This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 199412, “New Produced-Water Risk-Based-Approach Guidance,” by Mathijs Smit, Shell; Sean Hayes, More Energy; and Oliver Pelz, BP, et al., for the 2020 SPE International Conference and Exhibition on Health, Safety, Environment, and Sustainability, originally scheduled to be held in Bogota, Colombia, 17-19 March. The paper has not been peer reviewed.
A global trend has developed toward the application of risk- based assessment (RBA) techniques for managing environmental risks and considering potential effects of produced-water (PW) discharge. The main objective of the complete paper is to achieve harmony in the means by which operators execute RBA for offshore PW discharges. This coordination is likely to enhance broader understanding and acceptance of RBA techniques internationally.
Key Principles. An RBA approach to managing PW begins with an assessment objective (e.g., demonstrating no adverse effect outside an accepted zone). The RBA characterizes the risk (i.e., the likelihood that adverse effects may occur) to the environment of a PW discharge given the exposure resulting from effluent discharge and the sensitivity of the receiving environment to exposure. To assess the risks of discharge, existing international frameworks for ecological risk assessment are available.
These frameworks include data collection, hazard assessment, exposure assessment, and risk characterization. The specifics of data collection depend on the form of the hazard assessment and the exposure assessment, which, in turn, are dependent on the risk characterization, which allows compliance with the assessment objective to be evaluated. The purpose of the RBA for PW can be to target no adverse effect beyond an accepted zone or to serve as a management tool to drive continuous improvement. The risk-assessment steps usually are executed through a tiered process.
Regulatory Approaches to RBA. At the time of writing, only a handful of regulatory frameworks for offshore PW management include principles of RBA. Table 1 of the complete paper provides a comparison of different assessment objectives and endpoints for regulatory PW RBA approaches used in selected basins. The table makes clear that it is not practical or necessary to meet the required criteria at the end of the pipe. Common practice defines a zone where the defined threshold may still be exceeded. This zone is often referred to as the mixing zone. While the use of a 500-m mixing zone is common practice offshore Brazil, for instance, in the US Gulf of Mexico, a 100-m mixing zone is applied. Different thresholds are applied in the different jurisdictions that justify the mixing zones.
Defining the Adverse Effect Threshold. The three regulatory approaches presented in Table 1 of the complete paper apply different methodologies for defining the threshold level of adverse effects that should not be exceeded.