关键词: 主压裂, 停泵压降模型, 支撑剂运移, 支撑裂缝体积, 铺砂效果, 压降曲线拟合

Abstract: In view of the problem that the current fracturing pump-stopping pressure drop model takes no account of proppant migration and cannot explain the proppant laying effect, the paper proposes a set of pump-stopping pressure drop model suitable for main sand fracturing. The model considers the horizontal shifting and settlement movement of sand carrying fluid-proppant relying on the coupling between viscosity and velocity in the fracture system, as well as the three-dimensional flow of fracturing fluid driven by viscous force and gravity in the matrix system. Based on the coupled solution of fracture system and matrix system, it achieves the simulated calculation of proppant migration in the pump-stopping process of main sand fracturing, and the double logarithmic curve of bottom-hole pressure drop derivative presents the morphological characteristics of L-shape. Moreover, it can be divided into five main control stages according to the pump-stopping time sequence, i.e., proppant settlement, horizontal proppant migration, proppant decelerated migration, proppant compaction and proppant stopping migration. Research shows that the more uniformly the proppant is laid (the closer the sand amount in both the primary and secondary fractures), the more gentle the pressure drop derivative curve, the longer the proppant settlement control period and the shorter the proppant deceleration migration period, and the proppant compaction control stage will show a 1/4 slope section; the larger the proppant filling ratio (the smaller the total volume of fracture network), the steeper the pressure drop derivative curve, the shorter the proppant horizontal migration control period, and the pressure drop and derivative in the proppant migration control stage will tend to coincide. A typical fractured horizontal well in Fuling shale gas field is selected to carry out pump-stopping pressure drop curve fitting in each section sequentially, and the prop-fracture volume and sanding uniformity coefficient of each sand fracturing section are obtained by inversion, thus providing a theoretical basis for quantitatively evaluating the hydraulic sand fracturing effect and understanding the proppant migration law after fracturing.

Key words: main fracturing, pump-stopping pressure drop model, proppant migration, propped fracture volume, sanding performance, falloff curve fitting