Hydrate reservoir physical properties response and high-pressure gas-water reverse penetration during deepwater oil and gas cementing

Well cementing is an important stage during the process of energy extraction. When deep-water oil and gas cementing encounters hydrate formations, the hydration heat of cementing slurry will cause hydrate decomposition in the reservoir near the borehole wall and reverse penetration of high-pressure gas-water. To reduce and avoid the adverse effects of hydrate decomposition, it is critical to clarify the physical response of hydrate reservoirs and the law of high-pressure gas-water reverse penetration under different cementing conditions. In this paper, a two-dimensional cementing numerical model is established according to the SH2 exploration well of GMGS-1 project in Shenhu area in the north of the South China Sea, and numerical simulation software TOUGH+HYDRATE is used to reproduce cementing slurry penetration and hydration process. Then, the response law of reservoir properties near the borehole wall during the process is analyzed, and the critical conditions for high-pressure gas-water reverse penetration under the conditions of different cementing pressure difference and heat release rate are obtained. The idea of "continuous stage simulation" is innovatively adopted to solve the dynamic heat release issue of cementing slurry. The results show that the process before initial setting of cementing slurry can be divided into three stages: induction, decomposition and secondary hydrate formation. The penetration behavior mainly occurs during the pressure holding period, and the penetration depth basically no longer increases after the holding pressure is removed. The temperature rise caused by the exothermic heat of hydration leads to the massive decomposition of hydrates, and the resulting high-pressure gas-water migrate around. After the holding pressure is released, the high-pressure gas-water present a more obvious tendency to penetrate toward the annulus. The higher the hydration heat release rate is, the smaller the cementing pressure difference is, and the greater the possibility of gas-water reverse penetration, and the earlier it will occur. For shallow hydrate reservoirs, reducing the heat of hydration of cementing slurry can effectively reduce the occurrence of reverse invasion and improve cementing quality. For deeper reservoirs, higher cementing pressure difference can be used within the fracture pressure range. This study offers a good reference for parameters optimization during the cementing process in hydrate formations.