Low Permeability Reservoir Characteristics Evaluation and Pollution Factor Analysis of A Gas Well in East China Sea

There are huge reserves of low permeability oil and gas resources in the deep strata of East China Sea. Restricted by the physical properties of the reservoir itself and the impact of well drilling and completion, the protection effect of some gas wells is not ideal. Based on the low permeability reservoir core data of a gas well in East China Sea, the laboratory evolution experiments of wettability, nonlinear seepage, nuclear magnetic resonance and drilling fluid damage are carried out, and the basic characteristics and seepage law of low permeability reservoirs are revealed, and the availability of such reservoirs is evaluated. Combined with the drilling and completion of the well, the influencing factors of the low permeability reservoir pollution of the gas well are further analyzed. The study shows that the low permeability reservoir rock of this gas well is hydrophilic and the pore throat is small, so it is not easy to release the water lock after it occurs. The characteristics of nonlinear seepage are obvious under low pressure gradient. The percentage of movable fluid in the reservoir below 10×10⁻³ μm² is less than 57.86%, which belongs to the third class of reservoirs, and is hard to mobilize. Compared with the soaking time, the damage of drilling pressure differential is greater. Thus the drilling pressure difference should be controlled within 3.5 MPa as far as possible.