Abstract: The present invention relates to the petroleum drilling field and discloses a reservoir protecting agent composition comprising a structured nanometer film reservoir protecting agent and a water block preventing agent, a drilling fluid containing the same and use thereof for drilling in low-permeability reservoirs. The reservoir protecting agent composition comprises a structured nanometer film reservoir protecting agent and a water block preventing agent, wherein the structured nanometer film reservoir protecting agent comprises montmorillonite laminas, structural units represented by formula (1) and structural units represented by formula (2), wherein each of R1, R2, R3, R4 and R5 is independently selected from H, C1-C4 alkyl and C1-C4 alkoxy, R6 is C1-C6 alkylene. The present invention further provides a drilling fluid that contains the reservoir protecting agent composition according to the present invention.

Abstract: The present subject matter relates to a preparation method of a wettability reversal agent, comprising: (1) adding an emulsifier into water to prepare a mixed solution of emulsifier; (2) adding compounds represented by formula (1-a), (2-a), (3-a), (4-a), (5-a), and (6-a) to the mixed solution of emulsifier to obtain a pre-emulsion, adding an initiator, and initiating a polymerization reaction. When the wettability reversal agent and reservoir protecting agent composition disclosed in the present subject matter are used in a drilling fluid, they can effectively prevent the permeation of the water phase and oil phase in the drilling fluid into the reservoir, reduce the filter loss of the drilling fluid, and thereby effectively protect the reservoir against damages from the drilling fluid.

Abstract: The present subject matter relates to a reservoir protecting agent composition, consisting of non-fluorescent sulfonated asphalt, micron-sized cellulose, and a reservoir protecting agent, wherein, the reservoir protecting agent is composed of structural units denoted by the following formula (1), formula (2), and formula (3). The present subject matter further provides a broad-spectrum drilling fluid that contains the reservoir protecting agent composition. The present subject matter further provides a use of the broad-spectrum drilling fluid in oil and gas well drilling. When the broad-spectrum drilling fluid provided in the present subject matter is used in oil and gas well drilling in reservoirs with different structures, it exhibits good rheology property, temperature tolerance, and anti-collapse and protection performance.

Abstract: The present subject matter relates to a protecting agent composition for high/ultra-high permeability reservoirs, consisting of a protecting agent and a filler, wherein, the filler comprises calcium carbonate of 600-1,000 mesh, calcium carbonate of 300-590 mesh, and calcium carbonate of 50-200 mesh at 1:(1-30):(0-40) weight ratio, and the protecting agent comprises structural units denoted by the following formulae (1), (2), and (3). The present subject matter further provides a drilling fluid containing the above-mentioned composition. The present subject matter further provides a use of the drilling fluid for drilling in high/ultra-high permeability reservoirs. The drilling fluid provided in the present subject matter has advantages including easy use, high environmental friendliness, and outstanding reservoir protection, greatly reduces the damages of drilling fluid to high/ultra-high permeability reservoirs, and brings substantial economic benefits.