Unconventional liquid reservoirs are currently one of the most important sources of oil in North America. Oil production experiences a rapid decline in these reservoirs and this has been a major issue faced by many operators. Low oil recovery has been attributed to ultralow permeability, low porosity and oil-wet nature of the reservoir rock. Hence, wettability alteration using chemicals could provide a viable chemical enhanced oil recovery method (cEOR) to increase oil production from these reservoirs.
In this study a set of customized surfactant based chemical formulations have been developed to increase oil recovery from unconventional oil reservoirs in the Permian basin: Wolfcamp A, Wolfcamp B and Spraberry. Comprehensive laboratory experiments have been conducted to study the effect of the chemistry on wettability alteration, along with the result of intensity of micro-fractures on chemical performance has been explored through lab analysis and numerical simulation. Lab results showed that application of a specific chemical formulation leads to persistent wettability alteration and significant oil recovery compared to injection brine, without causing any emulsion issues. It also has been observed that, among other factors, salinity and hardness of the formation brine, oil characteristics, mineralogy of the reservoir, and the intensity of natural fractures play an important role on the chemistry's performance. In addition to the lab findings, a review of the design and execution of a recently completed CEOR huff-n-puff (HnP) trial and results from a two well fracture completion using the chemistry will be provided. The completions trial showed a 39% increase in the 180 cumulative recovery and increased oil cut versus the county type curve. The results for the HnP trial will be communicated in a future publication.
These results combined with previously published material further confirm the efficacy of this chemistry to persistently alter wettability and enhance oil recovery from tight oil reservoirs. The concepts and information here can also be translated to other unconventional basins either liquids or wet/dry gas reservoirs.