Patent NZ-736478-A (NZ)
Title: Casing flush fluid, recyclable cleanout fluids, and applications thereof
Inventor: NELSON SCOTT G
IPC: E21B21/00
Filed: 2016-03-30
Abstract: Nowadays a sizeable percentage of wells are overflushed in order to remove as much proppant from the bottom of the horizontal casing as possible. Proppant such as sand remaining in the bottom of the casing causes issues with the deployment and setting of mechanical tools such as bridge plugs. Leftover proppant can cause a plug to prematurely set in the casing uphole from its intended target depth, or if placed at the proper location can cause the plug to fail to set in order to seal off the already treated portion of the horizontal lateral. To combat this many operators have added the pumping of additional fluid that is above that required to flush the casing volume to the perforations. This additional fluid is intended to further flush the casing to remove unwanted proppant, but also carries with it added consequences. The additional fluid adds pumping time to the horsepower used on location, along with additional chemical costs that are associated with the extra treating fluid. It is also known that the overflush of frac stages in horizontal wells contributes to reductions in well productivity. The overflush of the wellbore can also displace proppant further into the fracture, thus harmfully removing proppant from the near wellbore region of the fracture. Therefore, there is a need in the ait for casing flush fluid having improved efficiencies. There is also a need for well cleanout fluids that are effective to suspend and carry small particles out of the well. It would be a further advantage if the cleanout fluids are recyclable. Disclosed herein is a method of removing residual proppant from a bottom surface of a casing or tubing string after a fracturing operation, the method comprising: circulating a casing flush fluid in the casing or tubing string of a horizontal or deviated wellbore, the casing flush fluid comprising a carrier, a superabsorbent polymer having a particle size of about 50 microns to about 10,000 microns, and a breaker; a composition, an amount, and a particle size of the superabsorbent polymer being selected such that the casing flush fluid is effective to lift and transport residual proppant from the bottom surface of the casing or tubing string to a fracture created by the fracturing operation; and transporting the residual proppant from the bottom surface of the casing or tubing string to a fracture created by a hydraulic fracturing operation; breaking the superabsorbent polymer with the breaker after the residual proppant is transported from the bottom surface of the casing or tubing string to the fracture; wherein the superabsorbent polymer comprises a plurality of recycled hydrated superabsorbent polymer particles, and the method further comprises adding water to a fluid returned from a wellbore to provide a thinned out composition comprising a slurry of hydrated particles of the superabsorbent polymer and debris; separating the debris from the slurry; and filtering the slurry through a mesh filter to provide the recycled hydrated particles of the superabsorbent polymer, the mesh filter having a mesh size smaller than a predetermined average size of the hydrated particles of the superabsorbent polymer. Also disclosed herein is a method of removing residual proppant from a bottom surface of a casing or tubing string after a fracturing operation, the method comprising: circulating a casing flush fluid in the casing or tubing string in a horizontal or deviated wellbore, the casing flush fluid comprising: a carrier comprising water or brine, about 30 pounds (13.6 kg) to about 60 pounds (27.2 kg) of a superabsorbent polymer per one thousand gallons of the casing flush fluid, and 0.1 pounds (0.045 kg) to 20 pounds (9.1 kg) of a breaker per one thousand gallons (3785.4 L) of the casing flush fluid, wherein the superabsorbent polymer has a particle size of about 50 to about 1,000 microns and comprises: a polyacrylamide having crosslinks derived from polyethylene glycol diacrylate; a copolymer of acrylamide with one or more of maleic anhydride, vinyl acetate, ethylene oxide, ethylene glycol, acrylonitrile; polyacrylic acid copolymer having crosslinks derived from a vinyl ester oligomer; a copolymer of acrylic acid and sodium acrylate having crosslinks derived from polyethylene glycol diacrylate; or a combination comprising at least one of the foregoing; and a composition, an amount, and the particle size of the superabsorbent polymer are selected such that the casing flush fluid is effective to lift and transport residual proppant from the bottom surface of the casing or tubing string to a fracture created by the fracturing operation; transporting the residual proppant from the bottom surface of the casing or tubing string to the fracture created by the fracturing operation; and breaking the superabsorbent polymer with the breaker after the residual proppant is transported from the bottom surface of the casing or tubing string to the fracture.