From CSG to LNG: Modeling and Understanding Key Subsurface Uncertainties for the Development of a Surat Basin Opportunity, in Queensland, Australia

Abstract

Abstract Arrow Energy intends to develop its certified coal seam gas reserves in the Surat Basin to supply gas to a proposed liquefied natural gas (LNG) plant located in Gladstone, Queensland. The large scale development of the Surat Basin for the LNG Project required basin-wide geological modeling. The Surat Basin coal structure and properties were reviewed in detail and modeled to estimate Gas Initially in Place. Dynamic simulation was subsequently performed to estimate total recoverable volume and generate a robust development plan for the LNG Project. Key subsurface risks consist of access to sufficient gas volumes within the area of interest and gas deliverability to meet and maintain gas supply to the LNG Project. To minimise the likelihood, and to reduce the consequences of these risks, subsurface uncertainties were identified and low and high values for each uncertainty were assessed with the aim to understand impacts on the LNG Project. Gas content, permeability and Net to Gross resulted in the biggest impact on the LNG Project, followed by relative permeability curves, coal heterogeneity, isotherms, permeability variation with pressure, coal compressibility and potential aquifer connection. Other uncertainties, including coal depth cut-off, sorption time and initial reservoir pressure had a lower impact on the number of wells required for the LNG Project. Subsurface sensitivity analysis combined with probabilistics was used to generate 90%, 50% and 10% probability subsurface models. These were carried forward for development planning to generate a range of development outcomes and production forecasts for economic evaluation to ensure a robust LNG field development plan. This paper describes the integrated reservoir data analysis and dynamic modeling methodology for the purpose of the large-scale development of this Surat Basin opportunity and outlines how key uncertainties were identified and addressed.