Successful Conversion of the Pikes Peak Viscous-Oil Cyclic Steam Project to Steamdrive
Authors: Miller K.A. , Stevens L.G. , Watts B.J. 
Published: December 2007

This paper describes conversion from steam stimulation to steamdrive in ahigh-viscosity oil reservoir. Field testing of operating strategies helped todevelop conversion and operating criteria. The successful steamdriveperformance was attributed to reservoir preheating and injector/producerinterwell communication that were established during cyclic operations. Steamdrag and gravity drainage are the main recovery mechanisms.

Introduction

The Waseca formation in the Lloydminster heavy-oil deposits of Alberta and Saskatchewan contains a viscous crude oil that was produced unsuccessfullyunder primary produced unsuccessfully under primary recovery. Steam stimulationwas initiated in 1981. Good response led to expansion of the pilot to itspresent 106 thermal wells, drilled pilot to its present 106 thermal wells, drilled in a general 3-ha inverted seven-spot configuration (Fig. 1). Pikes Peak wells exhibit very good cyclic performance until 20% to 30% of theperformance until 20% to 30% of the original oil in place (OOIP) has beenrecovered. On the basis of excellent reservoir properties and frequentobservation of properties and frequent observation of apparent heat and masstransfer between wells, evaluation of follow-up drive processes was initiatedin 1983. The major technical hurdle was the viability of a steamdrive processwith a high-viscosity (25 000-mPas) process with a high-viscosity (25 000-mPas)virgin oil. In 1984 a steamdrive test was initiated in a pattern where thefuture injector had communicated to five of six producers (Fig. 2). Thispattern has been used to identify the dominant production mechanisms and todevelop improved operating strategies. Following the early success of the firststeamdrive pattern, conversion criteria and operating strategies were refinedand additional patterns converted to drive. Despite the high initial oilviscosity, steamdrive has proved to be a technical and economic success, provedto be a technical and economic success, with pattern steam/oil ratios (SOR's)of 2.9 to 8.3.

Geology and Reservoir Description

The Lloydminster heavy-oil deposits (Fig. 3) form the southern end of thediscontinuous trend of Lower Cretaceous Mannville Group bitumen and heavy-oildeposits that also are present in the Athabasca and Cold Lake areas. Most Lloydminster deposits are able to produce 3 % to 8 % of the OOIP under primaryconditions, although sustained p production could not be achieved p productioncould not be achieved at Pikes Peak in 1981 because of sanding problems. Thereservoir contains viscous problems. The reservoir contains viscous crude oilwith a gravity of 0.99 g/cm3 and a gas-free viscosity of 25 000 mPas atreservoir temperature (18 degrees C). Most development in the Lloydminster areahas been in the Sparky formation, but other Mannville formations, including thesheet-like regional Waseca formation sandstone reservoirs in the easternportion, have also been exploited. Occasionally, as at Pikes Peak, areallyrestricted, clean, thick Pikes Peak, areally restricted, clean, thick channelfacies occur. Van Hulten concluded that deposition of the Pikes Peak channelfacies was contemporaneous with that of the regional Waseca sands, andchannel-sand thickness variations were the result of migrating point bars. Alocal structural high allows the project area to be free of bottomwater (Fig.1). The Waseca formation at Pikes Peak has been divided into a well-sorted, unconsolidated, predominantly quartz, highly permeable (5 to 10 darcies), homogeneous lower permeable (5 to 10 darcies), homogeneous lower unit and asand/shale interbedded upper unit (Table 1). Fig. 4 is a type log for the Waseca interval. The quality of the upper unit decreases upward as a result ofdecreasing grain size and increasing clay content, but the higher-quality"A" interbeds often are in communication with the homogeneous sand unitand contribute to pilot oil production. production. Initial Pattern Conversion(1A11–1)

Selection Criteria and Conversion.

Planning for conversion of mature areasto Planning for conversion of mature areas to steamdrive began in 1983. It wasfelt that, at the end of economic cyclic operations, a large undrained area ofhigh residual oil saturation would remain. The results of van Lookeren and Taber and Martins indicated that steam override would likely occur at pikespeak and that preheating would be required to reduce oil viscosity and tolessen the effects of steam channeling. Five developed patterns were examinedon the basis of well maturity (number of complete steam cycles, recovery) andoccurrence of interwell communication from the proposed injector to patternproducers. proposed injector to pattern producers. JPT

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