裂隙岩体同步压裂干扰机制的数值模拟研究

为认清裂隙岩体中同步压裂的应力扰动规律,指导页岩气储层压裂的优化设计,应用基于有限元的RFPA^2D-Flow软件,首先对配对井相同压裂段间裂缝静、动态诱导应力扰动机制进行研究,随后研究了天然裂缝对水力裂缝的影响机制,并对裂隙岩体的同步压裂进行模拟。结果表明,相向延伸水力裂缝的诱导应力相互叠加,其对地应力场产生的扰动作用相对单井裂缝更加明显。水平主应力差较小时,配对井相同压裂段裂缝在相向延伸过程中相互吸引的趋势越明显,分支缝越多;小主应力差、小逼近角且高脆性矿物充填的天然裂缝更易使水力裂缝转向;对于非完全充填雁列式裂缝型储层,大主应力方位与天然裂缝呈30°至60°夹角时,天然裂缝起裂及失稳压力适中,可有效降低施工难度,同时该角度范围也利于一定数量的分支缝形成。同步压裂技术可对目标储层实现充分改造,具有良好应用前景。

Numerical Simulation Research on the Perturbation Mechanism of Simultaneous Fracturing in Jointed Rock Masses

In order to get a clear understanding of the stress interference rule of simultaneous fracturing in jointed rock masses, and to guide the optimal design of shale fracturing, a numerical simulation by RFPA2D-Flow(Rock Failure Progress Analysis-Flow) based on FEM is carried out to study the mechanism of induced stress perturbation in the same fracturing stage of adjacent horizontal wells firstly. Then the impact mechanism of natural fracture to hydraulic fracture is studied, and the simultaneous fracturing in jointed rock masses is simulated finally. The calculated results indicate that when fractures extend towards each other, the induced stress overlaps, the interference to the original stress field is stronger than a single fracture. If the horizontal principal stress difference is small, fractures in the same stage of adjacent horizontal wells more like to attach each other. The small principal stress difference, small approaching angle and high brittleness filling material are conducive to the appearance of crack direction change; As to unfilled natural fractures in en-echelon arrangement, if the angle between nature fracture and the direction of maximum principal stress is between 30° and 60°, the initiation and instability pressure is moderate, which can effectively reduce the construction difficulty. meanwhile the range of angles are advantageous to the appearance of branching cracks. Simultaneous fracturing can obtain an efficient reconstruction to the reservoir, which has a good application prospect.