Study on evaluation method for the inhibition of hydrate decomposition in drilling fluid
In response to the problem of formation hydrate decomposition caused by drilling fluid intrusion during drilling in marine hydrate formations,which leads to wellbore instability,a hydrate decomposition system for drilling fluid is established.The inhibitory evaluation test device is established,and the evaluation test steps are determined.The temperature and pressure changes during hydrate generation and decomposition are analyzed,and the Peng-Robinson equation is introduced to calculate the amount of methane gas substances during hydrate generation and decomposition.A well parallel hydrate decomposition test method is established.The experimental results show that during the process of hydrate formation,the pressure decreases and the temperature increases,and then both tend to stabilize.During the process of hydrate decomposition,due to the injection of drilling fluid,there is a turning point in hydrate regeneration caused by pressure increase,followed by an increase in temperature and pressure,and then both tend to stabilize.By pre-heating,the interference from the inflection point of hydrate regeneration is eliminated,and the accuracy of hydrate decomposition inhibition evaluation experiments is improved.Meanwhile,multiple repeated experiments have shown that during the process of hydrate generation and decomposition,the temperature and pressure changes in the reaction vessel are relatively small,and the methane gas consumption is basically the same,which has good parallelism and repeatability,can meet the requirements of hydrate generation and decomposition experiments.It can be used to evaluate the hydrate decomposition inhibition performance of drilling fluids.
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