Summary
The Duvernay shale liquids play running along the foothills east of the Rocky Mountains, possesses all the prerequisites of being a successful unconventional play, and has gained the attention of the oil and gas industry in Alberta, Canada. Even though, the net shale thickness ranges between 25 and 60 m for most of the play, in places it thins further. Considering the poor vertical resolution of the available seismic data, it is not possible to identify and characterize the thin Duvernay sweet spot zones using seismicallyderived attributes. In a recent case study, we found it to be challenging to characterize the thin Duvernay reservoir zone, and consequently developed a workflow that successfully addressed the challenge and identified the thin sweet spots.
Introduction
Although conventional reservoirs remain a very important part of the world’s natural gas supply, horizontal drilling and multistage fracturing have now made it possible to develop and exploit unconventional reservoirs. With the successful development of unconventional shale reservoirs in North America, the oil and gas industry has shifted its attention to the Devonian Duverney shale liquids play in Alberta. The Duvernay shale play has been recognized as the source rock for many of the large Devonian oil and gas pools in Alberta, including the early discoveries of conventional hydrocarbons near Leduc. The Duvernay shale basin spans approximately 50,000 square miles, with an estimated 7,500 square miles within the thermally mature or wet gas window (Davis et Al. 2013), from northwest to southeast across Alberta. Its stratigraphic age is equivalent to the Muskwa Formation of the Horn River dry shale gas play to the northwest in the neighboring province of British Columbia (Rivard et al. 2013).
The Duvernay was deposited in a broad marine setting as a basin-filling shale, surrounded by equivalent aged Leduc reef build-ups. Due to rapid basin filling during maximum sea-level transgressions, enormous quantities of organic sediments were dumped in this deep, oxygen-starved basin that are the present day Duvernay source rocks, where TOC (total organic carbon) is as high as 20% (McMillan et al.,2014). The Duvernay shale is fine-grained and silica rich. As a result of the fine grains, rocks have increased total surface area that leads to a higher absorbed gas component in organic-rich rocks. Moreover, silica-rich rocks are more brittle and favorable for fracking.
