藻灰岩压裂裂缝扩展规律物理模拟

Physical simulation of fracture propagation patterns in algal limestone fracturing

郑宏林 马新仿 林海 郭得龙 刘永

ZHENG Honglin MA Xinfang LIN Hai GUO Delong LIU Yong

中国石油大学(北京)石油工程学院 中国石油青海油田钻采工艺研究院

School of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China Research Institute of Drilling and Production Technology, PetroChina Qinghai Oilfield Company, Dunhuang 736200, Gansu, China

柴达木盆地风西区块下油砂山组藻灰岩储层弱面发育，岩性复杂，物性变化大，非均质性强，其压裂裂缝扩展机理不明晰。采用岩屑电镜扫描实验分析了藻灰岩矿物组分特征，通过三轴压缩实验开展了基于能量演化的岩石脆性评价。为探究不同地质、工程条件下藻灰岩裂缝扩展规律，采用小尺寸真三轴水力压裂系统对含有结构弱面的藻灰岩开展了地层温压条件下的压裂物理模拟测试，分析了压力曲线与裂缝形态。研究结果表明：藻灰岩碳酸盐岩类矿物含量高，脆性特征明显，采用能量演化法计算脆性指数为0.56；低水平应力差、高注入排量、低压裂液黏度实验条件下，人工裂缝受应力控制作用减弱，结构弱面易被激活，局部裂缝迂曲程度提高，易形成复杂裂缝。该研究对藻灰岩储层压裂施工具有指导意义。

In Fengxi block of the Qaidam Basin, the weak surfaces are developed in the algal limestone reservoirs of the Lower Youshashan formation, exhibiting complex lithologies, significant variations in physical properties and strong heterogeneity. The mechanism of fracture propagation during hydraulic fracturing in this area is not well understood. Mineral composition characteristics of the algal limestone were analyzed using rock cuttings electron microscopy scanning experiments, and rock brittleness evaluation based on energy evolution was conducted through triaxial compression experiments. To explore the fracture propagation patterns of algal limestone under different geological and engineering conditions, small-scale true triaxial hydraulic fracturing tests were conducted on algal limestone containing structurally weak surfaces under reservoir temperature and pressure conditions. The pressure curves and fracture morphologies were analyzed. The research results indicate that the algal limestone has a high content of carbonate minerals and shows clear brittle characteristics, with a calculated brittleness index of 0.56 using the energy evolution method. Under experiment conditions of low horizontal stress difference, high injection rate and low fracturing fluid viscosity, the stress-controlled effect on artificial fractures is weakened, the weak structural surfaces are easily activated, and the local curvature of fractures increases, leading to the formation of complex fractures. This study provides a guidance for hydraulic fracturing operations in algal limestone reservoirs.

10.13639/j.odpt.202305033