Study On The New Dual-Crosslinked Water Shutoff Agent In Fractured Low-Permeability Reservoir

For fractured low-permeability reservoir, the existence of fractures and their state serves a double purpose for water injection development. They provide high permeable channels on the one hand, enhancing water absorption capacity in water injection well and production capacity in oil well; It may lead to water breakthrough along fractures on the other, producing water early, and even serious water channeling, so water content ratio increases dramatically in oil well. However, there is a great deal of oil left in the direction of inexistent fractures. So, recovery of oil is very low in this situation. How to utilize and reconstruct fractures is the key to water injection development of fractured low-permeability reservoir. One of the effective measures is to block fractures selectively with water shutoff agent.Aiming at the question in water shutoff of fractured low-permeability reservoir, the opinion of increasing crosslinking density to reduce gel absorption capacity and the opinion of confirming and toughening polymer with montmorillonite in composite material are introduced in synthesizing water shutoff agent. Acrylamide is adopted as monomer and initiated by oxidation - reduction initiating agent. The newly compound water shutoff material - MRSG is formed after polymerizing, twice crosslinking, crossblending with montmorillonite. The formulation of MRSG has been decided and MRSG performance in initial stage and later stage has evaluated. Thermogravimetry and dehydration kinetics of MRSG have been researched and selective water shutoff mechanism has been discussed. Major results and achievements required are as follows:(l)In accordance with definition of compressive strength and tenacity and evaluation mechanism, gel strength and tenacity are characterized by maximum pass-through pressure and transition pressure individually and a device is designed to evaluate gel strength and tenacity. This evaluation method has proved scientific, quick and simple operation. Meanwhile, MRSG strength has been evaluated qualitatively and quantitatively by eye survey code method and breakthrough pressure gradient method individually.(2) The process of gelling of MRSG is decided into two stages-the initial stage and the last stage. Preformed gel(montmorillonite/weak gel suspended substance ) is formed in the initial stage and MRSG is formed in the last stage. The factors affecting gel performance are discussed concretely and the synthetic conditions are optimized.(3)The rheological character of preformed gel(montmorillonite/weak gel suspended substance ), the initial stage product of MRSG gelling process, has been researched by HAAKERS600 rheometer. Experiment results show that preformed gel(montmorillonite/weak gel suspended substance ) is typical pseudoplastic fluid and yield stress can be gotten by extrapolating curve; Dosage of montmorillonite affects the rheological character of preformed gel(montmorillonite/weak gel suspended substance ) deeply; Shearing stress-shear rate experiment data of preformed gel(montmorillonite/weak gel suspended substance )have been handled by non-linear regression analysis using Herschel-Bulkley rheology model for the first time and the parameters of Herschel-Bulkley rheology model equation have been decided.(4)Filtration performance of preformed gel(montmorillonite/weak gel suspended substance ) has been evaluated by static state filtration measurement in homogeneous synthetic core. The fluid loss coefficient, filtration rate and spurt loss of MRSG are theinterpreted; Filtration behavior near well area has been simulated by long sand-stuffed m with double - porosity for the first time and the results have showed that leakoff is occt near well area.(5)Because of the formation of preformed gel(montmorillonite/weak gel suspei substance), the extent of harm to matrix is very low.(6)Crazing has been observed in the SEM pictures of MRSG broken surface montmorillonite improving tenacity mechanism is explained by crazing mechanism.(7)Easier dehydration mechanism of second crosslinked gel and the microcosmic ext why MRSG has perfect performance, have been researched by atomic force microscopy.(8)Thermostability has been reviewed when add montmorillonite or Thermogravimetry curve of MRSG and SCG have been analyzed and dehydration velc expression has been dealed approximately with Coast-Redfern method for the first ti fitting thermogravimetry experiment data with method of least square and calcula dehydration kinetic parameters, that is, dehydration reaction activation energy dehydration reaction number of stages. The thermogravimetry results and experiment ci fitting results show that dehydration is more difficult to proceed in MRSG than in SCG montmorillonite affects gel thermostability.(9)MRSG belongs to modified gel species water shutoff agent. Using achievem about selective water shutoff mechanism both here and abroad for reference and accordin the results of indoor experiments, selective water shutoff mechanism of MRSG has t conferred.