Efficient and variable viscosity fracturing fluid of deep coal rock gas and popularization in ultimate volume fracturing

LIN Bo; CHEN Shuai; YAN Xiangyang; CHEN Mengqi; DU Liangjun; CHEN Heng; LU Hongsheng; SUN Shuai

doi:10.13225/j.cnki.jccs.2024.0881

Abstract：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 frac-turing fluid research is fully meet the field condition,construction technology and physical characteristics of coal rock.Fo-cus 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 re-sponse material,designing switch reverse phase emulsion polymerization technology,condition controling of Multicom-ponent 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 ba-sic 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 days,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 contra-diction 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 advant-age of SFY-2,a efficient and variable viscosity fracturing fluid is constructed to fit the design idea of coal rock gas Ulti-mate volume Fracturing,the variable viscosity control scheme is formulated and the construction technology is optimiz-ated to achieve the goal of"Breaking"the coal rock sufficiently,creating complex sewing nets,filling sands fully and sup-porting 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 respect-ively reachs more than 66％,72％,77％,furthermore,the resistance retention rate of high viscosity fluid and middle vis-cosity fluid is over 100％under high shear conditions,thanks to the good shear dilution of fracturing fluid.The corres-ponding relationship between the suspended sand performance and the viscoelastic parameter tan δ for the fracturing fluid has been established,when the dosage of SFY-2 exceeds 0.2％(tan δ=0.84),the settling speed of fracturing fluid is obvi-ously reduced,When the dosage reaches 0.4％(tan 8=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 trans-formation 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 com-pletion rate,remarkable effect of increasing production,and so on,which provided power for realizing the scale benefit de-velopment of deep coal rock gas.