EHS Support’s Technical Experts, Tom Silverman, Remediation Service Line Leader and Tom Biksey, Risk Assessment Service Line Leader, gave presentations to the attendees of the Air and Waste Management Association’s (AWMA) Oil & Gas Conference in May.
A brief overview of each of the topics presented is outlined below:
Drilling Mud and Cuttings Assessment and Management Options Evaluation
Drilling muds and cuttings are a major waste stream produced during upstream oil and gas development with strict regulatory requirements often resulting in high cost management options. As part of a gas development project, approximately 800 wells per year are being drilled by the Australia-based client, generating around 250,000 tons of drilling muds and cuttings per year.
The objective of this project was to facilitate regulatory approval of a long-term management plan including burial and beneficial uses of drilling muds and cuttings. This was completed by undertaking a comprehensive assessment of the chemical composition of the drilling muds and cuttings, assessing the geochemical properties of the drilling muds and cuttings, and evaluating the mobility of metals and organic constituents bound within the muds and cuttings. In addition, a detailed ecological, phytotoxic and human health risk assessment was completed for a broad range of management and beneficial uses.
The risk assessment and resulting mud and cuttings management and beneficial reuse alternatives were approved by the regulator, saving the client on the order of $10 million per year in waste management costs.
Managed Aquifer Recharge using Treated Coal Seam Gas Water
A coal seam gas (CSG) to liquefied natural gas (LNG) will extract greater than 90 trillion gallons of low quality water from the coal seams over the next 35 years within the Surat Basin of Queensland, Australia. Concurrent with this development project, groundwater levels in the regional potable aquifer, which have declined by more than 250 feet over the past 100 years due to high demand and lower recharge, is expected to continue to decline further. The expected further decline of water levels in the potable aquifer provides an impetus to beneficially reuse treated CSG water and re-inject this treated water via a Managed Aquifer Recharge (MAR) program.
After 3 years of extensive studies, in 2012, approval was granted to conduct a trial using treated CSG water into the regional aquifer. The trial was undertaken over 3 months and tested several water types and their reactivity to the elements within the aquifer. Significant clogging occurred during the early stages of the trial which highlighted the importance of considering trace elements (such as montmorillonite) with respect to clay dispersions within the aquifer matrix and preferential flow zones.
EHS Support is now working with Santos to use the results from the trial to develop the engineering and operational design philosophy to improve operational efficiency before the full implementation of the scheme. These improvements are expected to save Santos > $5M in OPEX costs over the life of the project.
Well Integrity Risk Assessment
Inter-aquifer flow of gas and groundwater from both new coal bed methane wells and historical conventional oil and gas and water wells has been identified as a potential risk to beneficial use aquifers by Federal and State regulators as a result of multiple mega CSG projects currently in development in Queensland, Australia. For the historical wells, there is currently ongoing debate as to the ownership of liability and on-going management of these historical wells. Due to this uncertainty, the regulators are considering imposing on proponents a requirement to undertake a well by well field inspection program of these wells as part of the environmental approval applications. This has the potential to cause projects to become financially unfeasible. Therefore, to address this potential risk, EHS Support completed a desktop risk assessment evaluating common mechanism of failure for historic conventional oil and gas wells, unconventional wells, and private landholder water wells on a 5,000 square mile development area where 8750 new gas wells are to be drilled. The likelihood and consequence of failure was also evaluated, using a methodology that is adaptable to future development areas.
The risk assessment demonstrated that historical conventional oils and gas wells posed the highest risk for inter-aquifer gas and groundwater migration. Private landholder water wells pose a low risk due to the low consequences of inter-aquifer flow and the fact that most of these wells penetrate only one aquifer are completed above any gas target zones.
The findings of the risk assessment were approved by the State regulator and is expected to significantly reduce the time and expenses associated with a comprehensive well integrity survey.