Medium-scale tidally influenced meandering fluvial deposits of the middle McMurray Formation, Hangingstone SAGD project, Alberta, Canada

Abstract

The middle McMurray Formation is the most important reservoir of the Athabasca oil sands. In recent years many studies using 3D seismic data have revealed that the middle McMurray Formation consist of large point bar deposits formed by tidally influenced meandering fluvial systems. Most of these studies were carried out on deposits near the axis of the McMurray valley system where the McMurray Formation thickly deposited. In this study, a geological model was constructed in Hangingstone SAGD project area located in tributaries about 30km upriver from the main valley system. Scroll patterns which are characteristic of meandering channels are clearly observed in seismic slices in part of this area, but not clear in some part of this area where regional sequences (correspond to A1 to B2 sequences reported by EUB) spread in the upper McMurray Formation. The purpose of this study is to identify sediment bodies which consist of the McMurray Formation in this area without scroll patterns and to describe the geometry and sedimentological feature of the main reservoir deposits using lithological data, gamma ray log, dip log, borehole image of each wells and 3D seismic volume. The McMurray Formation in this study area was divided into 10 sedimentary units including point bar deposits and abandoned channel of tidal-fluvial channel system, lower unit which had not suffered channel incision, regional sequences and muddy channels incised lower sediment from each sequence base. In the south part of the point bar deposits, small erosional surfaces dipping gently to the southwest and large cross bedding dipping steeply to the northwest, indicating its flow direction, are observed in borehole images. In the northwest part of the point bar deposits low angle unidirectional dips to the southwest were predominant. The direction of the low angle dips is accord with the inclination direction of point bar surfaces observed in seismic sections. Based on these results, it is concluded that 1) The main reservoir in this study area consist of point bar deposits migrated to the southwest, with thickness of 20-30m surrounded by abandoned channel and muddy channels 2) Energy of the channel flow at bends was relatively strong in the south part, whereas flow energy was weak in the northwest part of the area. This is consistent with low gamma ray values of sand, around 30, in the south part, whereas high gamma ray values, 30-60, in the northwest part.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016