Coal seam gas associated water production in Queensland: Actual vs predicted

Abstract

Coal Seam Gas (CSG) development in Queensland is currently going through a transition from less than 300 billion cubic feet/year (~315 PetaJoules/year (PJ/yr)) for domestic consumption to ~1400 bcf/yr (nearly 1500 PJ/yr) by about 2019 driven by additional Liquid Natural Gas (LNG) export contracts. Prior to this ramp up in production, industry, government and academia have been forecasting not only gas but associated water production (produced water) for the various purposes of financial investment decisions and field development planning, prudent governance and regulatory planning, and estimation of potential environmental impacts for planning management, monitoring and mitigation strategies. During the course of resource development, prediction methodologies and model sophistication has varied greatly as more data becomes available and uncertainty is reduced. In Queensland, now that all 6 LNG trains are running and at various stages of ramping up to full production, there is a substantial and growing data inventory to history match numerical models and improve forward forecasting. We review the historical forecasting of CSG water production in Queensland leading up to the development and operation of CSG to LNG export, and compare that to the current actual produced volumes now that the projects have come on stream. The latest available measured produced water from CSG development (December 2016) equates to ~60.5Giga Litres/year (GL/yr) with combined operator forecasts defining a peak projected to occur for about 10 years at 70-80 GL/yr. When this is converted to cumulative water volumes over the life of the industry (based on combined operator forecasts), just over 1700 GL of water is expected to ultimately be produced. Current estimates of water and salt production in Queensland are about 25% of those made by government and academia prior to the expansion of CSG to LNG export and ~70% of the 2010-11 industry estimates. We show that this discrepancy can be attributable to a combination of the following factors:

From initial advice statement to export – a 10 year retrospective of Queensland's liquefied natural gas industry

“…This estimate was necessarily based on limited data, reflecting the lack of analogous CSG developments of this scale and the early stage of reservoir appraisal. This data informed FEED and arguably led to overdesigned water treatment facilities (Underschultz et al 2018) Over time, forecasts for water production have decreased as more performance data have become available. Additionally, the project design basis has evolved with changes to well construction scheduling and the construction of fewer LNG trains than originally planned.…”

Education in Ecological Engineering—a Need Whose Time Has Come

“…The average volume of associated water extracted from Queensland coal seams is estimated at 60GL/year or 1700GL over the life of the reserves [29], equivalent to around 3.4 times the volume of Sydney Harbour. The required attributes of any solution to manage this volume of associated water include: (i) the capacity to operate at scale; (ii) reliability to ensure capacity to support uninterrupted gas production; (iii) flexibility to accommodate fluctuations in water production volume and quality; (iv) sustainability-a threshold requirement for all options; (v) commerciality-the need to minimise costs and risks and maximise returns within the constraints of the other attributes; and (vi) capacity to leverage community and social benefits.…”

Impact of the Water Adsorption Monolayer on Methane Ad-/Desorption Behavior in Gas Shale Nanopores

“…38 Shale and coal have many similarities, as both are source rocks and contain a large volume of adsorbed gas. Unlike coal, which has a high initial water saturation compared to shale, 39 the initial water saturation in shale is ultralow, which is more conducive to the replacement of adsorbed methane by water. Therefore, the impact of water on methane ad-desorption behavior needs to be studied further.…”