Chen Dayong, Sun Zheng
State Key Laboratory of Coal Resources and Safe Mining, China University of Mining and Technology, Xuzhou 221116, China.
School of Mining, China University of Mining and Technology, Xuzhou 221116, China.
ACS Omega. 2023 Mar 29;8(14):12911-12921. doi: 10.1021/acsomega.3c00074. eCollection 2023 Apr 11.
The wellbore fluid flow characteristics and hydrate flow assurance problems during the deep-water gas well cleanup process seriously affect the safety of gas well testing. Aiming at the process of deep-water gas well cleanup where the liquid gas ratio changes dramatically, this study reveals the distribution law of gas-liquid flow patterns in the wellbore. Combined with the clean test conditions of deep-water gas wells, the transient numerical simulation and analysis are carried out. At the same time, a hydrate risk prediction model suitable for the well cleanup process is established to predict the hydrate risk under different cleaning conditions. The research results are as follows: (1) after flowback, the temperature at the wellhead and mud line presents different characteristics of temperature change, the wellhead temperature decreases first and then increases, while the flow temperature at the mud line rises first and then decreases; (2) slug flow and annular flow are more likely to occur in the wellbore under low wellhead pressure. Bubble flow often appears in the initial stage of flowback under high wellhead pressure and gradually changes into slug and annular flow patterns in the middle and late stages; (3) at the same flowback time, the wellbore will also present different flow patterns along the way. The lower part of the well bore mainly presents bubble flow and slug flow, and the upper and middle parts of the well bore mainly present annular flow patterns; (4) high liquid-gas ratio conditions, proper well cleaning speed, and the use of hydrate inhibitors can effectively reduce the hydrate risk during the cleaning process of deep-water gas wells.
深水气井排液过程中井筒流体流动特性及水合物流动保障问题严重影响气井测试安全。针对深水气井排液过程中气液比变化剧烈的情况，本研究揭示了井筒内气液流型的分布规律。结合深水气井的清洁测试条件，进行了瞬态数值模拟与分析。同时，建立了适用于排液过程的水合物风险预测模型，以预测不同排液条件下的水合物风险。研究结果如下：（1）返排后，井口和泥线处温度呈现不同的变化特征，井口温度先降低后升高，而泥线处流动温度先升高后降低；（2）井口压力较低时，井筒内更易出现段塞流和环空流。井口压力较高时，返排初期常出现泡状流，中后期逐渐转变为段塞流和环空流型；（3）在相同返排时间下，井筒沿程也会呈现不同的流型。井筒下部主要呈现泡状流和段塞流，井筒中上部主要呈现环空流型；（4）高气液比条件、适当的排液速度以及使用水合物抑制剂可有效降低深水气井排液过程中的水合物风险。
