Numerical simulation of hydrate reservoir hydraulic fracturing based on cohesive units

Abstract:

Natural gas hydrate is an efficient and clean energy， which is widely distributed in the sedimentary strata in the South China Sea. China has successfully carried out two trial productions in 2017 and 2020 respectively. However， due to the special occurrence conditions of marine natural gas hydrate， there are still some problems with single well trial production， such as small production range and short time for high and stable production. In order to improve the exploitation range of hydrate， the two-dimensional hydraulic fracturing numerical model is studied based on cohesive units. Through simulation， the half length and width of cracks of the two models 100m×100m and 20m×20m are compared. It is concluded that at the injection pressure of 30MPa， the half length of the crack is 6m for both models， and the maximum width is 5.8mm and 5.5mm respectively. The more accurate experimental results can be obtained by constructing a larger model. Moreover， the variation law of fracture width with injection time is studied. With the continuous increase of injection pressure and injection volume， the initial fracture width increases rapidly， and then the fracture propagates “step by step” under the action of in-situ stress and injection fluid pressure. The research has been successfully applied in the hydraulic fracturing model analysis of unconventional energy reservoirs such as shale gas， coalbed methane， and provides some technical guidance for marine natural gas hydrate reservoir hydraulic fracturing .

Key words:marine natural gas hydrate;reservoir stratum;hydraulic fracturing;cohesive unit;numerical simulation;fracture morphology;propagation mechanism