The present disclosure provides a temperature-responsive self-degradable temporary plugging agent and a preparation method thereof as well as its application in plugging the wellbore, which relates to the technical field of oilfield exploitation. The temporary plugging agent provided in the present disclosure includes preparation raw materials of the following mass percentages: monomer 4-6%, crosslinker 0.2-1%, initiator 0.02-0.06%, degradation catalyst 0.05-0.1%, chain transfer agent 0.01-0.05%, and the balance water. The temporary plugging agent of the present disclosure is liquid before gelling, with a low viscosity and a good fluidity, and easy to be pumped. When being pumped into the wellbore, the temporary plugging agent may crosslink at the temperature of the reservoir section, with good gelling properties. At the end of the operations, it can be degraded by itself, without drilling tools, with no need for gel breaking, and with no need for additional degradation promoters.

The invention discloses an organic-inorganic nanocomposite gel sealing agent and oil-based drilling fluid. The sealing agent used for the oil-based drilling fluid is organic-inorganic nanocomposite gel, and the synthetic raw materials of the organic-inorganic nanocomposite gel includes molybdenum disulfide, 2-ethyl acrylic acid, N, N-dimethylacrylamide and N,N-methylene bisacrylamide; the drilling fluid includes the organic-inorganic nanocomposite gel provided by the invention. The organic-inorganic nanocomposite gel is used as a nano sealing agent, the particle size distribution of the organic-inorganic nanocomposite gel is 50-200 nm, the organic-inorganic nanocomposite gel can effectively prevent drilling fluid filtrate from intruding into stratums and prevent accidents such as borehole wall collapse, the organic-inorganic nanocomposite gel is particularly suitable for nano-sealing of shale stratums, and the preparation method of the organic-inorganic nanocomposite gel is reliable in principle and has a wide market prospect.

The invention discloses an organic-inorganic nanocomposite gel sealing agent and oil-based drilling fluid. The sealing agent used for the oil-based drilling fluid is organic-inorganic nanocomposite gel, and the synthetic raw materials of the organic-inorganic nanocomposite gel includes molybdenum disulfide, 2-ethyl acrylic acid, N, N-dimethylacrylamide and N,N-methylene bisacrylamide; the drilling fluid includes the organic-inorganic nanocomposite gel provided by the invention. The organic-inorganic nanocomposite gel is used as a nano sealing agent, the particle size distribution of the organic-inorganic nanocomposite gel is 50-200 nm, the organic-inorganic nanocomposite gel can effectively prevent drilling fluid filtrate from intruding into stratums and prevent accidents such as borehole wall collapse, the organic-inorganic nanocomposite gel is particularly suitable for nano-sealing of shale stratums, and the preparation method of the organic-inorganic nanocomposite gel is reliable in principle and has a wide market prospect.

Polyacrylamide (PAM)-coated nanosand that may be a relative permeability modifier (RPM) and that is applied to treat a wellbore in a subterranean formation. The treatment may be for excess water production. The PAM-coated nanosand is PAM-hydrogel-coated nanosand. The PAM-coated nanosand os nanosand coated with PAM hydrogel. The PAM hydrogel includes crosslinked PAM in water. Application of the PAM-coated nanosand may reduce water production from the subterranean formation into the wellbore. The PAM hydrogel of the PAM-coated nanosand may expand in a water zone of the subterranean formation to restrict water flow into the wellbore. The PAM hydrogel of the PAM-coated nanosand may contract in an oil zone of the subterranean formation so not to significantly restrict crude oil flow into the wellbore.

Provided is a method for mitigating a lost circulation zone. The method may include providing a lost circulation treatment composition that may include an acid responsive polymer that may include at least one monomer, at least one comonomer, and at least one crosslinker; a carbonate-based solvent; and a carrier fluid that may include water. The method may also include introducing the lost circulation treatment composition into a wellbore within a subterranean formation, wherein the subterranean formation may include the lost circulation zone; placing the lost circulation treatment composition into the lost circulation zone, hydrolyzing the carbonate-based solvent to generate carbon dioxide, and causing the swelling (change of shape) of acid responsive polymer to mitigate the losses.

Provided is a method for mitigating a lost circulation zone. The method may include providing a lost circulation treatment composition that may include an acid responsive polymer that may include at least one monomer, at least one comonomer, and at least one crosslinker; a carbonate-based solvent; and a carrier fluid that may include water. The method may also include introducing the lost circulation treatment composition into a wellbore within a subterranean formation, wherein the subterranean formation may include the lost circulation zone; placing the lost circulation treatment composition into the lost circulation zone, hydrolyzing the carbonate-based solvent to generate carbon dioxide, and causing the swelling (change of shape) of acid responsive polymer to mitigate the losses.

A method for controlling the permeability of an oil well includes the steps of preparing a polymerizable bicomponent system having at least a fluid with at least an olefinically unsaturated first polymerizable compound; optionally, at least one radical polymerization initiator I.sub.A, the initiator I.sub.A being activated thermally or in the presence of an accelerating compound and a fluid with a radical polymerization activator, the activator being selected from: a radical polymerization initiator I.sub.B for polymerizing the polymerizable compound, the initiator I.sub.B having an activation temperature equal to or lower than the temperature of the thief zone, an accelerator of the initiator I.sub.A, The method further includes injecting one of the fluids into the well annulus until the thief zone is reached, and injecting the remainder into the tubular element, until it comes into contact with the fluid injected through the annulus to form a blocking polymer at the thief zone.

A method for controlling the permeability of an oil well includes the steps of preparing a polymerizable bicomponent system having at least a fluid with at least an olefinically unsaturated first polymerizable compound; optionally, at least one radical polymerization initiator I.sub.A, the initiator I.sub.A being activated thermally or in the presence of an accelerating compound and a fluid with a radical polymerization activator, the activator being selected from: a radical polymerization initiator I.sub.B for polymerizing the polymerizable compound, the initiator I.sub.B having an activation temperature equal to or lower than the temperature of the thief zone, an accelerator of the initiator I.sub.A, The method further includes injecting one of the fluids into the well annulus until the thief zone is reached, and injecting the remainder into the tubular element, until it comes into contact with the fluid injected through the annulus to form a blocking polymer at the thief zone.

A pH-sensitive temporary plugging agent and its preparation method, and the use thereof in exploitation of a low-permeability oil reservoir are disclosed. The temporary plugging agent is prepared by raw materials including, in percentages by mass, 3-8% of carboxymethyl chitosan, 0.2-0.7% of gelatin, 0.1-0.6% of an initiator, 5-15% of a toughener, and a balance of water, wherein the initiator is a solution of AgNO.sub.3 in ammonia water having a concentration of 0.1-0.3 mol/L, and the toughener is a carboxyl-terminated hyperbranched polyester.

A method of reducing lost circulation includes introducing a lost circulation solution comprising Saudi Arabian volcanic ash, a curing agent, and a resin into a subsurface formation through a wellbore, wherein the Saudi Arabian volcanic ash comprises SO.sub.3, CaO, SiO.sub.2, Al.sub.2O.sub.3, Fe.sub.2O.sub.3, MgO, and K.sub.2O; and allowing the lost circulation solution to thicken within the subsurface formation, thereby forming a barrier between the subsurface formation and the wellbore to reduce lost circulation.