Barrow Island's Windalia reservoir is Australia's largest onshore waterflooding operation and has been under active waterflood since 1967. The highly heterogeneous reservoir consists of fine-grained, bioturbated argillaceous sandstone that is high in glauconite clay. The high clay content results in a low average permeability (5 md) despite high porosities (25-30%) and hence fracture stimulation is required to achieve economic production rates.The Windalia reservoir and fluid properties preclude the use of traditional EOR technology, with thermal, miscible and mobility control processes all deemed unfeasible through screening studies. Consequently, the in-depth flow diversion mechanism was developed and applied, which utilizes a low molecular weight polymer to drive the growth of induced hydraulic fractures in the treated injection wells. A 3-injector pilot was executed involving polymer injection for two years, with no detrimental injectivity losses observed for polymer concentrations up to 750 ppm. Considerable fracture growth, oil production rate uplift and reduction in water cut were observed throughout the pilot pattern, in line with predictions: Fracture half-lengths increased from 6 ft to 400 ft in one injector and from 141 ft to 322 ft in another  An initial oil rate uplift of 38% relative to the production baseline was observed; a more conservative estimate suggested that at least half of this was attributable to the tertiary recovery process  The water-oil ratio was observed to fall from 15 to 11, similarly timed with the oil production increase.These improvements were observed consistently throughout the pilot area and were distinct from the waterflood behavior elsewhere in the field. This paper briefly summarizes the technology screening and pilot execution stages, after which the results from the pilot are presented and discussed. This technology may be of use in other low-permeability waterfloods with induced injector fractures, for which traditional EOR practices are believed to be unfeasible.

The Wheatstone gas field located in the Northern Carnarvon Basin offshore Western Australia achieved first gas in mid-2017. All seven foundation producers are equipped with permanent downhole gauges (PDHGs) for real-time pressure monitoring. Data from these gauges have been instrumental in understanding dynamic reservoir performance and reducing static uncertainties. The scope of this paper specifically covers the use of pressure and rate transient analyses (PTA and RTA) and the insights that have been gained during the first two years of production. Significant offset distances exist between each PDHG and the reservoir. Corrections were developed to convert the gauge pressure to a reservoir datum, which primarily account for frictional and gas density changes with varying rates and temperatures within the wellbore. Other physical constraints and effects have been found to be more challenging to overcome, limiting the quality and interpretability of the pressure transients, particularly in the middle-time region. These include interference from non-reservoir pressure signals such as liquid fallback during shut-in, extremely low signal-to-noise ratios in the higher quality formations, and proximity to boundaries that render a short infinite-acting radial flow (IARF) period that could be masked by wellbore storage. Attempts to circumvent these issues have included the use of drawdown transient analysis to complement build-ups. The step-rate test can eliminate liquid fallback entirely, which allows for better resolution of the IARF period. Rapid choke movements were also trialled to boost the reservoir response in some instances. Interpretations using the drawdown data were further verified in one producer through analysis of the buildup data acquired following a routine downhole safety valve closure, which benefitted from the trapping of condensed liquid above the closed valve. This provided the cleanest PTA data seen outside of drill stem testing during field appraisal. While successful in the example presented, no methods have yet been found to reliably increase IARF interpretability in those wells producing from the best quality sands. Regarding RTA, the authors have found very few documented cases in the literature of applying this technique to conventional gas fields. To field-test its applicability in such an environment, evaluations of drainage volume by producer were performed and found satisfactory when compared with other estimates of gas in-place. It is hoped that a presentation and discussion of this finding will be additive to the reservoir engineering toolkit.

Barrow Island’s Windalia reservoir is Australia’s largest onshore waterflooding operation, developed in 1965 with waterflooding starting in 1967. The Windalia reservoir is highly heterogeneous and geologically complex, showing low permeabilities and extensive fault networks. Presently, injection rates are constrained by water availability because of aging source water facilities and increased injector failures because of high integrity risks, highlighting the importance of optimised distribution of injection volumes. Static allocation of injection water has historically been conducted on a pattern basis. This approach, however, is not grounded on the relationships between injection and production wells; instead, it honours the geometric layout of the wells. A more dynamic approach was required to account for the changes in status of injectors and water availability that are often encountered in mature waterflood systems. The successful completion of the Windalia capacitance-resistance model (CRM) was leveraged to develop a comprehensive ranking system of all capable injectors, quantifying short-term normalised oil response to maximise the oil production achieved for a given volume of water injected. Improved understanding of injector-producer communication has also provided the ability to extract the maximum value from limited injection water volumes and has the potential to reduce water cycling and the associated water-handling costs. It can also improve the ability to identify and prioritise workover and stimulation opportunities. This work describes the advances in reservoir management capabilities by quantifying the relationships between injector-producer pairs and the dynamic allocation of injection volumes.

Waterflood development drilling of the Windalia reservoir on Barrow Island at 40-acre spacing started in 1968, using five-spot and nine-spot inverted drive flood patterns. There was a general conversion to line drive in mid-1970 with various infill and realignment projects. The field comprises more than 220 active injectors and 400 producers. The reservoir is geologically complex, with low permeability and significant heterogeneity. Historically, empirical techniques and fractional flow models were used for forecasting, but these approaches have many inherent limitations; for example, they do not provide individual well performance and they are not sensitive to changes in operating conditions. More recently, a capacitance-resistance model (CRM) that uses historical injection and production data has been used to establish long-term behaviours between water injection and oil production wells, including inter-well connectivity, delay time constants and productivity indices. The evaluation of these behaviours allows direct quantification of waterflood efficiency at well-to-well level and improves identification of opportunities for changing injection patterns and prioritisation of operations and well workovers. Optimisation and forecasting of the Windalia waterflood is performed by maximising cumulative oil production by reallocating the available field wide injection water and evaluating individual injection wells target rates. Numerous optimisation scenarios were built into the models to account for the impact of changing operating conditions such as water availability and aging of wells and processing facilities. CRM is robust and is appropriate for simultaneous optimisation of well rates in a field where water injection and oil production wells are shut-in frequently. The PowerPoint presentation is not available to APPEA.