深部页岩压裂缝网体积模拟及应用

深层页岩受埋深影响储层地应力高，水平应力差异大，压裂裂缝延伸困难，改造体积受限，同时压裂时缝内净压力小，天然裂缝张性和剪切破坏难度增大，缝网复杂度偏低。通过构建简化三维Wiremesh模型，考虑正交天然裂缝和深层页岩力学性质，推导不同方向裂缝净压力分布，采用Richtmyer线性化方法编程求解，最终获取了不同参数下缝网体积变化特征。研究结果表明:增加施工时间，缝网体积近似呈线性增加，椭圆长轴与短轴的轴比持续增大，但后期短轴方向延伸有限；提高施工排量时裂缝半长及缝网波及体积随之增大，压裂效率显著提高；压裂液黏度增大导致缝宽增大，缝长减小，缝网体积明显减小；均匀地应力场条件裂缝在各个方向上均较好地扩展，长轴和短轴相当，改造体积较小。基于深层页岩压裂缝网体积模型优化后的压裂方案在涪陵页岩气田江东区块深井现场应用30井次，压后G函数曲线分析表明裂缝复杂度高，测试压力和测试产量较高，取得了理想的应用效果，该研究为深层页岩气藏增产改造提供了技术支撑。

Deep shale hydraulic fracture network volume model and its application

Due to the influence of burial depth, deep shale suffers high reservoir stress, large horizontal stress difference, difficult propagation of hydraulic fractures and limited stimulated reservoir volume. What’s more, the intra-fracture net pressure in the process of fracturing is low. As a result, the tension and shear fracture of natural fractures is more difficult and the complexity of fracture network is lower. The simplified 3D Wiremesh model was constructed to derive the distribution of fracture net fracture in different directions by considering the mechanical properties of orthogonal natural fractures and deep shale. Then, programming solution was carried out by means of Richtmyer linear method. Finally, the variation characteristics of fracture network volume at different parameters were figured out. It is indicated that with the increase of construction time, the fracture network volume increases approximately linearly and elliptic major/minor axis ratio increases continuously, but the propagation along the minor axis is limited in the late stage; with the increase of construction displacement, half fracture length and fracture network sweeping volume increase and the fracturing efficiency is improved significantly; the increase of fracturing fluid viscosity results in the increase of fracture width, the decrease of fracture length and the obvious reduction of fracture network volume; under the condition of uniform stress field, fractures propagate better in all directions, equivalent in major axis and minor axis, and the stimulated reservoir volume is smaller. The fracturing scheme optimized on the basis of the deep shale hydraulic fracture network volume model is applied on site in the deep wells of Jiangdong Block of Fuling Shale Gas Field 30 well times. The analysis on the postfrac G-function curve shows that the fracture complexity is high and testing pressure and testing production rate are higher, indicating satisfactory application effect. This study provides technical support for the stimulation of deep shale gas reservoirs.