Developing a Chemical EOR Pilot Strategy for a Complex, Low Permeability Water Flood

Abstract

A screening study and subsequent chemical EOR application pilot strategy for a complex, low-permeability waterflood is presented. Our focus has been on developing appropriate field application options allowing flexibility of operation against a background of reservoir complexity and uncertainty. Australia's Barrow Island Windalia reservoir, the nation's largest onshore waterflood, was developed in the late 1960's. Cumulative oil production to date is approximately 288 MMSTBO. Planning a chemical EOR scheme needs to address the following reservoir and production characteristics:○Highly heterogeneous, very fine grained, bioturbated argillaceous sandstone, high in glauconite;○High porosity (0.28) but low permeability (5 mD with 20 mD+ streaks);○Production and injection necessarily stimulated by induced fractures○Highly saline and hard brine;○Large waterflood pattern volumes (10 MMbbl at 20 acre well spacing). Despite 40 years of production involving water flooding, well-work, and changes in operating philosophy, the nature of the reservoir presents significant uncertainties. These uncertainties flow-on to difficulty in constructing predictive reservoir models. Initial screening recommended that polymers be considered for sweep improvement and conformance control although reservoir complexity presented a challenge. Subsequent laboratory work focused on issues of polymer injectivity, rheology, and retention, in parallel with an assessment of how SCAL properties are measured in the laboratory and related to water flood performance. Dynamic modelling studies have assessed field response and economics for a range of chemical EOR pilot designs. We have focused on developing options for field application of polymers, as opposed to extensive stand-alone laboratory and dynamic modelling studies, in order to address reservoir uncertainties and forecast production response. Results from the proposed polymer pilot flood will allow assessment of further chemical EOR applications and potential field-wide scale up. We propose a mechanism, termed in-depth flow diversion (IFD), which may operate in low permeability, fractured injector water flood. This would allow polymer EOR to operate in lower permeability water flood than currently envisaged. Introduction Australia's Barrow Island Windalia water flood has been on production for 40 years, producing more than 288 million barrels. Windalia is both geologically complex [Hatcher; Williams] and difficult to characterise due to the absence of good seismic reflectors and poor log response. In addition, the Windalia water flood is located in a Class A nature reserve, and hence subject to environmental concerns and responsibilities. Despite these complexities, it is believed there is in excess of 100 million barrels of oil that may be potentially produced through the application of EOR technology.

Assessing Productivity Impairment of Surfactant-Polymer EOR Using Laboratory and Field Data

“…Despite the volatility of oil prices, it is fair to conclude that operators are showing a growing interest on chemical EOR flooding. This trend is also supported by the increase of screening studies to evaluate or re-estimate the EOR potential of chemical flooding in different basins (Alvarado et al 2008;Costa et al 2008;Fletcher and Morrison, 2008;.…”

Historical and recent observations in polymer floods: An update review

“…For example, the laboratory evaluation of Windalia polymer flood reported the emulsion formation tendencies between the reservoir oil and different injection brines. Fletcher and Morrison (2008) reported in their study that higher salinity (TDS = 38,000 ppm) brine showed less emulsification tendencies than lower salinity (TDS = 29,000 ppm) injection brine. However, it is not clear if high polymer retention (≥130 mg/g of rock) and RRF (8 to 45) values reported in this study are due to low permeability (1.0 -13.8 mD) of the reservoir core plugs used and/or the emulsification of oil-waterpolymer in-situ during the corefloods.…”

“…Windalia field (Fletcher and Morrison, 2008;Haynes, Clough, Fletcher &Weston, 2013) is a high clay content sandstone and low permeability light oil (36°API) reservoir (65°C) in Australia. Windalia reservoir has an OOIP of 819 MMbbls and it is under line-drive water injection since 1967 reporting a recovery factor of 37%.…”

Enhanced Oil Recovery: An Update Review

“…Therefore and despite the volatility of oil prices, it is fair to conclude that operators and surfactant manufacturers are showing a growing interest in EOR chemical flooding [132,133]. This trend is also noticed with an increase of screening and lab studies to evaluate or re-estimate EOR potential of chemical flooding in different basins [134][135][136][137][138][139][140][141].…”