元坝气田低渗透致密砂岩气藏压裂优化技术

四川盆地元坝气田上三叠统须家河组、下侏罗统自流井组砂岩气藏具有埋藏深、低孔低渗、温度高、异常高压、岩性致密、非均质强、破裂压力及延伸压力高等特点，为了解决该类储层水力压裂破裂压力高、施工难度大的难题，对现有的气藏压裂技术进行了以下优化：①研制新的低伤害压裂液体系，其降阻率为72%~79%，对岩心基质伤害率小于17%；②采用集成创新技术，如低应力小相位集中射孔技术、最优前置液多级粒径降低压裂液滤失技术、低砂比造长缝技术、超高压压裂技术、高效返排技术等；③配套140 MPa采气井口，140 MPa超高压设备和地面管汇、高压压裂管串、高压井下工具，将施工限压提高至120 MPa，确保成功压开致密储层。该优化技术在元坝气田现场试验4口井5层次，取得了良好的应用效果：施工最高压力达到118.5 MPa，最大排量5.5 m³/min，平均砂比15%~20%，最大加砂量40 m³，施工成功率达100%；降低了延伸破裂压力，增大了施工排量，增加了人工裂缝长度和宽度，易于加砂，提高了储层渗透率。

Optimization of fracturing technology for low-permeability tight sandstone gas reservoirs in the Yuanba Gas Field,Sichuan Basin

In Yuanba Gas Field, the Xujiahe Formation of Upper Triassic and the Ziliujing Formation of Lower Jurassic are characterized by deep burial depth, low porosity and low permeability, high temperature, abnormal pressure, tight lithology, strong heterogeneity, high fracturing pressure and high extending pressure. In view of these challenges for operations, the existing gas reservoir fracturing technologies were optimized as follows. Firstly, a novel low-damage fracturing fluid was developed with friction reduction of 72%-79% and core matrix damage less than 17%. Secondly, techniques were innovatively integrated, including centralized perforation technology of low stress and small phase, fracturing fluid loss reducing technology of optimal prepad multi-stage particle size, long fracture-building technology of low sand concentration, overpressured fracturing technology and high-efficiency flowback technology. Thirdly, the operation pressure limit was increased to 120 MPa by equipping the 140 MPa gas wellhead with 140 MPa ultra-high pressure equipment and choke lines, ultra-high pressure fracturing pipe string and high-pressure downhole tools, so that tight reservoirs could be successfully fractured. In the Yuanba Gas Field, the optimized technology was tested on site in 4 wells/5 layers and presented good effects with the maximum operation pressure of 118.5 MPa, the maximum flow rate of 5.5 m³/min, average sand concentration of 15%-20%, the maximum sand volume of 40 m³ and success ratio of 100%. Obviously, it can decrease Fracturing and extending pressures, increase flow rate in operation, increase the length and width of hydraulic fractures, facilitate gravel input and improve reservoir permeability.