考虑注水温度及储层堵塞的注水破裂压力计算

长期注水造成的储层温度变化和堵塞都会影响注水破裂压力。基于多孔介质弹性力学理论,得到了考虑储层温度变化及堵塞时的井壁处有效应力分布规律,建立了相应的注水破裂压力计算模型,并分析了储层温度变化及堵塞程度对注水破裂压力的影响规律。计算结果表明:注水破裂压力随注水温度的降低而降低,且成线性变化关系,弹性模量和线膨胀系数越大,注水破裂压力的变化幅度越大;与储层内部的污染带相比,滤饼厚度及其渗透率对破裂压力的影响更大,随着滤饼厚度的增加及其渗透率的降低,破裂压力将会升高;井壁存在滤饼时,污染带范围的增加将降低破裂压力,而其渗透率对破裂压力则影响很小,当滤饼不存在时,储层内部污染带不会影响注水破裂压力。

Calculation of fracturing pressure during waterflooding with considerations of water temperature and reservoir plugging

The fracturing pressure is affected by the reservoir temperature change and the formation plugging during the long-term water injection. However, the two influencing factors have not been considered in the existing fracturing pressure calculation model. So it is necessary to incorporate the two factors into the model. Based on the poroelasticity theory, the stresses induced by the in-situ stress and the fluid flow are calculated. And the temperature stresses are calculated based on the theory of elasticity. According to the superposition principal, the effective stresses on the borehole wall are obtained. With the considerations of the reservoir temperature and the plugging, a fracturing pressure analytical model during the waterflooding is established. This analytical model is verified by the conventional calculation model. The influences of the reservoir temperature and the plugging are analyzed. It is shown that the fracturing pressure decreases linearly with the decrease of the water temperature. And with the increase of the elastic modulus and the coefficient of linear expansion, the change extent of fracturing pressure is getting larger. Compared with the formation plugging zone, the filter cake thickness and the permeability have a greater impact. With the increase of the filter cake thickness and the decrease of its permeability, the fracturing pressure would increase. If the filter cake exists, the fracturing pressure decreases with the increase of the plugging zone radius. However, the permeability of the plugging zone has little impact on the fracturing pressure. And the plugging zone in the formation would not affect the fracturing pressure if the filter cake does not exist.