The Impact of Mining Fluids on Enhanced Oil Recovery

The development of enhanced oil recovery (EOR) technology has sparked a new oil boom in America. Also known as tertiary mining, EOR is a variation on hydraulic fracturing (“fracking”) that has enabled American oil producers to more than double the amount of oil and/or natural gas recoverable from otherwise tapped-out reservoirs. On average, recovery of crude oil from an oilfield is typically no more than 40 percent of a reservoir’s potential, after primary and secondary recovery operations have been performed. EOR was developed to improve this recovery factor.

 

Three Approaches

EOR can be achieved using any of three different methods. All involve injecting substances deep underground to boost recoverable oil production by about another 20-30 percent. Thus, otherwise abandoned minefields may be rendered productive again.

The first technique relies on thermal energy injection. This accounts for up to 40 percent of American EOR technology in use today, primarily in California. The second method involves the injection of gases, such as nitrogen or carbon dioxide, to further pressurize underground oil, forcing the oil into the wellbore, and reducing viscosity, so the oil flows more freely. This method accounts for about 60 percent of present EOR production in the United States.

Chemical injection (also known as “chemical flooding”) is the third category of EOR technology gaining traction in American oilfields. This method uses one or more compounds, including surfactant(s), alkali and long-chain polymers, such as polyacrylamide, to alter the rheological properties of the fluid used for injection into the reservoir. Together, these chemicals act to lower the viscosity of oil, reduce surface tension, and make oil flow more freely, significantly increasing oil and gas recovery. It’s estimated that this method presently accounts for just 1 percent of domestic EOR production.

 

New Opportunities to Capitalize on an Underutilized Methodology

Polymers are among the most important chemicals used in chemical flooding EOR, whether used alone or in combination with other agents. Typical chemical flooding projects involve mixing polymers with other agents, diluting them with water, and injecting them continuously into a well until about half to one-third of the reservoir pore volume is filled. This is followed by long-term water flooding, to drive the polymer “slug” toward the oil bank. This forces the viscous polymer solution through the rock, with its payload of oil/gas, and into the production well(s) for retrieval. Polymer injection may continue for several years, followed by several years of water injection.

The injection of polymer solution into a reservoir boosts water viscosity (a property that can be described as “thickness”), reduces the permeability of the water, and ultimately increases fractional flow of oil, enabling its recovery at lower pressures. Polyacrylamide is a synthetic polymer. Most often a form called partially hydrolyzed polyacrylamide (HPAM) is used in EOR. HPAM is relatively inexpensive, and possesses well-documented viscoelastic properties.

Those who wish to capitalize on this efficient and relatively underutilized EOR technology will require appropriate liquid mixing equipment capable of continuous mixing. The right continuous mixing equipment achieves proper rheology modifier dispersion and allows for the uninterrupted production of appropriate EOR fluids throughout the rather lengthy polymer injection phase.