Efficient and variable viscosity fracturing fluid of deep coal rock gas andpopularization in Ultimate volume Fracturing

Limit volume Fracturing Technology is the effective means to achieve high yield industrial flow for deep coal rock gas, on the basis of this technique,fracturing fluid is the key to fully "Breaking" coal seam, establish filling sand complex crack network, realize Anatonosising-Desorption promote for coal rock,therefore, the focus of coal rock gas fracturing fluid research is fully meet the field condition, construction technology and physical characteristics of coal rock.Focus on the research of the friction reducer with high stability, instant, low dosage but high efficiency and on-line viscosity change integration,a switch-type emulsion resistance reducer was prepared by introducing inorganic salt stimulation response material,designing switch reverse phase emulsion polymerization technology, condition controling of Multicomponent copolymerization and compounding desorption promote agent.The influence law on fracturing fluid performance by important parameters of emulsion resistance reducer was clarified by combining Characterization and Evaluation of basic performance, the expected coal rock gas special resistance reducing agent SFY-2 was obtained with the optimization conditions of hydrolysis ratio for 50%～55%, molecular weight for about 18 million and effective content for 29%～34%, the stability is improved to over 50 day, the low temperature resistance is below﹣15 ℃, the dissolution time is reduced to 10 s, the viscosity increasing rate is over 90% in 3 min, and the viscosity increasing ability is strong,the highlight contradiction of convention emulsion friction reducer between stability and instant solubility was resolved,as well as provided a guarantee for the online integrated construction of deep coal rock gas Ultimate volume Fracturing.By taking the advantage of SFY-2, a efficient and variable viscosity fracturing fluid is constructed to fit the design idea of coal rock gas Ultimate volume Fracturing, the variable viscosity control scheme is formulated and the construction technology is optimizated to achieve the goal of "Breaking" the coal rock sufficiently, creating complex sewing nets, filling sands fully and supporting effective.Performance evaluation of fracturing fluid indicated that: after simulate variable shearing of 170 s⁻¹～1 500 s⁻¹～100 s⁻¹ at 70 ℃, the viscosities of high viscosity fluid and middle viscosity fluid were kept 35 and 20 mPa·s respectively; The drag reduction rates of high viscosity fluid,middle viscosity fluid and low viscosity fluid can respectively reachs more than 66%, 72%, 77%, furthermore, the resistance retention rate of high viscosity fluid and middle viscosity fluid is over 100% under high shear conditions, thanks to the good shear dilution of fracturing fluid.The corresponding relationship between the suspended sand performance and the viscoelastic parameter tanδfor the fracturing fluid has been established, when the dosage of SFY-2 exceeds 0.2% (tanδ=0.84), the settling speed of fracturing fluid is obviously reduced, When the dosage reaches 0.4% (tanδ=0.395), the viscoelasticity of fracturing fluid is significant, which is conducive to high strength continuous sand adding for seam mesh saturation support, and increases the effective transformation volume of seam mesh.There is almost no residue in fracturing fluid gel breaker,the surface tension is as low as 26 mN/m or below, the gel breaker can effectively improve the wettability of coal rock surface, increase the contact angle up to 108.2°, reduce the desorption damage rate of coal rock as low as 13%. This technology has been applied more than 350 Wells (more than 2 000 stages/times in total) in the deep coal reservoir of Ordos Basin, with the advantages such as stable liquid performance, high construction efficiency, the real-time Drag reduction rate reachs 84.4%, highly sand completion rate, remarkable effect of increasing production,and so on,which provided power for realizing the scale benefit development of deep coal rock gas.