Executive Summary The Bear River prospect, in the Souris permit, Prince Edward Island, is situated within the Magdalen Basin.
The Magdalen Basin, along with the North-East New Brunswick shelf, also called the Bradelle Platform, forms the Central Maritimes Basin (CBM), which covers an area of 150,000Km2-(one third the size of the Western Canadian Sedimentary Basin in the Province of Alberta). This is a Carboniferous basin, originated after the Appalachian-forming Acadian Orogeny as a successor trough due to right lateral movement along major structural breaks.
In early Mississipian times, several small separated rift-like basins subsided and initiated fluvio-lacustrine sedimentation and volcanic depositions. With increasing subsidence, marine deposition laid down fossiliferous limestone and a thick sequence of evaporites, the Windsor Group, over a wide area. Thereafter until early Permian, thick continental successions of shales, sandstones and silts blanketed the whole basin in response to tectonic uplift on its periphery. Recent work by the Bedfor Institute of Oceanography shows that at the base of the supposedly continental succession several marine invasions contributed significantly to the sedimentation of the basin. These findings greatly increase the potential for hydrocarbon generation and trapping in the Magdalen Basin.
A variety of structures have developed in the basin due to basement block movements but mainly as a result of salt tectonics. Many favorable structures have developed in the basin and only a few have been tested to this day.
Exploration drilling in the seventies and eighties on land in Prince Edward Island and offshore, North and North-East of the Island, have encountered rare but good reservoirs in the Riversdale sandstones (Wetsphalian) which also provided encouraging gas shows. One wildcat, East Point E-49 has been classified a 'Significant Discovery', having tested 5.5 MMcf/d of gas.
The most likely source rocks for hydrocarbons are the shales of the Horton Group, Mabou and Cumberland Shales as well as coal seams and marine mudstones of the Riversdale and Cumberland formations. Most of the area has reached oil maturation.
The Basin is still unexplored, with one wildcat for every 9,000km2. Only salt pillows which appeared large and high, have been drilled.
The Bear River prospect in the Souris permit has been selected according to petroleum geology text book. The objective is the Riversdale, a good sandstone reservoir. It is located in the most favourable sector of the basin: the ancient depocenter of the Mabou and Riversdale sediments, and now a regional high, in the shape of saddle or arch. The trapping mechanism is due to a listric faulth, which serves as very good seal to the North, and a salt-wall, or salt-roller, formed on the South side of and against the fault which created a good trap, and contributed to the closure to the south. The regional dip and the peripheral syncline caused by the flowage of the salt, enhanced the trap, and assured its closure.
The Bear River fault was active during the Riversdale time, and synchronous with the incipient salt movement and sedimentation. Under marine influence the conditions were favorable for deposition of clean sandstone with good reservoir characteristics. A trap available at the time of primary migration should be considered most favorable, and preferred over even larger structures created much later such as the salt pillows drilled so far.
The seismic signature of the Riversdale reflection in the Souris Permit and immediate surroundings indicates multi-layered sandstones. Each sandstone layer must have a minimal thickness of 25 metres in order to be detected by seismic. A change of character and AVO (Amplitude versus Offset) Study could indicate gas. Calculated projections of the Bear River prospect, which covers 33km2, could give potential reserves of greater that 1 Tcf of gas. cheers, jerry |
