加压时间对储层岩心渗透率的影响

Effect of pressure time on reservoirs core permeability

目前储层应力敏感性研究仅限于有效覆压对渗透率的影响,忽略了加压时间对岩石变形的作用。在高压孔渗仪上用拟三轴岩心夹持器和天然岩心,考察了加压时间对岩石渗透率的影响,提出并计算了单位覆压下渗透率绝对变化速率和相对变化速率。结果表明,岩石变形或渗透率变化与时间有关,渗透率随加压时间的延长而降低。在加压初期渗透率变化幅度较大,随着时间的延长,渗透率变化逐渐变缓;幂函数在总体趋势上能拟合渗透率随时间的变化,其拟合误差在工程应用的合理范围内;基础渗透率大于4.6×10-3μm2的岩心,渗透率下降主要发生在4 h内;渗透率绝对变化速率随时间的延长而降低;渗透率绝对变化速率和相对变化速率与岩石物性有关,岩心基础渗透率越高,渗透率绝对变化速率越大,相对变化速率越小。渗透率相对变化速率的建立,为储层应力敏感性评价提供了一个新的定量参数。

The previous research on stress sensitivity is usually limited to the effect of confining pressure on permeability, while the effects of acting time on rock deformation, porosity and permeability change are neglected. Laboratory tests were conducted to study the relatioship of permeability change and time under high confining pressure by using a precision instru- ment with pseudo-three-axis core holder and natural core samples. Data of absolute rate of permeability change （ ARPC ） and relative rate of permeability change （RRPC） for different cores were measured and analyzed. The test results show the following conclusions： Rock deformation and permeability change are related to time, and the permeability decreases with time prelonging. At the beginning of forcing, core permeability changes quickly and then slowly. Power function can be used to describe the relationship of permeability and time, and the error is in the region of engineering application. The permeability changes mainly in 4 hours for the cores when permeability is more than 4.6 × 10^-3 μm^2. ARPC decreases with time prelonging. ARPC and RRPC are related to cores physical properties, ARPC increases and RRPC decreases with the basic premeability of cores increasing. ARPC is a new quantity parameter for evaluation of reservoirs stress sensitivity.