考虑压裂液污染的低渗透垂直井产能计算

PRODUCTIVITY CALCULATION FOR THE VERTICALLY FRACTURED WELLS CONSIDERING THE DAMAGE BY THE FRACTURING FLUID

为计算压裂液污染的低渗透油藏垂直压裂井的产能,采用Heber Cinco-Ley等人提出的压裂液污染带的简化模型,通过压降叠加原理得到因压裂液污染导致的附加压降公式,然后依据扰动椭圆理论推导出不考虑压裂液污染的垂直压裂井稳态压差公式,并根据叠加原理将两公式相结合,最终得到考虑压裂液污染的低渗透油藏垂直压裂井产能公式。这个公式考虑了启动压力梯度、污染带厚度和污染程度的影响。进行参数敏感性分析认为:增产倍数对裂缝半长最敏感,其次为启动压力梯度、污染程度与污染带厚度。因此,进行压裂增产时应该尽量增加裂缝半长,提高压裂液与地层液体的配伍性,减小压裂液对地层岩石的伤害以避免污染程度过高,提高压裂液的返排率以降低污染带的厚度。

In order to calculate the productivity of the vertically fractured wells damaged by the fracturing fluid in the low-permeability oil reservoir, by means of the simplified model for the damage zone by the fracturing fluid pro- posed by Heber Cinco-Ley et al, the additional pressure drop formula resulted from the fracturing fluid damage is established through the superposition principle of the pressure drop. And then, the steady-state pressure-drop equa- tion of the vertically-fractured wells without considering the damage is derived according to the disturbing elliptical theory. And moreover, according to the the superposition principle, the productivity equation of the vertically frac- tured well considering the damage by the fracturing fluid in the low-permeability reservoir is finally derived out. The formula can integrate the following influences： threshold pressure gradient, thickness and degree of the damage zone. The sensitivity analysis of the parameters shows that the fracture half-length has the greatest influence on the stimulation multiple, the next are the threshold pressure gradient, damage degree and thickness of the damage zone. Therefore when the fracturing stimulation occurs, the fracture half-length should be increased as possible as we can, improve the compatibility between the fracturing fluid and formation fluids, lease the damage to the rock resulted from the fracturing fluid so as to avoid excessive damage degree and enhance the flowback ratio of the frac-turing fluid to decrease the thickness of the damage zone.