Geothermal Reservoir Characterization of the South Swan Hills Oil Pool, Swan Hills, Alberta
Creators: Noyahr, Christopher V.
Publisher: name: University of Alberta Library
Year: 2022

<p>Research in the South Swan Hills oil pool was performed to accurately delineate the geometry of the subsurface reservoir and subsequently quantify the amount of thermal energy that can be extracted for geothermal use from the reservoir water volume. </p>

<pre><code>South Swan Hills is an active oilfield developed in a reef atoll known as the Swan Hills Formation, in Swan Hills, central Alberta, Canada. The Swan Hills oil pool is an attractive geothermal prospect because it currently produces 700 to 1100 m3 of  &gt;100 °C water daily from a high porosity and permeability reservoir. That hot water is currently is re-injected but could be available for electrical power production and other direct uses.

The reservoir model is based on lithofacies analysis from high-resolution core descriptions that recorded lithologies, bioclast type and characteristics, and sedimentary structures. Core descriptions were correlated to well logs, enabling 9 distinct lithofacies to be mapped across the field. Lithofacies distributions permit identification of three distinct reef geometries; a reef interior, a reef margin and a terminal shoal, capping deposition. The vertical variability is described using sequence stratigraphic interpretations. Six sequence stratigraphic surfaces were identified and correlated across the reef.  These surfaces affected reef growth and areal extent, captured in the model. 
</code></pre>

<p>The geological analysis was transformed into a 3-D geocellular model using a sequential indicator simulator that describes lithofacies and, in turn, porosity and permeability distributions based on strong relationships between lithofacies and petrophysical properties. The reef is divided into three representative regions; the interior, margin and terminal shoal. The interior deposits formed the bulk of non-reservoir material in the centre of the reef build-up.  The margin surrounded the interior and formed a continuous 1 – 2 km band of reservoir material around it. The reservoir thickness is 20 – 30 m and primarily composed of reef flat material. The terminal shoal is disconnected from the bulk of reef deposits by a thick layer of impermeable clay. The shoal is a reservoir body that spans the reef area at the capping the reef complex. The reservoir has an average reservoir thickness of 10 – 15 m and is composed of a heterogeneous mix reservoir and non-reservoir material. The P10 to P90 range of porosity of the reservoir units is from 3.2 and 14.5 %  and the range of permeability is between 0.21 and 73 mD. The distribution of reservoir facies is more uniform in the margin compared to the shoal. </p>

<pre><code>Estimates of potential power production from the South Swan Hills reef are achieved by applying flow simulations to the heterogeneously populated geocellular model. The simulations tested the production capabilities of isolated shoal and margin reservoirs from well doublets inserted into the model grids. The variables tested included varying flow rate and varying well spacing. The model also captured the range of power production by considering reservoir quality at different percentile (P10, P50 and P90) porosity and permeability values.  The optimal spacing that balanced well spacing and flow rates was determined to be between 400 – 500 m in both shoal and margin grids. The range of power production estimates for a single doublet in the shoal ranged from 32.8 – 2726.31 kW. The range of power production estimates in the margin for a single doublet ranged from 64.61 kw – 3197 kW. Historical production data reports indicate that the thermal potential of a doublet likely exists between P50 and P10 values for both shoal and margin grids between 546.08 kW – 2726 kW in the shoal and 1005.77 – 3197.63 kW in the margin.
</code></pre>