Research On Water Shutoff Technology In The Western Zone Of South China Sea Oil Field

Under the condition of western zone oil field in South China Sea, plugging agent formulas and their toxicity, matching technology and their support agents were researched in the paper. Because of the feature of low cost and disproportional permeability reducing for oil and water, Gel is suitable for bullheaded water shutoff. In the paper, gel formulas research mainly include common gel and polyethyleneimine(PEI) gel. Serial gel formulars were obtained, having different gel time and gel strength. Then, the formulars were assessed by application characters such as water plugging rate, shearing resistance behavior, and etc.It was researched in detail how the factors, such as temperature, salinity, polymer, crosslinking agent, and pH value, affect gel time, loss modulus and storage modulus of PEI gel,. Apparent activation energy of South China Sea brine preparing gel was measured. Gel time power decline with the increase of polymer mass concentration. Gel time and PEI mass concentration has similar tendency. Increasing temperature, polymer and crosslinking agent mass concentration tend to shorten gel time and harden gel strength. While increasing salinity of brine for gel or decreasing pH value of base gel solution have invert tendency. Physical simulation results indicate that PEI gel can disproportionally reduce oil and water permeabilty obviously. The phenomenon can be interpreted by swelling/contracting mechanism.Environmental behavior evaluation method for shutoff agent in offshore oil field was researched. Photosbacterium phosphoreum was chosed as the representative specie for marine environment. Environmental behavior of polymer, crosslinking agent, gel and producing fluild after gel treatment was assessed by bioluminescent bacteria bioassay. The toxicity of different gel was graded and ordered. It was found that gel toxicity mainly attributes to crosslinking agent, and toxicity of polymer and crosslinking agent in gel shows antagonistic action.Bullheaded water shutoff was the most importand method in South China Sea western zone oil field. The mechanism of the method was researched by visual physical simulation. Polymer diverting and sea water broadening method was prososed to solve the problem discovered in the simulation, that the low permeable path was prone to be damaged in bullheaded water shutoff. The method was proven to be more effectively to protect the low permeable path and has more cheering results by physical simulation. Support agents for the matching technology of water shutoff were also researched, such as preflush fluid, overdisplacement fluid, temporary blocking gel and water block remover fluid. In the physical simulation, a little of oxidizing reagent solution was injected after overdisplacement polymer, to protect researvoir by degrading polymer and gel remaining near wellbore.