A polyoxalate copolymer that includes main ester units of oxalate linked together like a straight chain, and branched ester copolymer units derived from a trifunctional or more highly functional alcohol or an acid. The polyoxalate copolymer initially undergoes the hydrolysis in a suppressed manner.

The present invention relates to a composition comprising (i) at least 10 wt % of an inorganic and/or organic, water soluble salt, based on the total weight of the composition; (ii) water; and (iii) an ether monocarboxylic acid. Further aspects of the invention relate to the use of an ether monocarboxylic acid of the invention, an amide, a salt or an ester thereof as a lubricant preferably in salt based drilling systems.

The present invention relates to a composition comprising (i) at least 10 wt % of an inorganic and/or organic, water soluble salt, based on the total weight of the composition; (ii) water; and (iii) an ether monocarboxylic acid. Further aspects of the invention relate to the use of an ether monocarboxylic acid of the invention, an amide, a salt or an ester thereof as a lubricant preferably in salt based drilling systems.

The present invention relates to the well drilling field in petrochemical industry, and discloses a drilling fluid additive composition comprising a nano-plugging agent, a bionic wall bracing agent, a bionic shale inhibitor, an emulsifier, and an amphiphobic wettability reversal agent, wherein, the nano-plugging agent is modified silicon dioxide nano-particle, and its modifying group includes a modifying copolymer chain; the bionic wall bracing agent is carboxymethyl chitosan with a dopamine-derived group grafted on its main chain; the bionic shale inhibitor is composed of structural units of arginine and structural units of lysine; and the amphiphobic wettability reversal agent is a dual-cation fluorocarbon surfactant. The present invention further provides a pseudo oil-based drilling fluid suitable for horizontal shale gas wells containing the above composition. When the water-based drilling fluid contains the drilling fluid additive composition provided in the present invention, the water-based drilling fluid would have high temperature-resistance, high plugging and high inhibition performance, is environment friendly, especially have high density, and is especially suitable for horizontal shale gas well mining.

The present invention relates to the well drilling field in petrochemical industry, and discloses a drilling fluid additive composition comprising a nano-plugging agent, a bionic wall bracing agent, a bionic shale inhibitor, an emulsifier, and an amphiphobic wettability reversal agent, wherein, the nano-plugging agent is modified silicon dioxide nano-particle, and its modifying group includes a modifying copolymer chain; the bionic wall bracing agent is carboxymethyl chitosan with a dopamine-derived group grafted on its main chain; the bionic shale inhibitor is composed of structural units of arginine and structural units of lysine; and the amphiphobic wettability reversal agent is a dual-cation fluorocarbon surfactant. The present invention further provides a pseudo oil-based drilling fluid suitable for horizontal shale gas wells containing the above composition. When the water-based drilling fluid contains the drilling fluid additive composition provided in the present invention, the water-based drilling fluid would have high temperature-resistance, high plugging and high inhibition performance, is environment friendly, especially have high density, and is especially suitable for horizontal shale gas well mining.

A stabilized water-dispersible latex additive useful in both freshwater-based and brine-based drilling fluids, may be formed by mixing an effective amount of a compound containing at least one pyrrolidone ring, such as, polyvinylpyrrolidone, a vinylpyrrolidone-vinyl acetate copolymer, poly(1-vinylpyrrolidone-co-2-dimethylaminoethyl methacrylate), a vinylpyrrolidone-acrylic acid copolymer, and combinations thereof, with the water-dispersible latex additive before or after the water-dispersible latex additive is introduced to the drilling fluid.

A stabilized water-dispersible latex additive useful in both freshwater-based and brine-based drilling fluids, may be formed by mixing an effective amount of a compound containing at least one pyrrolidone ring, such as, polyvinylpyrrolidone, a vinylpyrrolidone-vinyl acetate copolymer, poly(1-vinylpyrrolidone-co-2-dimethylaminoethyl methacrylate), a vinylpyrrolidone-acrylic acid copolymer, and combinations thereof, with the water-dispersible latex additive before or after the water-dispersible latex additive is introduced to the drilling fluid.

Wellbore fluids and methods of use thereof are disclosed. Wellbore fluids may include an aqueous base fluid, a rate of penetration enhancer, and a shale dispersion inhibitor, wherein the volume ratio of the rate of penetration enhancer to the shale dispersion inhibitor is greater than 1:1. Methods may include circulating the wellbore fluid into a wellbore.

A water-based drilling fluid containing high molecular weight crosslinked polyacrylic acid as viscosifying agent exhibits stability at well temperatures in excess of 150° C. The drilling fluid may further contain a lubricant, weighting agent and/or a wetting agent as well as laponite clay. The aqueous based drilling fluid exhibits a coefficient of friction which is substantially close to the coefficient of friction of oil based drilling muds.

A water-based drilling fluid containing high molecular weight crosslinked polyacrylic acid as viscosifying agent exhibits stability at well temperatures in excess of 150° C. The drilling fluid may further contain a lubricant, weighting agent and/or a wetting agent as well as laponite clay. The aqueous based drilling fluid exhibits a coefficient of friction which is substantially close to the coefficient of friction of oil based drilling muds.