Development of a novel chemical water shut-off method for fractured reservoirs: Laboratory development and verification through core flow experiments

Most of the extended reach horizontal wells and also the vertical wells with permeability heterogeneities often experience premature and excessive water production from multiple, high permeability streaks and conductive fractures. Bullhead and Relative Permeability Modifier (RPM) treatment often fails to achieve the desired result, as in most cases the situation warrants isolation and protection of the oil producing zones, from highly damaging polymeric gels. Protection of oil zones in a highly fractured reservoir is technically and economically a huge challenge because of knowledge on the complexity of fracture network. This paper describes the application of three chemical fluid compositions in sequence, as an alternate rigless water control option whose self-selectivity and effectiveness in controlling water production are verified in the laboratory in simulated fractured reservoir condition. The first fluid is designed to protect the matrix by creating an impermeable filter cake on low permeable oil saturated zones, keeping the water swept fractures open for gel treatment. The second fluid is a cross-linkable polymer gelant to shutoff the fractures and the third fluid is an enzyme breaker for cleaning the filter cakes form matrix zones. After completion of the treatments, return permeability measurement was carried out which shows 85-90% reduction of water permeability with less than 15% reduction of oil permeability. Microscopic investigations on treated core plug show very little invasion of polymer gel into the matrix area, whereas the fractures are almost completely sealed. The technology could be suitably applied without rig deployment and at a low cost. However, the fluid composition, pumping pressure and flow rate need to be customized based on the candidate well and the actual reservoir parameters.