含热力学抑制剂钻井液侵入天然气水合物地层扰动模拟

深水油气勘探开发过程中,为防止井筒内生成天然气水合物,在钻井液中添加水合物热力学抑制剂是有效措施之一。然而含水合物热力学抑制剂钻井液侵入水合物地层的扰动影响鲜有报道。为探究水合物热力学抑制剂对水合物层的扰动规律,利用超声波测试手段,研究了NaCl、乙二醇两类水合物热力学抑制剂钻井液侵入水合物岩样的过程,并讨论了适用于水合物地层钻井液的设计要点。结果表明:含水合物热力学抑制剂的钻井液相比未含抑制剂的钻井液会显著促进水合物分解,且随着抑制剂浓度的增加,水合物分解速度会大幅度增加;NaCl盐类抑制剂促进水合物分解的作用明显强于乙二醇醇类抑制剂;钻井液侵入水合物地层引发的水合物分解呈现非匀速现象。深水钻探水合物地层时,防止地层中水合物的分解与抑制井筒中水合物的生成是相互矛盾的,研发适合水合物地层的钻井液配方来平衡这个矛盾是有效途径。

Perturbation Simulation of Invasion of Drilling Fluid Containing Thermodynamic Hydrate Inhibitors into Natural Gas Hydrate Formation

During the exploration and development of deepwater oil and gas, it is one of the effective ways to prevent gas hydrate formation in the wellbore by adding thermodynamic hydrate inhibitors in drilling fluid. However,the perturbation effect of drilling fluid containing thermodynamic hydrate inhibitors on natural gas hydrate formation rarely reported. In order to investigate the disturbed regularity of hydrate formation by the thermodynamic hydrate inhibitors, this paper studies the process of invasion of drilling fluid containing two different types of thermodynamic hydrate inhibitor, the salt-type inhibitors and alcohol-type inhibitors, into hydrate samples by ultrasonic testing, and the design essentials of drilling fluid for hydrate formation are discussed. Results show: compared with the drilling fluid without inhibitors, the drilling fluid containing inhibitors can significantly promote hydrate dissociation, and the dissociation rate of hydrate will increase greatly with the increase of inhibitor concentration. NaCl, a kind of salt-type inhibitor, promotes the dissociation of hydrate significantly stronger than ethylene glycol, which is the alcohol-type inhibitor. With the increase of thermodynamic hydrate inhibitor concentration, the perturbation effect of the salt-type inhibitor to hydrate formation increased more than that of the alcohol-type inhibitor. The dissociation rate of hydrate caused by drilling fluid invasion presents a nonuniform phenomenon. The perturbation influence of thermodynamic hydrate inhibitors on natural gas hydrates formation should be fully considered in deepwater oil and gas drilling operations. In the deepwater drilling, prevent dissociation of hydrate formation and inhibit hydrate formation in wellbore is contradictory. So, it is an effective way to develop a drilling fluid formula suitable for hydrate formation to eliminate this contradictory.