Post Core Analysis to Determine the Steam Flow Path In the McMurray Oil Sands
Authors: Leshchyshyn T. , Kennedy W. 
Published: March 2010

Core analysis was performed on core material extracted from three post-recovery core holes drilled at distances varying from 12 to 20 m from a wellbore that had experienced eight cycles of steam injection/production (I/P). The objective was to evaluate the success of cyclically steaming the McMurray oil sand by ascertaining steam placement and the effect of steam on the reservoir mineralogy. Post core-hole analysis was compared to the original core of the centrally located I/P well using standard techniques plus a number of special core analyses. X-radiography, connate water analysis, tracer analysis, absolute and effective permeability measurements, petrographic analysis, in addition to selected open-hole and cased-hole logs were included in these special studies. Results showed that reduction in oil saturation over the oil sand interval was attributed to steaming and/or a combination of condensed steam invasion and drilling mud invasion. The actual steam-invaded zone was shown to be a lesser portion of the total oil sand pay which could be correlated with the special core analyses and with temperature logs. This paper describes the procedures used to assist in determining steam zones and includes an interpretation of the data as well as a critique of the analyses.

Introduction

In-situ bitumen recovery from the Athabasca oil sands, the largest oil sand reserves in the world, has not yet been commercialized. Successful steam recovery processes such as cyclic steam at Cold Lake(1) or steam drive at Peace River(2), have had limited success when applied in the McMurray oil sands formation at PCEJ(3,4) and GLISP(5). A number of factors have been recognized which make in-situ recovery from this resource more difficult:Lower reservoir temperature and pressure, higher bitumen viscosity, and sand migration prevent primary production. Typical reservoir properties in the PCEJ Hangingstone lease are presented in Table 1.Shallow depth of burial and low initial breakdown pressures(6) combined with very high bitumen saturation, limits leak-off of the injected steam and encourages fracturing. Less placement of heat near the wellbore results in lower calendar day oil rates (CDOR).A combination of vertical and horizontal fractures(3,7,8) ("T" Fractures) tend to make bitumen recovery schemes more complicated and less productive. A ("T" fracture is shown in Figure 1 as an initial vertical fracture climbing at 45 degrees from the perforations up into the shaley oil sand above, where it turns horizontal and can even travel back to the well, but at a shallower depth. Horizontal fractures in the upper shaley oil sand do not characteristically produce much bitumen even though it may hold up to 40% of the total injected steam.

TABLE 1: Typical properties of McMurray oil sand (Hangingstone). (Available in full paper)

Steam injection fractures were utilized to heat the formation at the PCEJ Hangstone Pilot Project located 45 km south-west of Fort McMurray. Different steam placement strategies were rested in individual cycles and in various isolated wells in an attempt to keep the heat within the rich oil sand. This was done by controlling injection rates, quality and volume injected.