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Abstract The Court Bakken heavy oil reservoir (17 °API) in Saskatchewan has been under successful water flooding for many years. Laboratory studies have indicated that caustic flooding can enhance heavy oil recovery significantly after water flooding. This paper describes design and implementation of the first caustic flooding pilot in a heavy oil reservoir of this viscosity range in the Western Canadian basin. It reviews results of laboratory studies and a single well test. It also discusses challenges experienced at Court during the early piloting phase. Introduction The Court Bakken heavy oil reservoir is located in west central Saskatchewan, approximately 100 km from the Alberta border, as shown in Figure 1. The pool was discovered in 1982 and primary development started in the same year. The 17° API heavy oil is produced from the Middle Bakken formation at an average depth of 870 m. Water flooding was implemented in 1988 with 40-acre well spacing in irregular patterns. There are currently 20 injectors and 28 active oil producers in the Court main unit, which is jointly owned by Nexen and Pengrowth. The Court pool has an estimated 16.5x106 m3 (103.8 mmbbl) of original oil in place (OOIP). It has achieved 24% oil recovery of OOIP after 20-year water flooding. The ultimate water flooding recovery is predicated to be 30%. The production in 2007 averaged 240 m3/d with 95% water cut. The water flooding at Court is deemed to be very successful given the oil viscosity and adverse mobility ratio. Since there was a significant amount of remaining oil in place even after water flooding, a high-level EOR screening study was conducted to evaluate several EOR technologies that would be feasible to enhance oil recovery after water flooding. Caustic flooding was chosen over other EOR schemes due to its promising laboratory results, relative simplicity and low upfront implementation costs. This paper presents the design and implementation of the first caustic flooding pilot in a heavy oil reservoir of this viscosity range in the Western Canadian basin. Reservoir Description The lower Mississippian Bakken formation in the Court area was deposited in a marine shelf environment and later reworked into a series of tidal ridges. This area has a relatively gentle SW regional dip structure, which has been modified by differential Prairie Evaporite salt solutioning and local Torquay collapse features. Pre-Cretaceous erosion has cut down to or through the Bakken and oil is trapped stratigraphically in the preserved Court Bakken sand trend. The Middle Bakken sand is typically fine to very fine grained and composed almost entirely of quartz with very minor amounts of feldspar and clay. The reservoir sand is commonly unconsolidated and may be interrupted by some minor and discontinuous shale interbeds. The intergranular porosity of the Court pool averages around 29% while the permeability averages 2.1 Darcies. The initial water saturation is about 23% and the thickness of sand ranges from 2 to 18 meters. The net pay thickness averages 7.6 meters. The existence of bottom water is rare. Table 1 summarizes some basic reservoir data.
- North America > United States > North Dakota (1.00)
- North America > Canada > Saskatchewan (1.00)
- North America > Canada > Manitoba (1.00)
Abstract A number of vertically-oriented heavy oil depletion experiments have been conducted in recent years in an attempt to investigate the impact of gravitational forces on gas evolution during solution gas drive. Although some experimental result indirectly suggest the occurrence of gas migration during these tests (especially at slow depletion rates), a major limitation of such an interpretation is the difficulty in visualising the process in reservoir rock samples. In contrast, experimental observations using transparent glass models have proved invaluable in this context and provide a sound physical basis for modelling gravitational gas migration in gas-oil systems. The experimental observations often exhibit somewhat contradictory trends however - some studies showing dispersed gas migration, whilst others describe fingered, channelised flow - and, to date, there appears to have been little systematic effort towards modelling the wide range of behaviours seen in or inferred from laboratory tests. To this end, we present a new pore network simulator that is capable of modelling the time-dependent migration of growing gas structures. Multiple pore filling events are modelled dynamically with interface tracking allowing the full range of migratory behaviours to be reproduced, including braided migration and discontinuous dispersed flow. Simulation results are compared with experiments and are found to be in excellent agreement. Moreover, simulation results clearly show that a number of network and fluid parameters interact in a rather complex manner and as a consequence, the competition between capillarity and buoyancy produce different gas evolution patterns during pressure depletion. The implications of evolution regime on recovery from heavy oil systems undergoing depressurisation are extensively discussed. Introduction Improved recovery by depressurisation, primarily involving solution-gas drive and fluids of considerable density difference (gas/oil, gas/water), has previously been implemented at the field scale, and proved successful as evidenced by the increased hydrocarbon ultimate recovery, Gallagher et al., (1999). In addition to oil recovery by depressurisation, such buoyancy-driven, immiscible gas migration in porous media is central to a number of other processes, including gas injection to stimulate the biodegradation of volatile organic contaminants in saturated aquifers (gas sparging) and the study of CO2 migration for designing effective sequestration strategies. In the context of hydrocarbon reservoir engineering, a number of depletion experiments have been carried out in the last decade using vertically orientated core samples in order to investigate the impact of gravitational forces on gas evolution during solution gas drive - both for light oil (Piccavet et al., 2006; Drummond et al., 2001; Naylor et al., 2000) and heavy oil (Tang et al., 2006; Bayon et al., 2002; Tang et al., 1999) systems. Although some experimental core results suggest the occurrence of buoyancy-driven gas migration (Piccavet et al., 2006), such behaviour can only be inferred - by means of heterogeneity in measured gas saturation profiles - and not observed explicitly. Experimental observations in transparent glass models and in bead/sand packs, however, have demonstrated observable migratory behaviour (Geistlinger et al., 2006; McDougall and Mackay, 1998; Birovljev et al., 1995; Frette et al., 1992; Dumoré, 1970) and such observations can be used as a sound basis for model development. Generally, the temporal evolution of gas clusters during pressure depletion is a consequence of the interplay between gravity, viscous and capillary forces, which govern the displacement sequences and affect the overall gas topology.
- North America > United States (0.93)
- Europe > United Kingdom > North Sea > Central North Sea (0.28)
- Research Report > New Finding (0.34)
- Research Report > Experimental Study (0.34)
- Geology > Petroleum Play Type > Unconventional Play > Heavy Oil Play (1.00)
- Geology > Geological Subdiscipline (0.88)
- Information Technology > Modeling & Simulation (0.54)
- Information Technology > Communications > Networks (0.47)