Favorable Reservoir Facies Zone Prediction Based on Seismic Inversion in Block a of Venezuela

Abstract

Block A located in the Venezuela Orinoco heavy oil belt is generally a northward monocline, and the target layer is Oligocene-Miocene braided river delta plain sand body, and the burial depth is shallow in the north and is deep in the south. The Miocene Oficina Formation in the Eastern of the Orinoco heavy oil belt was selected as the research area, and the distribution prediction of favorable reservoir sand body was carried out based on seismic inversion analysis methods and techniques, so as to deepen the understanding of spatial distribution law and evolution characteristics of favorable reservoir facies belt, and provide geological basis for the development scheme design of heavy oil.

The sandstone reservoirs of the Block A characterized by shallow burial depth, great thickness, poor cementation and interbed/intercalated mudstone. Most wells are horizontal wells without sonic and density curves in this block. In these cases, it is difficult to achieve the conventional seismic inversion. This paper provides a new method to improve seismic inversion using both vertical and horizontal well data. Firstly, on the basis of sequence stratigraphic framework established, carried out the horizon picking based on the well and seismic data. Then, by jointing the vertical-well inversion and horizontal-well forward, based on Bayesian theory, seismic, logging and geostatistical information are integrated to predict the spatial distribution of sand bodies of the Oficina Formation. The results show that the sand bodies in the Oficina Formation are developed as a whole, and the favorable reservoirs are distributed in the direction of NE-SW, and the distribution range and thickness of the reservoirs gradually decrease from the bottom to the top. The distribution range of mudstone in the lower reservoir is small, with a thickness of 10–30 ft, mainly forming mudstone interlayer; the distribution range of mudstone in the upper reservoir is larger, with a thickness of 20–40 ft, forming a certain scale of interlayer.