Report DescriptionHorizontal wells and multiple hydraulic fracture stimulation technology have unlocked immense gas resources in the Montney tight gas / shale gas play fairway of northeastern British Columbia. These operations require large quantities of water -- up to several thousand cubic metres per wellbore. In addition, safe disposal must be ensured for substantial volumes of contaminated produced and flow-back water.
Deep subsurface aquifers carrying saline waters are ideal sources and sinks for the water volumes required. Following upon successful completion of the Horn River Basin Deep Subsurface Aquifer Characterization Project, Geoscience BC commissioned Petrel Robertson Consulting Ltd. and Canadian Discovery Ltd. to undertake a similar study of deep saline aquifers in the Montney play fairway, as a component of the regional Montney Water Project.
The fairway was divided into Plains and Foothills study areas, based primarily on subsurface stratigraphic and structural aspects. In the Plains, potential aquifers ranging from Middle Triassic Halfway to Upper Cretaceous Cardium were assessed. The best aquifer characteristics -- thick net porous sandstones, high storativity, good to excellent potential deliverability, moderate to low salinities, and little or no H2S -- were found in the Cadomin and Nikanassin aquifers. The Baldonnel, Bluesky, and Peace River formations offer more modest aquifer characteristics, but may still have local importance.
In the Foothills, potential aquifers range from the Mississippian Debolt to the Lower Cretaceous Bluesky; younger Cretaceous strata have shaled out in this area. In general, more extensive diagenetic degradation has reduced aquifer quality in the sandstone reservoirs, compared to the Plains Study Area. Aquifer quality in Debolt and Baldonnel carbonates is difficult to assess from logs, but test data indicate variable aquifer quality, with waters of moderate salinity and some H2S present. Foothills drilling and gas production are focused on the crests of regional northwest-southeast structural (anticlinal) trends, so there are insufficient data to adequately characterize aquifer quality off-trend.
Key observations arising from the project include:
- Deep subsurface aquifers with sufficient quality to support Montney water requirements are distributed unevenly across the play fairway.
- The northern Plains Study Area contains substantial stacked aquifer potential, while there is much less potential in the southern Plains area, where a Deep Basin (gas-saturated) regime occurs in many of the units.
- Good aquifer potential is present only in the southeastern Foothills area. More detailed work is required to determine whether gas production along regional anticlinal trends can be linked to fracturing, and whether such fractured reservoirs are capable of water production outside of established pool areas.