Formation Characteristics and the Drilling Fluid Technology Countermeasures of the Shengbei Block in Tuha Oilfield
During the drilling process in the Shengbei block,there are complex downhole situations such as wellbore instability caused by tripping obstacles,reaming,and sticking,which have restricted the speed and efficiency of drilling.Taken the Shengbei 508H as a representative well,the mineral composition and physicochemical properties of rock debris samples from different layers were measured,and the main characteristics and wellbore instability mechanism of the upper and lower strata were analyzed.Research has shown that mudstone is commonly present in the strata.The clay mineral content in mudstone is relatively high,and its composition is mainly composed of illite and illite mixed layers,as well as montmorillonite,which are geological factors that lead to complex underground situations.A drilling fluid technology measure has been proposed to enhance the coating performance of polymers and the inhibition performance of composite salts in response to the easy hydration,dispersion,slurry making,and diameter reduction of upper formation mudstone.After optimization,the rolling recovery rate of the drilling fluid is as high as 88.40%,and the expansion rate is 1.17%.In response to the tendency of mudstone in the lower strata to peel off and collapse,a drilling fluid technology measure was proposed that combined micro nano full size sealing with activity control of composite salts and polyamine enhanced inhibition performance.After optimization,the equilibrium pressure time of the drilling fluid was significantly extended to 160 hours.The activity of drilling fluid is lower than 0.76,and the strength decrease of mudstone core soaked in drilling fluid for 72 hours decreases.The optimized drilling fluid has achieved good results in the application of two wells of SH5s21-2 and SH5s13-2 in the Shengbei block.No complex accidents occurred during the drilling process,achieving the goal of maintaining wellbore stability and improving drilling efficiency.
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