Mitigating Water Production from High Viscosity Oil Wells in Unconsolidated Sandstone Formations

Abstract

Summary Large reserves of high-viscous oil in Kuwait call for improved oil recovery scenarios. In Kuwaiti unconsolidated sandstone formations, the sandstone intervals represent extensive reservoir intervals of sand separated by laterally extensive nonreservoir intervals that comprise finer-grained argillaceous sands, silts, and muds. The reservoir is shallow with high permeability (above 1,000 md) and under bottom aquifer pressure support. Due to strong viscosity contrast between oil and water, after breakthrough, the water cut rises quickly, resulting in strong loss of production efficiency. Mitigating water production is thus mandatory to improve production conditions. The candidate wells have two to three open intervals in different rock facies with comingle production. The total perforated length is between 38 and 48 ft. Production is through progressing cavity pumps (PCP) at a rate of around 300 B/D, and basic sediment and water is between 71 and 87%. The technology applied utilizes pregelled size-controlled product [small microgels (SMG Microgels)] having relative permeability modification (RPM) properties; that is, inducing a strong drop of relative permeability to water without affecting oil relative permeability. The size is chosen to selectively treat the high-permeability water producing zones while preserving the lower-permeability oil zones. The chemical can also withstand downhole harsh conditions such as salinity of around 170,000 ppm and presence of 2% H2S. The treatment consisted of bullhead injection of 300 bbl of pregelled chemical through-tubing. The first results seem very favorable, since for two wells, the water cut has dropped from 80 to 40% with almost same gross production rate. The incremental oil is more than 100 BOPD. The third well did not show marked change after water system operation (WSO) treatment. The wells are under continuous monitoring to assess long-term performance. Such result, if confirmed, may lead to high possibilities for the improvement of heavy oil reservoir production under aquifer support by mitigating water production with simple chemical bullhead injection.