The Mobile Bay gas field is located offshore Alabama in the northern Gulf of Mexico. Production is from eolian dunes of the Jurassic Norphlet sandstone at depths exceeding 6100 m (20,000 ft) and temperatures greater than 200C. Reservoir connectivity and compositional variation, including the distribution of nonhydrocarbon gases (H2S and CO2), are critical factors in production strategy. To evaluate the controls on compositional variation and connectivity, detailed molecular and isotopic analyses were conducted for 29 wells. Analysis of volatiles in fluid inclusions suggests that the field was originally filled with oil that subsequently cracked to gas. In addition to the thermal destruction (cracking) of oil, the process of thermochemical sulfate reduction (TSR) continues to destroy the remaining hydrocarbons through oxidation of gas and reduction of sulfate to form H2S and CO2. The variable extent of the TSR process at Mobile Bay results in a wide range of hydrocarbon and H2S compositions. Condensates are almost exclusively composed of diamondoids whose composition appears controlled by H2S concentrations. In contrast to hydrocarbon and H2S contents, CO2 concentrations are relatively constant throughout the field. Carbon isotopic ratios for CO2 correlate positively with those for wet-gas hydrocarbons but are heavier than expected for CO2 originating from hydrocarbon oxidation via TSR. The narrow range of CO2 contents and heavy isotope ratios suggests that CO2 is regulated by water-rock equilibration and carbonate precipitation. The destruction of the hydrocarbon gas and mineralization of the carbon dioxide product create a volume reduction and an associated drop in reservoir pressure. This process creates several internal sinks (or exits) that may control the spill direction for gas in the field.

Gas geochemistry of the Mobile Bay Jurassic Norphlet Formation: Thermal controls and implications for reservoir connectivity

Using petroleum inclusions to trace petroleum systems – a review

The Wyoming carbon underground storage project: Geologic characterization of the Moxa Arch and Rock Springs Uplift

Mass Spectrometry Techniques for Analysis of Oil and Gas Trapped in Fluid Inclusions

Late Mesozoic and Cenozoic thermotectonic history of eastern, central and southern Mexico as determined through integrated thermochronology, with implications for sediment delivery to the Gulf of Mexico

Downdip-Oil Potential for an Onshore Abu Dhabi Petroleum System

The objectives of the basin modeling part of the South East Abu Dhabi (SEAD) charge evaluation study were twofold: (1) to reconstruct the charge history and explain the known hydrocarbon accumulations including distribution of various oil families (2) to provide a framework for the charge risking in ADCO’s exploration portfolio. The basin model was constructed in ADCO’s offices in Abu Dhabi, using the modeling software PetroMod®. Key input for the model were 29 regional depth maps and 10 associated erosion maps constructed based on the latest 2 and 3D seismic. Isopach maps of the Middle Cretaceous and Base Tertiary tectonic events were created to allow accurate modelling of the basin tilt, which drives the hydrocarbon migration. The model was calibrated with temperature data from available 46 wells and pressure data from 15 wells. The Bab and Hanifa/Jubaila Formations were identified as the main source intervals, with additional contributions from 2nd order source rocks in the Thamama dense zones. Oil and gas migration from these source rocks and the filling of accumulations in the Hanifa, Habshan, Asab, Thamama and Bab reservoirs were all modelled in an integrated way. The model clearly demonstrates that the formation of the Oman foredeep and the tilting of the basin are the main drivers behind the oil generation and migration to SEAD. The migration of the oil generated by the Hanifa/Jubaila source interval in the North is largely lateral until the oil reached the main east-west trending fault zone in SEAD, where vertical leakage along the fault planes took place with most of the oil accumulating in the shallow Thamama reservoirs. The model accurately explains the distribution of various oil families, all discovered accumulations and their phase, as well as the temperature and maturity profile of the basin. New model allowed ADCO to update its existing charge risking matrix and strategy towards de-risking prospects in SEAD.

Ahmed Khouri

Papers

Downdip-Oil Potential for an Onshore Abu Dhabi Petroleum System

Charge Evaluation of South East Abu Dhabi(Part II, Basin Modeling)

Downdip Oil Potential for an Onshore Abu Dhabi Petroleum System