User:Rrieff2/Cisco Hydrocarbon Field

Location
The Cisco hydrocarbon field is located offshore, west of Lougheed Island in the Nunavut Territories of Canada (77° 24' 18", 106° 26' 02").The field is a part of the greater Sverdrup Basin. The field is also located within the Artic Circle, so this presents a unique challenge to hydrocarbon extraction.

Discovery and Drilling
The surface geology of the Sverdrup Basin was mapped by the Geologic Survey of Canada during the early 1960s. Onshore wells in the basin were first drill in the late 1960s, these being the Drake Point field in 1969 and King Christian field in 1970. By 1973, further evaluation of the Sverdrup Basin by Panarctic caused an increased to hydrocarbon exploration and extraction in western part of the Sverdrup Basin. Development of ice platform drilling technology permitted drilling, first of offshore delineation wells followed by the first wildcat well at Jackson Bay in 1976. The Cisco field was originally drilled from February 1, 1981 to May 4, 1981. The drill site is located on an ice sheet, so this causes drilling to only be available during the winter, when the ice sheet is sufficient enough to bring drilling equipment across. Specialized drill platforms were constructed to be placed on the ice sheet. The peak season for offshore drilling were mid December to mid May, when the ice sheet is thick enough to establish a drill site. The Cisco well reaches a depth of 2412 meters. A total of one hundred and fourteen wells (eighty-eight exploratory) were drilled by 1983, twenty-eight of which were offshore.

Basin Geology
The Sverdrup Basin is an extensional basin formed as a result of rifting over an Early Paleozoic fold belt. The Sverdrup Basin is approximately 313 000 square kilometers; 145 000 square kilometers onshore; 168 000 square kilometers offshore. The basin extends for about 1300 km in a NE –SW direction and is up to 350 km wide. The basin contains up to 13 km of Carboniferous to Tertiary sediment.

Early sedimentary deposits in the basin consisted of carbonate rock around the perimeter of the basin with thick evaporite sequences within the center. This thick evaporite sequence will later give rise to diapiric salt and thinning of the basin. Later, clastic deposition from the continental interior dominated deposition within the basin. Subsidence was regular within the basin until the Early Cretaceous. At this time, the Amerasia Basin was opening to the north, causing the Sverdrup Basin to experience broader, more accelerated subsidence as well as basaltic magmatism. Basaltic magmatism was widespread through the basin in the form of sills and dikes in Early Cretaceous strata. Another result of the opening of the Amerasia Basin was the destruction of a land body known as Crockerland and formation of a large rim shoulder, dubbed the Sverdrup Rim. This rim is the location of Axel Heiberg Island today.

The western portion of the Sverdrup Basin contains the overwhelming majority of hydrocarbons within the basin. This is due to the eastern portion of the basin has high maturation of source rocks, a lack of porous reservoirs, and widespread outcropping of potential source rocks.

Reservoirs
The Awingak Formation servers as the Cisco field's primary hydrocarbon reservoir. The sediment was deposited during the Upper Jurassic. The Awingak was deposited as a result of a large delta which prograded northward from the southeast. The formation is around 300 meters of intercalated sandstone and shale. From samples and log profiles, it was determined that the formation consists of three intervals exhibiting a coarsening upward trend from dark grey shaly siltstones to light grey, medium-grained, porous quartz sandstones. The sandstone contains large amounts of angular carbonaceous fragments and light colored chert grains. Sandstone deposits through the formation are overlain abruptly by an interval of shale. The confining layers around the Awingak are the Deer Bay and Ringnes Formations.

The Schei Group serves as a potential source rock for the hydrocarbons found within the Awingak Formation. During the Middle and Upper Triassic, the Shei group sediment was deposited in a stable, oxygenated, shallow-marine environment that was effected by regular storm conditions or strong tides. The Schei Group contains two smaller members; the Cape Caledonia Member and the Eden Bay Member. The Eden Bay Member was found to have varying TOC levels, ranging from 0.33-2.75 wt%. The Cape Caledonia Member was found to have a similar range in TOC values, from 0.30-3.97 wt%, indicating poor to good source rocks. Both the Cape Caledonia and Eden Bay members were found to contain Type I and Type II organic material, with the majority in both members being Type II. The Schei group as a whole is comprised of calcareous siltstone, with local changes to siliciclastic and limestone. Migration of hydrocarbons within the Schei Group can be attributed to the diapiric evaporites found throughout the Sverdrup Basin.

Seals
The confining seals surrounding the hydrocarbon reservoir are the Deer Bay and Ringnes Formation.

The Ringnes Formation is made of dark-brown to black silty shale/siltstone. The Ringnes sediment was deposited in a broad shallow-marine shelf. The facies of the formation are interpreted as a prodelta and distal-basin. The Ringnes was also found to be a potential hydrocarbon source to the overlying Awingak sandstone reservoir. The Ringnes contains high levels of Type III organic matter with minor levels of Type II organic matter as well as TOC values ranging from 1.81-8.65 wt%, indicating very good source rocks.

The Deer Bay Formation is composed of black, silty marine shales deposited during the Upper Jurassic and Lower Cretaceous. Macrofauna found at the base of the Deer Bay indicate that formation originated in shallow-marine conditions. The upper part of the formation was deposited as prodelta muds resulting from the adject delta lobe deposits of the Isachsen Formation. The Deer Bay Formation was not found to contain any potential source material for hydrocarbon generation.

Traps
The main trapping mechanisms through the Cisco field are from salt diapirs coring through an anticlinal limb. The anticlinal structures within the basin formed as a result of relatively recent Eurekan Orogeny in the Paleogene. In the western Sverdrup Basin, the Carboniferous evaporite succession became active during the Early Triassic, and diapiric salt subsequently affected both depositional patterns and structural style. The largest diapiric structure within the basin also occurs west of Lougheed Island, near the Cisco field. This diapir measures to be 40 km long and 8 km wide.

Hydrocarbon Reserves
The Cisco field was determined to contain approximately 175 (MMBO)^2 of recoverable oil and 204 (BCFG)^2 of recoverable gas as of 2008.