Steam Conformance Along Horizontal Wells at Cold Lake

Abstract

Abstract This paper describes Imperial Oil's success in identifying and remediating poor steam conformance in a horizontal well used in Cyclic Steam Stimulation operations. Imperial Oil is conducting Horizontal Well Cyclic Steam Stimulation (HWCSS) at nine horizontal wells located at two pads in Cold Lake. Steam conformance along horizontal wells is a significant issue in these types of thermal applications. The horizontal wells are completed with Limited Entry Perforations (LEP) to improve distribution of steam along the liner. One of the HWCSS pads, D36, has been the subject of both 4D seismic and injectivity analyses to characterize steam conformance along the horizontal section over the fi rst three cycles. These analysis techniques showed that four out of the five wells on the pad had excellent steam distribution along the horizontal liners. However, one of the wells, D36-H1, showed little or no steam conformance along the last half of the liner. This lack of horizontal steam conformance put the recovery expectations of this well at risk. A workover conducted on D36-H1 successfully removed sand that had been obstructing the liner. Steam injection subsequent to the clean-out showed steam distributed across the majority of the liner (most of the LEPs accepting steam). Introduction Imperial Oil has been conducting commercial operations at Cold Lake using Cyclic Steam Stimulation (CSS) since the mid- 1980s. CSS involves injecting steam at fracture pressure (>10 MPa) and producing a mixture of water, bitumen, and gas from the same wells. Approximately 3,000 wells are in operation at Cold Lake, the vast majority of which are deviated vertical wells. These wells are drilled from common surface pads, typically in groups of 20. As an enhancement to the CSS process, Imperial has been piloting Horizontal Well CSS (HWCSS) at nine 500 m long wells located at two pads. One of the main challenges of the HWCSS process is the control of steam conformance in the reservoir. To aximize recovery, it is necessary to contact as much of the reservoir as possible with steam. This becomes more difficult with advancing cycles because steam preferentially accesses channels that have already been heated and depleted of oil. Horizontal wells with conventional perforations or slotted liners could be further compromised by preferential steam injection into the heel of the well. To overcome this problem, Imperial Oil uses its patented Limited Entry Perforation (LEP) design to control the distribution of steam along the horizontal well liners(1). A schematic of the well completion and LEP design is shown in Figure 1. A previous publication has described the use of 4D seismicnd injectivity analyses to evaluate the effectiveness of LEPs at a 1,000 m infill horizontal well injector(2). This paper follows a similar analysis technique for D36 pad, one of the HWCSS pads at Cold Lake. Excellent steam conformance over the first four cycles is inferred from this analysis at four of the five wells on the pad. However, the analysis identified a steam conformance problem atne of the wells designated as D36-H1.