热交变循环次数对水泥石弹性参数的影响

Effects of thermal alternating cycle number on the elastic parameters of set cement

严攀 李军 柳贡慧

YAN Pan LI Jun LIU Gonghui

中国石油大学（北京）石油天然气工程学院 北京工业大学

College of Petroleum Engineering, China University of Petroleum (Beijing), Beijing 102249, China Beijing University of Technology, Beijing 100124, China

页岩气藏普遍采用水平井多级分段压裂方式开发，压裂过程中水泥环受到循环热应力的作用，其力学性质受到影响，导致井筒完整性变差，套管变形或损坏。针对这一特点，进行水泥石热交变循环实验，研究压裂级数对套管应力的影响规律。首先利用示波器测试水泥石在经历热交变循环后的纵横波速，计算水泥石的弹性参数，然后模拟计算套管应力，在此基础上分析在不同的冷却条件下，不同热交变循环次数后，水泥石弹性参数和套管应力的变化规律。研究结果表明：在小排量压裂条件下，水泥石的弹性模量随热交变循环次数的增加先逐渐减小后趋于稳定；在大排量压裂条件下，随热交变循环次数的增加，水泥石的弹性模量持续减小；在两种不同压裂方式下，水泥石的泊松比均随热交变循环次数的增加而增加；套管应力随着热交变循环次数的增加逐渐增大，且在大排量压裂条件下，增幅更明显。研究结果可为页岩气水平井多级分段压裂过程中套管应力分析提供依据。

Shale gas reservoirs are commonly developed by means of multi-stage fracturing of horizontal well. In the process of fracturing, the mechanical performance of cement sheath is impacted by the cyclic thermal stress. As a result, the borehole integrity is deteriorated and the casing is deformed or damaged. To solve this problem, the thermal alternating cycle experiment was conducted on set cement to investigate the influential laws of fracturing stage number on casing stress. Firstly, the compressional and shear velocities of set cement after thermal alternating cycle were measured by using an oscilloscope, and the elastic parameters of set cement were calculated. Then, the casing stress was simulated and calculated. Finally, the change laws of set cement elastic parameters and casing stress after different thermal alternating cycle numbers under different cooling conditions were analyzed. It is indicated that the elastic modulus of set cement increases firstly and then decreases gradually to a constant value with the increase of thermal alternating cycle number when low-displacement fracturing is carried out while it decreases continuously when high-displacement fracturing is carried out. The Poisson's ratio of set cement and the casing stress in both fracturing modes increase with the increase of thermal alternating cycle number, and the increase amplitude of casing stress is greater in the mode of high-displacement fracturing. The research results can provide the basis for analyzing the casing stress in the process of multi-stage fracturing of shale gas horizontal wells.

10.13639/j.odpt.2018.03.008