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Challenge: Optimize production from a well with formation damage caused by excessive oil-base drilling fluid losses in a naturally fractured reservoir.
Solution: Use SXE superX emulsion to maximize acid penetration and bypass the damaged zone in the critical matrix.
Results: Achieved production 162% greater than expected from offsets and petrophysical analysis.
Pemex’s Samaria 6117 well in southern Mexico is in a naturally fractured reservoir with an average temperature of 279 degF [137 degC). It was drilled to 15,150 ft [4,618 m] with oil-base mud as the drilling fluid.
Excessive drilling fluid losses were reported to be 70 m3 [440 bbl] in the productive zones. This fluid loss could cause formation damage from solids bridging and emulsions due to fluid incompatibilities. Pemex expected oil production in this area to be 800 bbl/d [127 m3] based on offset well production and petrophysical property analysis.
Schlumberger used the PowerSTIM well optimization service to generate a stimulation proposal that considered reservoir knowledge, fluid selection, treatment design, execution, and evaluation. The model predicted that the lost drilling fluid had invaded the critical matrix and plugged the fracture system, reducing well productivity. This prediction was supported by a laboratory compatibility test for the drilling cuttings, oil sample, and stimulation fluids.
The proposal outlined two stages:
SXE acid is a viscous, highly retarded, concentrated acid system (70% HCl, 30% oil), stabilized with an emulsifier. Because it can penetrate farther into the formation than any live acid, SXE acid was used for deep penetration. The dissolving power of the HCl-base SXE acid system, coupled with slower carbonate reaction time, creates deeper wormholes and makes the emulsion less corrosive to steel casing and tubing.
The SXE acid treatment delivered a 162% production increase over expected production (2,100 bbl/d versus 800 bbl/d [334 m3/d versus 127 m3/d]) of oil. Pemex will use this treatment in wells with similar temperature conditions.
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