Application Of Wellbore Instability Mechanism And Drilling Fluid Of Deep Hard Brittle Shale In Subei Basin

With the Subei basin exploration and development trending to "low and deep,hidden,difficult and unconventional direction of development,exploration and development more and more deep wells of deep sag reservoir,more and more construction difficulty,met the unprecedented bottleneck of acceleration in drilling.The main lithology of deep formation of Subei basin in Jiangsu oilfield is mudstone,the formation fracture development,the phenomenon of mudstone hydration swelling resulting in mudstone intensity decreased,near wellbore formation collapse pressure rising is extremely easy to appear in drilling process.Difficult trip and wireline logging operation,lost circulation and others wellbore complications often occurred,and the period of dealing with wellbore complications is very long.The thesis carry out the related research of common drilling fluid properties,formation lithology test,preliminary master the Subei Basin deep hard brittle shale formation wellbore instability mechanism,through vast drilling history review and downhole complications statistics.Aiming at the shortage of the performance of common drilling fluid,the research and selection of strong inhibition and strong plugging water base drilling fluid system were put forward.Optimization salt,polymer,PLUS,polyamines,and the inhibitors were compound,studied poly amine drilling fluid compatibility,through optimization of filtration reducing agent and asphalt type plugging agent,plugging agent,formed a strong inhibition strong plugging polyamine paraffin emulsion lubrication anti sloughing drilling fluid.The drilling fluid system has applied in 10 wells in Jiangsu oilfield,the average depth is reached 3650.8m,average open hole depth is 2851 m,average rate of penetration is 7.85m/h,wellbore complications and accidents caused by drilling fluid are decreased greatly,the average expansion rate of hole size is 6.17%,the one-time success rate of wireline logging reached 90%.To further enhance inhibition and sealing properties of poly amine base drilling fluid system,combination tests are carried out for different varieties of polyamine,polyamine and potassium chloride,potassium acetate,formed a strong inhibition strong plugging poly amine acetate potassium drilling fluid system,the system performance is stability,laboratory test data show that the inhibition,plugging stronger than strong inhibition strong plugging polyamine paraffin emulsion lubrication anti sloughing drilling fluid,more suiTablefor drilling the deep hard brittle mudstone in Subei basin.