Evaluatioll1l of CycHc Steam Perfornnance And Mechalllislms In a Mobile Heavy On Reservoir At Elk Point Thermal Pilot
Authors: Karyampudi R.S. 
Published: March 2010

This paper describes an evaluation of the Elk Point cyclic steam (CS) process performance and dominant reservoir mecha nisms in the unconsolidated Cummings formation containing mobile heavy oil. A simple but effective fracture detection and prevention technique was developed during the early field tests. Based on the multi-cycle performance analysis, a model of the major reservoir mechanisms. is proposed. Key reservoir mechanisms indicated by this evaluation included a shift in near-wellbore rock wettability to oil-wet behaviour m high temperatures following steam injection, phenomenon of "foamy oil behaviour" as well as geomechanical effects and sand production.

Laboratory tests were conducted to verify a key hypothesis: the formation around the wellbore becomes oil-wet following the injection of high temperature steam-condensate (hot-water) which results in a reduction of effective permeability to oil. The experiments included water-oil relative permeability measurements at steam injection and production phase conditions as well as determination of temperature effects on contact angles of the Cummings crude-oil/brine/rock system. In view of the field and laboratory test results, it was concluded that high temperature steam injection into the Cummings formation renders the sand irreversibly oil-wet and adversely affects oil rates. One other important mechanism identified is the impact of the steam injection on the heavy oil primary production-enhancing mechanism. foamy oil behaviour. A modified set of screening guideline') are proposed for CS process in mobile heavy oil reservoirs.

Introduction

PanCanadian's cyclic steam pilot in the Elk Point Heavy Oil Project is located in Section 03. Township 56 of Range 06 WEST OF 4TH Meridian, approximately 80 km northwest of Lloydminster in east central Alberta (Figure 1). The first well in thus section, 11A-03-56-06 W-M, was drilled and completed in the Cummings formation in 1981. Subsequently, 15 verticle wells were drilled on 16 ha spacing and put on production by early 1984. A total of 36 direction infill wells on 4 ha spacing were drilled in the SW. NW and NE quarters in 1985, 1988, and 1991 respectively (Figure 2). Some of these wells have very good cold or primary production capacities of up tp 12 m3/d; the typical range is 4-8 m3/d although rates can be as low as 2 m3 (see Table 2 and Figure 20). The current primary production rate from this section is about 85m3/d. The original oil in place (OOIP) in this section is approximately 7.6 X 103 m3 and the ultimate primary recoverable reserves are expected to be about 15% of (OOIP). These cold or primary production rates and recoveries are much higher than the range of predictions by conventional theory, due to reasons which are not completely understood to date. Dusseand1 cites the following four factors as the likely major causes. Enhanced drainage radius, gas bubble expansion for "foamy oil behaviour", grain movement, and continuous pore deblocking.

During 1983–84, a cyclic steam pilot was initiated in Section 03-56-06 W4M and was operated until 1990.