Bioremediation Study on Formation Damage Caused by Hydraulic Fracturing: A Microfluidic Approach

Abstract

Abstract Hydraulic fracturing has been applied to unconventional reservoirs with low permeability to achieve higher productivity and economic potential. However, polyacrylamide-based friction reducer and guar gum, two of the most common components in fracturing fluid could cause formation damage by penetrating into the matrix and blocking the flow path. To regain the conductivity of the damaged area, a bioremediation method was developed and validated by a microfluidic approach. Modified nutrients were used to stimulate the indigenous bacteria that could consume or break the polymer residues. Indigenous bacteria were extracted from oil field produced water collected with customized anaerobic sampling kits which have been sterilized. Feasibility studies were conducted to investigate the indigenous bacteria activity with and without nutrient supply. Fracturing fluid, field water, and a modified nutrient recipe which contained 300 ppm of inorganic salts were loaded into anaerobic sample vials in a 140°F - 150°F incubator. Microfluidic tests were performed in 150°F oven with microfluidic chips designed and fabricated based on the topology of matrix networks. Fracturing fluids were injected into a chip saturated with field water to simulate formation damage. Remediation fluid consisting produced water, injection water and nutrient was injected into the chip. After two weeks soaking, 2% KCl brine was then injected into the chip at 200 nl/min until a stable pressure drop was achieved. Microscopic pictures were taken before and after soaking to demonstrate the polymer damage and the remediation of microfluidic chips. The indigenous bacteria were successfully stimulated with and without the existence of the friction reducer based on the results of feasibility tests. Microfluidic tests showed there is a significant difference in precipitations between the case with and without nutrient supply, which indicates that the bioremediation method could regain conductivity of the damaged formation. This work is novel research on bioremediation application in unconventional reservoirs with only indigenous bacteria involved. The customized sampling technology and laboratory approach could prevent contamination of other microbes and oxygen, which could improve the quality of the research. Microfluidic chip is a great simulation of porous media and a proof of concept between scientific hypothesis and field application which requires small sample size and provides good reproducibility. In field applications, only an extremely low amount of nutrient is required in this process which provide great economic potential. Additionally, the injected nutrients will be fully consumed by the bacteria which makes this technology is an Environmental, Social and Governance (ESG) approach in energy industry.