The economic downturn of 2020 led many oil and gas (O&G) companies and exploration and production (E&P) operators looking for ways to reduce cost while also trying to reduce their carbon footprint. For oilfield-waste-disposal providers, waste-slurry injection is one way to accomplish both economic and environmental objectives.
What Is Slurry Injection?
Slurry injection is used to treat, dispose of, and contain toxic and nontoxic waste without damaging the environment while efficiently producing a dependable resource. It involves the grinding and processing of solids into small particles, which are mixed with water or liquids to create a slurry.
Waste management companies such as Advantek and Milestone Environmental Services use slurry injection to deposit oilfield waste deep underground where it poses a reduced risk to the environment. In some cases, it is a cost-effective method of oilfield-waste disposal, reducing the need for transportation.
Slurry-injection wells have been used around the world since the 1980s. In the US, slurry injection is permitted on a regular basis in Alaska, Texas, and California, and at offshore locations in the Gulf of Mexico.
An article from the 7th International Symposium on Mining and Environmental Protection released in March 2020 titled Deep Underground Injection of Waste from Drilling Activities (Gaurina-Međimurec et al. 2020) summarized data on formations selected for deep underground waste-slurry injection projects worldwide in the period from the late-1980s until today.
Data showed most of the waste is injected in sandstone formations (67% of all analyzed projects), which includes US locations in Alaska, Texas, Louisiana, Colorado, and California. This was followed by mudstone and shale formations (13% each) and limestone formations (7%).
According to water and waste management consulting company Veil Environmental, oil and gas regulatory officials from the Mid-Continent states do not use the procedure widely because most companies there prefer to dispose of drilling waste through burial in pits.
But more US states are looking into the use of slurry injection and slurry wells.
Slurry Injection Expanding to Other US States
In September, Milestone announced plans for an oilfield-waste-slurry-injection (WSI) facility in the New Mexico side of the Permian Basin. The New Mexico Oil Conservation Division approved the company’s permit for an oilfield WSI facility near Jal, in Lea County. It is Milestone’s first move into the, and the facility is the first of its kind in the state, requiring multiple permits, including one to inject oilfield waste and one for solid-waste management.
The company said its proprietary slurry-injection process captures drilling, completion, and production waste, reinjecting it back into the earth through a network of facilities in the Permian Basin and Eagle Ford shale.
The disposal methods help E&P operators avoid soil and groundwater contamination risks associated with onsite disposal methods that dispose of waste above the water table.
The New Mexico facility announcement follows the April opening of Milestone’s Upton Landfill facility near Midland, Texas, which handles drill cuttings, contaminated soils and other E&P waste materials approved for landfill disposal. The landfill is Milestone’s second landfill and sixth oilfield-waste-disposal facility in the Permian, close to its three Midland Basin slurry-injection facilities—South Midland, Stanton, and Big Spring.
In North Dakota, plans for slurry-injection wells and a treating plant remain in the early stages.
The North Dakota Industrial Commission approved KT Enterprises’ proposed slurry-injection well and treating plant in late March near the Williston Basin in McKenzie County. The treating plant would take in oilfield wastes, drill cuttings, and soil contaminated by spills and process them for injection, including blending with saltwater. The waste product would then be injected into a saltwater disposal well to be drilled in the Broom Creek formation.
KT Enterprises’ plan comes 1 year after Hydroil Solutions first proposed building two wells north of Alexander, North Dakota. That project, however, is on hold amid market uncertainty and COVID-19.
Key Challenges Remain
The most common challenge during WSI is the continuous loss of well injectivity due to poor engineering design of the injection parameters for most of the current existing WSI wells, according to SPE 199295. The Advantek authors discussed three different case studies, highlighting the importance of injection monitoring, the steps necessary to maintain the injectivity and perform a healthy WSI operation, along with mistakes that caused significant formation damage development in injectors in the Eagle Ford, Haynesville, and Permian Basin shale plays.
Results from case studies were used to prepare a set of guidelines to maintain well injectivity and extend the well life. The comparison of various nonmonitored injection wells to the monitored injection wells at different locations in Texas led to the following conclusions:
- Lack of proper pressure analysis after each injection batch raises the risks of formation damage and may lead to permanently plugged wells.
- Correct flow rate and injection pressure are necessary to laterally propagate solids farther away from the wellbore and into the formation for a successful WSI operation.
- It is important to post-flush with filtered water as the unfiltered/untreated water will suspend the solids, which when settled near the wellbore may accelerate the filter cake formation and lead to premature plugging.
- Formation damage while performing WSI is inevitable, but in order to extend the well life and delay or avoid the filter cake formation, field operators must change the injection strategy, pressure, rate, and slurry properties.
The rising interest in slurry injection has caused environmental concern, especially regarding the disposal of radioactive material. Advantek and Veil Environmental said environmental problems associated with slurry injection are rare. Properly managed slurry-injection operations typically pose few environmental and health risks compared with conventional surface disposal methods because the wastes are injected deep below drinking water zones.
New regulations and growing concerns for the environment are leading operators to minimize their generated waste volume through recycling, reusing, and selecting the best available methods for permanent waste disposal.
Gaurina-Međimurec et al. also showed advantages of the waste-injection method into suitable deep geological formations over other waste-disposal methods (biodegradation, thermal treatment) to minimize harmful impacts on groundwater, reduce required surface area for waste disposal, and reduce the negative impact on the air and long-term risks for the environment.
The authors said future progress is necessary for better understanding of disposal domain characterizations during the planning and execution phases, including the use of 3D simulators and real-time monitoring of injection parameters and improved disposal domain models and fracture networks. Continuous monitoring of all parameters and real-time visualization of disposal domains were recommended to maximize the volume of slurry-waste disposal in the safest and economically most-efficient manner.