| Title | Geothermal Reservoir Characterization in Carbonate-Hosted Oil and Gas Fields from the Western Canada Sedimentary Basin |
|---|---|
| Authors | Nicholas B HARRIS, Christopher NOYAHR, Evan RENAUD, Jonathan C. BANKS, John A. WEISSENBERGER |
| Year | 2020 |
| Conference | World Geothermal Congress |
| Keywords | carbonates, hydrocarbon reservoirs, Western Canada Sedimentary Basin |
| Abstract | We investigate the potential for geothermal energy production and characterize geothermal reservoirs from two active oil and gas fields in the Western Canada Sedimentary Basin, Alberta and British Columbia. These fields have had a long history of hydrocarbon production and are now evaluated for electric power production from hot water, in one case for public power consumption and the second for power to drive downhole pumps. Formation water temperatures locally in excess of 100°C suggest that electric power can be economically generated. Characterization of the subsurface reservoir is a critical step in geothermal development of the field. We present static and dynamic reservoir models that describe the distribution of reservoir properties and the flow of hot water from the reservoir with various production and injection well scenarios. The Clarke Lake field in northeastern British Columbia occurs in carbonate sediments of the Middle Devonian Slave Point Formation, which were deposited within a rimmed carbonate platform environment flanking the Horn River Basin. The development of porous and permeable reservoir resulted from hydrothermal alteration of parent limestone to dolomite. High quality reservoir zones exist at the reef margin due to hydrothermal alteration preferentially occurring in more porous and permeable sediments that are stratigraphically trapped by shales of the Horn River and Muskwa formations. High quality reservoir zones also extend some distance into the back-reef within porous and permeable carrier beds of back-reef facies, which display average porosity and permeability of 6.4 % and 124 md, respectively. The field displays anomalously high reservoir temperatures and strong water drive. Clarke Lake field has shown water production rates upward of 2800 m3/day between in two wells, with an average reservoir temperature taken from DST measurements is of 98.2°C. Simple flow simulations show that to the reservoir at Clarke Lake field is capable of sustaining 25 years of hot water production. Estimates of geothermal power potential are 300 kW using a doublet well model and 2400 kW using a four injector and eight producer well model. The South Swan Hills oil field in central Alberta is developed in the Upper Devonian Swan Hills Formation, which is composed of two units, a regionally extensive carbonate platform and an overlying unit that comprises a series of atoll reef complexes. Several controls affect the porosity and permeability of the reef: the lateral and vertical distribution of lithofacies, sedimentation stacking patterns and diagenetic cement cycles. We use core data to identify key lithofacies and assemble them into a depositional model that distinguishes zones of high porosity and permeability, specifically reef flat and reef margin deposits. We apply a sequence stratigraphic analysis to a “rim-bounded reef†depositional model and recognize three sequences distinguished by exposure surfaces. At paleo-water tables, porosity is enhanced by heavy strong dissolution. Porous and permeable zones are also developed in reef margin facies that stack vertically as the reef aggraded. Active wells in the field produce annually over 200,000 m3 of hot ≥100° Celsius water. This heat energy of the water has potential for conversion to electrical power. A 3D geo-cellular model is created in order to simulate the flow of water through the effective aquifer and eventually model the complicated rock-water chemical interactions of cool-water brine injection. |