摘要：

暂堵剂被广泛用于水平井压裂过程中的裂缝暂堵与转向，对提高压裂改造效果具有重要作用。目前国内外关于暂堵剂运移规律的研究多局限于室内实验，对暂堵剂在井筒中的运移、在缝中封堵过程的宏观模拟研究还不充分。本文基于计算流体力学(CFD)与离散元(DEM)耦合的数值模拟方法，模拟了水平井压裂暂堵过程中暂堵剂颗粒井下运移与封堵过程。模拟时，将暂堵剂颗粒视作离散相，将压裂液视作连续相，对离散相与连续相单独建立数学模型，同时耦合离散相与连续相之间的相互作用，从而实现暂堵剂—压裂液多相体系的流固耦合。针对暂堵剂从井口到封堵井段的运移过程，建立了井筒模型、井筒—炮眼—单一裂缝和井筒—炮眼—多条裂缝模型。揭示了暂堵剂浓度、暂堵剂粒径、压裂液黏度和泵注排量对暂堵剂运移完整性的影响规律，探究了不同裂缝形态下工艺参数与施工参数对暂堵剂封堵效果的影响。研究表明，暂堵剂体系颗粒浓度、压裂液黏度与泵注排量是影响暂堵剂体系运移完整性的重要因素，暂堵剂粒径与浓度是决定暂堵剂体系能否有效封堵裂缝的关键因素。暂堵剂粒径大于20目时，暂堵剂质量浓度的改变只会影响缝内封堵段长度，而不会影响缝内暂堵有效性；当裂缝末端缝宽达到4 mm时，选用20~70目粒径的暂堵剂难以在缝高方向完全封堵裂缝。本研究为水平井暂堵压裂施工过程中工艺参数与施工参数的选取提供了理论依据。

关键词: 缝内暂堵, 暂堵剂运移, 暂堵机理, 水平井, CFD-DEM

Abstract:

Temporary plugging agents are widely used in temporary plugging and steering fracturing in horizontal wells, playing a critical role in enhancing reservoir stimulation efficiency. Current study on temporary blocking agents conducted both domestically and internationally are mostly limited to experimental methods, and there is a lack of macroscopic simulation research on the migration and plugging processes of temporary plugging agents. In this paper, a numerical simulation method based on the coupling of Computational Fluid Dynamics (CFD) and Discrete Element Method(DEM) was used to simulate the downhole migration and plugging process of temporary plugging agents during the fracturing temporary plugging process of horizontal wells. In the simulation, the plugging agents were regarded as the discrete phase composed of individual particles, while the fracturing fluid was regarded as the continuous phase. Separate mathematical models were established for the discrete phase and the continuous phase, and the interaction between the discrete phase and the continuous phase was coupled at the same time, so as to realize the fluid-solid coupling in the multi-phase system of temporary plugging agent and fracturing fluid. For the migration process of temporary plugging agent from the wellhead to the target plugging well section, the wellbore model, “wellbore-borehole-single fracture” and “wellbore-borehole-multiple fractures” models were established. The effect of the temporary plugging agent particle size, concentrations, fracturing fluid’s viscosity and pumping rate to the migration integrity was investigated, and the effect of fracture shape to the plugging effect was also explored. The results indicate that the concentration of the temporary plugging agent, fracturing fluid’s viscosity and pumping rate are important factors affecting the integrity of the temporary plugging system. The particle size and concentration of the temporary plugging agent is the key factor that determine whether the temporary plugging system could effectively plug fractures. If the particle size of the temporary plugging agent is above 20 mesh, the change in mass concentration of the temporary plugging agent will only affect the length of the blocking section, but will not affect the effectiveness of the temporary plugging in the fracture. Once the width at the end of the fracture reaches 4 mm, it is difficult to completely plug the fracture in the direction of the fracture height using a temporary plugging agent with a particle size of 20-70 mesh. The study provides reasonable theoretical guidance for the selection of process parameters and construction parameters for the temporary plugging fracturing in horizontal wells.

Key words: in-fracture temporary plugging, the migration of temporary plugging agents, the mechanism of temporary plugging, horizontal well, CFD-DEM

中图分类号: 

• TE319

• TE357.12