Study On Formation Protection Technology Of Tight Gas Reservoir In Linxing-shenfu Block

In recent years,energy strategy deployment of CNOOC has been developing toward land,and exploring and developing coalbed methane,shale gas and tight gas.At present,tight gas exploration has been carried out in Linxing and Shenfu blocks of Ordos Basin,and pilot development tests have been carried out.In view of the tight gas drilling in Linxing-Shenfu block,it is necessary to study the key technologies of reservoir protection and drilling and completion fluid in tight gas field development.Its quality is closely related to the efficient development of tight gas.It is also important to carry out the key technology research of tight gas drilling and completion fluids.In this paper,the porosity,permeability,saturation,clay mineral type and relative content,pore throat size and distribution of reservoir rocks are analyzed by means of mercury intrusion test,X-ray diffraction,scanning electron microscopy and thin section analysis,and the physical and chemical properties of reservoirs are defined.The velocity sensitivity,acid sensitivity,alkali sensitivity,salt sensitivity,water sensitivity and stress sensitivity of the reservoir are evaluated and analyzed by the reservoir sensitivity evaluation experimental.The formulation of drilling and completion fluid system is optimized and field test is carried out,combining with the experimental results of wettability test,grain size test,water lock evaluation,reservoir sensitivity evaluation,water saturation and permeability damage value evaluation,and filter and solid particle migration damage evaluation.The results show that the tight sandstone gas reservoir in Linxing-Shenfu block is a typical low porosity and low permeability reservoir with dense rock cementation and microdevelopment of pores and fractures.There should be speed sensitivity and water sensitivity damage in reservoirs.The pore throat size of tight sandstone reservoirs in Linxing-Shenfu block is small,and the capillary effect is remarkable,so there should be strong water lock damage.The clay in the rock is easy to hydrate,expand,fall off and migrate and may block the throat and cause damage to the reservoir.The optimized drilling fluids system has good plugging,good lubricity and strong inhibition.The surface tension of the solid less brine completion fluid system used in the field is large,and the water lock damage of the reservoir core is serious.The surface tension value is small after adding the waterproof lock agent FC,and the wettability of the rock surface becomes hydrophobic,which makes the formation fluid displacement easier and the core permeability recovery value is larger under lower displacement pressure.Therefore,the waterproof lock agent FC can be used as reservoir protective agent to effectively restore core permeability and protect the reservoir.