低渗透油气藏爆炸压裂模拟试验及裂缝分形特征

Explosive fracturing simulation experiment for low permeability reservoirs and fractal characteristics of cracks produced by explosive fracturing

基于爆炸压裂模拟实验,分析各试样爆炸压裂后裂缝的发育情况,并结合分形几何理论,研究各试样的裂缝分形特征,分析了炸药量、围压对裂缝分形维数的影响规律。设计了各试样在爆炸压裂模拟实验中的炸药量和围压,采用盒维数计算方法求取实验后各试样的裂缝分形维数,结果表明:相同围压下,随着炸药量的增加,试样表面裂缝数量、长度、宽度增加;相同炸药量条件下,随着围压的增大,试样表面裂缝长度、数量减少;同一围压下,裂缝分形维数随炸药量的增加而增大,围压较小时裂缝分形维数与炸药量间近似呈线性关系,围压较大时裂缝分形维数与炸药量间呈非线性关系;同一炸药量下,裂缝分形维数随围压的增大而减小。建议采用轴向耦合、径向不耦合布药方式,现场施工时应使炸药量和地下围压相匹配。

Based on the explosive fracturing simulation experiment for low permeability reservoir, growths of the cracks produced by the explosive fracturing in the samples were analyzed. And associated with fractal geometry theory, the cracks fractal characteristics were studied and the influences of explosive quantity and confining pressure on the cracks fractal dimension were analyzed. Different explosive quantities and confining pressures under which the simulation experiment was carried out were designed. After the experiment, the fractal dimension of the cracks produced by explosive fracturing in different samples was got by the box dimension calculation method. The results show that： With the increase of explosive quantity, the amount, length and width of the cracks on the surface of the sample produced by explosive fracturing simulation experiment under the same confining pressure increase. The amount and length of the cracks produced by explosive fracturing under the same explosive quantity decrease with the increase of confining pressure. Under the same confining pressure, the cracks fractal dimension increases with the increase of explosive quantity, and the relationship between them is approximately linear when the confining pressure is relatively low and approximately nonlinear when the confining pressure is relatively high. Under the same explosive quantity, the cracks fractal dimension decreases with the increase of confining pressure. It is suggested that site operation should match the explosive quantity with the confining pressure, and the charge pattern of axial coupling and radial uncoupling should be applied.