碳酸盐岩缝内暂堵转向压裂裂缝扩展规律实验

溶洞是塔河油田缝洞型碳酸盐岩储层的主要储集空间，且井周许多发育储集体位于非水平最大主应力方向上，采用暂堵转向压裂可以实现非水平最大主应力方向上的储层改造。采用30 cm×30 cm×30 cm的天然碳酸盐岩露头进行缝内暂堵转向压裂模拟实验，通过CT扫描技术对一次压裂和暂堵压裂后的裂缝形态进行观测，探究了地应力差、天然裂缝和压裂液黏度对裂缝形态的影响，并进行暂堵起裂理论分析。研究结果表明:岩样天然裂缝或层理发育以及足够的暂堵压力是实现缝内暂堵转向压裂的必要条件；不同水平应力差下，均能实现缝内暂堵转向，并且地应力差越小，裂缝形态越复杂，改造越范围越大；暂堵剂进入裂缝内是保证转向压裂成功的重要条件，压裂液黏度过低时携砂能力差，形成的一次裂缝开度相对较小，易导致暂堵剂难以进入。研究结果为塔河油田缝洞型碳酸盐岩储层压裂方案设计提供了理论依据。

Experimental study on fracture propagation during in-fracture temporary plugging and diverting fracturing in carbonate rock

Karst caverns are the main storage space in the fractured-vuggy carbonate reservoirs in the Tahe oilfield, and many accumulations around wellbores are not located in the direction of the maximum horizontal principal stress. Therefore, the temporary plugging and diverting fracturing is demanded for stimuilation of reservoirs deviating from the maximum horizontal principal stress. The simulation experiments of in-fracture temporary plugging and diverting fracturing (ITPDF) were performed using 30 cm × 30 cm × 30 cm outcrop specimens of carbonate rock. The fracture morphology after conventional fracturing and ITPDF was observed via CT scanning to analyze the effects of the in-situ stress difference, natural fractures, and fracturing fluid viscosity on the fracture morphology, and the fracture initiation in ITPDF was theoretically investigated. The research shows that well-developed natural fractures or beddings in rock and sufficient temporary plugging pressure are essential for a successful ITPDF. ITPDF is workable under varied in-situ stress differences; the smaller the in-situ stress difference, the more complex the fracture morphology, and the larger the stimulated volume. Entry of temporary plugging agent into fractures is critical for diverting fracturing. A fracturing fluid with too low viscosity is less capable of sand carrying and may induce primary fractures with small aperture, hindering the smooth entry of temporary plugging agent. The research results provide a theoretical basis for the fracturing design of fractured-vuggy carbonate reservoirs in the Tahe oilfield.