深水油基钻井液中抑制水合物形成的实验研究

在温度为4℃、压力为20MPa条件下,利用水合物综合模拟实验系统,对用于南海深水钻井的油基钻井液体系进行了抑制水合物生成的评价实验。结果表明,由于天然气在油相中的溶解度远高于在水中的溶解度,油基钻井液又是分散的乳化液,使得油基钻井液中水合物形成的诱导时间比水基钻井液中少。因此含水的油基钻井液体系在深水环境下(高压和低温)很容易生成天然气水合物,含水量越高,生成的量越大。所以在钻井作业过程中,要适当降低泥浆中水的含量,增加泥浆密度,防止地层水和气大量进入井内随油基钻井液一起循环。高浓度乙二醇能较好地抑制油基钻井液中水合物的形成。为了达到最佳抑制效果,可在钻井液中配合加入适量聚合醇与无机盐。

Experimental study on inhibition of hydrate in oil-based drilling fluid for deepwater drilling

Oil-based drilling fluids (OBDF) were used in deepwater drilling of South China Sea. The formation characteristics of gas hydrate in oil-based drilling fluid were investigated under the conditions of 4℃ and 20 MPa by using the experimental system of gas hydrate integrative simulation. The experiments showed that the induction time of hydrate formation in OBDF is less than that in water-based drilling fluid because natural gas solubility in oil is greatly higher than that in water, and OBDF is dispersive emulsion. It means that the formation of gas hydrate in the oil-based drilling fluid was easier and quicker than that in the water-based drilling fluid under the condition of deep water (high pressure and low temperature). The higher content of water in oil-based drilling fluid could generate large amount of hydrate. In the deepwater drilling process, the content of water in the oil-based drilling fluid should be reduced, and the density of drilling fluid should increase and prevent the formation water and gas from entering into well bore. High-dosage ethylene glycol can effectively inhibit gas hydrate from forming in the oil-based drilling fluid. Addition of proper polyol or inorganic salts such as polyethylene glycol and NaCl can effectively inhibit hydrate from forming in the oil-based drilling fluid.