1. APPLICATION OF MULTIPLE WELL DECONVOLUTION METHOD IN A NORTH SEA FIELD EMMA THORNTON 1 SUPERVISORS: ALAIN GRINGARTEN (IMPERIAL COLLEGE) JALAL MAZLOOM, ALI ODABASI (NEXEN)

2. 2 PROJECT BACKGROUND DATA North Sea oilfield which has just completed an initial drilling campaign. Pre-existing well test analysis affected by: –Interference –Short buildups AIMS 1.Perform multiwell deconvolution on two groups of interfering wells. 2.Use the results to locate boundaries. 3.Assess the reliability and practicality of the algorithm. P2 P1 I1 N P12 P15 P10 P11 P13 P14 N Testing group 2 I14 I12 ft Testing group 1

3. 3 DECONVOLUTION Pressure drop is the convolution product of rate and reservoir response (1). SINGLE-WELL DECONVOLUTION Multi-rate test Single drawdown of constant unit rate. –Extends the zone of investigation further into the reservoir. Traditional deconvolution is only applicable in single-well reservoirs (2). MULTI-WELL DECONVOLUTION Traditional deconvolution algorithm has been extended to accept multiple interfering wells (2). DECONVOLUTION 1.von Schroeter, T., Hollaender, F., and Gringarten, A. C.: “Analysis of Well Test Data from Permanent Downhole Gauges by Deconvolution,” paper SPE 77688 presented at the 2002 SPE Annual Technical Conference and Exhibition, San Antonio, Sept 29 – Oct 2. 2.Cumming, J. A., Wooff, D. A., Whittle, T., and Gringarten, A. C. : “Multiple Well Deconvolution,” paper SPE 166458 presented at the 2013 SPE Annual Technical Conference, Sept 30 – Oct 2.

4. 4 METHODOLOGY Define which wells are in the interfering group. Filter pressure data for each well to between 5 and 25 points per log cycle. Normalise pressures to a common depth. Load the convolved pressure drop into a pressure transient analysis software and apply a unit rate. Analyse for boundary effects as usual. Apply boundary model obtained from deconvolution to regular well test analysis to determine k, skin DATA PREPARATION ANALYSING DECONVOLVED RESULTS MULTIWELL DECONVOLUTION An interference pressure drop and deconvolved derivative is also output for every pair of wells in the deconvolution. The algorithm outputs a deconvolved derivative for each well which reflects only the geology of the surrounding reservoir – interference effects have been removed. Pressures and rates for each well are input into the deconvolution algorithm.

5. 5 METHODOLOGY Define which wells are in the interfering group. Filter pressure data for each well to between 5 and 25 points per log cycle. Normalise pressures to a common depth. Load the convolved pressure drop into a pressure transient analysis software and apply a unit rate. Analyse for boundary effects as usual. Apply boundary model obtained from deconvolution to regular well test analysis to determine k, skin DATA PREPARATION ANALYSING DECONVOLVED RESULTS MULTIWELL DECONVOLUTION An interference pressure drop and deconvolved derivative is also output for every pair of wells in the deconvolution. The algorithm outputs a deconvolved derivative for each well which reflects only the geology of the surrounding reservoir – interference effects have been removed. Pressures and rates for each well are input into the deconvolution algorithm.

6. 6 TESTING GROUP 1 Two producers and one injector. Deconvolutions were run with all 3 wells included in the algorithm. Additional deconvolutions were run with wells ignored from the algorithm. P2 P1 I1 N

7. --- The P1 deconvolution with only I1 interference removed. --- The P1 deconvolution with I1 and P2 interference removed. --- The P1 deconvolution with no interference removed. --- The P1 deconvolution with only P2 interference removed. 7 RESULTS FROM TESTING GROUP 1 P2 P1 I1 N Limited communication between P1/P2. –In agreement with independent reservoir simulation models. Interference pressure drop between P1/P2 is always less than between P1/I1 ft

