顺北碳酸盐岩储层长期酸蚀裂缝导流能力预测方法

顺北碳酸盐岩油气藏温度压力高，储层酸压改造难度大。为解决在闭合应力长期作用下，酸蚀裂缝导流能力损失，导致酸压效果大幅降低的问题。通过酸蚀裂缝导流能力评价实验，研究不同酸液质量分数、温度和闭合时间条件下的酸蚀裂缝导流能力变化规律。综合各条件下酸蚀裂缝导流能力关系式，建立并验证了顺北碳酸盐岩储层长期酸蚀裂缝导流能力预测方法，模拟计算了不同时间和排量下的酸蚀裂缝导流能力变化规律。结果表明：低闭合应力下，酸液反应速率是酸蚀裂缝导流能力主控因素。高闭合应力下，闭合应力、岩石特征和岩面非均匀性是酸蚀裂缝导流能力主控因素。闭合应力是影响岩石表面变形的主控因素，是长期酸蚀裂缝导流能力的决定因素。闭合应力长期作用时裂缝深部导流能力下降幅度比缝口大。人工裂缝中长期酸蚀裂缝导流能力分布规律受酸岩反应速率控制。

Method of Predicting Flow Conductivity of Long-Term Acid-Etched Fractures in Carbonate Reservoirs in Shunbei Oilfield

Acid fracturing has been performed with difficulties in the high temperature high pressure carbonate rock hydrocarbon reservoirs in the Shunbei block. The main problem is the dramatic reduction of the effect of acid fracturing resulted from the losses of the flow conductivity of the acid-etched fractures under the long-term action of the closure stresses. In laboratory experiment, the flow conductivity of acid-etched fractures is evaluated to study the changing patterns of the flow conductivity of the acid-etched fractures under different mass fractions of acid, temperatures and closure time. Based on the equations of the flow conductivity of acid-etched fractures under various conditions, a method for predicting the conductivity of long-term acid-etched fractures in Shunbei carbonate reservoir is established and verified. Use this method, the changing pattern of the flow conductivity of the acid-etched fractures at different lengths of time and flow rates is simulated. The simulation results show that at low closure stresses, the reaction rate of the acid is the dominant factor affecting the flow conductivity of the acid-etched fractures. At high closure stresses, however, the dominant factors affecting the flow conductivity of the acid-etched fractures include closure stress, rock characteristics and the nonuniformity of the rock surfaces. The closure stress, on the other hand, is the dominant factor controlling the deformation of the surfaces of the rocks and is also the decisive factor affecting the flow conductivity of the long-term acid-etched fractures. Under long-term action of closure stress, the flow conductivity of a fracture at the deep part of the fracture is decreased in an amplitude larger than the decrease in the flow conductivity of the fracture at its mouth. The distribution of the flow conductivity of artificial fractures produced under mid-term and long-term acid-etching is controlled by the rate of reaction between the acid and the rock.