Study On Oil - Based Drilling Fluid For Protection Reservoir

Compared with water-based drilling fluids, the oil-based drilling fluids has been traditionally regarded as a variety of advantages, which is resist to high temperature, resist salt and calcium contamination, favore well bore stability. And it also has good lubrication. small extent of damage to hydrocarbon reservoir. It was a critical tool used in the tough drilling of high temperature and deep depth well, high angle deflected well, horizontal well and in the process of bad grounds such as the strong water sensitive strata. There are problems to be resolved, for instance, the poor stability of oil-based drilling fluids, the insufficient understanding of formation damage mechanism and the lack of methods to evaluate reservoir protection performance.This thesis develops oil-based drilling fluid technology in the Da Bei area reservoir of Tarim oil-field. On the basis of clear geologic characteristics, which is low permeability and micro-fracture reservoir and its damage mechanism. And research comprehensive performance evaluation on the oil-based drilling fluid, through prefer treatment agent with excellent performance, and combine with the study of reservoir protection performance, develop an oil-based drilling fluid system for reservoir protection.The Da Bei area reservoir is typical of low permeability and ultralow seepage reservoir. Its crack and micro crack grow well, content of clay minerals higher. The result shows that the water sensitivity, salt sensitivity and alkali sensitivity strong and hydrochloric acid sensitivity moderate or strong. In general, block rock stress sensitivity presents weak while fractured rock stress sensitivity strong. Evaluation experiments on the comprehensive performance of oil-based drilling fluid indicate that it’s unsufficient in its system stability and reservoir protection still to be improved. The degree of damage can up to30%.Through the selection of various treating chemicals and the optimization of their additive heft, the finally chosen treating chemicals are such as organic clay AJ, primary emulsion EMUL-2, assisting emulsion TLMFR, fluid loss additive Duratone+Geltone and humectant TLMRSJ. Combined with the compatibility, based on a large amount of experiments, the ultimately determined oil-based drilling fluid system:diesel oil+3%organic clay AJ+3%primary emulsion EMUL-2+1%assisting emulsion TLMFR+CaCl2saline (formula for diesel oil-water ratio:80:20)+2.5%CaO+2%fluid loss additive Duratone+2%as fluid loss additive Geltone+1.5%humectant TLMRSJ+barite (p=1.80g/cm3)Based on the characte of Da Bei area reservoir and the oil-based drilling fluid system which has been used, combined with the reservoir protection technology, and determined basic formula of shielding temporary blocking oil base drilling fluid system:with oil-based drilling fluid (p=1.80g/cm3)+1%fibrous temporary blocking agent HF+2%was CaCO3+0.5%acid soluble manganese (KGD)+0.5%fatigue particle (FEP)+other. Through the experiment on combination of dynamic damage evaluation, it can be known that the design of the shielding temporary blocking oil base drilling fluid system can meet the requirements of the protection of pore and fracture. Finally, permeability and flow back recovery rate after temporary blocking reached90%, achieving the purpose of reservoir protection.