8. 8 RESULTS FROM TESTING GROUP 1 Final deconvolution results for wells P1, P2 and I1. Boundaries initially modelled from faults observed in seismic. –Leakage adjusted/Extra baffles to flow added. –In agreement with reservoir fluid models of the region P1: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) P2: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) I1: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) ft Convolved pressure Deconvolved derivative Pressure drop from model Derivative from model

9. 9 RESULTS FROM TESTING GROUP 1 Final deconvolution results for wells P1, P2 and I1. Boundaries initially modelled from faults observed in seismic. –Leakage adjusted/Extra baffles to flow added. –In agreement with reservoir fluid models of the region P1: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) P2: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) I1: 0.1 0.01 1e-3 1e-4 0.10.011 10 100 1000 10000 T(hr) P (psi) ft Convolved pressure Deconvolved derivative Pressure drop from model Derivative from model

10. 10 TESTING GROUP 2 Six interfering producers and two injectors. Well P13 was the focus of this Testing Group Groups of wells were deconvolved with P13 I14 P12 P15 P10 P11 P13 I12 P14 N ft

11. 11 RESULTS FROM TESTING GROUP 2 Uncertainty over fault between P11 and P13 Interference effect only significant after 500 hours –Implies fault leakage is minimal. I14 P12 P15 P10 P11 P13 I12 P14 N Next Step: Wells were added to the deconvolution group one-by-one. ft

12. 12 RESULTS FROM NORTHERN TESTING GROUP

13. I14 P12 P15 P10 P11 P13 I12 P14 N 13 RESULTS FROM NORTHERN TESTING GROUP Boundaries of the system were initially modelled from faults observed in seismic. –Leakage of faults was adjusted. P13 0.1 0.01 1e-3 0.10.011 10 100 1000 10000 T(hr) P (psi) Interference response for P13/P10 ft Convolved pressure Deconvolved derivative Pressure drop from model Derivative from model

14. I14 P12 P15 P10 P11 P13 I12 P14 N 14 RESULTS FROM NORTHERN TESTING GROUP Boundaries of the system were initially modelled from faults observed in seismic. –Leakage of faults was adjusted. P13 0.1 0.01 1e-3 0.10.011 10 100 1000 10000 T(hr) P (psi) Interference response for P13/P10 ft Interference response for P13/P10 Convolved pressure Deconvolved derivative Pressure drop from model Derivative from model

15. 15 BENEFIT OF MULTIWELL DECONVOLUTION Regular well test analysis provides limited information Deconvolution extends the zone of investigation Single-well deconvolution can be distorted by interference. Only through multiwell deconvolution is it possible to obtain a reliable derivative which represents the geological characteristics. Normal well test analysis Single-well Multi-well

16. 16 DISCUSSION OF ALGORITHM RELIABILITY The multiwell algorithm was used to perform single-well deconvolution. –Result was compared to the Total Least Squares Deconvolution tool. –Confirmed that the deconvolutions calculated using the new algorithm were consistent P13 single-well deconvolution ALGORITHM RUN-TIMES Typical deconvolutions were carried out.

17. 17 CONCLUSIONS MULTIWELL DECONVOLUTION Multiwell deconvolution has the capability of extending the benefits of deconvolution to producing fields. Results have been consistent with other reservoir engineering studies. INTERFERENCE Conclusions can be drawn about well interference. Interference responses can be interpreted. PRACTICALITY OF USE Run-times of the algorithm are reasonable.

18. 18 ACKNOWLEDGEMENTS I wish to extend thanks to Nexen CNOOC for supplying the data for this project and for providing financial support throughout the project and for accommodating me in their Uxbridge offices. I also would like to thank Jonathan Cumming of Durham University for his help and support with the coding of the algorithm. Finally, I thank my supervisors Jalal Mazloom and Ali Odabasi of Nexen CNOOC and Alain Gringarten in Imperial College for all their excellent technical expertise over the duration of the project, and Jon Wardell for welcoming me into his team for the summer.