Comprehensive Study of Offshore Gulf of Mexico Shale when Exposed to Several Reservoir and Completion Fluids

Abstract

Abstract Ensuring shale stability while drilling the reservoir and completing a well is critical to guarantee well integrity and to enable the reservoir to product at its maximum potential. Drill-in fluid type, completion brine, and shale inhibitors play an important role in maintaining well integrity and preventing formation damage as they have different effects on shale. Reactivity of shale samples from offshore Gulf of Mexico was studied using several reservoir and completion fluids. The shale was first characterized using X-Ray diffraction (XRD) and X-Ray fluorescence (XRF). Then, the effect of fluids on shale was determined by performing several tests including linear swell meter (LSM), capillary suction time, and cuttings dispersion. Water-based (WB) and oil-based (OB) drill-in fluids, synthetic formation water, and completion brines with and without shale inhibitor were used to study the shale reactivity. XRD and XRF test showed presence of 5wt% illite and 6wt% kaolinite in the shale sample. Performance tests conducted on the shale samples showed a similar trend of high reactivity with improvements when inhibitor is added. Some brines showed poor synergistic effects when inhibitors were present in the fluid formulation. The type of drill-in fluid has a large impact on the LSM test results. Type of brine in the WB drill-in fluid also showed a major influence on the shale behavior. Oil-based drill-in fluids are commonly used to drill sections with very reactive shales. Nevertheless, water-based fluids are sometimes required due to performance preferences, environmental concerns, economic and logistic reasons, and/or synergistic effects with logging tools. Filtrate invasion and drill-in fluid/completion brine losses could cause detrimental effects in the reservoir if the fluids have not been designed to inhibit the shale hydration and swelling or fines migration. Therefore, improving the clay inhibition and shale stability while using water-based fluids is fundamental when drilling through reactive shale sections. Performing a comprehensive test matrix to determine the feasibility of using water-based fluids is imperative. Achieving excellent inhibition for a very reactive GOM formation shale while maintaining performance is possible when a precise and well-engineered combination of brine/shale inhibitor in the drill-in and completion fluids are found.