Successful Cold Heavy Oil Production with Sand (CHOPS) Application in Massive Heavy Oil Reservoir in Sudan: A Case Study

摘要

This paper demonstrates application of Cold Heavy Oil Production with Sand (CHOPS) in Sudan, which has been successfully applied in B heavy oil reservoir of FN field. B reservoir is a series of massive sandstones with strong bottom water drive, which are loosely consolidated and interbedded with shale barriers. Burial depth is 1250 m, average net pay thickness is 35 m. In-situ viscosity is around 300 mPa.s. Cold production well tests indicated average productivity of 500 BOPD, 2-3 times of sand controlled productivity. Global heavy oil fields with successful CHOPS histories have been investigated to confirm applicability in B reservoir and identify two major challenges of CHOPS application in B reservoir: 1) arresting rapid bottom water coning; 2) managing sand production in borehole and surface. CHOPS production strategy has been optimized by following approaches: 1) perforation ratio optimization based on fine barriers (interbed/ intrabed) characterization and numerical simulation to avoid rapid coning; 2) borehole PCP lifting and surface de-sanding facilities optimization for sand control. 70 producers have been commissioned from 2004 to 2006 with optimized perforation ratio of 30% (total net pay), water cut has been kept below 10% with 2% annual offtake rate. Since 2007, 40 infill wells inclusive of horizontal wells have been drilled to further suppress water coning. Recovery factor to date is 13% with WCT of 46% as of 2010, demonstrating better performance than similar heavy oil reservoirs. Producers’ up-efficiency has been kept above 85%. Conclusions drawn from successful CHOPS application in B reservoir were as follows:1) optimized perforation contributed to low water cut in early stage; 2) infill well beneficial to suppressing WCT in middle stage; 3) optimized lifting and facilities contributed to high production up-efficiency. Heavy oil reserves takes 40% of Sudan’s total reserves, therefore CHOPS has wide applications for similar Sudanese and African fields. Successful CHOPS in this paper highlighted fine barriers (interbed/ intrabed) characterization and optimized perforation strategy, infill well drilling, optimized borehole lifting and facilities design, giving a cost-effective staircase for CHOPS implementation.