Production Optimization at Connacher
- Merle Duane Johnson (Connacher Oil & Gas Ltd.) | Lyle Hansen (Connacher Oil & Gas Ltd.) | Tim Lau (Connacher Oil & Gas Ltd.) | Trevor Phenix (Connacher Oil & Gas Ltd.) | Steve Breen (Connacher Oil & Gas Ltd.)
- Document ID
- Society of Petroleum Engineers
- SPE Enhanced Oil Recovery Conference, 19-21 July, Kuala Lumpur, Malaysia
- Publication Date
- Document Type
- Conference Paper
- 2011. Society of Petroleum Engineers
- 4.6 Natural Gas, 2.4.3 Sand/Solids Control, 1.6 Drilling Operations, 5.2.1 Phase Behavior and PVT Measurements, 5.8.5 Oil Sand, Oil Shale, Bitumen, 5.6.1 Open hole/cased hole log analysis, 5.3.9 Steam Assisted Gravity Drainage
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Connacher's first oil sands project, the Pod One facility at Great Divide, has been operational since 2007. The successful SAGD project has produced approximately 7 million barrels of bitumen. During the past three and a half years, the impacts of certain predicted reservoir challenges and opportunities have become apparent.
While the quality of the oil sands in this first phase of Pod One is generally good, Pad 101 South in particular has geological zones that affect SAGD operation. This includes a bitumen lean zone, and a gas cap overlying the main bitumen channel/s. Early field results matched with detailed simulations have shown positive results in maximizing well pair production. For the purposes of this paper a lean bitumen zone differs from an aquifer in two ways. The lean zone is not charged, and is limited in size. The operation is also complicated by the fact the gas bearing zone has been depleted through earlier production.
Connacher's operating practice at Great Divide attempts to achieve a pressure balance between the 3 zones (rich oil sands, lean zone, gas cap) to reduce steam loss and maximize production rates. Reducing the pressure encourages steam chamber development growth horizontally and ensures that steam contacts the highly saturated bitumen areas. How this is achieved with the highest positive impact on well productivity is illustrated with operational data and analysis including the results of simulations that recommended the optimum operating strategies.
Pod One's operational performance to date has been impacted by the overlying depleted McMurray gas cap. Steam chamber communication with the lower pressure zone has occurred on several of the Pad 101 South wells after steam rose to the top of the bitumen portion of the reservoir. This subsequent loss of steam to the gas cap initially reduced well productivity. Currently, Connacher is managing the reservoir challenge by installing down-hole pumps to drop the steam chamber pressures to a value closer to the pressure of the gas cap. This successfully recaptures most of the individual well productivity. Analysis has also shown that re-pressuring the associated McMurray gas cap will reduce steam losses, as well as improve future development potential on known reserves in the southern area of Pod One.
The McMurray formation in the area of Connacher's Great Divide commercial SAGD project consists of fine to medium sands with generally increasing muddy interbeds that are highly bioturbated toward the top of the reservoir. The basal sediments of the McMurray Formation were deposited in an incised valley and consist of fluvial sediments deposited in high-energy, sand-dominated environments. The upper parts were generated in estuarine to marginal marine environments, resulting in a fining upward sequence of sands and muds. The sequences often include massive cross bedded sands overlain by interbedded sands and shales capped by laminated mudstones. These tight mudstones are considered a barrier to fluid flow and act as a caprock.
The lean zone, is seen in the upper parts of the Great Divide reservoir and interpreted by Connacher to be part of a depleted gas zone. It is a zone of relatively low oil saturation (2-5% bitumen) by weight, with a wireline induction response of ~10-20 ohm*m, whereas, a typical McMurray water wet zone in this area has a wireline induction response of ~6-10 ohm*m (Figure 1). In some instances, the wireline logs will still show crossover in the depleted zone due to some residual gas.
The gas directly above the bitumen resource is termed an associated gas cap. Where present, in Pod One, the associated gas cap is between 1 and 8 m thick. The associated McMurray S Pool was discovered in 1987 by Canadian Worldwide Energy Limited with the 5-16-82-12W4M well. This first well, 5-16, drilled into the reservoir only showed gas above bitumen, while subsequent wells drilled in the area show the development of the lean zone as mapped in Figure 2 and shown in cross-section in Figure 3. As expected, the gas/lean zone contact is also variable throughout the reservoir as gas from various wells was produced at different times.
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