深水井筒天然气水合物形成预测及风险评价

1. 中国石油大学(北京)机械与储运工程学院;2. 中海石油(中国)有限公司湛江分公司

深水钻井;井筒环空;OLGA;水合物预测;过冷度密度

Prediction and risk assessment of natural gas hydrate formation in deepwater wellbores
SHI Jingyi1, FAN Jianchun1, WU Shengnan1, LI Lei2

1. College of Mechanical and Transportation Engineering, China University of Petroleum (Beijing); 2. CNOOC (China)Limited Zhanjiang Branch

deepwater drilling, wellbore annulus, OLGA, hydrate prediction, subcooling density

备注

深水浅层钻井过程井筒内生成水合物会影响作业安全,需要对井筒环空内水合物形成范围和 程度进行预测分析。以南海陵水气田某开发井为例,基于CSMHyK 水合物动力学模型和OLGA 多 相流流动方程,建立深水钻井水合物形成数值模拟方法,计算多种工况下井筒温度-压力场,引入过 冷度密度表征水合物形成可能性,预测了井筒环空水合物形成范围和程度,分析了钻井液排量、入口 温度、密度及浅层气储压的参数敏感性。结果 表明:在设定的工况条件下,泥线附近的隔水管环空具有水合物形成风险,水深800~1 000 m 的环空内水合物形成量最多;钻井液排量越小,入口温 度越低,水合物形成风险越大,危险管段的水合物生成量超过40 kg/m3。选取过冷度密度、水合物 生成井段长度、生成总量及峰值速率作为评价水合物生成情况的特征值,建立井筒水合物风险水 平量化分析方法。研究结果可为深水浅层钻井过程水合物的防治和钻井方案的优化设计提供理 论指导。(图6表4,参[27]

Hydrate formed in the wellbore during deepwater shallow drilling will affect the operation safety, so it is necessary to predict and analyze the hydrate formation range and degree in the wellbore annulus. One development well in Lingshui Gas Field in South China Sea was taken as the research object, and the numerical simulation method for hydrate formation in deepwater drilling was built based on CSMHyK hydrate dynamics model and OLGA multiphase flow equation. The temperature-pressure field of the wellbore under various working conditions was calculated, the subcooling density was introduced to present the possibility of hydrate formation, the range and degree of hydrate formation in the wellbore annulus were predicted, and the parameter sensitivity of drilling fluid displacement, inlet temperature, density and shallow gas storage pressure was analyzed. The results show that under the assumed working conditions, the riser annulus near the mudline has the risk of hydrate formation, with the largest amount of hydrate formation in the annulus with a water depth of 800-1 000 m. The smaller the displacement of drilling fluid is, the lower the inlet temperature is, the greater the risk of hydrate formation will be, and the amount of hydrate formed in hazardous pipe section may exceed 40 kg/m3. The subcooling density, length of interval where hydrate is formed, total amount of hydrate formed and peak rate were selected as the characteristic values for assessing hydrate formation, and the quantitative analysis method for wellbore hydrate risk level was built. The research results are expected to provide theoretical guidance for hydrate control and optimization design of drilling schemes during deep water shallow drilling. (6 Figures, 4 Tables, 27 References)