A simplified method for predicting the penetration distance of cementing slurry in gas hydrate reservoirs around wellbore

摘要

The permafrost region in the Qinghai-Tibet Plateau of China is abundant in natural gas hydrate (NGH) resources. In this region, there is a great probability of meeting gas hydrate when conducing conventional oil and gas well cementation operations. Because of the relatively developed fractures and not very high pore pressure (usually 3.5-3.6 MPa) in the gas hydrate reservoirs in this area, it is easy for the cementing slurry to penetrate into the gas hydrate reservoirs under the pressure difference during cementing process, undergo hydration and release heat, thus causing hydrate dissociation and cementing quality reduction or even failure. Therefore, it is necessary to first determine the penetration distance of the cementing slurry in the gas hydrate reservoirs to evaluate the effect of hydration of the cementing slurry on the hydrate stability in the reservoirs. In this paper, theoretical and experimental methods for determining the penetration distance value of cementing slurry were established for the first time. The permafrost layer in the Muli area of the Qinghai-Tibet Plateau was selected as the research object and the proposed computational model was verified by using low-density cementing slurry and common cementing process experiments. The results show that the penetration distance calculated by the established computational model is in good agreement with that measured in the experiment, and the computational model can provide technical support for the cementing process design in gas hydrate occurrence area.