中文摘要：

为钻前对缝洞型油藏是否垮塌进行预测,以塔河缝洞型油藏为背景,提出确定溶洞临界垮塌埋深的二分深度折减法,分析溶洞垮塌对多因素的敏感性,通过多元回归分析建立溶洞临界垮塌深度随顶板厚度、洞跨和侧压力系数变化的预测公式。对大量工况的数值进行计算分析,获得不同形态、不同尺寸溶洞的垮塌破坏过程、垮塌破坏模式、垮塌影响范围以及垮塌深度的变化规律,利用建立的溶洞垮塌深度预测公式对塔河油田实际分布的溶洞进行预测分析。结果表明：矩形和城门洞形溶洞为竖向剪切破坏,而圆形溶洞产生压实破坏;溶洞垮塌影响范围随顶板厚度和洞跨的增加而增大,最终趋于稳定,最大垮塌影响范围约为2.6倍洞跨;洞跨是影响溶洞垮塌的最敏感因素,其次为顶板厚度,侧压力系数对溶洞垮塌的影响最不敏感;溶洞的顶板厚度越大,溶洞越不容易出现垮塌;圆形溶洞最稳定,城门洞形溶洞次之,矩形溶洞稳定性最差。预测结果与油田生产实际相吻合。

英文摘要：

The karstic caves in fractured-vuggy oil reservoirs may collapse during drilling. A model was proposed to predict the critical burial depth of the caves,which may cause cave collapse during well-drilling operations. The model was based on a method of depth dichotomy reduction and the data from the fractured-vuggy reservoirs in Tahe Oilfield Northwest China were used. Various factors that may affect the collapse of the cave were analyzed. A correlation for predicting the critical collapse depth was given through a multivariate regression analysis method,considering the influence of the coping thickness and span of the caves,and the lateral pressure coefficient. A case study for different caves in Tahe Oilfield was conducted. The analysis results show that the collapse of rectangle and horseshoe-shaped caves can be attributed to vertical shear failure,while the collapse of circular caves can be due to compaction failure. The influence area of the collapse increases with cave＇s coping thickness and span,the largest influence area can be extended to 2. 6 times of the cave span,which is the most sensitive factor to cave collapse. The lateral pressure coefficient is a less sensitive factor in comparison with the cave＇s coping thickness and span.The circular caves are more stable than the horseshoe-shaped caves,and the rectangle caves are most vulnerable for collapse.The predicted results agree well with oilfield data.