Disclosed are a high-temperature-resistant tertiary amine-grafted silica nano-plugging agent and water-based drilling fluids, relating to oil-gas field drilling. The nano-plugging agent is prepared from a hydrazine compound, a diallyl compound, an enamine compound, silica particle, and an amino-containing silane coupling agent by stepwise reaction. The nano-plugging agent has a grain size of 58-280 nm.

A method of treating a subterranean formation can include: introducing a first fluid into a wellbore penetrating the subterranean formation; introducing a second fluid into the wellbore after introduction of the first fluid, wherein the second fluid comprises: a base fluid comprising water; a viscosifier; and a stabilizer, and wherein the second fluid has a rheological 3-rpm dial reading to 300-rpm dial reading ratio in the range of 1:1 to 1:3; and introducing a third fluid into the wellbore after introduction of the second fluid, wherein the second fluid inhibits or prevents the first fluid from mixing with the third fluid. The second fluid can be a liquid plug that substantially inhibits or prevents the first fluid from mixing with the third fluid. The first fluid can be a drilling mud or spacer fluid. The third fluid can be a spacer fluid or a cement composition.

A device for forming one or more wellbore sealants in a wellbore can include a wellbore barrier and a cured polymer. The wellbore barrier can be positioned in the wellbore. The cured polymer can be positioned with respect to the wellbore barrier for swelling the device from a compressed configuration to a swelled configuration for forming one or more wellbore sealants in the wellbore.

The present invention refers to a method for removing fouling in carbonate reservoirs and/or depleted reservoirs by adding carbon dioxide to industrial or desulphated water to produce carbonic acid, in producing well stimulation operations, to be used as a weak acid for removing fouling in remote operation aiming at keeping the productivity of producing wells and lessening the need for remote operations with stimulation vessel, and therefore reducing operating costs.

A wellbore fluid may include an oleaginous fluid forming a continuous phase; a non-oleaginous fluid forming a discontinuous phase; at least one emulsifier stabilizing an emulsion of the non-oleaginous continuous phase within the oleaginous continuous phase; and at least one viscosifier dispersed into the oleaginous continuous phase in a concentration of at least 4 ppb; wherein upon subjecting the wellbore fluid to shear rate of at least 10,000 s-1, the emulsion is disrupted and the non-oleaginous fluid contacts the at least one viscosifier, thereby solidifying the wellbore fluid.

Methods for the fracking or stimulation of a hydrocarbon-bearing formation are provided in multiple embodiments. According to one method, it comprises the steps of: providing a wellbore having a casing; inserting a plug in the wellbore at a predetermined location; inserting a perforating tool and an acidic composition into the wellbore; wherein the acidic composition includes a corrosion inhibiting composition comprising at least two compounds selected from: Group A-I, and wherein at least two compounds are selected from different groups of the Groups A-I.

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 includes methods for stimulating a hydrocarbon-bearing formation by perforating a wellbore and introducing an acidic composition in the wellbore. A preferred embodiment includes inserting an isolation plug in the wellbore at a predetermined location followed by inserting a perforating tool and a breakdown acid into the wellbore. The wellbore is perforated by the tool to create a perforated area. The breakdown acid is allowed to come into contact with the perforated area for a predetermined period of time sufficient to prepare the formation for stimulation. The tool is then removed from the wellbore wherein stimulation of the perforated area is thereby initiated. Also disclosed is a corrosion inhibiting composition for use with the acidic composition.

A tubing string may include a swellable metal material for providing a seal downhole. The swellable metal material may react with a silica material and a water-based fluid to cause the swellable metal material to swell and form a seal within a flow path defined in part by the tubing string.

A salt-tolerant polymer microsphere plugging agent and a preparation method thereof, the agent being made of white oil, fumed silica, acrylamide monomer, acrylic acid, sorbitan fatty acid ester, N,N′-methylene bisacrylamide, ammonium persulfate, sodium bisulfite, hydrophilic surfactant and water. The present general inventive concept synthesizes salt-tolerant polymer microspheres with ultra-low interfacial tension by adopting inverse phase emulsion polymerization. The prepared polymer microsphere plugging agent is a new type of polymer microspheres with ultra-low interfacial tension, such that the tension can reach 4.3×10.sup.−3 mN/m, and the salt tolerance can reach 50000 mg/L salinity, which improves the problem of low interfacial tension and poor salt tolerance in existing polymer microspheres.