Understanding Energy | Produced Water 101
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THERE seems to be a heightened sense of concern for the environment in Guyana with the production of oil and gas — understandable for a country largely focused on sustainable development.

Safe and responsible development of Guyana’s offshore oil and gas resources requires careful analysis of processes that are new to the country. The matter of produced water comes to mind. However, this does not appear to have been lost on regulators and international consultants in considering environmental impact assessment (EIA) and production licences for offshore development projects. For as long as the pages allow, let us examine the concept of produced water; a 101 of sorts.
Simply put, produced water is water trapped in underground formations that is brought to the surface along with the oil and gas during production. As the oil, gas and water enter a floating production offloading and storage (FPSO) vessel offshore, they are separated and used for different purposes. The oil is stored on the FPSO and later offloaded to tankers to be sold on world markets, and the associated gas is either used on the FPSO to generate power, re-injected into the reservoir to maintain pressure or brought to shore if the necessary facilities exist. Produced water, in contrast, is either treated and discharged overboard, re-injected into reservoirs or injected through a dedicated well.
According to experts, there are several environmental, technical and economic factors that determine how produced water is handled. Environmentally, produced water has higher levels of oil, grease, barite and calcite compared to surface water. As a result, most onshore oil and gas operations utilize reinjection of produced water into wells to avoid potential mixing with groundwater. The risks are much lower offshore, and Australia, Canada, Trinidad, and the United States Environmental Protection Agencies allow projects to discharge produced water to the ocean after appropriate treatment. Globally, nearly all offshore produced water is managed this way, and the Liza Destiny also began utilizing this method after production began.
Treatment of produced water prior to discharge is a critical technical step in this process. Treatments onboard an FPSO separates and collects most oil and grease prior to discharge and enables continuous monitoring for compliance with regulatory limits. If levels are above limits, produced water is routed to storage tanks on the FPSO for further treatment. After this process, the environmental effects of produced water discharge are considered negligible.

Economic considerations of handling produced water are linked to environmental and technical factors. Treatment of these non-toxic compounds is technically challenging and economically costly, and re-injection leads to build-up of barite and calcite that can damage wells and reduce production. Additional maintenance is required, and drilling new wells is sometimes necessary. Ultimately, re-injecting produced water leads to additional air emissions and can lead to significant quantities of filter waste to handle barite and calcite. Because these compounds are already widespread in ocean environments, overboard discharge is safe and common.
Considering the environmental, technical and economic factors, it’s not surprising that only 3 out of 62 FPSOs projects started by the two largest contractors in the past decade use re-injection as the sole method for managing produced water. An additional 12 FPSOs use re-injection as a complement or back-up to discharge overboard.
Like many complex processes in the offshore oil and gas sector, new studies about the environmental factors are always taking place. New technologies are developed and economic considerations sometimes change. Regulators and operators must therefore regularly review oil and gas processes to ensure that Guyana’s natural resources are developed safely and responsibly.

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