深水水合物试采过程中地层沉降及井口稳定性研究

Research on Stratum Settlement and Wellhead Stability in Deep Water during Hydrate Production Testing

李莅临 杨进 路保平 柯珂 王磊 陈柯锦

LI Lilin YANG Jin LU Baoping KE Ke WANG Lei CHEN Kejin

中国石油大学（北京）安全与海洋工程学院，北京 102249 中国石化石油工程技术研究院，北京 100101

College of Safety and Ocean Engineering, China University of Petroleum(Beijing), Beijing, 102249, China Sinopec Research Institute of Petroleum Engineering, Beijing, 100101, China

在深水非成岩地层天然气水合物试采过程中，随着试采时间增长，大面积弱固结地层中的水合物分解后，可能造成海底地层沉降，损坏井口和海底管汇，导致试采工程失败。为此，建立了非成岩地层水合物试采过程中的海底地层沉降和井口稳定性分析模型，分析认为水合物分解后产生的负摩阻力和下拉载荷是导致井口失稳的主要因素，并采用有限元强度折减法模拟研究了水合物分解对地层沉降和井口稳定性的影响，结果发现，水合物分解后管柱周围的负摩阻力主要分布于表层导管底部向上约1/3的区域，且水合物分解半径越大、水合物饱和度越高，负摩阻力越大。自主研发了天然气水合物开采井口模拟试验装置，进行了水合物分解对井口稳定性影响的室内模拟试验，负摩阻力的模拟试验结果与数值模拟结果相比，相对误差在10%以内，验证了计算模型和数值模拟结果的可靠性。研究成果可为深水非成岩地层水合物试采时间控制和井口安全评估提供理论参考。

During hydrate production testing in deep-water non-diagenetically altered formations, subsea stratum settlement may occur after the decomposition of gas hydrate in a large area of weakly consolidated formation accompanied by an increase of production test time, resulting in wellhead and subsea manifold damage as well as the failure of the production testing project. To solve this problem, an analytical model of subsea stratum settlement and wellhead stability in non-diagenetically altered formations during hydrate production testing was established. Negative friction and drop-down load produced by hydrate decomposition were considered to be the main factors leading to wellhead instability, and the finite element strength reduction method was used to simulate the influence of hydrate decomposition on stratum settlement and wellhead stability. The results showed that the negative friction resistance around the pipe string after hydrate decomposition was mainly distributed in the area about 1/3 the length of conductor above the bottom, and the larger the hydrate decomposition radius, the higher the hydrate saturation, and the greater the negative friction resistance. The laboratory simulation test was carried out to explore the influence of hydrate decomposition on wellhead stability by means of the self-developed wellhead simulation device for gas hydrate production. The results showed that the relative error between the test result and simulation result of negative friction resistance was less than 10%, which verified the reliability of the calculation model and numerical simulation results. The research results can provide a theoretical reference for the time control and wellhead safety assessment of hydrate production test in deep water non-diagenetic formations.

国家重点研发计划项目“极地冷海钻井关键技术研究”（编号：2016YFC0303300）、国家重大科技专项“海上复杂地层安全快速钻完井关键技术”（编号：2016ZX05033-004-002）和北京市科技计划项目“30MPa、1500L天然气水合物开采模拟动态监测及配套研究”（编号：Z181100005118010）联合资助

https://doi.org/10.11911/syztjs.2020095