Location of Natural Gas

Natural gas and oil are not distributed equally around the world; only about one third of the world’s land surface is covered by the sediments that produce petroleum. Over the years, petroleum geologists have developed increasingly sophisticated and accurate mapping techniques and specialized instruments. Nonetheless, the search for petroleum remains something of a gamble as even the more advanced technologies can still only predict where natural gas and oil are most likely to be found.

Most of the large gas and crude oil fields being produced today were formed in sedimentary basins, depressed areas of the Earth’s surface where a thick organic sludge could accumulate. The sedimentary basins in which much of the world’s petroleum has been found date

back to the Mesozoic period of 65 to 245 million years ago. As the tectonic plates that comprise the Earth’s crust shift, mountains emerge, rock buckles, seas drain, sedimentary basins sink, and gas and oil accumulate. Over these millions of years, gas and oil have migrated out of the harder sedimentary source rock, shales and limestones, into more permeable and porous reservoir rock, typically sandstones (Pembina and Joarcam) and porous limestone (Leduc and Redwater). The most likely place to find a productive reservoir is in a trap where the rock has been distorted, pushed into folds, creating an open space that is sealed by a dense rock cap; the petroleum gathers in the void and is trapped in place by the cap.

Within the trap, weight differences will cause vertical layering. As gas is the lightest, it will accumulate at the top; oil will collect beneath the gas, and water will create the lowest layer. Traps are formed in a variety of shapes, sizes, and types and can exist at almost any depth. Most petroleum found so far has been discovered in a kind of trap called an anticline. Other traps that might harbour gas or oil include salt dome traps, fault traps, reef traps, stratographic and pinch-out traps. Sometimes traps can even form atop one another creating producing zones at different depths. Leduc, Alberta, contains four producing zones, one gas field and three oil fields, stacked one above another.

Nearly half of Canada lies atop sedimentary basins. In fact, every single Canadian province and territory can claim at least some part of a sedimentary basin. These vast basins are divided into seven distinct regions with the Western Canada Sedimentary Basin, the one Alberta claims, the most laden with hydrocarbons.

Thus, the Western Canada Sedimentary Basin of Alberta has seen the majority of exploration for these valuable resources. Within recent years, however, as many of the producing reservoirs have become depleted, exploration has moved towards unconventional sources of gas.