Julio Henriquez Member Name
Environmental Engineer
Salinity is a growing problem for the oil and gas industry, particularly at Natural Gas Liquid (NGL) storage facilities and oilfields sites. Traditional remediation techniques designed to meet regulatory requirements can be challenging and, in many cases, are neither sustainable nor practical. Dynamic 3D conceptual site models are an alternative evaluation method that can be used to better visualize and understand salinity-impacted sites, adequately evaluate source-pathways-receptors, and assess risks.
NGLs are commonly stored in underground caverns built in salt-rich geological formations. Large-scale storage of these products is necessary in times of low demand. The construction of these caverns involves injecting fresh water into the salt formation using one or more injection wells. As the freshwater dissolves the salt, the saline solution, primarily sodium chloride (NaCl), or brine, is returned to the surface. Then, more freshwater is cycled into the formation until it forms a usable cavern. At the surface, the resulting brine is retained in large ponds. When required for distribution, the NGLs are displaced to the surface by injecting brine back into the caverns.
Environmental risks from brine ponds
Historically, brine ponds were constructed of earthen berms and compacted clay, without any synthetic liner. The storage capacity is typically 50,000 m3 (or more) and chloride levels are greater than 100,000 mg/L. The main environmental liability with older brine ponds (or those that are not sufficiently lined) is that over time, the clay liner can become saturated with brine and affect the soil properties and hydraulic performance. This will often result in brine leakage and migration.
The risks associated with brine leakage and migration are:
- The chloride ion (Cl-) is highly mobile and concentrations in water are not affected by chemical reactions (i.e. it does not biodegrade, volatilize, or bioaccumulate).
- Cl- does not readily adsorb into soil particles, so concentrations remain high in water and porewater.
- When released into the environment, it can travel large distances and affect large areas.
- The migration rate of CI- in the saturated zone is highly dependent on the hydraulic conductivity, hydraulic gradient & porosity of the soil medium.
Regulatory standards for chloride in groundwater are stringent and orders of magnitude lower than chloride concentrations measured at brine-impacted sites.
An innovative, modern-day answer using 3D modelling
Golder has been providing advice to clients in evaluating alternative and innovative solutions to better visualize, understand, and assess the impacts and risks from brine storage facilities. Key goals include gaining a better understanding of the sources, pathways, receptors, and associated environmental risks; establishing multi-year data gap plans based on site-specific conditions; and evaluating mitigation options for unacceptable risks.
Previously, each aspect was analyzed in isolation which was a cumbersome, time consuming process. This process made it extremely difficult to identify data gaps and collaborate with team members without having to review numerous reports.
To address these challenges, a dynamic 3D conceptual site model was created, combining data from:
- Soil and groundwork chemistry
- Digital elevation maps
- Aerial photographs
- Geophysical surveys (i.e., electrical resistivity tomography [ERT], electromagnetic surveys [EM], downhole geophysics),
- Geological and hydrogeological information
- Borehole log data
- Groundwater elevations
Dynamic 3D conceptual site models are an alternative evaluation method that can be used to better visualize all site data in one interface.
Dynamic 3D conceptual site models are an alternative evaluation method that can be used to better visualize all site data in one interface.
Dynamic 3D conceptual site models are an alternative evaluation method that can be used to better visualize all site data in one interface.
How can a 3D model help?
The 3D model provides the oil and gas industry with a tool that allows them to visualize all their site data in one interface and moves the conceptual site model from a 2D static figure to a 3D dynamic model. This increases Golder’s ability to review and advise our clients on risk and mitigation options. The 3D model serves as a technical basis to identify data gaps, aid in planning, and optimize future data collection, and it can be easily updated as new data become available. This allows the targeting of key areas to reduce the required monitoring well network, while maintaining an adequate understanding of site conditions.
Clients have realized significant value in using a 3D model compared to the more traditional approach of slide presentations and reports. The model provides a more efficient and effective approach to access information for businesses that need to monitor environmental conditions. It can be shared in a secured interactive web application and does not require any specialist software for review. This means collaboration with team members, stakeholders, and clients is efficient even from remote locations.
Our approach outlined above will continue to evolve and provide tremendous value for our oil and gas clients or organizations dealing with salinity issues. More broadly, real-time 3D interactive will help organizations to plan and adequately allocate resources, managing risk levels and addressing data gaps in a systematic manner, ultimately saving time and money.
