User:Nathanfigueredo/Manifa Oil Field

Manifa Oil Field
Manifa Oil Field, operated and owned by Saudi Aramco, is the world's largest offshore hydrocarbon production increment built in a single phase. It is located 200 km northwest of Dhahran in the western Arabian/Persian Gulf in the shallow coastal waters off the Eastern Province of Saudi Arabia. It is 15% larger than the size of Singapore with an aerial extent of 800 kilometers squared under shallow waters with a general depth of 5 meters. The six-reservoir field is 45 kilometers in length and 18 kilometers in width with a producing capability of 900,000 barrels per day. The oil field was discovered in 1957, but was not successful until 2013. Often referred to as a true grassroots venture, it is considered to be a megaproject and the world's largest extended reach oil project having more than 80% of the wells being extended or mega-reach wells.

Geologic Setting

The Manifa field is located in the tectonostratigraphic province known as the Arabian Platform/Unstable Shelf. It formed when sediment deposited into a passive margin setting after the supercontinent, Gondwana, break up. The field is primarily composed of a sub horizontal sedimentary sequence that includes basement-induced and diapiric folds. The majority of the known oil and gas is present in anticlinal/domal structures in the sediment sequence.

Tectonics

All Saudi Arabia oil fields are located in the northeastern part of the country, including those offshore in the Saudi Arabian portion of the Persian Gulf. All of these hydrocarbon structures were created through extensional block faulting of the basement. The Manifa field originated from basement faulting running parallel with a northwest trend along the Persian Gulf. The basement faulting is a right lateral slip fault that follows the Erythraen Sea Trend to the northwest. The faulting transected the Upper Precambrian salt beds, known as the Hormuz Series, allowing salt to move upwards forming a salt wall. Deep seated salt diapirism caused by basement faults pushed phanerozoic strata into an elongated, doubly plunging, brachy anticline.

Reservoir

Manifa is a six-reservoir field with each reservoir stacked on top of each other with each section being up to 40 kilometers long. The main reservoir formed during the early Jurassic period. It is overlain by a weak interbedded sand/shale formation and carbonate formations from the upper and lower cretaceous period. The most important oil producer for the Manifa field is the late Tithonian Manifa carbonate, specifically the Arab formation. The anhydrite Hith formation that rests on top of the Arab formation acts as a seal. The Tithonian Manifa carbonate was affected by a variety of diagenetic processes including recrystallization, dissolution, cementation, and karstification.

Arab Formation

The Arab formation acts as the source rock for this field and includes four members. Each of these members represent a cycle of deposition which all started with shallow-water, normal marine carbonate, and ended with precipitation of pure anhydrite. This anhydrite layer acts as a separator for each member. The capping anhydrites are diachronous in at least two members. An episodic pattern of deposition is documented by 5 - 50-meter-thick intervals of alternating shallow-water shelf limestone. The thickness of the formation generally ranges from 100 - 180 meters. The four members are:

Arab A - member is largely shoal facies and contains significant amounts of oil. Contains a thin widespread layer of shelf limestone that alternates in sequence with normal marine carbonate and bedded evaporite

Arab B - member proportionally contains about ~20% carbonate rocks

Arab C - member contains shallow-water sediments with the lower portion being open-shelf neritic limestone and upper portion being bedded evaporite

Arab D - member is composed of clean, neritic limestone and abundant carbonate sand and gravel

While all members contain oil, accumulation is less extensive in the A, B, and C member carbonates than the D member.

Permeability and Porosity

The reservoir generally has relatively low permeability at 1171 mD due to the viscosity of the heavy-crude oil. Porosity if generally high throughout the reservoir at ~20%. The reservoir is underlain by an immovable heavy tar layer.

Production

Production originally began in 1964 producing 40,000 BOPD but was stopped in 1984 due to low demand, lack of technology, and production of crude oil was too minimal. Saudi Aramco began development of the Manifa field megaproject in 2006 with the intent of creating infrastructure for production capacity of ~900,000 barrels a day of Arab Heavy crude oil. 350 wells were required in the Manifa field development. The 350 wells included 183 producers, 100 injectors, 15 observation wells, 13 cutting re-injection wells, and 39 water supply wells. The Manifa field produces crude oil with an average API of 25 degrees. The project concluded and oil production began again in 2013, producing 500,000 barrels per day. The 900,000 barrel per day goal was eventually reached in 2017. Today the field is considered one of the largest offshore crude oil production increments and is the world's fifth largest oil field in 2015.

Environmental Challenges

Conventional shallow water drill rigs require dredging of access channels which could cause immense damage to the marine environment. Manifa is one of few areas in the Persian Gulf characterized with high primary productivity involving shallow estuaries that contain rare species and vibrant marine life beneath the surface of the bay. This makes it a critical area for marine ecology. It contains several fragile environments including algal habitats, dense kelp beds, and scattered coral reefs. The ecosystem, that includes several varieties of fish and shrimp, is relied upon by local fishermen as a livelihood and acts as an integral part of the local economy. In order to avoid damage several radical and unconventional environmental technologies were researched for risk mitigation and later implemented. This includes the building of the causeway and island system. Manifa's environmental offset program set this field apart as an environmental steward. Manifa field is the perfect balance between environmental stewardship, safety, and operational excellence. Since Manifa's development, it has become one of the most important shrimp nursery and fishing areas in the Persian Gulf.

Causeway and Islands

The Manifa project consists of 21 kilometers of primary causeways, 21 kilometers of lateral causeways, and 27 drilling islands made from sand reclaimed from the seabed. A focus on preserving the marine environment surrounding the field has been present throughout the field's developmental history. 70% of the offshore field was converted into an onshore development through 27 islands being constructed and linked with 41 km of causeway. This included 14 bridges with the longest being 2.4 kilometers connecting the islands and coast together. The creation of this infrastructure allowed for the reduction of contaminated sediments, restoring health of aquatic ecosystems, prohibits further erosion from wave attacks by dissipating storm waves, prevents recession of backshore, and maintaining water circulation. All this resulted in offshore platform requirements and environmental footprints to be reduced by 50%.