Application of Oil Gas-Chromatography in Reservoir Compartmentalization in a Mature Venezuelan Oil Field

Nicolas G. Munoz, Luis Mompart, Suhas C. Talukdar

Gas chromatographic oil "fingerprinting" was successfully applied in a multi-disciplinary production geology project by MARAVEN, S.A. to define the extent of vertical and lateral continuity of Eocene and Miocene sandstone reservoirs in the highly faulted Bloque I field, Maracaibo Basin, Venezuela. Seventy-five non-biodegraded oils (20°-37.4° API) were analyzed with gas chromatography. Fifty were produced from the Eocene Misoa C-4, C-5, C-6 or C-7 horizons, fifteen from the Miocene basal La Rosa and ten from multizone completions. Gas chromatographic and terpane and sterane biomarker data show that all of the oils are genetically related. They were expelled from a type II, Upper Cretaceous marine La Luna source rock at about 0.80-0.90% Ro maturity. Alteration in he reservoir by gas stripping with or without subsequent light hydrocarbons mixing was observed in some oils. Detailed chromatographic comparisons among the oils shown by star plots and cluster analysis utilizing several naphthenic and aromatic peak height ratios, resulted in oil pool groupings. This led to finding previously unknown lateral and vertical reservoir communication and also helped in checking and updating the scaling character of faults. In the commingled oils, percentages of each contributing zone in the mixture were also determined giving MARAVEN engineers a proven, rapid and inexpensive tool for production allocation and reservoir management. The oil pool compartmentalization defined by the geochemical fingerprinting is in very good agreement with the sequence stratigraph c interpretation of the reservoirs and helped evaluate the influence of structure in oil migration and trapping.

AAPG Search and Discovery Article #91020©1995 AAPG Annual Convention, Houston, Texas, May 5-8, 1995