Delineation of gas sands by seismic stratigraphy in the Pericocal area, Orinoco Heavy Oil Belt, Venezuela

The purpose of this study is to define the extent of gas sand bodies found in the Oficina Formation by well SDZ-79X, in the Pericocal area of the Orinoco Heavy Oil Belt. True amplitude processing was applied to 30 km (19 mi) of seismic survey lines in the vicinity of this well. The processing showed amplitude anomalies on lines ZB-5, SC-B, and PE-2, produced by the interfaces between the relatively low-velocity gas sands and the high-velocity lignites and shales. A model generated from the sonic log of well SDZ-79X was used in order to recognize the gas sands on the seismic section. The pinch outs of the sand bodies were located by the decrease of high amplitudes. Stacking velocities from the seismic, and average velocities from the surrounding wells, shows the existence of a lowvelocity anomaly typical of gas accumulations, thereby confirming the zone of high-amplitude anomalies. As a final result, three isopach maps of the gas sands were prepared, and a volume of 34 billion ft of gas in place was estimated.