close approach tolerances need not be set 1 : Tolerable Collision Risk = 1 in V = C = F = VF C VF C VF C C VF F M = = 1 V = H.Williamson, SPR Well Design Marnock A01Y Parallel S/T in Reservoir Sidetracking an existing well (A01Z) by paralleling it through the reservoir section. Original well is sidetracked below the 13 3/8” casing drilling 12 1/4” and 8 1/2” hole sections. The original well, under conventional rules is classed as MINOR risk as it is closed in and abandoned. Interference occurs in 8 1/2” hole from 4060m to 4590m. 1. Estimated treatment due to contamination from original wellbore and potential mud loss £ 50k Mud loss is not expected, merely contamination through barite sag in the original hole requiring treatment to the sidetrack hole system. 2. Potential well control due to reservoir fluid on the highside of the original wellbore £ 200k (est. 2 days rig time @ £100k/day) 3. Plugback and sidetrack well (est. 6 days rig time @ £100k/day) £ 600k Moving South edges of the drillers target North by 10m at entry and 63m at TD would result in: 1. Increased directional control to achieve smaller targets, cost in extra rig time = 8 days 2. Increased risk of sticking by 25% through greater sliding requirement, potential impact of becoming stuck, 12 days rig time. 0.25 x 12 days = 3 days Total = 11 extra days @ £100k/day £ 1.10 m 20 0.05 0.065 15 850k Use this sheet to justify classifying a well as Minor risk and to establish the Tolerable Collision Risk for use in risk-based well separation rule. Ref. BPA-D-004 (Dir. Svy. H’book) Sections 4.2, 4.3 Scenario Name: (Be specific. Include all factors which affect either the cost of collision or the cost of reducing the risk) Description: Key Assumptions (Elements of the drilling program which are critical to the above analysis)

361. BP Amoco BPA-D-004 Directional Survey Handbook C-24 Data and Work Sheets September 1999 Issue 1 List all the consequences of collision and the necessary remedial action STOP Use Conventional rule - Major risk Are the consequences of collision predictable ? Do the consequences of collision include a risk to personnel or the environment ? Estimate the total cost of collision Estimate the value of the planned well to the BU Is there a practical way to substantially reduce either the probability of collision or the severity of the consequences ? no yes no no yes yes Prepared by: Larry Wolfson 12/6/96 Authorised by: Adrian Clark 15/6/96 How could the probability of collision or the severity of the consequences be reduced ? How might this impact the drilling operation ? Accepting a finite risk of collision will reduce the value of the planned well. What reduction, as a fraction of the total value, are you prepared to tolerate ? (guideline = 0.05) Tolerable Collision Risk = Estimate the total cost of substantially reducing the risk Given the uncertainty in the above estimates, by how many times must the savings made from not reducing the risk outweigh the risk itself ? (guideline = 20) M = Tolerable Collision Risk Worksheet = 1 in = 1 : close approach tolerances need not be set 1 : Tolerable Collision Risk = 1 in V = C = F = VF C VF C VF C C VF F M = = 1 V = H.Williamson, SPR Well Design Niakuk Segment 3/5 Development Wells New development wells drilled to segment 3/5 locations encountering interference with adjacent wells. Shallow nudges and varying KOPs used to move the interference depth below the surface casing. • Collision with a producer/injector results in a side-track of that well: $2-$2.5 million (based on P2-50B) • Plug back and side-track the drilling well: $200k - $500k • The cost of delayed production/injection from both wells is estimated at $60 per bopd. NK-10 is a significant injector that supports 12,000 bopd and the average production from the producers is 3,000 bopd. The cost of a collision includes delayed production for both wells: - Injector: $900k - Producer: $360k • Estimated total cost (range): $2.56 - $3.90 million. 0.103 10 $3.9 million $8.0 million 0.05 Use this sheet to justify classifying a well as Minor risk and to establish the Tolerable Collision Risk for use in risk-based well separation rule. Ref. BPA-D-004 (Dir. Svy. H’book) Sections 4.2, 4.3 Scenario Name: (Be specific. Include all factors which affect either the cost of collision or the cost of reducing the risk) Description: Key Assumptions (Elements of the drilling program which are critical to the above analysis) Surface casing set above start of zone of interference (6,600 ft MD)

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