体积压裂套管温度应力计算分析

Calculation and analysis of casing thermal stress during stimulated reservoir volume fracturing

 董文涛 2 申瑞臣² 梁奇敏¹ 张弘¹ 代宇¹

中国石油勘探开发研究院，北京 100083 中国石油集团钻井工程技术研究院，北京 102206）

 体积压裂过程中大量压裂液经套管持续注入使井筒温度产生较大变化，温度变化引起的套管热应力对体积压裂过程中井筒完整性有较大影响。以我国南方某页岩气井体冬季、夏季体积压裂中井筒降温情况为例，文中对体积压裂过程中井筒降温情况进行了计算，计算结果表明，体积压裂过程中井筒降温幅度较大，最大温度降低值近76 ℃。针对体积压裂中套管温度应力问题，文中基于热传导理论及热弹性力学理论，建立了体积压裂中套管温度应力计算模型。同时，推导了体积压裂中温度影响下套管抗外挤强度计算公式。依据推导的公式，对体积压裂过程中套管抗外挤强度进行了校核分析，计算结果显示，温度应力对套管抗外挤强度有较大影响，冬季施工过程中温度应力使套管抗拉强度降低23%，内压与温度应力联合作用下，套管抗外挤强度降19%。

 The large amount of injected fracturing fluid through casing during stimulated reservoir volume fracturing process causes great wellbore temperature change, and great temperature change has great influence on the casing thermal stress. Taking the southern shale gas well as example, this paper calculates the temperature decline during stimulated reservoir volume fracturing in both winter and summer. The results show that stimulated reservoir volume fracturing causes dramatic wellbore temperature decrease, and the maximum temperature decrease is nearly 76℃. For the problem of casing thermal stress in stimulated reservoir volume fracturing, based on the theory of heat conduction and thermal elastic mechanics theory, the casing thermal stress calculation model for stimulated reservoir volume fracturing is established in this paper. Furthermore, this paper also deduces the casing collapse resistance formula of shale gas stimulated reservoir volume fracturing under the influence of temperature, and analyzes the relationship between thermal stress and the casing collapse resistance. The results show that the thermal stress caused by the process of stimulated reservoir volume fracturing can induce casing axial load to decrease nearly 23% in winter and casing collapse resistance to reduce about 19% when the heat stress is combined with the inner pressure.

10.6056/dkyqt201605029