SAFELY UNLOCKING the potential of shaleHydraulic fracturing, commonly known as fracking, is a well completions technique that’s required to produce oil and natural gas from unconventional plays.
Hydraulic fracturing involves pumping a mixture of mostly water and sand, and a small amount of additives, under high pressure into the reservoir to create fractures, or cracks, in the target rock formation. This increases the production rate and ultimate recovery of oil and natural gas from a well. In combination with advanced horizontal drilling, hydraulic fracturing makes it possible to develop shale plays that were previously uneconomic. These technologies have unlocked oil and gas deposits for Marathon Oil in the South Texas Eagle Ford shale, North Dakota Bakken shale, Oklahoma STACK and SCOOP, and New Mexico Permian Basin. In keeping with our commitment to environmental stewardship, we take steps to minimize the impacts from hydraulic fracturing by ensuring well integrity, conserving water, reducing air emissions from flaring and other sources, and managing waste responsibly.
Well integrity is essential to protecting the environment, particularly freshwater aquifers. To ensure well integrity, Marathon Oil follows industry best practices, internal procedures, and applicable laws and regulations for proper well construction, including selecting the appropriate tubing and casing materials, testing, monitoring, hydraulic fracturing and production operations.
Marathon Oil’s Environmental Management Standard requires each business unit to develop a plan to conduct pre-drill sampling to evaluate the baseline quality of water sources located within a quarter mile of drill sites. Water sources are tested for common naturally occurring components and other parameters that can be found in hydraulic fracturing fluids or produced water.
To create physical barriers and protect groundwater, we use steel casing and cement in the wellbore. We maintain a list of approved mills and suppliers whose tubular materials meet API specifications and our own expectations for manufacturing, as well as the chemistry quality of steel for casing and tubing. If our pre-drilling evaluation indicates potential for hydrogen sulfide, known as sour gas, we select tubing that meets the relevant ANSI/NACE sour service standards based on the region. This helps ensure lifetime material integrity with respect to corrosion.
During well construction, we use industry best practices and comply with state rules for drilling and completions. These best practices include pressure testing, cement bond logging and pressure testing the cement on every surface casing string in every well. We also perform pressure tests to determine the integrity of casing connections. Any casing left isolated is filled with packer fluid, a mixture of water, corrosion inhibitors and biocide, to mitigate corrosion. Our onsite well control specialists conduct regular exercises focused on maintaining wellhead pressure control and perform regular well control audits.
Before we perform hydraulic fracturing operations, we identify potential fracturing corridors in relation to surrounding wells to determine any wells to be decompleted, shut in or monitored to prevent communication. We also identify wells that require special considerations to ensure casing integrity.
Hydraulic Fracturing Operations
While hydraulic fracturing is under way, Marathon Oil digital oilfield control center operators create a dashboard using our telemetry system. The dashboard includes pressure alarms established for each individual monitor well based on our engineers’ criteria. These alarms notify the control center if hydraulic fracturing operations approach the maximum acceptable pressure. Our control centers operate around the clock to provide updates on the status of current operations and notify Marathon Oil staff if action is required.
During production, casing pressure is monitored continuously via telemetry by our operations personnel. Additional production safeguards include packer isolation and fluid, casing chemical treatments flushed with corrosion inhibitor and casing integrity testing such as caliper logs and pressure testing any time potential issues are identified. Known production casing integrity repairs are documented in WellView, our central well history repository, for knowledge management.
All of these activities ensure well integrity.
Water Management and Use
Marathon Oil looks for ways to use less freshwater in our hydraulic fracturing operations to reduce stress on local watersheds. We pursue alternative sources for water, such as aquifers whose supply doesn’t meet standards for municipal or agricultural use. We also evaluate technologies for recycling and treating produced water for reuse.
To protect surface and groundwater resources and natural habitat, we manage and dispose of our produced fluid waste from hydraulically fractured wells in accordance with all federal, state and local regulations. Fluids are recovered and stored with care to minimize any spills or leaks. In addition, we reuse or dispose of these fluids at locations we have reviewed to verify vendors have proper permits and approvals to operate. Marathon Oil has been a leader in developing an API recommended practice on the use of layflat lines for water transfer in the oilfield. The goal of the recommended practice is the safe, environmentally sound transfer of fresh, alternative and recycled produced water in the field.
Marathon Oil supports state-level disclosure of fracturing fluid components. We worked with other operators and trade organizations to implement FracFocus, a voluntary online chemical registry for hydraulically fractured wells. Marathon Oil has entered all of our wells drilled and hydraulically fractured in the U.S. in FracFocus, a total of 3,027 wells through December 2018. Our contracts routinely require our service companies to disclose their fracturing components to FracFocus, but we cannot contractually require a service company to disclose constituents that are protected by trade secret laws.
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