Hebron-Ben Nevis oil field

The Tehtys phase occurred in the late Triassic and continued in the Early Jurassic. During this time the Jeanne d'Arc Basin was formed due to rifting forming half grabens as major crustal detachment occurred. This phase is most important phase in the construction of the Jeanne d'Arc Basin as it gave it its size.[2]

The North Atlantic phase occurred in the late Jurassic to early Cretaceous. The basin formed in the Tethys phase experienced faulting with a North to South trend. The southern boundary of the Jeanne d'Arc Basin was formed by the reactivation of the Egret Fault. The central ridge of the basin was formed along the Voyager Fault. After this period of faulting the Avalon Uplift, a series of rift basins, occurred that allowed for uplift and erosion to occur within the basin. During this time the Atlantic Ocean continued to expand along the Newfoundland Transform Fault Zone. During the early Cretaceous in the Kimmeridgian the source rock, called the Egret Source Rock, was deposited in the basin which provided the basin oil fields a source for their oil, mainly the Hebron.[2]

The Labrador phase occurred from the middle to late Cretaceous. This rifting phase began with northwest to southwest trending faults fragmenting the basin. One of the major faults formed was the Trans Basin Fault Zone which formed some of the traps to the adjacent oil fields. The major event happening at the end of this period was the deposition of the Ben Nevis formation which forms the main reservoir for the Hebron Oil Field.[2]

The Tethys, North Atlantic, and Labrador Phases were all followed by periods of tectonic subsidence and post rift thermal subsidence. At the end of the rifting phase, a passive rift margin phase occurred allowing for new depositional areas within the basin.

This shows the stratigraphy of the Hebron fault block within the Jeanne d'Arc Basin. The four main reservoirs which are depleted are labeled.

This period begins with the Mesozoic break up of Pangea and the beginning of the basin formation in the Grand Banks of Newfoundland. In the Late Triassic sediments begin to be deposited in what is now the Jeanne d'Arc Basin during a series of Mesozoic rifting events. During the lower Jurassic period, a marine environment existed in the area allowing for the deposition of interbedded carbonates and evaporates.[2]

During this upper Jurassic period, the deposition of oolitc limestones, shales and carbonated cemented sandstones were deposited in the basin. The deposition of these sandstones creates ideal seismic reflectors to aid in the understanding of formations deep within the Jeanne d'Arc Basin. In the middle Kimmeridgian the deposition of the Egret source rock occurred. This source rock is composed of marls and organic rich laminated shales. After the deposition a period of uplift and erosion occurred due to the further expansion and rifting of the Atlantic Ocean that forms an unconformity at the top if the middle Kimmeridgian deposits.[2]

This period began with the deposition of the Jeanne d'Arc Sandstone formation which provides a minor reservoir to the Hebron field. Sandstones were deposited from the southwest of the Grand Banks. This deposition also led to the creation of the Hibernia sandstone reservoir that is also produced in the Hebron Oil field. However, it expresses poor reservoir quality.[2]

This period began with minor uplift resulting in erosion after the Hibernia sandstone was deposited. After the uplift and erosion period, overlaying sandstanes, shales and limestones were deposited into the Hebron field. Subsidence and faulting continued to occur in the basin during this time.[2]

The main reservoir for the Hebron Oil field was deposited. The Ben Nevis Sandstone contains roughly 80% of the producible hydrocarbons for Hebron. It was formed in a marine shore face environment and is 80 to 120 meters thick. The deep part of the Ben Nevis contains good quality sands, carbonate cemented sandstones and has good reservoir properties. It has a porosity ranging from 16% to 30% and a permeability of 360 millidarcies. The shallow section contains silty, bioturbated sands with poor reservoir quality.[1]

During the late Cretaceous major faulting occurred due to the continued rifting of the Atlantic Ocean at the Newfoundland Transform Fault Zone. The lower reservoirs, Hibernia and Jeanne d'Arc formations, are trapped along the up dips of Anticlines and faulted tilted blocks. The main reservoir, the Ben Nevis, is trapped due to a stratagraphic trap occurring above the sandstone and trapped on the sides due to the Egret Fault.[3][4]