Characterization and mechanism analysis of drilling fluid damage in tight sandstone reservoirs:A case study of Ahe Formation in Dibei Section of Kuqa Depression
Tight sandstone reservoir is an important field of oil and gas replacement in China,with abundant resources.However,the pore throat structure of tight sandstone reservoir is complex,and it is very easy to be damaged in the process of drilling,completion and exploitation,which leads to the decrease of reservoir permeability and ultimately affects the flow and production of oil and gas.Taking the tight sandstone reservoir of the Ahe Formation in the Dibei section of the Kuqa Depression as the research object,using casting thin sections,XRD and other tests,on the basis of clarifying the mineral composition,porosity and permeability characteristics and reservoir space types of sandstone,the drilling fluid damage evaluation experiment was carried out.Combined with the micro-CT in-situ scanning technology,the characteristics of sandstone pore throat changes before and after drilling fluid damage were analyzed.The results show that the average permeability of sandstone in the study area is 0.92 mD,the average porosity is 5.84％,and the pore type is mainly micropore.The damage degree of drilling fluid to the reservoir is generally low,and the average damage rate is 20.2％.The mechanism analysis shows that the damage type of drilling fluid to the reservoir is mainly water sensitive damage.Clay minerals and sandstone pore throat morphology are the main factors of drilling fluid damage to the reservoir.The content of illite/smectite mixed layer in clay minerals and the type of reservoir throat determine the degree of drilling fluid pollution damage.The research results have guiding significance for the efficient development of tight sandstone reservoirs in Ahe Formation.
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