Water Blocking of Deep Marine Shale Gas Reservoirs at In Situ Pressure and Temperature Conditions

Water blocking is a key factor that restricts the exploitation of deep marine shale gas. Conventional investigation of such formation damage extent mainly focuses on the core permeability decline without considering the in situ high-temperature and -pressure conditions of a deep shale gas reservoir. Meanwhile, it cannot reveal the damage degree of a specific pore structure, which restricts the development of low-damage fracturing fluid. In this work, core flow experiments and microstructural modeling are conducted at in situ temperature and pressure conditions to reveal the mechanisms of water blocking in a deep shale gas reservoir from the perspective of pore scale, and the extent of water-blocking damage was determined. The results indicate that the pores with D < 100 nm dominate the storage space and serve as the main sites of fracturing fluid retention, leading to a low flowback efficiency and significant permeability damage. A fracturing fluid flowback model was established based on the true pore structure and has been proven to be applicable for gas–water flow simulations for the deep shale under in situ conditions. On the basis of simulation results, the water-blocking mechanisms of deep marine shales were elucidated, and the role of contact angle in governing fluid transport capacity across different pore structures was examined. A pore-scale method for evaluating water-blocking damage was developed, and the water blocking severity of the previously constructed pore structure models was systematically assessed. This work is helpful for production system optimization and low-damage fracturing fluid design for deep marine shale gas reservoirs.