Abstract

A high resolution 3-D seismic survey was conducted at an Athabasca Tar Sands Thermal Pilot for the ultimate purpose of locating and monitoring the progress of in-situ heat fronts.

In order to obtain the required seismic expression, it is imperative that the field data have exceptionally good signal-to-noise and frequency content. This paper addresses some of the specialized acquisition, processing, and display techniques which could give the necessary resolution.

The geology of the pilot site is characterized by a 50 m thick section of McMurray tar sands, resting on a Devonian unconformity surface, 240 m deep. Imaging of this erosional surface, critical to the pilot, is demonstrated by various interactive displays. The definition of a narrow channel has shown that exceptional spatial and temporal resolution can be achieved. This will be necessary for the future seismic mapping of the in-situ heat Fronts, as well as potentially making reservoir parameter descriptions possible on a scale never before thought achievable.

Introduction

A high resolution 3-D seismic base survey was conducted at Amoco's (AOSTRA and Petro-Canada) Gregoire Lake In-situ Steam Pilot (GLISP) located in northeastern Alberta, Canada, approximately 40 km south of Fort McMurray, The prime purpose for acquiring the base survey was to use this information as a basis of comparison with future monitor surveys of a similar type.

In order to achieve the required seismic expression for mapping the heated zones, it is imperative that the field data have an extremely good signal-to-noise ratio over a broad frequency band.

This paper addresses the specialized acquisition, processing and display techniques which were used to gather and manipulate the 3-D data. Imaging of the Devonian unconformity surface, at a depth of 240 m, demonstrates that exceptional spatial and temporal resolution, so necessary for accurately mapping heat fronts, has been achieved.

The well configuration for the pilot site was to consist of a central injector surrounded by three equidistant producers and three infill observation wells. Only two, the H-3 injector the HO-7 observation hole, had been completed at the time of writing.

The geology of the GLISP site, shown in Figure 1, is characterized by a 50 m thick section of discontinuous McMurray (Cretaceous) tar sands resting on a Devonian unconformity. approximately 240 m below the surface. The first well drilled was the H-3 injector which encountered a 4 metre sand aquifer directly above the erosional surface. It was assumed that this basal wet zone would influence the performance of the steam based recovery process. Later drilling of HO-7 indicated this aquifer was absent, leading to a potential problem with the proposed heating method. An additional objective for the 3-D seismic then became the accurate imaging of the Devonian unconformity surface in the hope of defining tile distribution of this sand.

FIELD TESTING

A comprehensive set of field tests was conducted to establish the field acquisition parameters Which would produce data having exceptionally high signal-to-noise ratio and broad band frequency content.

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