INNOVATION May-June 2012

f ea t ures

Utilization and Protection of BC’s Water Resources in the Production of Oil and Gas from Unconventional Reservoirs

Dr Brad J Hayes PGeo

I n the March/April issue, Dr Richard Jackson PEng and Alan Kohut PEng wrote an interesting article on shale gas extraction and the protection of shallow groundwater aquifers. This article will offer additional perspectives on water issues associated with unconventional gas and oil production in northeastern BC, and the initiatives being undertaken addressing these issues by Geoscience BC in cooperation with industry, government agencies, and academic institutions. Unconventional Hydrocarbons, Reservoirs and Resources Northeastern BC hosts immense resources of hydrocarbons, primarily gas, in unconventional reservoirs. These rocks are considered unconventional because although they contain oil and gas, their naturally occurring permeability is so poor that the resources cannot be produced at economic rates using tried-and-true conventional drilling and completion methods. Recent advances in drilling and completions technologies, particularly horizontal drilling and multistage hydraulic fracturing (fracs), have allowed producers to artificially enhance permeability, and thus access hydrocarbon resources economically. There are three main types of unconventional reservoirs: • Coal beds (producing CBM, short for coal bed methane); • Tight formations, consisting of sandstones or carbonate rocks like conventional reservoirs, but with very low permeabilities; and • Shale reservoirs. Coal bed reservoirs are important only locally in northeastern BC, and generally are not economically viable at current low gas prices. Tight formations have been exploited in the Deep Basin area south of Dawson

Creek for over 30 years, although horizontal wells and multistage fracs have become common only in the last decade. The Montney Play, which currently stretches from the Alberta border east of Dawson Creek northwestward to Pink Mountain, is an immense tight gas fairway being explored in some areas and actively developed in others. Shales, originally made up primarily of mud, have long been regarded only as “source” rocks. They generated hydrocarbons, which migrated to conventional reservoirs very slowly over geologic time, but could not produce them. Oil and gas are generated by the application of heat and pressure over geologic time within source rocks, and migrate over millions of years into conventional reservoir rocks. Now, however, with horizontal drilling and multistage fracs, the shales themselves have become economically viable reservoirs. Shales of the Horn River Basin, north of Fort Nelson, are BC’s best-known shale gas play, but many others offer good potential. One can find many different estimates of the oil and gas resource potential in unconventional plays. Gas-in-place can be calculated from a variety of reservoir parameters measured in wells and from core samples. Estimating recoverable or marketable gas or oil is more difficult because one must make a variety of assumptions about the fraction of hydrocarbons in the ground that can be produced profitably (you can’t count reserves as marketable if you can’t make money marketing them!). The most authoritative report on Horn River Basin gas resources is by the BC Ministry of Energy and Mines and the National Energy Board, entitled “Ultimate Potential for Unconventional Natural Gas in Northeastern British Columbia’s Horn River Basin” (www.neb-one.gc.ca/

WEST

EAST

QUATERNARY CHANNEL AQUIFERS

SURFACE

0

DUNVEGAN

BASAL CRETACEOUS

CRETACEOUS (BUCKINGHORSE) SHALE

DEBOLT / RUNDLE AQUIFER

metres

DEBOLT / RUNDLE

1000

JEAN MARIE

MISSISSIPPIAN / DEVONIAN SHALES

SLAVE POINT

MUSKWA SHALE GAS RESERVOIR

Figure 1. Schematic cross-section showing Debolt aquifer in the Horn River Basin, more than 1,000 metres above the Muskwa Formation shale gas reservoir.

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