致密油藏裂缝动态渗吸排驱规律

为明确裂缝性致密油藏注水动态渗吸特征，解决水驱采收率低下等问题，以姬塬油田延长组长6油层组为研究对象，采用高压压汞、核磁共振T₂谱、扫描电镜和铸体薄片分析等方法研究了目标储层微观孔隙结构特征，建立了3类储层分类评价标准，并对代表性岩心开展了基于核磁共振在线扫描的动态渗吸实验，模拟了水驱过程中裂缝-基质间的动态渗吸过程，从微观孔隙尺度定量表征了不同孔径孔隙原油的动用程度，评价了8个储层物性参数对动态渗吸效率的影响程度。实验结果表明，目标储层孔隙结构可划分为3类，随着储层孔隙结构变差，孔隙类型逐渐单一化、储集性能和渗流能力不断降低，导致动态渗吸效率不断下降。Ⅰ类和Ⅱ类储层动态渗吸过程可以划分为3个阶段：大孔隙在驱替作用下采出程度快速上升阶段、微小孔隙在渗吸作用下采出程度缓慢上升阶段和动态渗吸平衡阶段；而Ⅲ类储层在实验中仅存在前2个阶段。随着储层孔隙结构变差，微小孔隙动用比例增大，渗吸作用明显，虽然对岩心总采收率贡献程度增加，但总采收率低下。渗透率、可动原油饱和度、孔隙半径、可动原油孔隙度、黏土矿物含量和润湿性是影响动态渗吸效率的主要因素，对渗吸效率的影响程度依次逐渐减弱。分选系数和孔隙度是影响动态渗吸效率的次要因素，对渗吸效率的影响程度相对较小。

Dynamic imbibition and drainage laws of factures in tight reservoirs

To clarify the dynamic imbibition characteristics of water flooding in fractured tight reservoirs and solve the problems of low water flooding recovery, this paper studies the characteristics of microscopic pore structure of Chang 6 oil layer of Yanchang Formation in the Jiyuan oilfield by means of high-pressure mercury injection, nuclear magnetic resonance T₂ spectrum, scanning electron microscope and cast thin section analysis, establishes the classification and evaluation criteria for three types of reservoirs, and carries out dynamic imbibition experiments on representative cores based on NMR online scanning. This paper also simulates the dynamic imbibition process between the fracture and the matrix during water flooding, quantitatively characterizes the producing degree of crude oil in pores with different pore sizes at the microscopic scale, and evaluates the degree of influence of eight reservoir physical parameters on the dynamic imbibition efficiency. The experimental results show that the pore structure of the target reservoirs can be divided into three types. With the pore structure deterioration of reservoirs, the pore types gradually become simplified, and the reservoiring performance and percolation capacity continue to decrease, resulting in the continuous decline of dynamic imbibition efficiency. The dynamic imbibition process of type I and II reservoirs can be divided into three stages:(1)under the action of displacement, the recovery percent of macropores rises rapidly; (2)under the action of imbibition, the recovery percent of tiny pores rises slowly; (3)the stage of dynamic imbibition equilibrium. However, the type III reservoirs only experienced the first two stages in the experiment. With the pore structure deterioration of reservoirs, the producing proportion of tiny pores increases, and the imbibition effect is obvious. Although the contribution to the total core recovery increases, the total recovery rate is low. Permeability, movable crude oil saturation, pore radius, movable crude oil porosity, clay mineral content and wettability are the main factors affecting the dynamic imbibition efficiency, and their degree of influence on the imbibition efficiency successively gradually decreases. Sorting coefficient and porosity are the secondary factors that affect the dynamic imbibition efficiency, and their degree of impact on the imbibition efficiency is relatively small.