COUPLING THE DISPOSAL OF CO2 AND PRODUCED WATER FROM UOG RESERVOIRS INTO CONVENTIONAL DEPLETED OIL RESERVOIRS

Produced water from unconventional oil and gas (UOG) reservoirs is characterized by high concentrations of total dissolved solids (TDS) and variable concentrations of heavy metals whose concentrations in most cases largely exceed EPA maximum contaminant levels (MCLs). However, produced water is also characterized by containing indigenous microbial communities which are well adapted to extreme deep subsurface (high temperate, pressure and salinity) conditions. Disposal of produced water into depleted oil reservoirs and deep saline aquifers are two common practices to prevent the pollution of underground source of drinking water (USDW) by contaminants contained in produced water.

The risk of USDW pollution by heavy metals due to the possible upward migration of disposed produced water into deep saline aquifers will be discussed based on our experimental results showing that the mobility of heavy metals is much higher in shallow freshwater aquifers than in deep saline aquifers.

The feasibility of using indigenous microbial communities present in produced water from UOG reservoirs to recover crude oil as CH₄ from conventional depleted oil reservoirs will be discussed based on our experimental results showing that the combined supply of CO₂ and a nutrient solution to produced water can stimulate crude oil biodegradation via methanogenesis in depleted oil reservoirs.