Preparation And Application Of Residue-free Fracturing Fluid For Low Permeability Oilfields

Fracturing is an important measure for increasing oil production.Although the traditional guar gum fracturing fluid can meet the high temperature requirements during fracturing,its shortcomings of water insoluble matter and incomplete gel breaking cannot be ignored.The fracturing fracture support zone and formation Permeability causes irrecoverable damage,especially in low-permeability oilfields.Therefore,in order to reduce the damage of the fracturing fluid to the formation,a new type of low-damage,low-cost new water-based fracturing fluid suitable for the reservoir reconstruction of ultra-low permeability oil fields was developed.In the fracturing construction of high-temperature wells,the temperature resistance of fracturing fluid is one of the key factors that determines the success or failure of construction.From the experience of fracturing reforms at home and abroad,the main problem brought by high-temperature fracturing is the fracturing fluid with poor high-temperature resistance.After undergoing long-term shear in the high-temperature environment of the reservoir,it is difficult to maintain continuous fracture formation and sand suspension.Capacity,leading to fracturing failure.In this paper,polyvinyl alcohol was used as a thickener,and potassium tartrate was used as a single organic ligand to prepare a boron cross-linking agent BOF with a high temperature resistance through a complexation reaction with borax.SDGL-1,glycerol,and mannose were used.Alcohol and THNM-3 are composite organic ligands and borax to obtain an organic boron crosslinking agent BOM with high temperature resistance.Polyvinyl alcohol was cross-linked with two synthetic boron cross-linking agents to obtain two sets of polyvinyl alcohol fracturing fluid systems with good temperature and shear resistance,and the gel viscosity,Cross-linking time is compared,and comprehensive evaluation is carried out based on the general technical requirements of water-based fracturing fluids.(1)The optimal formula for polyvinyl alcohol fracturing fluid is:the mass fraction of polyvinyl alcohol(2488)base fluid is 2%,the optimal cross-linking pH is 10,and the cross-linking mass ratio is 100:1.(2)Organic boron cross-linking agent BOF suitable for polyvinyl alcohol fracturing fluid.The optimal synthesis conditions are determined as follows:18%borax mass,15%potassium sodium tartrate,1.0%sodium hydroxide,and reaction time.4.0h,reaction temperature 80℃.BOF cross-linked polyvinyl alcohol fracturing fluid has the characteristics of delayed cross-linking.The cross-linking time is between 170~200s,shearing at 80℃,170s~-11 for 60min,and the final viscosity is 67 mPa·s.The temperature resistance limit is 90℃,suitable for medium and high temperature reservoirs;good sand-carrying performance,small filtration loss coefficient,complete gel breaking,residual mass concentration of 72 mg/L,almost no residue.Core damage experiment results show that the fracturing fluid system has little damage to artificial cores,and the polyvinyl alcohol fracturing fluid cross-linked by organic boron crosslinking agent BOF can fully meet the requirements of fracturing site construction.(3)Organic boron crosslinker BOM suitable for polyvinyl alcohol fracturing fluid.The optimal synthesis conditions are determined as follows:borax mass fraction 18%,ligand mass fraction 16%,and its mass ratio is greater than SDGL-1:glycerol.:Mannitol:THNM-3=1:15:15:10,sodium hydroxide mass fraction 1.0%,reaction time 4.0 h,reaction temperature 80℃.BOM crosslinked polyvinyl alcohol fracturing fluid has the characteristics of delayed crosslinking,and the crosslinking time is between 230 and 280s.Shear at 80℃,170s~-11 for 60min,the final viscosity is 100mPa·s,the temperature resistance limit is 95℃,suitable for medium and high temperature reservoirs;good sand-carrying performance,small filtration coefficient,thorough gel breaking,gel breaking liquid The surface tension is 26.8 mN/m,and the mass concentration of the residue is 69 mg/L,with almost no residue.Core damage experimental results show that the fracturing fluid system has little damage to artificial cores,and the polyvinyl alcohol fracturing fluid crosslinked by organic boron crosslinking agent BOM can fully meet the requirements of fracturing site construction.