Dynamic analysis on edge of sand detachment of natural gas hydrate reservoir

Dynamic change of edge of sand detachment (ESD) is still unclear during the depressurization mining of gas hydrate reservoirs. Considering multi-physics such as the depose of NGH and its impact on the change of formation temperature and conductivity, a novel numerical method is provided which could be utilized to simulate and analyze the behavior of the edge of sand detachment (ESD). The simulation results show that the expansion of ESD has mainly consists of three phases, which has a tendency to be fast first, then slow, and finally tend to the ESD limit (ESDL). In our basic model referring to Shenhu field, the ESD rapidly reached around 44 m from day 0–360 days, then the increase rate slowed from 360 days to 720 days, and finally stabilized at 58 m (ESDL) after 720 days. In addition, the expansive rate of ESD and the ESD limit (ESDL) have great effect on the sand productions. The sand production rate increases rapidly and then reach peak in a rushed stage of ESD expansion, then decrease significantly and tend to be zero when ESD expands to the ESDL in NGH reservoirs. Based on the prioritization analysis of influencing factors, for a NGH reservoir with lower hydrate saturation, higher absolute permeability, higher initial reservoir temperature, lower bottom hole pressure, ESD expands much more fast and the ESDL is much larger. Our work could shed light on the dynamic behavior of ESD for the development of NGH reservoirs, and the finding of ESDL is helpful to determine the safe development area and facilitates adjustment on the sand controlling arrangements.