3.4 Resource development scenario

Unconventional gas resources are found in a range of geological settings in the Cooper GBA region and include shale gas, tight gas and deep coal gas. Unlike conventional reservoirs, unconventional reservoirs have low permeabilities and require innovative technological solutions to move the trapped hydrocarbons to the surface (refer to Section 2.2 in baseline synthesis and gap analysis (Holland et al., 2020)).

The resource development scenario differs from a specific project-based environmental impact assessment where the location, scale and nature of planned activities are well delineated. For this assessment where the exact nature of the development is unknown, a resource development scenario is used to describe the characteristics of activities for the impact assessment. Two development scenarios are considered:

• a fast development scenario based on unconventional gas production matching the current Cooper GBA region conventional gas production, which is approximately 92 petajoules per year
• a slow development scenario, which is one-quarter of the fast development scenario (23 petajoules per year).

As there is no way of knowing exactly what future development may look like, the resource development scenario is based on the relative prospectivity of unconventional gas plays in the Cooper GBA region (refer to Stage 2 petroleum prospectivity technical appendix (Lech et al., 2020)), as well as potential restrictions prescribed in regulatory frameworks. Gas production increases in the first 5 to 10 years to meet the desired energy production rate. Relative prospectivity determines the likelihood of discovering a given resource (for example, oil, gas, groundwater) through analysis of geological properties (for example, formation depth and extent, rock properties, reservoir characteristics). A relative prospectivity threshold of 0.75 was chosen based on the distribution of values and as it indicates high scores for several input parameters ( Figure 2 ).

It is assumed that a well pad is up to 4 ha (Senex Energy, 2016; Santos, 2015) and typically requires 5 km of access road with a width of 10 m. Prior to drilling, 3 km² of additional dimensional seismic surveys is needed (Holland et al., 2020). Seismic lines are assumed to be between 4 and 5 m wide (Doudy and Cockshell, 2016). All seismic lines, well pads and access roads are progressively rehabilitated to meet regulatory requirements (Holland et al., 2020).

A resource development footprint of 8.85 to 26.55 km ² includes the following disturbed areas:

• well pad area of 5.9 km² to 11.8 km²; 4 to 8 wells per well pad, 63 to 1,180 wells drilled on 52 to 295 well pads (Pan et al., 2021).
• roads of 2.95 km² to 14.75 km²; 5 km of access road with a width of 10 m per well pad
• 3-dimensional seismic surveys of 442 km² to 885 km²; additional 3 km² seismic surveys per well pad.

The spatial extent for the entire unconventional gas resource development scenario, which is a combination of development area ― for example, roads, well pads and seismic lines ― as well as the areas between well pads and seismic lines, is estimated to be between 586 and 7,350 km² (or 0.5 to 5.6% of the Cooper GBA region) of which the estimated disturbed area is less than 27 km². This estimate assumes that the development of unconventional gas resources in the Cooper GBA region would require drilling of a maximum of 1,180 wells with 4 to 8 wells per well pad over a 50-year development period ( Figure 5 ). The well pad area extends to the limit of disturbance where a well is to be drilled and where drill rigs, pumps, engines, generators, mixers and similar equipment, fuel, pipes, and chemicals are located.

By way of comparison, the existing physical footprint of the oil and gas industry is relatively small (878 km²), covering approximately 0.7% of the Cooper GBA region. This excludes disturbances associated with seismic exploration activities (831 km², approximately 0.6%), which typically persist for 7 to 8 years, and 10 to 20 years in gibber plain land systems (Doudy and Cockshell, 2016). The disturbance footprint is estimated to increase by 27 km² (or 3%) under the maximum development scenario ( Figure 5 ).

Based on this resource development scenario, a total volume of 9,210 to 19,680 megalitres of water is required over a 50-year time period (Pan et al., 2021), equivalent to less than 400 megalitres per year in the entire Cooper GBA region. Likely water sources are groundwater (from aquifers in and above the Great Artesian Basin) and co-produced water extracted during conventional oil and gas development (Section 3.1.4 in baseline synthesis and gap analysis (Holland et al., 2020)). Water supply for unconventional gas resource development activities is governed by a water allocation plan and regulatory conditions overseen by the Queensland and South Australia governments. Surface water is not considered a reliable water source for unconventional gas resource development.