Study On Blocking System Of Gel For Fractured Reservoirs In The HH Oilfield

The HH oilfield is a fractured tight reservoir with porosity of 10.8%,permeability of 0.4×10^-3?m2,and current recovery of 1.23%.In the pilot test,there was a serious problem of waterlogging when replenishing water,and the water sputum showed less water injection and faster waterline propulsion.In view of the compactness of the long M reservoir and the large pressure gradient of the matrix displacement,it was necessary to have a blocking agent with good strength and to withstand a high water injection pressure.Based on the problems above,this thesis studied the suitable profile control blocking agent for fractured tight reservoirs in the HH oilfield,inhibited the injection of water along the fractures,blocked the water channel of the formation,and solved the technical problem of energy replenishment in tight reservoirs.This also provided technical support for the economic and effective development of the HH oilfield.This thesis studied organic chromium gel and phenolic resin gel.The gelation time,gel strength and stability were used as evaluation indexes.The contents of catalysts,crosslinkers,polymers and additives were adjusted to optimize the freezing.The rubber system prepared different strengths of gel to meet the requirements of multi-segment design.All the systems above were selected to determine the rheology of the gelation.The flow resistance of the gelation was studied during the migration process to evaluate the injectability of the gelation.Furthermore,the effects of migration process,temperature and formation water on the properties of gel were studied.According to the aging time of the gel and the fractures of different sizes,the blocking performance of the gel in the fractures was comprehensively evaluated(breaking pressure gradient,re-blocking ability and erosion resistance).The results showed that the gelation time of 0.5%7136 polymer,0.3%chromium acetate,0.03%malonic acid and 0.3%QC-W was 28 h.Adding phenolic to form a double cross-linking system enhanced the gel strength.The NH₄Cl in the water-soluble phenolic resin gel had a significant effect on the gelation time at low concentration.When the amount of the cross-linking agent was too high or too low,the gel was a broken state and easy to dehydrate.The addition of the stabilizer QC-W greatly improved the stability.Different strengths of water-soluble phenolic resin gel was formulated with different mass fractions of polymer,the elastic modulus of gel with mass fraction greater than 0.4%exceeded 10 Pa.At the same time,with the increase of the mass fraction,the viscosity of the gelation was increasing,and the gelation time became shorter.The elastic modulus of 0.5%G3515 polymer,0.5%water-soluble phenolic resin,0.2%NH₄Cl and 0.3%QC-W was 15.5 Pa,and the dehydration rate was less than 4%when aged at 70°C for 180 days,still maintaining high strength and strong salt tolerance.The flow resistance gradient of the gel-forming liquid above in the wellbore was less than 3.77×10^-4 MPa/m,and the flow resistance gradient in the fracutres was 0.02 MPa/m(width 1.0 mm,550 m/d)and 0.045 MPa/m(width 0.5 mm,733 m/d),the gelation time wad delayed during the migration process.The gelation time at 65°C,70°C and 75°C was 68 h,48 h and 40 h,respectively.The gel soaked in formation water(salinity below 30,000 mg/L)swelled.The blocking performance of gel aged for 10 days was better.The blocking strength and re-blocking ability of the gel in small width fracures were better,and the erosion resistance in wide fractures was strong.The breakthrough pressure gradient was higher than the standard(1.5 MPa/m)of the gel,which was much higher than the crude oil starting pressure gradient.