Genetic Facies Characterization of Unstructured Deltaic Reservoirs Using Detailed Stratigraphic Correlations and Computer Generated Maps

Abstract

Ancient deltaic environments contain the predominant light oil producing reservoirs in the United States. Similar deltaic reservoirs in Venezuela, both in the Maracaibo Basin as well as in the Eastern Venezuelan Basin have produced significant amounts of hydrocarbons for the past 60 years. The geologic characteristics of these reservoirs influence the volume distribution and potential recovery of remaining mobil and ommibile oil. One of the primary geological factors that can affect recovery potential is the original condition under which the reservoir sediments were deposited. The depositional processes involved determine reservoir characteristics. In order to understand the major constraint to oil production, the reservoir heterogeneities, E-logs from 1007 wells in 4 townships (144 mi[sup 2]/373 km[sup 2]) in east central Louisiana were correlated in detail. An 800-ft Paleocene Middle Wilcox interval containing stacked deltaic reservoirs was investigated. The correlations include 16 tops and 16 net sand intervals. The resulting data set was loaded into the Terrasciences mapping program from which detailed structural as well as net sand isopach maps could be generated. The net sand geometries and the stratigraphic relationships between the sands, shales and lignites permitted the authors to isolate and identify individual genetic facies within each deltaic sequence. Themore » observed facies found to be oil prone include distributary channel deposits, overbank bay fill and transgressive barrier sands. Understanding the heterogeneities found in deltaic reservoirs are fundamental for planning advanced production methods such as infill and horizontal/slant well drilling and related enhanced oil recovery processes.« less