Thermal maturity history and petroleum generation modelling for the Lower Cretaceous Abu Gabra Formation in the Fula Sub-basin, Muglad Basin, Sudan

Comprehensive source rock evaluation, burial history modeling, and thermal maturity of oil generation have been investigated in petroleum system of Jake oil fields. The consideration of geological, geochemical, and palynofacies data was used for source rock and thermal maturity. Basin Mod® software was applied to construct the burial and thermal histories and to determine the timing of hydrocarbon generation and expulsion. The modeling was achieved through transient heat flow and collaborated with measured %Ro. The Lower Cretaceous Abu Gabra Formation was believed to be organic-rich shale and characterized by source rock of excellent abundance and potential that possesses total organic carbon (TOC) ranging from 0.37 to 6.27 wt% and production yield 1.31–49.23 mg HC/g rock. Kerogens can be classified as oil-prone types I–II. Vitrinite reflectance (Ro) and Tmax values suggested that most samples were of early maturation for oil generation. Palynofacies and geochemical combination indicated that amorphous phytoclasts of plant debris were dominated by high TOC and hydrogen index (HI), whereas assemblage kerogens confirmed the presence of oil source rock. Geohistory models showed the highest rapid subsidence rates during the Early-Late Cretaceous. The results demonstrated that petroleum could be generated in the upper (1950–2500 m) and the lower intervals (2550 total depth) of Jake South field. Maturity and hydrocarbon generation modeling indicated that the source rocks reached the early maturation stage in the Early Cretaceous (127 Ma) at a temperature of 90 °C. The middle maturation stage began in the Late Cretaceous (64 Ma) with a temperature of 110 °C. Essential oil generation started approximately 63 Ma ago and continues to the present day.

The organic-rich claystone and shale sediments of Lower Cretaceous Abu Gabra Formation are considered an important regional source rock in the Muglad Basin, Sudan. A total of 20 cutting samples from these organic-rich sediments were collected from six wells drilled at oilfields in the Fula sub-basin, Muglad Basin, in order to geochemically assess the type of organic matter, thermal maturity, and palaeoenvironmental conditions. Results reveal that Abu Gabra organic-rich sediments contain high organic matter more than 2.0 wt% TOC and have a very good to excellent oil-generation potential. This is supported by high bitumen extractions and hydrocarbon yields with values exceeding 5,000 and 3,000 ppm, respectively. The investigated biomarkers indicated that the Abu Gabra sediments contain a mixture of algal and amorphous organic matter that were deposited in a lacustrine environment setting. This has been identified from kerogen microscopy and normal alkane distributions, which are characterized by dominance of types I/II kerogen and low-medium molecular weight n-alkane compounds, respectively. This is also supported by high abundance of C27 regular sterane concentrations, high C27/C29 regular sterane ratios and relatively low value of the biomarker sterane/hopane ratio as well as the presence of tricyclic terpanes. A mainly suboxic to relatively anoxic preservation conditions is inferred from Pr/Ph ratios (1.01–2.51). This is further supported by lower amounts of acyclic isoprenoids compared to n-alkanes (e.g., pristane/n-C17 and phytane/n-C18 ratios). Based on the analyzed biomarker thermal maturity indicators, it may be deduced that the Abu Gabra sediments have entered an early mature stage for oil generation. This is also supported by vitrinite reflectance values of 0.58–0.72 % Ro indicative that these sediments have reached oil window maturity.

Origin of a Tertiary oil from El Mahafir wildcat & geochemical correlation to some Muglad source rocks, Muglad basin, Sudan

History of hydrocarbon generation, migration and accumulation in the Fula sub-basin, Muglad Basin, Sudan: Implications of a 2D basin modeling study

Organic geochemical heterogeneity of the Cretaceous Abu Gabra Formation and reassessment of oil sources in the Sufyan sub-basin, Sudan

Source rock characteristics of the Lower Cretaceous Abu Gabra Formation in the Muglad Basin, Sudan, and its relevance to oil generation studies

Tectono-sequence stratigraphic analysis of the Lower Cretaceous Abu Gabra Formation in the Fula Sub-basin, Muglad Basin, southern Sudan

Sedimentology, diagenesis and reservoir quality of the upper Abu Gabra Formation sandstones in the Fula Sub-basin, Muglad Basin, Sudan

