Gas chimney interference and fracturing stimulation for developing stratified marine hydrate reservoirs

In this work, a stratified hydrate reservoir model incorporating a gas chimney was established based on data from station W03 in the Qiongdongnan Basin. The potential for co-producing methane hydrate (MH) layers I and II, along with the free gas layer, was evaluated to determine the optimal production interval. A 5-year depressurization process of the reservoir was conducted to assess the potential interferences of gas chimney on production performance, with a focus on the vertical permeability and extension. Furthermore, a hydraulic fracturing combined with an artificial barrier was applied to enhance gas recovery from the reservoir. Results showed that higher production efficiency could be achieved through the co-production of the MH layer I and free gas layer, particularly when the production interval was positioned at a distance from the upper adjacent layers. Throughout production, the free gas layer was the primary contributor to wellbore gas production. The presence of a gas chimney negatively impacted gas recovery, especially in cases where it had higher vertical permeability and greater extension. The implementation of long-length hydraulic fractures within MH layer I resulted in a magnitude increase in wellbore gas production, with gas output rising up to about 26 times compared to the scenario without hydraulic fracturing. The effects of fracture thickness and density on hydrate dissociation and gas output were less pronounced compared to the impact of fracture length. When combined with hydraulic fracturing, the use of artificial barriers helped stabilize the gas production rate and improve the gas-water ratio at the wellhead. However, the overall effectiveness of this approach was limited and did not yield significant gains in production efficiency. During actual reservoir stimulation, greater attention should be given to controlling water flow within the reservoir, while also considering the impact of natural gas chimneys.