Evaluation on Water Block in Low Permeability Formations and the Research of Water Block Control

Abstract

Oleic permeability is severely impacted by the invasion of aqueous working fluids, especially in low porosity and low permeability reservoirs. This study mainly targeted at low permeability reservoir of Dongying Formation, Chengdao Offshore Oilfield. Water influx and its influence on oil threshold pressure were evaluated with constant-pressure injection, in which way the injuring extent of water block could be quantitatively expressed. Results indicated that, oil threshold pressure could be increased by 1.3 times merely with a water influx of 0.3 pore volumes. In addition, researches related to the system of fluid loss control had been conducted on the basis of the functional mechanism of water block. An emulsion working over fluid system had been developed by biodiesel with excellent emulsification characteristic. It can be inferred from water invasion tests that the emulsion system performed well in fluid loss control both in water phase and oil phase. The fluid loss rate could be decreased to 55.6%∼86.4%. Meanwhile, mutual solvent ethylene glycol monobutyl ether (EGMBE) had been efficiently adopted in water block remediation. The threshold pressure can be reduced by 79.7% according to evaluation tests.