Numerical Simulation of Ground Subsidence Due to Oil and Gas Extraction from Creeping Reservoirs

Ground subsidence presents a multitude of hazards, including an increased probability of flooding, deformation of underground pipelines, leakage and even explosions. The over-exploitation of deep groundwater, oil and gas resources over an extended period can result in an acceleration of the ground subsidence rate. In order to ascertain the extent of ground subsidence resulting from oil and gas extraction and to consider the impact of creep in rock formations, it was necessary to conduct a comprehensive study. In this paper, we analyse the data from creep experiments on underground shale rock and establish a coupled calculation model of creep and seepage for ground subsidence, taking into account the creep characteristics. The model parameters for shale rock layers are inverted according to field observation data. The results of numerical simulations indicate that, as pore pressure and formation creep mechanical behaviour are continuously reduced, ground settlement initially decreases and then rebounds slightly, although the overall trend is subsidence. The application of pressure to the formation results in an immediate increase in pore pressure, which subsequently dissipates over time. This is accompanied by an increase in effective stress and ground creep, which in turn leads to ground subsidence. 1. INTRODUCTION Ground subsidence presents a multitude of hazards. The consequences of this phenomenon include the following: 1. The risk of flooding, which is particularly evident in Cangzhou and other coastal cities(ZHAO et al., 2003); 2. The potential for deformation of underground pipelines, leakage and even explosion, endangering the lives and properties of the local population(LUO et al., 2015); 3. The occurrence of ground cracking, causing distress within the local community(PENG et al., 2007); 4. The distortion of geodetic observation and measurement markers, affecting related work(XING et al., 2004). Once formed, ground subsidence is difficult to recover. Therefore, it is of great importance to study the formation mechanism of ground subsidence, accurately predict the amount of future ground subsidence, and then put forward targeted measures to control ground subsidence. The causes of ground subsidence can be divided into two categories: natural factors and human factors(BAKR et al., 2015). Natural factors include crustal movement, stratigraphic structure, stratigraphic mechanical properties (elastic-plastic, viscous), and so on. The anthropogenic factors that contribute to ground subsidence include groundwater, geothermal energy, oil and gas extraction, tunneling, and large-scale building construction. As the study of subsidence has progressed, the technology used to monitor ground subsidence has also become increasingly sophisticated. Currently, the most common method of monitoring ground subsidence is through the use of GPS and InSAR monitoring(HE et al., 2006). Those methods have been shown to significantly enhance the accuracy of monitoring, reduce the cost of monitoring, and provide a foundation for the development of ground subsidence models.