URICH, ALFREDO, and TIBAYDE SANTIAGO, Corpoven, S.A., Caracas, Venezuela

ABSTRACT: Patterns of Sedimentation in the Oficina Formation Central-West Part of Greater Oficina Area, and Their Relationship to Occurrence of Oil and Gas

The Chimire-Boca-Nipa fields are located in the western part of the greater Oficina area an the study covers approximately 800 sq km. A geological model for the Oficina Formation (lower-middle Miocene) based on electric log analysis, petrophysical evaluation, core, electrofacies and isopach maps, seismic data analysis, has been made. The Oficina formation is formed by successive transgressive and regressive cycles, being the most important the ones located in the lower-middle section of this formation.

In this area a fluvial-deltaic system has been identified, where a great number of transgressive-regressive parasequences prevailed. This system consists of three (3) main sub-environments: alluvial valley, delta plain and delta front. The main sand bodies are formed in distributary channels, meander bars and deltaic couples. Occasionally crevasse splays, with associated sandy rupture facies, caused by flooding of the interdistributary bay are recognized. In general, these main sand bodies have a northerly orientation.

The structure of the area is dominated by a gentle (2 to 3 degrees) northerly dip. Oil and gas reservoirs are associated with east-west trending normal faults which cuts this homocline. There is also an element of stratigraphic trapping, as the reservoirs change laterally to shale or low porosity sandstone.

This study has highlighted 20 new prospects which increased the STOIP probable and/or possible by 350 mmb of light oil. Additionally the new geological interpretation of these mature fields will allow improved recovery projects in this area.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.