Abstract：In the Changning Block of Changning-Weiyuan National Shale Gas Demonstration Area in the Sichuan Basin, the shale-gas cluster horizontal section is 1 200-2 800 m long, and the lateral distribution of high-quality reservoirs is heterogeneous, so the trajectory of horizontal sections is adjusted frequently, and the wellbore stability in target layers is poor with severe lost circulation, hole shrinkage and collapse. As a result, 80-90% of the horizontal wells undergo the difficulty of casing running, and even the casing in some of them cannot run to the expected depth, which causes huge economic loss. Based on actual measurement data of casing running in the shale-gas horizontal wells of the Changning Block, this paper analyzed centralizer, hole curvature, well deviation, well diameter, friction coefficient and other key factors by making comprehensive use of the modified 3D soft string friction calculation model and the data statistical analysis method. Accordingly, one new method for comprehensively evaluating the risks of casing running in a long horizontal section was proposed. And the following research results were obtained. First, compared with the hole curvature, the cumulative hole curvature can reflect the influence degree of the casing running friction more objectively. When the cumulative hole curvature is greater than 170°/m, the casing running friction begins to increase rapidly. Therefore, as for the horizontal wells with greater hole curvature, it is necessary to avoid frequent trajectory adjustment, so as to reduce the difficulty of casing running. Second, the variation coefficient of well diameter can accurately describe the variation range of well diameter in the direction of the horizontal wellbore. As for the horizontal wells with complex geological conditions, hole shrinkage and severe collapse, the prediction accuracy can be improved effectively by evaluating the influence of casing running friction based on the statistical analysis of the variation coefficient of well diameter. When the variation coefficient of well diameter is less than 2%, the influence of casing running friction is less, otherwise, the influence is greater. In conclusion, the application results in 5 wells indicate that the evaluation result is basically accordant with the actual measurement data in the construction site, which proves this method can accurately evaluate the risks of casing running in long horizontal wells under complex reservoir conditions.
李文哲，文乾彬，肖新宇，唐梁，冯伟，李倩，刘素君. 页岩气长水平井套管安全下入风险评估技术[J]. 天然气工业, 2020, 40(9): 97-104.
LI Wenzhe, WEN Qianbin, XIAO Xinyu, TANG Liang, FENG Wei, LI Qian, LIU Sujun. Risk evaluation technology for safe casing running in long horizontal shale gas wells. NATURAL GAS INDUSTRY, 2020, 40(9): 97-104.
