Abstract: Described are a viscosity reducer and a preparation method therefor and the use thereof, and a method for improving the crude-oil pollution resistance of a drilling fluid. The viscosity reducer includes a matrix and particles attached to the surface of the matrix and/or wrapped in the matrix. The matrix includes an oleophilic moiety and a hydrophilic moiety. The particles do not melt at 100° C. or lower. The number of the particles in the viscosity reducer in an area of 10*10 ?m is 1-1500 according to analysis using a scanning electron microscope. The viscosity reducer can be applied to an oil-based drilling fluid and a synthetic drilling fluid to improve the crude-oil pollution resistance of the drilling fluids; and the viscosity reducer can also be used in a drilling fluid permeated by crude oil, so as to alleviate the problem of thickening caused by crude oil permeating the drilling fluid.

Abstract: Described are a composite emulsifier and an oil-based drilling fluid. The composite emulsifier includes a main emulsifier and an auxiliary emulsifier. The auxiliary emulsifier is a sulfonated substance and/or carboxylation product of the main emulsifier. The composite emulsifier has a good emulsification effect and good electrical stability and thermal stability, and can greatly reduce difficulties in compounding at a drilling site.

Abstract: A park screen has a base tube, a communication layer and a protective tube arranged in sequence from an inner side to an outer side thereof. At least one first through hole is arranged on the base tube, and at least one second through hole is arranged on the protective tube. The communication layer includes a packing tube and a sand filter arranged in juxtaposition along a circumferential direction. At least one third through hole is arranged on a wall of the packing tube and in fluid communication with the second through hole. The fluid from the packing tube flows out of the pack screen through the third through hole and the second through hole. The sand filter is configured to cover the first through hole on the base tube so that the fluid enters the base tube via the first through hole after flowing through the sand filter.