Research On Degradation Mechanism Of Guargum Fracturing Fluid Without Backflow In Tight Reservoir

Tight oil is a new bright spot in exploration and development of unconventional energy resources.Its development mainly depends on horizontal well large-scale fracturing and volume fracturing.During this process,the volume of in-situ fracturing fluid is huge.It has broad prospects to effectively reduce the damage of fracturing fluid to reservoirs and to use non-return gel breaking fluid to imbibe oil.In this paper,guanidine gum fracturing fluid breaking and residue degradation are studied to improve the gel breaking effect of fracturing fluid and reduce the residue content in gel breaking fluid,effectively reduce the damage of fracturing fluid to the reservoir.Firstly,the gel breaking performance and core damage level of the current fracturing fluid system in the study area were evaluated by laboratory experiments.On the basis of this,a thickener and a crosslinking agent are preferred.Through the fracturing fluid breaking test,the fracturing fluid temperature and shear resistance,the viscosity of the gelling solution and the residue content are used as evaluation indexes,and the high efficiency breaker and degradant are selected from the conventional 11 kinds of gel breakers and 9 kinds of degradant systems.The five-factor and four-level orthogonal experiments were further designed to organically compound the breaker and the degradation agent,and the influence rules of the main factors of the gel-breaking agent were analyzed,and the high-efficiency gel-breaking agent system and its optimal use conditions were optimized.The common performance of the low-injury non-returning guar gum fracturing fluid system was evaluated by laboratory experiments.Finally,through molecular weight and residue particle size test analysis,the mechanism of low damage of the system was clarified.Thickener G-3 and organic boron crosslinker J-3 were screened out,when the cross-linking ratio was determined to be 100:10,the reasonable concentration was 0.3% and3.5%,respectively.The high efficient breaker P8 and residue degradation agent M2 were screened out.The degree of influence of control factors on the effect of gel breaking degradant is as follows: temperature > p H > gel breaker concentration > degradation agent concentration > salinity.The best application temperature for the low-injury non-returning guar gum fracturing fluid system is 60 ?,the optimum salinity was 40000 mg/L,and the optimum p H value was 9.0,when the cross-linking ratio is 100:10,the optimum concentration combination of breaker and degrader is 0.06% and 0.7% respectively.Its crosslinking time,static sand carrying performance,temperature and shear resistance and static and dynamic filtration performance meet the requirements.The viscosity of gel breaker is 1.93 m Pa·s,reduced by about 23.7% compared to the current formulation.The residue content is 212mg/L,which is about 56.0% lower than that of field formulation.The damage rates of fracturing fluid filtration,fracturing fluid dynamic filtration and gel breaker filtration to core matrix permeability are 16.06%,27.93% and 14.88% respectively,which are slightly lower than those of field formulation.The damage rate of dynamic filtration of gel breaker to core matrix permeability is 19.08%,which is about 23.8% lower than the value of field formula.Compared with bio-enzymes,oxidizing breakers have stronger ability to reduce the viscosity of breaking solution and bio-enzymatic degradants have stronger ability to reduce the content of residue in breaking solution.The viscosity of gel breaker was positively correlated with the average molecular weight of guanidine gum,and the content of gel breaker residue was positively correlated with the particle size of gel breaker.