BENEFICIAL USE OF PRODUCED WATER IN DEPLETED OIL RESERVOIRS: IN-SITU CRUDE OIL CONVERSION TO METHANE GAS

Produced water contains crude oil degrading and methanogenic microbial communities that are very well adapted to deep subsurface conditions. This property of produced water can be used to enhance the recovery of residual crude oil (mostly n-alkanes) from depleted oil reservoirs by stimulating the microbial conversion of residual crude oil to CH₄ (natural gas). CH₄ is easier to recover than crude oil and its generation in-situ can also serve to restore reservoir pressure. The proposed method to enhance the recovery of residual crude oil as CH₄ consists of the co-injection of CO₂ and produced water supplied with protein-rich matter. CO₂ is co-injected to increase the availability of CO₂ for CH₄ production as well as to decrease the pH of the injected water to moderate acidic pH levels where the activity of H₂-producing fermentative microbes is highest. Protein-rich matter is supplied to the injected produce water to provide indigenous crude oil degrading and methanogenic microbial communities key nutrients such as trace metals and amino acid compounds. In this presentation, we will introduce new batch experimental results showing that the proposed method can be used to enhance the recovery of residual crude oil from depleted oil reservoirs of Oklahoma; and based on this new results, we will discuss the potentiality of the proposed method to make a beneficial use of produced water to both reduce the release of CO₂ into the atmosphere and enhance the recovery of residual crude oil from depleted oil reservoirs.