Investigations of subsurface mineral precipitation reactions associated with brine injection

Abstract

Brines are injected into the subsurface every day for a variety of reasons including enhanced oil recovery, hydraulic fracturing, carbon sequestration, and wastewater disposal. Mixing of these injected brines with brines in injection formations in the subsurface can drive mineral precipitation, which can alter the porosity and permeability of the injection formation, and thus the ability to continue to inject fluid into or pump fluid out of the formation. The potential of mineral precipitation to damage a formation, makes the understanding of brine interaction in the subsurface incredibly important for energy development in the United States. For oil and gas production brine injection occurs for two reasons: hydraulic fracturing and the disposal of water produced alongside hydrocarbons (produced water). Hydraulic fracturing requires 2-11 million gallons of water per well, and more 55% of wells in the United States are in drought affect areas. Continued development of wells increases the demand for water resources, and alternative sources of non-potable water for hydraulic fracturing would reduce demand on fresh water resources. For each barrel of oil produced it’s estimated that 7 barrels of water are produced. In the United States 14-21 billion barrels of water are produced every year. 92% of this produced water is injected into the subsurface, with 71% for enhanced oil recovery and 21% for disposal in injection wells. Treatment of produced water to reduce precipitation has the potential to increase the lifetime of disposal wells. Oil and gas activity in Texas creates 35% of the produced water in the United States and Texas has 12,000 wastewater disposal wells. The Permian Basin in Texas is one of the most productive oil basins in the United States, and is located in a high water stress region due to prolonged drought and water demands from diverse sources. This dissertation uses data from the Permian Basin to evaluate the potential for mineral precipitation in subsurface formations driven by injection and mixing of brines of differing compositions in numerical simulations derived from general conceptual models of hydraulic fracturing and produced water disposal. In the first manuscript in this dissertation batch and reactive transport models are used to investigate brines as an alternative water source for hydraulic fracturing from a mineral precipitation perspective. Injection rate, represented by injection volume and injection time vary widely by well and operator; geologic formations vary widely in porosity and permeability, and the effects of these variations on mineral precipitation in disposal wells are unknown. In the second manuscript, reactive transport simulations investigate the effects of porosity, permeability, injection time, and injection volume on mineral precipitation volumes caused by brine mixing in the subsurface. Produced water management is one of the biggest challenges associated with oil and gas development, and 21% of produced water in the United States is managed using disposal wells. This costs between $0.05-$2.65 per barrel, and can add significantly to the cost of production. Increasing the lifetime of these wells through the understanding of how to reduce mineral precipitation could lower costs. In the third manuscript in this dissertation, reactive transport simulations investigate how reduction in ion concentrations could increase the lifetime of disposal wells. Results from this dissertation provide insight into the effects of brine mixing in the subsurface and how variations can effect mineral precipitation.