(1. Key Laboratory of Unconventional Oil & Gas Development//China University of Petroleum - East China, Qingdao, Shandong 266580, China; 2. School of Petroleum Engineering, China University of Petroleum - East China, Qingdao, Shandong 266580, China; 3. Sinopec Research Institute of Petroleum Engineering, Beijing 100101, China; 4. ENN Energy Holdings Limited, Shanghai 200120, China)
In the process of drilling offshore gas hydrate ("hydrate" for short) formations, the invasion of drilling fluid into formations may lead to hydrate decomposition, which will result in borehole instability. In order to solve these difficulties, this paper experimentally studied the decomposition law of methane hydrate under different decomposition modes. Then, the Peng–Robinson equation was introduced to calculate the change of methane gas mole number, and the experimental method for evaluating the inhibition of hydrate decomposition by drilling fluid was optimized. Finally, the effects of the kinetic inhibitor DY-1 and modified lecithin on the decomposition characteristics of hydrate were experimentally analyzed using this method, and the water-based drilling fluid suitable for gas hydrate formations was further optimized. And the following research results were obtained. First, the best way to evaluate the inhibition of drilling fluid on hydrate decomposition is to inject cold solution without relieving the pressure. Second, the DY-1 and modified lecithin can retard hydrate decomposition by adsorbing in hydrate surface to inhibit heat and mass transfer, so they can be used as hydrate decomposition inhibitors of drilling fluid. Third, the optimized drilling fluid system has good low-temperature rheological properties and shale inhibition and lubricity and can inhibit the formation and the decomposition of hydrates, so it can meet the basic requirements of drilling fluid technology for offshore gas hydrate formations. It is concluded that the research results can provide a drilling fluid technical support for the development of hydrates in China.
邱正松,张玉彬,赵欣,何青水,陈曾伟,赵超. 海洋天然气水合物地层钻井液优化实验研究[J]. 天然气工业, 2019, 39(12): 104-109.
Qiu Zhengsong, Zhang Yubin, Zhao Xin, He Qingshui, Chen Zengwei & Zhao Chao. An experimental study on the optimization of drilling fluid in offshore gas hydrate formations. NATURAL GAS INDUSTRY, 2019, 39(12): 104-109.