AAPG ANNUAL CONFERENCE AND EXHIBITION
Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA
Geophysical Characterization of an Oligo-Miocene Prospective Interval in Copa Macoya Field, Guárico Sub-basin, Venezuela
(1) Teikoku Oil & Gas Venezuela, Caracas, Venezuela.
(2) IGS Services & Consulting, Caracas, Venezuela.
(3) Universidad Simón Bolívar, Caracas, Venezuela.
The study objective was to determine the boundaries of the gas reservoir within a combine structural /stratigraphic trap located in the eastern side of the field. The prospective interval comprises 89 feet of vertically stacked channel belt sandstones deposited as a response of avulsion and lateral migration of individual channels until its complete abandon. At the same time, seismic attributes evaluation has also been applied at different stratigraphic intervals in the rest of the 3D volume in order to find additional potential gas bearing reservoirs in the field. To accomplish the aim of the study, it was applied a combination of different techniques (AVO, Spectral Decomposition, Seismic Inversion and Coherence) to obtain the best estimation of the remaining gas potential bearing within the 3D block. Three main results were obtained from this methodology: 1) Degree of reliability and applicability of each attribute, 2) classification of each anomaly in based on combination of different attributes, and 3) selection of those with high probabilities of gas. Several variables were analyzed: attribute vs. logs calibrations to discriminate between water and gas sands, areas of intersection of all attributes, evidence of gas in the area and the geological model. The results show that the new gas reservoir within the prospective interval is associated with one anomaly. This anomaly was confirmed by the evidence of gas in one well. Also, it was identified the presence of a flat spot that has been mapped in time and depth maps. The flat spot confirmed the gas-water contact which was reported also in two wells that drilled the reservoir. Stratigraphic and structural features where interpreted using the coherence and spectral decomposition. One of the most important stratigraphic features was an abandoned channel whose geometry is interrupted by the presence of a synsedimentary fault. The fault could have been syntectonic with the deposition of the prospective interval. Finally, the response observed by different attributes was validated by the sedimentological model and also, confirmed the presences of the gas. Regarding AVO analysis, the anomaly P is classified as a Class 3 AVO anomaly associated with a negative gradient and intercept. The fluid factor also confirmed the presence of gas in the prospective interval. The methodology applied in this study allowed an accurate delineation of the potential gas reservoir associated with anomaly P in the study area.