The Fula sub‐basin is a fault‐bounded depression located in the NE of the Muglad Basin, Sudan, and covers an area of about 3560 km2. Eleven oilfields and oil‐bearing structures have been discovered in the sub‐basin. The Lower Cretaceous Abu Gabra shales (Barremian – Aptian), deposited in a deep‐water lacustrine environment, are major source rocks. Reservoir targets include interbedded sandstones within the Abu Gabra Formation and sandstones in the overlying Bentiu and Aradeiba Formations (Albian – Cenomanian and Turonian, respectively).Oil‐source correlation indicates that crude oils in the Aradeiba and Bentiu Formations are characterized by low APIs (<22°), low sulphur contents (<0.2%), high viscosity and high Total Acid Number (TAN: >6 mg KOH/g oil on average). By contrast, API, viscosity and TAN for oils in the Abu Gabra Formation vary widely. These differences indicate that oil migration and accumulation in the Fula sub‐basin is more complicated than in other parts of the Muglad Basin, probably as a result of regional transtension and inversion during the Late Cretaceous and Tertiary.The Aradeiba‐Bentiu and Abu Gabra Formations form separate exploration targets in the Fula sub‐basin. Four play fairways are identified: the central oblique anticline zone, boundary fault zone, fault terrance zone and sag zone. The most prospective locations are probably located in the central oblique anticline zone.

Sedimentologic and reservoir characteristics under a tectono-sequence stratigraphic framework: A case study from the Early Cretaceous, upper Abu Gabra sandstones, Sufyan Sub-basin, Muglad Basin, Sudan

Fula Sub-Basin, located in NE of Muglad Basin, is the most important production base for block 6, which is one of the important overseas project of CNPC. After more than 20 years’ exploration and development, big and shallower traps such as Bentiu/Aradeiba reservoir have been discovered and drilled for most area, remained traps are limited with small area, deep targets, and complex structure which are difficult to identify. How to exploring deeper targets as Abu Gabra has become more and more urgent. Many challenges are faced for detailed exploration of Abu Gabra such as poor data quality in deep parts and complex fault system identification etc. Some specific techniques and methods have been tried and tested to identify new traps, including target filter processing for deep parts, well-controlled fault point identification integrated with detailed well correlation, fault polygon generation with multiple attributes etc., and finally a combined work flow for detailed exploration of complex faulted trap has been generated. These techniques have been applied in Fula and other Sub-basin in block 6 and a series of new faulted traps have been discovered. Drilling candidates are selected from them through detailed trap appraisal and good results come out, with 11 successful wells from 12 candidates, which indicate that integrated fault identification techniques are effective for detailed exploration and development of rifting sub-basins in Muglad basin and similar basin.

Hydrocarbon potential evaluation of the source rocks from the Abu Gabra Formation in the Sufyan Sag, Muglad Basin, Sudan

99/00155 Depositional environments and oil potential of Jurassic/Cretaceous source rocks within the Seychelles microcontinent

Organic geochemical characteristics of the Lower Cretaceous Abu Gabra Formation in the Great Moga oilfield, Muglad Basin, Sudan: Implications for depositional environment and oil-generation potential

The Muglad Basin is the largest sedimentary basin in the Central African Rift, covering an area of more than 120,000 km2. It is also the basin with the largest discovered geological reserves in the Central African Rift, and it has a total of more than 8 billion barrels of discovered geological reserves. In order to evaluate the petroleum resource potential and optimize the exploration target of the Abyei slope, a modeling study of petroleum systems was carried out. Through the simulation of burial history, thermal history, hydrocarbon generation history and migration and accumulation history, the history of source rock thermal evolution and hydrocarbon generation was clarified. Moreover, the favorable direction of hydrocarbon migration and accumulation was also determined. Based on the research of petroleum simulation, the division and evaluation of petroleum systems were completed. According to the research, the source rock of Abu Gabra formation has the strongest hydrocarbon generation ability, the Baraka formation’s is the second, and the Ghazal formation’s is the worst. The Abu Gabra organic matter starts to generate hydrocarbons from 113 Ma, and it has entered a high-mature and over-mature stage. The peak oil generation period is from 80 Ma to 60 Ma, and the gas production is dominated after 60 Ma. The organic matter of Ghazal and Baraka formation start to generate hydrocarbons from 65 Ma to 60 Ma, and the peak of oil generation is from 20 Ma to the present. Vertically, Bentiu formation, the middle Aradeiba, and lower Ghazal, Baraka, and Nayil are the effective hydrocarbon accumulation layers. Horizontally, the central and west are the favorable areas for oil and gas accumulation. There are three sets of petroleum systems in the study area and they are Abu Gabra-Bentiu, Aradeiba, Zarqa(!), Ghazal- Gazal(*), Baraka-Baraka, Amal, Nayil(*). The source-reservoir-cap rock combinations, pathway system and conservation conditions of two sets of petroleum systems in Cretaceous formation are comprehensively superior to that of the Tertiary, and they present a better exploration and production potentials. Based on the simulation and comprehensive evaluation of the petroleum system, the favorable zones and trap targets were selected and the exploration well locations were proposed. The research results point out the direction for Cretaceous oil and gas exploration in the Abyei slope.KeywordsBasin modelingSource rockPetroleum systemMuglad Basin