There is a common saying within the oil and gas industry that the best place to find oil is in an oil field.
It is less common to expect to find hydrocarbons in a meteor crater. But an enterprising group of folks in the Ukraine are hoping to prove, through the application of 3-D geomodeling and inversion, that this might be the perfect place to start looking.
The researchers, who hail from the Ivanko-Frankivsk University of Oil and Gas, Deproil Ltd., and Naftogaz of Ukraine, outlined their findings during a group of talks related to unconventionals at the recent European Association of Geoscientists and Engineers meeting. Their study area is the Obolon astrobleme in the central part of Ukraine.
The authors noted that the search for this type of exploration target has been necessitated by the depletion of conventional oil and gas reservoirs in the country. In addition to shale gas, basin-centered gas, and coalbed methane, they found the potential for hydrocarbon deposits associated with impact structures to be promising, partly based on the work of Richard Donofrio, who indicated 1 in a 1998 paper that drilling around North American astroblemes had resulted in 50% drilling success.
But one does not simply go poking holes in the ground around the rim of a crater. The study approached the Obolon astrobleme with the idea of revealing reservoirs associated with the impact structure. Based on the complex geology, the researchers applied extensive geophysical research including 3-D seismic; gravity and magnetometric surveys; and geochemical, emanational, and thermometric studies.
The authors broke the study down into a series of steps. Step one consisted of the construction of a 3-D structural model based on the 3-D seismic, which included five structural horizons. This model indicated that the crater is roughly isometric and has a low-amplitude central uplift.
Step two included the construction of the initial 3-D property model. The researchers used rock density as a parameter for this model since maximum variations of density are associated with an increase in porosity and hydrocarbon saturation.
Step three used gravity inversion to determine the model’s optimal parameters and added more geophysical and geological data. The final step used model analysis to delineate the lowest density areas within target rocks, ejecta, and the overlying filling complex.
Overall the study determined that the astrobleme has favorable structural settings. Then it was time to high-grade the prospects. Here is where the magnetic survey and geochemical, emanational, and thermometric surveys came into play. “The last ones were used as indicators of integrity/tectonic fragmentation of predicted reservoirs and as indicators of areas with potential deposits destruction characterized by higher activities of hydrocarbon migration,” the authors noted. “As a method of geophysical and geochemical data joint analysis, we used statistical methods for classifying the territory using multiple parameters.”
The researchers concluded that this complex study made it possible for them to confidently identify areas of reservoir presence within the Obolon astrobleme with a high probability of hydrocarbon saturation and high-grade prospects for exploration. “The studies give evidence of the special importance of data integration, joint geophysical inversion, and analysis of multiple datasets for effective studying of unconventional and complex objects [such as] astroblemes,” the authors concluded.
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