The Spring Gully coal seam gas field of the Bowen Basin in Queensland, Australia has historically been developed using vertical wells that have been stimulated by either cavitation or hydraulic fracturing of the Bandanna coal measures. However, as the field development expands into lower reservoir quality in the fringe area of the field, there has been a shift to applying horizontal well designs with the objective of increasing economic return and minimizing environmental footprint.

Surface to inseam (SIS pairs) have been successfully implemented in Queensland low permeability Permian coal seam gas fields. Four Surface-to-Inseam (SIS) well pairs (horizontal wells intercepting vertical producers) were drilled in Spring Gully in 2012 and 2013. Production performances of these pilot horizontal wells show improvement when compared to offset vertical wells. In order to understand the more complex fluid flow mechanism a detailed multi-segment horizontal well (MSW) fine scale simulation model was built to calibrate rate and pressure performance. Following the pilot well performance study, a large scale development optimisation exercise including spacing, pattern, orientation and well design was carried out on all future development regions. This work when coupled with a risk quantification exercise has provided an informed view on the cost benefit of applying this optimised horizontal well development in Spring Gully.

One of the unique challenges in implementing optimised SIS horizontal wells in the Spring Gully field is the undulating topography with very steep, narrow ridgelines that are bounded by cliffs and very deep and generally inaccessible valleys. Therefore during early planning phase, the operator, Origin on behalf of Australia Pacific LNG applied practical compromise between subsurface and surface objectives in order to achieve the greatest overall value

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