Coupled 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 Delaware Basin.
- ensuring well integrity,
- conserving freshwater,
- reducing air emissions from flaring and other sources, and
- managing waste responsibly.
To ensure well integrity, Marathon Oil follows industry best practices, internal procedures, and applicable laws and regulations for proper well construction. This includes 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. Groundwater wells are resampled if there are any indications that a casing integrity issue may exist.
To protect groundwater, we use steel casing and cement in the wellbore as physical barriers. We ensure our suppliers’ 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, 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 apply industry best practices and comply with state rules for drilling and completions. These 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 to maintain 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 detect any wells that need 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 or in the loss of pressure, which could indicate a casing integrity issue. Our control centers operate around the clock to provide status updates of current operations and notify Marathon Oil staff if action is required.
In areas in Oklahoma that may be sensitive to induced seismicity, we conduct a risk assessment and deploy temporary monitors, if necessary. We are considering expanding this program as we assess the risk of induced seismicity for all of our assets.
During production, our operations personnel monitor casing via telemetry. Additional production safeguards include packer isolation and fluid, casing chemical treatments with corrosion inhibitor, and casing integrity testing such as caliper logs and pressure testing. Known production casing integrity repairs are documented in our central well history repository for knowledge management.
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 utilizing electronic or physical monitoring and secondary containment 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. We use a 24-hour automated system to monitor injection pressure and rate for company owned saltwater disposal wells. Regular casing integrity verification is performed as directed by state and/or federal regulations or if monitored operating conditions indicate a more frequent check is advisable.
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 3,338 wells through December 2019. 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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