页岩气水平井大型体积压裂套损预测和控制方法

Prediction and control of casing damage in large volume fracturing of horizontal gas wells

大规模体积压裂导致的页岩气水平井套管损坏(简称套损)或套管变形(简称套变)在现场施工过程中一直都存在,极大地影响了现场施工效率和开发项目的经济效益。为了解决上述问题,通过分析四川盆地威远页岩气区块100余口水平井的压裂资料,探讨了该区页岩气水平井套损或套变的原因和规律,并据分析结果提出了预测和控制的方法。研究结果表明:①发生套变的主要地质因素为储层地质特点、地应力和压裂规模;②对于岩石物性非均质性特别强、甜点区厚度小、压裂时储层难以吸收大规模体积压裂的"能量"的上奥陶统五峰组水平井段、A靶点附近井段、钻遇井漏的天然裂缝带井段等容易套损井段可依据录井和测井解释来预测套变;③产量受水平段轨迹所控制的页岩气水平井应提高水平井段钻进时的导向水平,让水平井段的轨迹都落在地质气藏工程精确刻画的甜点区;④对于水平井段非均质性强的储层,宜采用"分段完井、分段固井"、优化井网井距、适当降低压裂规模等工程技术措施。

The casing damage/deformation in shale gas horizontal wells caused by massive volume fracturing has always been a problem in the process of field construction, and it has a great impact on the field construction efficiency and the economic benefit of development project. To solve this problem, this paper analyzed the fracturing data of more than 100 horizontal wells in the Weiyuan Shale Gas Block of the Sichuan Basin. Then, the causes and laws of casing damage/deformation of shale gas horizontal wells in this block were discussed.And based on the analysis results, a prediction and control method was proposed. And the following research results were obtained. First,the main geological engineering factors for the occurrence of casing deformation are reservoir geological characteristics, ground stress and fracturing scale. Second, mud logging and well logging interpretation can be taken as the basis for casing deformation prediction in the hole sections where casing damage tends to happen easily, e.g. the horizontal section in the Upper Ordovician Wufeng Fm where the petrophysical properties are particularly heterogeneous, the sweet spot areas are thin and the reservoirs can hardly absorb the "energy" from massive volume fracturing, the hole section near the target A, and the hole section with lost circulation in natural fracture interval.Third, as for the shale gas horizontal wells whose production is controlled by the trajectory of horizontal section, it is necessary to increase the steering level during the drilling of horizontal section so as to keep its trajectory in the sweet spot areas which are precisely characterized in geological gas reservoir engineering. Fourth, for the horizontal sections in the reservoirs of strong heterogeneity, it is suggested to adopt engineering technical measures of "segment completion, section cementing", optimization of well spacing, and appropriate reduction of fracturing scale.