In the last decade, shale resource exploitation has transformed North American production capacity through technological improvements in horizontal drilling and the ability to efficiently stimulate horizontal wellbores using multiple hydraulic fractures. The 2011 U.S. Energy Information Administration estimates there are unproved, technically recoverable shale gas resources of 827 Tcf (in addition to 20.1 Tcf of reserves) in the USA alone. Exploration and exploitation of Middle East organic-rich shales are just beginning, and discovery of economically viable resources requires a concerted effort. While Middle East resources in place could be much greater than those in North America, "sweet spots" need to be found in which established source rocks can also function as reservoirs. Evaluating these opportunities requires refined reservoir characterization workflows rather than the statistical approach that characterized early development of North American shale plays, which benefited from high gas prices, numerous existing wells, and infrastructure to support drilling and fracturing. With lower well density and higher well costs than in North America, successful exploration for unconventional hydrocarbon resources in the Middle East will necessarily rely more on modeling. A petroleum systems–oriented approach defines sweet spots by predicting reservoir quality and potential completion quality. Using proven and effective tools, sweet spots are identified early in the life of unconventional plays. Since reliable, comprehensive data concerning the behavior of shale resource systems under varying conditions are not widely available in the Middle East, petroleum systems modeling would yield key risk and value information. Standard petroleum systems modeling tools have recently been improved, providing more accurate results based on experience of modeling unconventional plays. By extending traditional basin and petroleum systems modeling with sophisticated adsorption functionality, the modeling of hydrocarbon adsorption on kerogen and primary migration within tight source rocks has been significantly enhanced. These methods have the potential to improve the efficiency and effectiveness of Middle East shale resource evaluation.

No abstract

Prediction of pore pressure and porosity in an unconventional resource assessment area of Abu Dhabi was performed by using petroleum systems modeling techniques, combining seismic and well data and geological knowledge to model sedimentary basin evolution. The study objective was ultimately to reconstruct basin history and key geological structures as a basis for further geomechanical and fracture prediction studies. Twelve surfaces were interpreted from seismic data and derived from isopach maps. These maps were used to construct the basin model. The model was built from the top of the surface sediment down to the Shuaiba formation. Sediment decompaction was modeled, which enabled the reconstruction of the formation structures through time. Athy's law, formulated with effective stress, was used in the forward modeling simulator for the calculation of pore pressure. Information such as formation ages, erosional events, and hiatus periods were taken into account during simulation. The evolution of porosity, pore pressure, temperature, and thermal maturity through time were simulated and calibrated to measured data. Model porosity is dependent on burial depth, weight of the overburden sediment columns, and lithology properties. Porosity calibration was achieved by adjusting the compaction curve to effective stress. Pore pressure was calibrated by adjusting lithology porosity-permeability relationships. Lowpermeability lithologies result in high pore pressure. A regional Paleocene pore pressure reduction was observed, caused by substantial erosion of the Simsima formation. Generally, formation overpressure is observed at greater depth. Additionally, modeled overpressures depend on the evolution of connate water vectors over geological time; these vectors depend on multiple lithology parameters as well as the capillary entry pressure of adjacent model layers. In the Shilaif fm, overpressure zones were identified at the anticlinal structures. Interestingly, higher overpressure was observed in the shallower anticlinal structure. The simulation results provide the estimated porosity and pore pressure in the unconventional play, as well as the reconstruction of the overall basin geometry through time. The resulting models were subsequently used as the basis for further fracture prediction studies; results were ultimately consistent with faults derived from existing seismic interpretation. Model porosity, pore pressure, and predicted fractures will be used for the development of static geological and dynamic reservoir models.

No abstract

Petroleum system modeling has mostly been the preserve of exploration departments in major oil companies, which have the specialist resources to execute these studies. However, as it is a dynamic tool for petroleum system analysis, it also has significant applications in the development stages.It may provide information on several different aspects of the areas surrounding a discovery: taken place (e.g.biodegradation, multi-phase hydrocarbon filling, thermal maturation, water washing, gravitational segregation, hydrocarbon migration along faults, etc). This provides the best possible definition of the charge, temperature and pressure histories, which will then be available to improve analyses of the genesis and distribution of Hydrocarbons.