Geological characteristics and fluid distribution of the Upper Devonian Duvernay shale in Simonette block in the Western Canada Sedimentary Basin

 North America is the region with the earliest discovery and the most successful development and utilization of shale oil and gas in the world. According to EIA data, U.S. shale gas production in 2020 was approximately 7378×108m³, accounting for more than 95% of global shale gas production, mainly from the Marcellus, Permian, Utica, Haynesville and Eagle Ford regions.

With the help of core technologies such as horizontal well volume fracturing, microseismic monitoring, and multi-well factory production, the United States has achieved breakthroughs in shale gas and industrialized production, setting off a “shale gas revolution” in the energy field on a global scale. It has changed the global oil and gas supply pattern and affected the global energy development trend and oil and gas price trends.

Following the great achievements in shale gas development, the United States has shifted its development focus to shale oil while continuing to develop shale gas.

The main reason for promoting the development of shale oil in the United States is that the rapid development of shale gas has caused a sharp drop in natural gas prices, widening the oil and gas price gap, and prompting the United States to shift its development focus from natural gas to oil.

Therefore, the development of shale oil and gas reservoirs rich in liquid hydrocarbons has received more and more attention, and oil companies have increased their efforts in the exploration and development of shale oil. Since the beginning of 2017, shale oil production, led by the increase in shale oil production in the Permian Basin of the United States, has shown rapid growth.

In 2020, the US shale oil production will be about 3.8×108t, accounting for 44% of the total annual crude oil production in the US.

The Duvernay Shale is the main source rock of the Upper Devonian in the Western Canadian Sedimentary Basin (referred to as the Western Canadian Basin). It is a set of asphaltene-rich dark shale formed during the maximum transgression period.

The total area of Duvernay shale is approximately 2.43×104km², and the natural gas, liquid hydrocarbon and crude oil resources are 23.22×1012m³, 115.54×108t and 250.60×108t respectively.

The Duvernay shale has a large amount of resources and is a set of mature shale in global shale oil and gas exploration and development, which is an important representative in North America.

Controlled by special geological conditions, the Duvernay shale shows the changing characteristics of “oil-condensate-wet gas-dry gas” from northeast to southwest. Currently, the liquid hydrocarbon-rich strip in the middle of the basin is mainly developed.

This article takes the Duvernay shale of PetroChina’s Simonette block as the research object, systematically explains the structural and sedimentary evolution characteristics, stratigraphic and sub-layer distribution characteristics, and reservoir characteristics of the Duvernay shale, and analyzes the oil and gas accumulation characteristics.

Based on the condensate oil content distribution, Reveal the fluid distribution rules in the Simonette block.

This study will help provide a reference for the selection of domestic shale oil and gas exploration zones, to promote the priority use of domestic high-quality shale oil and gas resources, thereby accelerating the pace of exploration and development.

The study area is located in the western part of the Alberta subbasin in the central part of the Western Canada Basin, and the main target layer is the Devonian Duvernay Shale.

The West Canada Basin, located between the Rocky Mountains and the Canadian Shield, is a typical foreland basin.

Geographically, the basin spans the provinces of British Columbia, Alberta, Saskatchewan and Manitoba in the Northwest Territories of Canada, and partly extends southward to Montana, North Dakota and South Dakota in the United States. The area is 140×104km².

From the Precambrian to the present, the Xiga Basin has experienced three tectonic evolution stages, including the stable craton stage from the Precambrian to the Middle Jurassic, the back-arc foreland stage from the Middle Jurassic to the Eocene, and the Eocene stage. Pliocene—the present intracraton stage.

The West Canada Basin was close to the equator during the Devonian period.

The warm and humid climate and the clean water away from the provenance promoted the fine-grained sediments and nutrients to enter the basin under the action of geological forces such as ocean currents, making the Devonian reefs and platforms Carbonate rocks are developed, and organic-rich shale is developed between reefs and in basins.

In the Late Devonian, the structure of the West Coast Basin was relatively stable, and reefs were mainly distributed on the western edge of the basin and the Rimbey-Meadowbrook area.

The Rimbey-Meadowbrook bioherm belt that develops in the northeast-southwest direction separates the Duvernay shale depositional area into two shale basins in the east and west.

The Duvernay shale was formed in the normal marine facies of the Early Phraian in the Late Devonian and was rich in organic matter.

It was synchronized with the growth and evolution of the reefs and banks of the Leduc Formation in the basin.

The reefs and banks of the Leduc Formation reduced the water circulation capacity, and the anoxic water body It is beneficial to the preservation of organic matter in the Duvernay group.

Marine transgression continued from the early Devonian to the late Devonian.

As the extent of transgression increased, the water body gradually deepened and the development scope of the reef gradually shrank. During the deposition of the Woodbend Group, the scope of the Leduc Formation reef was the smallest, making The Duvernay shale was most extensive during this period.

During the depositional period of the Duvernay Formation, the paleowater depth was greater than 100m, and the water depth near the reef shoal was less than 40-80m. Spatially, the water deepened from the Rimbey-Meadowbrook reef zone to the west.

The distribution area of Duvernay shale is about 2.43×104km², and it is generally a southwest-dipping monoclinic.

The shale burial depth is 500~5500m. The lithology of the Duvernay shale is dominated by bitumen-rich mud shale, overlying the marl of the Ireton Formation, underlying the marl of the Majeau Lake Formation in the west shale basin, and underlying the limestone of the Cooking Lake Formation in the east shale basin.

The Duvernay Shale is mainly distributed between the Rimbey-Meadowbrook bioherm zone and the Peace River uplift.

The thickness of shale deposits near the reef is large, up to 100m, while in the northern part of the West Shale Basin near the Peace River uplift and far away from the reef, the thickness of shale deposits is small, only 10-20m.

The Duvernay shale in the Simonette block is located in the slope of the foreland basin, and the shale deposition is controlled by the reefs of the Leduc Formation in the basin.

After the shale was deposited, it experienced tectonic movement, but the shale formation was not damaged on a large scale, and there were no large-scale fractures or folds, and the formation was gentle and stable.

The tectonic subsidence of the basin controls the thermal evolution of the Duvernay shale, but the anomaly of local heat flow caused by basement faults will affect the degree of local thermal evolution.