Synthesis Of Relative Permeability Modifier And Simulation On Water Controlling Effect For Hydraulic Fracturing In Low Permeability Reservoirs

Hydraulic fracturing is the most effective method for improving hydrocarbon production in low or ultra-low permeability oil reservoirs.But the crack would become loop channel for invalid injected water or edge and bottom water after the fracturing treatment of low permeability reservoirs near water formation or in high water-cut formation.It causes the water rise faster.The water-free oil production period is shorten.This severely restricts the hydraulic fracturing technology in such oil field.Relative permeability modifier(RPM) is a kind of selective water controlling agent, it only decreases the permeability of formation water phase, and causes little or even no impact on oil phase.According to the principle of molecular design, Relative permeability modifier was synthesized by inverse emulsion polymerization with acrylamide(AM) as main monomer and 2–acrylamido-2-methylpropanesulfonic acid(AMPS) and N,N-dimethylacrylamide (DMAA) as functional monomers.The recation conditions were obtained by the study of inverse emulsion stability and orthogonal experimental design and single factor optimization test.The results showed that the optimum synthetic conditions were V(oil):V(water)=2:3, the amount of emulsifier 6%, the concentration of monomer 30%, the ratio of monomer AM:AMPS:DMAA=95.9:2.5:1.6, the amount of initiator 0.12%, the value of pH 7, reaction temperature 50℃, reaction time 8h.The structure of RPM was characterized by Infrared Spectra. The particle size of RPM was about 80nm which was analyzed by the Laser Particle-size Analyzer.The heat resistance, salt tolerance, anti-shearing, flushing resistant and water control performance of polyelectrolyte complex solution were evaluated, respectively.The results showed that 2500mg/L RPM emulsion in salt water had viscosity 15.9mPa·s (30℃) and when the temperature was 90℃, the viscosity was 16.2mPa·s, the viscosity retention was 82.7% in the 170s-1 under continuous shear 2h.In core flooding testing at 60℃, the residual resistance factor of the RPM solution was 3.44 after the 62PV saline displacement.The RPM had good performance of ablation resistance. When compared with that before modifier injection, core permeability decreased, but the irreducible water saturation increased, while water permeability reduced more than 80%, while oil permeability reduction was less than 20%.This reflected the significant characteristic of disproportionate permeability reduction of RPM.Selective water controlling effect was obvious.Through simulation on water controlling effect of RPM for hydraulic fracturing in oil well, Sensitivity factor analysis results show that: in a certain range, the ratio of resistance factors, which is the begger. The more effective the RPM treatment is, the higher the value of the mobility ratio between the reservoir oil and water.The treatment is more effective for lower permeability.After the RPM treatment, the water cut is rising slowly.The lower the fracture flow conductivity is, the lower the water cut.The water cut reduction is greater, the larger the penetration depth is.The RPM could effectively control the growth of rapidly rising water after the fracturing treatment of low permeability reservoirs, in order to reduce the in-situ treatment risk.