Wellbore Enhancing Technology for 444.5 mm Openhole Section in Well SHBP1 by Means of Drilling Fluid Optimization

We developed a wellbore enhancing technology by means of drilling fluid optimization to tackle the problems of hydration,swelling and wellbore instability of Triassic mudstone strata encountered by the 444.5 mm open hole section in Well SHBP1,as along with a number of additional drilling-related problems such as well-developed fracture pores,collapse/caving and leakage,and other drilling issues in the massive Permian igneous strata.Countermeasures designed to prevent collapse and leakage were proposed and developed,based on the analysis of mechanisms contributing to wellbore instability when drilling the Triassic formation and those causing leakage in the Permian strata.We incorporated key additives such as inhibitor SMJA-1,anti-collapse agent SMNA-1 and plugging agent SMGF-1 to develop the strong inhibition/blocking drilling fluid system.Field applications showed that during the second spud drilling,the performance of drilling fluid was stable,and mudstone cuttings were characterized by sharp edges and completeness.When the operations followed the new protocols,the open hole section was stable,the trip operation was smooth,and the average wellbore expansion rate was only 4.7% for over 90 days of drilling.Field testing the application and analyzing the results suggest that it is possible to solve wellbore instability by incorporating a strong inhibition/plugging drilling fluid.In addition,the technology solves wellbore instability in Triassic strata and leakage issues in Permian strata of Well SHBP1.This technology could provide reference for subsequent drilling in similar wells in Shunbei Block.