In October 1986, steam injection was initiated into an inverted four-spot pilot at Gregoire Lake n northern Alberta. The target is a thick Athabascaa tar sands in the McMurray formation at a depth of 200 m. In the pilot area, the upper third of this formation contains low tar saturation zones that have mobile water present. All production wells were fractured and steam stimulated prior to the start of the steam drive portion of the project. Efforts were made to obtain heat communication between the injector and the producer wells low in the rich tar body. However, upon injection of steam into the central injector, a temperature response was observed in the upper part of the mcMurray formation, indicating that heat injected low in the formation preferentially flows through the water zones toward the producing wells. The steam then travels downward to the completion intervals of the production wells through the communication channels established during the production well stimulations.
Significant oil production was obtained from each well and a simulation of the process was undertaken for the purpose of understanding the reservoir production mechanisms end projecting the pilot performance into the future. History matches of the pilot revealed that elements of both steam "drive" and steam "drag" were important in the reservoir production performance. Initially, the dominant production mechanism was found to be steam "drive". After the upper zones were depleted of the hest mobilized oil, the predominant mode of oil production came from the steam "drag" effect working on the rich body of bitumen lower in the McMurray formation. Upon completion of the history match, a production forecast was made.
Amoco Canada has actively pursued production of bitumen from the Athabasca tar sands since 1955. In the period from 1955 until 1976, Amoco Canada conducted a total of seven pilot projects in the area most of them being fireflood pilots of various types. The last one, the Block I Pilot, was operated near Gregoire Lake from 1976 until 1981. 1. This pilot was the last fireflood pilot attempted at Athabasca and utilized the COFCAW Combination of Forward Combustion and Water) process. Thus, Amoco's involvement in the Athabasca tar sands has spanned some 35 years. It is significant that, in this time period, no commercial plant utilizing an in-situ process has operated in the McMurray tar sands, This steamflood pilot is Amoco's latest attempt to develop a process that will make such a plant economically possible.
The main causes inhibiting tar production from the McMurray formation are lack of both tar mobility and injectivity into the formation. This pilot was an attempt to overcome such problems through he use of fracturing in conjunction with steamflooding. The main object of the pilot was to evaluate the technical feasibility of the process. To do this properly, a good understanding of the associated production mechanisms in the reservoir is necessary. To obtain this understanding, a numerical simulator6 was used to test two models (differing only in vertical grid spacing) of the reservoir by history matching production data and observation well data.
