Natural fractures and caves serve as the main reservoirs of fractured-vuggy carbonate reservoirs, and acid fracturing is the main technical means to improve the well productivity. Only if hydraulic fractures connect the natural fractures and caves are there obvious hydraulic fracturing effects. However, the faults, caves, and natural fractures distributed in the bedrock resulted in the distribution of the complex in-situ stress field, which restricts the direction and geometry of hydraulic fracture, thus deciding whether hydraulic fracture could connect with natural fractures and caves. Therefore, an accurate description of the magnitude and direction of the stress field in different regions of faults and caves is of great significance. In this paper, a series of hydraulic fracturing experiments on artificial carbonate samples with presetting faults and caves were performed. And high-precision strain sensors prefabricated in the rock sample were used to monitor the stress field during fracturing. Four kinds of fault-cave geological combinations are investigated, and the results show that the presence of fault-karst can significantly change the distribution of in-situ stress and result in deflecting of the fracture, which may or may not be beneficial to connection of caves and faults, depending on well placement. There is high stress concentration at the end of the fault, and the maximum and minimum principal stresses are obviously higher than the far-field stresses. The lateral stress of a single fault is very low in the direction perpendicular to the fault plane, and there is little change in the direction parallel to the fault. Due to low maximum and minimum stress, the intersection of intersecting faults will exert a kind of “attraction” to hydraulic fractures. The stress distribution around the cave is lower than that in the distance. The results can provide theoretical guidance for optimizing hydraulic fracturing design in fractured-vuggy carbonate reservoirs.

天然缝洞是碳酸盐岩缝洞型油气藏的主要储集层，酸压是提高油井产能的主要技术手段。只有水力裂缝将天然裂缝和洞穴连接起来，水力压裂效果才会明显。但基岩中分布的断层、洞穴和天然裂缝导致地应力场分布复杂，限制了水力裂缝的方向和几何形状，从而决定了水力裂缝能否与天然裂缝和洞穴连通。因此，准确描述断层和洞穴不同区域应力场的大小和方向具有重要意义。在本文中，对具有预设断层和洞穴的人工碳酸盐样品进行了一系列水力压裂试验。并利用预制在岩样中的高精度应变传感器监测压裂过程中的应力场。对4种断陷地质组合进行了考察，结果表明断层岩溶的存在会显着改变地应力分布，导致裂缝偏斜，这可能有利于也可能不利于断层的连通。洞穴和断层，取决于井的位置。断层末端应力集中度高，最大和最小主应力明显高于远场应力。单个断层在垂直断层面的方向上的侧向应力很低，与断层平行的方向变化不大。由于最大和最小应力较低，相交断层的交汇将对水力裂缝产生一种“吸引力”。洞穴周围的应力分布低于远处的应力分布。研究结果可为缝洞型碳酸盐岩储层水力压裂设计优化提供理论指导。