低频波动下考虑孔隙度与压力不同程度变化的岩土固结渗流分析

Analysis of seepage changes during poroelastic consolidation process with porosity and pressure variation under low-frequency vibration

低频波动激励下实际开发储层物性发生改变,开展一维定压或定压力梯度情形岩土固结分析,难以反映具有变化流速、压力梯度的实际储层近井带波动激励效果。推导了低渗孔隙介质固结模型控制方程,建立了考虑不同孔隙度、压力变化程度的3种饱和单相渗流流体孔隙介质固结模型,开展一维、径向物理模型模拟求解,进而评价低频波动在恒定或变压力梯度、不同固结模型下的作用效果及参数影响敏感性。结果表明,考虑低渗储层渗流惯性作用和较强应力敏感性时,波动作用下(恒定压力梯度)一维模型的压力、流速、孔隙度增幅整体减小,(变压力梯度)径向物理模型波诱导作用出现不同变化,压力、孔隙度增幅增加,流速增幅降低;随振动参数增加,径向物理模型物性最大增幅数值波动性变化更为剧烈。研究结论反映了实际储层低频波动激励效果的复杂性及动力学分析的必要性。

The physical properties in actual developed reservoirs change under the stimulation of low-frequency vibration. However,no change in porosity and pressure is usually assumed in classic consolidation model. The analysis of solid deformation is often based on a one-dimensional physical model with constant pressure(or pressure gradient) condition. Therefore, it is usually inadequate to simulate the effect of seismic production technology near the wellbore in actual developing reservoirs, which are with varying flow velocities and pressure gradients, with the classic mathematic model and one-dimensional physical model. The control equations of consolidation model for low permeability porous media are re-derived from the continuity equations of fluid and solid. Considering different assumptions of variation extents of porosity and pressure, three consolidation models are given. Numerical simulation is then carried out with one-dimensional(with constant pressure gradient) or radial(with changing pressure gradient) physical model.The effect of seismic production technology as well as its sensitivity under different fluid and vibration parameters are evaluated with different consolidation models. Because of the influences of the inertia effect of initial flow and the strong stress sensitivity in low permeability reservoir, the increases of pressure, flow velocity, and porosity are found to be lower under vibration than the case without vibration in one-dimensional model. However, the wave-induced effect behaves differently in radial physical model. The increases of pressure and porosity are both higher under vibration than the case without vibration, and the increase of flow velocity becomes lower under vibration. As the vibration parameter increases, the volatility of values representing the wave-induced effect becomes stronger when simulated with radial physical model and different consolidation models. The results reflect that it is necessary to carry out a dynamic analysis on the complex effects of artificial seismic technology in actual developing reservoirs.