Improving Recovery of Liquids from Shales through Gas Recycling and Dry Gas Injection

摘要

The objective of this paper is to investigate the possibility of using gas injection to improve liquids recoveries from containers in shale condensate and shale oil reservoirs. Liquids recoveries from shales are known to be very low. A method is proposed to increase these recoveries through gas recycling and by using dry gas that is available within relatively short distances of the shale condensate and oil containers considered in this study. This dry gas is not being produced at this time due to current market conditions. In practice, some shale reservoirs such as the Eagle Ford in the United States and the Duvernay in Canada present the challenge of unconventional fluids distribution: shallower in the structure there is black oil, deeper is condensate and even deeper is dry gas. So the fluids distribution is exactly the opposite of what occurs in conventional reservoirs. Differences in burial depth, temperature, and vitrinite reflectance are used to explain this unique distribution. Ramirez and Aguilera (2014) have shown that fluids in shale reservoirs have remained with approximately the same original distribution (i.e. approximately the same dry gas-condensate contact and approximately the same condensate-oil contact) over geologic time. These fluids are the target of the research results presented in this paper. The investigation involves three basic cases, all of them with horizontal wells. In the first case, a single porosity compositional simulation is used to investigate the possibility of improved liquid recovery from the condensate container by using dry gas injection obtained from the recycling process plus dry gas from the deeper part of the structure. Fluid properties are similar to those of the Duvernay shale. In the second case, dual permeability compositional simulations are used to investigate practical aspects of the condensate container that can lead to improved recoveries in the Eagle Ford shale. Sensitivities are run that include bottomhole pressure (BHP), natural fracture permeability and spacing, hydraulic fracture length and spacing, and distance between parallel wells. Results from dual permeability simulations are compared with dual porosity behavior. Fluid properties are similar to those of the Eagle Ford shale.