The invention relates to the technical field of oil and gas drilling, and discloses an amphiphilic block polymer ultralow-permeability agent and an intelligent temporary plugging type water-based drilling fluid. The ultralow-permeability agent contains a structural unit provided by styryl hydrophobic monomer, maleic anhydride and acrylamide; the drilling fluid contains two or more of water, sodium bentonite, Pac-Lv, the ultralow-permeability agent, calcium carbonate, one-way plugging agent, white asphalt and barite which are stored in a mixed manner or independently stored. When the amphiphilic block polymer provided by the invention is used as the ultralow-permeability agent of the intelligent temporary plugging type water-based drilling fluid, the self-adaptive characteristic is realized; according to the amphiphilic block polymer, temporary plugging layer gaps formed in pore and throats by plugging materials in drilling fluid can be fully filled under the condition that the sizes and the distribution of the pore and throats of reservoirs are not required to be clear, so that the permeability of temporary plugging layer is greatly reduced, ultralow-permeability is realized, and the amphiphilic block polymer is weak in tackifying effect, has gel-improving effect and can improve the rheological property of the drilling fluid.

A method for reducing water production from a hydrocarbon bearing subterranean formation includes identifying a high permeability zone in the formation and injecting a dense CO.sub.2 composition from a production well into the high permeability zone. The dense CO.sub.2 composition includes dense CO.sub.2 and a thickener soluble in the dense CO.sub.2. The thickener includes a copolymer that is the polymerized reaction product of monomers that include at least one alkenyl ether or dialkenyl ether monomer, at least one acrylate or methacrylate monomer, at least one structural monomer, and at least one allyl ester monomer. After injecting the dense CO.sub.2 composition into the high permeability zone, the method includes withdrawing hydrocarbons from the hydrocarbon bearing subterranean formation through the production well. The dense CO.sub.2 composition blocks pores in the high permeability zone to reduce or prevent flow of water from the high permeability zone into the production well.

A method of forming a barrier to overcome lost circulation in a subterranean formation. The method includes injecting a polymer-sand nanocomposite into one or more lost circulation zones in the subterranean formation where the polymer-sand nanocomposite is formed from sand mixed with a polymer hydrogel. Further, the polymer hydrogel includes a hydrogel polymer, an organic cross-linker, and a salt. The sand additionally comprises a surface modification. The associated method of preparing a polymer-sand nanocomposite lost circulation material for utilization in forming the barrier is provided.

A method for enhanced oil recovery from a hydrocarbon bearing subterranean formation includes withdrawing hydrocarbons from a production well extending into the formation, identifying a high permeability streak in the formation, and injecting a dense CO.sub.2 composition from an injection well into the high permeability streak. The dense CO.sub.2 composition includes dense CO.sub.2 and a thickener soluble in the dense CO.sub.2. The thickener includes copolymer. The method includes, after injecting the dense carbon dioxide composition into the high permeability streak, injecting an aqueous treatment fluid into the formation. The dense CO.sub.2 composition blocks the high permeability streak to divert at least a portion of the aqueous treatment fluid into bypassed regions of the formation during the injecting of the aqueous treatment fluid, and the injecting of the aqueous treatment fluid into the hydrocarbon bearing subterranean formation drives hydrocarbons in the hydrocarbon bearing subterranean formation towards the production well.

A method for enhanced oil recovery in a reservoir is provided. The method includes injecting a microsphere suspension, including polymeric microspheres dispersed in seawater, into an injection well in the reservoir and injecting a low salinity tailored water (SmartWater) into the injection well in the reservoir. Oil is produced from a production well in the reservoir.

The present invention relates to the field of oil extraction. More specifically, it relates to a particular polymerization process, which provides access to formulations of polymers that may be used in particular for modifying rheology and fluid loss control during extraction operations and that have a better heat stability.

A PVA excellent in resistance to melting at high temperature is provided. The polyvinyl alcohol-based polymer is a saponificated product of a homopolymer composed of a vinyl ester monomer, a copolymer of a vinyl ester monomer and a monofunctional monomer other than the vinyl ester, a copolymer of a vinyl ester monomer and a polyfunctional monomer, or a copolymer of a vinyl ester monomer, a monofunctional monomer other than vinyl ester, and a polyfunctional monomer has a particle size of 50 nm or more at a cumulative frequency of 50% in particle size distribution by dynamic light scattering measurement of a 0.4 mass % aqueous solution of the polyvinyl alcohol-based polymer at 25° C.

A system and method for water shutoff, including providing a treatment fluid including a polymer and a nitrogen-generating compound through a wellbore into a water zone in a subterranean formation, generating nitrogen gas in the water zone by a reaction of the nitrogen-generating compound, generating foam from the nitrogen gas and the treatment fluid in the water zone to give foamed polymer in the water zone, and sealing the water zone with the foamed polymer.

A particulate plugging agent, such as a diverting agent and/or loss circulation material, using a particular polyvinyl alcohol with a certain amount of monovalent metallic salt, which is water-soluble and has a buffer effect even if the environment is acidic, and thus stable, which in particular finds use in various subsurface oil production operations.

Provided herein are drilling muds, including water-based drilling muds. The components of the drilling muds are a degradable fluid loss additive, for example, synthetic degradable nanoparticles, a clay mineral, for example, a smectite, and a base fluid, for example, water. Also provide are methods for preventing leak-off during a drilling operation and for automatically cleaning-up filter cake after completion of a drilling process both of which utilize the drilling muds and water-based drilling muds.