Enhancing Oil Recovery from Shales: Reservoir-Specific and Economical Approach

Enhancing Oil Recovery from Shales: Reservoir-Specific and Economical Approach

Harpreet Singh

National Energy Technology Laboratory, Morgantown, WV

Ultra-tight hydrocarbon reservoirs like shales present two major challenges to enhance oil recovery from these formations: i) negligible fluid movement outside the fractures limits the possibility of having an injection well to sweep the fluids towards the production wells, ii) the wettability of these reservoirs tend to be oil-wet that keeps the oil in the smallest pores compared to gas or water, making it difficult to drive most of the oil out. Oil rates from these formations can decline by a half in just first year due to their low permeability, which also leads to large amount of oil remaining in smaller pores that is not able to move out. Declining oil rates from oil-rich shales in a low oil-price environment would benefit by enhancing the oil recovery from these formations if implemented in an economically competitive way.

To solve this coupled challenge of enhancing oil recovery while being economically prudent, this study presents field scale simulations comparing the impact of miscible gas injection and surfactant injection on enhancing oil recovery by a novel, but economical, scheme of injection/production from the same well using different hydraulic-fractures. This injection/production scheme has economical advantage over huff-n-puff scheme such that there is no lag-period between injection and production. Oil recovery by miscible gas injection or by surfactant injection follows different physical mechanisms, where the former works by swelling the oil through miscibility and the latter works by reducing the interfacial tension between oil and water. Suitability of each method is based on reservoir-specific parameters such as pore pressure and the in-situ brine salinity, besides the investment/infrastructure required for each method. This study may help motivate further research in this area that will benefit the shale industry by enhancing oil rates through an economically competitive way.