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Abstract: The Origin of Oil and Gas in Onshore Abu Dhabi, UAE

Awad Mohamed, Ibrahim Ennadi

Although geochemical investigation in onshore Abu Dhabi dates back to the seventies, the origin, maturation, migration and distribution controls of oil and gas are still poorly understood. This paper reviews the previous geochemical studies in onshore Abu Dhabi and documents the work conducted by ADCO during the past few years.

New conclusions, pertinent to hydrocarbon origin and migration, are drawn through the analyses and interpretation of hundreds of oil, gas and rock samples. Structural, stratigraphic and geophysical data are used to support these conclusions.

Analyses of sulphur content, carbon isotopes, porphyrin and biomarkers are used to characterize, group and correlate the samples. Long-range gas chromatography and reservoir geochemistry are applied to validate the charge directions.

At least three source rocks have been identified. However, the types of oil and gas found in onshore Abu Dhabi are genetically related to the Upper Jurassic source rocks. Contributions from other source levels, if any, are considered minimal. The geochemical differences recognized among the oil groups can be attributed to maturation and local facies variations within the Upper Jurassic source.

Vertical routes are envisaged for oil and gas migration. Lateral oil movement by spill-over to neighbouring structures can be seen locally. Both geological and geochemical evidence point to the lack of long-distance lateral oil migration.

Sequences of finer-grained strata became progressively sealing with increased depth of burial. Seal effectiveness and faulting provide the critical controls on the distribution of oil and gas both vertically and laterally.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France