海洋天然气水合物地层钻井液优化实验研究

海洋天然气水合物（以下简称水合物）地层钻井过程中,钻井液侵入地层有可能造成水合物分解,进而引发井壁失稳等问题。为了破解上述难题,实验研究了甲烷水合物在不同分解方式下的分解规律,引入Peng-Robinson方程计算实验过程中甲烷气体摩尔数的变化,优化了钻井液抑制水合物分解评价实验方法,并利用该方法实验分析了动力学抑制剂DY-1和改性卵磷脂对水合物分解特性的影响规律,进一步优化出适用于水合物地层使用的水基钻井液。研究结果表明：①注冷溶液不卸压的方式是钻井液抑制水合物分解最佳的评价实验方法;②水合物动力学抑制剂DY-1和改性卵磷脂均可通过吸附在水合物表面阻缓传热传质来延缓水合物分解,可作为钻井液水合物分解抑制剂;③优化出的钻井液体系具有良好的低温流变性和抑制水合物生成及分解性能,同时具有良好的页岩抑制性和润滑性等,可以满足海洋水合物地层钻井液技术的基本要求。结论认为,该研究成果可以为我国水合物开发提供钻井液技术支撑。

An experimental study on the optimization of drilling fluid in offshore gas hydrate formations

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.