Delta Field (Niger Delta)
The Delta Field is located offshore from Nigeria on Oil Mining Leases 49 and 95. This is located within the Niger Delta Basin and sits in 12 feet of water. In 1965, the Delta 1 well was completed and the Delta Field opened in 1968 for production.
The Niger Delta is a wave-dominated delta located on the continental margin of the Gulf of Guinea that formed in the Paleogene. The delta is fed with sediment from the Niger River, which has the ninth largest drainage area in the world and the third largest in Africa at 2.23 million km2. The delta is 75,000 km2 in size and reaches a maximum thickness of 12 km in the center of the basin. The Niger Delta is one of the world's major hydrocarbon provinces; specifically, it ranks 12th in terms of known accumulation of hydrocarbons with reserves exceeding 34 billion barrels of oil and 93 trillion cubic feet of gas. Oil and gas is predominantly extracted from the [|Agbada Formation] and is targeted from structural traps there.
The Delta Field produces from the only identified petroleum system in the Niger Delta region, the Tertiary Niger Delta Petroleum System. Throughout the region, oil and gas is predominantly extracted from the Agbada Formation where it is targeted from structural traps.
Geologic history and depositional processes
The Niger Delta Basin is an extensional rift basin where rifting occurred from the Late Jurassic to the Late Cretaceous. Cretaceous fracture zones, expressed as trenches and ridges, control the tectonic framework of the delta and separate the margin into individual sub-basins, which form the boundary faults of the Cretaceous Benue-Abakaliki trough. The Niger Delta Basin is the youngest and most southern sub-basin in the Benue-Abakaliki trough. The Benue-Abakaliki trough represents a failed arm of a rift triple junction associated with the opening of the South Atlantic.Key to understanding the Delta Field is the formation of the Niger Delta. Since the Eocene, the Niger Delta has been prograding to the southwest with sediment coming from the Niger River. As the delta progrades, growth-fault-bounded depobelts are created. These depobelts represent the most active portion of the delta at each stage of its development. They also represent a change in regional dip of the delta. Each depobelt is composed of genetically similar sediments that are diachronous. There are three main provinces of depobelts within the delta: the northern delta province, central delta province, and the distal delta province. The provinces are delineated based on structure. The Delta Field falls into the northern delta province, which has the oldest growth faults compared to the other provinces.
Stratigraphy
The Cretaceous lithology of the Niger Delta Basin is only known due to the adjacent basin to the northeast, the Anambra Basin. There, the Cretaceous section is exposed and we get a glimpse into the stratigraphy. Lithology of the Niger Delta Basin above the Cretaceous is known from drilling and coring efforts within the basin.Akata Formation
The Akata Formation underlies the entire base of the delta. It is composed of marine pro-delta shales and turbidite sands that have been deposited since the Paleocene. Minor amounts of clay and silt are also present. Since the formation has not been drilled, it is only estimated that the formation is up to 7,000 meters thick.Agbada Formation
The Agbada Formation, which overlies the Akata Formation, contains paralic siliciclastics and are considered to be the main deltaic sequence. The formation contains the most economically exploitable hydrocarbon in the region. According to biostratigraphy— specifically the presence of Sphenolitus heteromorphis, Praeorbulina glomerosa, Discoster deflandreim and Sphenolithus moriformis—the formation was deposited over 6-7 million years during the Middle to Late Miocene. In the Delta Field, gamma ray logs show a coarsening upward trend within the Agbada Formation, which shows the regression of depositional environments within the delta. In the Delta Field, the top of the Agbada Formation is at approximately 3000 feet below sea level, at the base of freshwater sands. The base of the formation is 8000 feet below sea level. The formation thickens basinwards towards the offshore depocenter.Benin Formation
A fluvial and upper coastal plain facies that has been deposited since the Oligocene and, like the Akata and Agbada Formations, extends across the entire delta. The Benin Formation overlies the Agbada Formation, and consists of sands that are up to 2000 meters thick at some places in the delta.Structure
The stratigraphy of the Niger Delta is complicated by clastic wedge syndepositional collapse that occurred as the result of marine shales being mobilized. When the delta was deposited, it was a prograding extensional complex with marine shales below. The extensional system contains large scale, basin-dipping normal growth faults that trend northeast to southwest and northwest to southeast. The growth faults in the northern delta province are mostly rotational, increase in steepness seaward, and are evenly spacedAlong with the growth faults, rollover anticlines, shale ridges, and shale diapirs exist in the basin and can be seen in the schematic structural profile of the Niger Delta.
The Delta Field is located on the dominantly extensional proximal margin of a major collapse structure. The general structure of the Delta Field has two main fault blocks that are separated from one another by a major normal fault; the western block is the footwall that is dropped relative to the eastern block. Another fault exists in the NE part of the field and is characterized by a minor horst.