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AAPG Bulletin, V.
Production characteristics of the 
fractured
reservoirs of the La Paz
field, Maracaibo basin, Venezuela
fractured reservoirs of the La Paz
field, Maracaibo basin, VenezuelaR. A. Nelson,1 E. P.
Moldovanyi,2 C. C. Matcek,3
I. Azpiritxaga,4 E. Bueno5
1BP Amoco Corporation, 200 WestLake Park Boulevard, Houston,
Texas 77079-2696; email: [email protected]
2Geological Consultant, present address Vanco Energy Company, One Greenway
Plaza, Houston, Texas 77046; email: [email protected]
3BP Amoco Corporation, 200 WestLake Park Boulevard, Houston, Texas 77079-2696;
email: [email protected]
4Maraven S.A., Caracas, Venezuela; email: [email protected]
5The Andrews Group, Calle 33 No. 145, Cuidad del Carmen, Mexico; email: emilio_bueno@agi_cdc.com.mx
AUTHORS
Ron Nelson has worked professionally within the oil and gas
industry for 25 years, first with Amoco and now with BP Amoco. He provides technology
support and applications in structural geology and fractured reservoir evaluation
company-wide. Ron has worked as a specialist and manager in all the major technical
organizations within his company, including a four-year period on Amoco's Prospect Quality
Team, assigning technical risk to all of Amoco's drilling prospects and acreage capture
worldwide. He holds a B.S. degree in geology from Northern Illinois University and an M.S.
degree and Ph.D., also in geology, from Texas A&M University. He has been an AAPG
Distinguished Lecturer twice, an SPE Distinguished Author, and author of a textbook, Geologic
Analysis of Naturally Fractured Reservoirs.
Eva Moldovanyi received her B.A. degree in geology from Wellesley College (1977), an M.S. degree in geology from the University of Michigan, Ann Arbor (1982), and a Ph.D. in geology from Washington University, St. Louis, Missouri (1990). In 1977 she joined Lagoven S.A. as an operations and development geologist in the Maracaibo basin. Later she joined the carbonates group at PDVSA's research institute, Intevep S.A. With almost 20 years of industry experience in production geology, Eva has also worked for Amoco and is currently an independent contractor, providing consulting services for the evaluation of producing properties and marginal fields.
Charles Matcek has worked for BP Amoco for 23 years as a reservoir engineer, holding various oil and gas assignments in Texas, North Sea, Argentina, Trinidad, and Venezuela. He is currently working in the Anadarko Asset, developing gas reserves in the Texas panhandle area.
Izaskun Azpiritxaga received her engineering degree from the Universidad Central de Venezuela (UCV) in 1979 and an M.S. degree in sedimentology from the University of Texas at Austin in 1991. She formerly worked for Maraven in Caracas and currently works in the Production Technology Department of PDVSA E & P as a stratigraphy-sedimentology specialist focusing on reservoir characterization and modeling technology, including geologic and flow fluid simulation.
Until 1998, Emilo Bueno was a geologist with Maraven, S.A., later PDVSA, Caracas. Emilo is currently a geoconsultant for The Andrews Group, a Core Laboratories Company.
ACKNOWLEDGMENTS
We extend our thanks to members of the former Maraven Management Team, especially Alban Lugo, Ricardo Piña, and Alfonso Riascos, for creating the opportunity to perform these analyses. The team also acknowledges the former Amoco Venezuela and Maraven Management for providing the latitude to pursue this study and, along with BP Amoco, for permission to publish its results. Special thanks are due to the talented technical teams led by Godofredo Diaz and Amelia Quintero, of Maraven's Production Office in Maracaibo, for their cooperation, patience, and generous hospitality extended during the on-site evaluation phase. Special recognition is given to Alvaro Rodriguez, who shared his valuable insight and knowledge regarding La Paz field. Special recognition is also given to Maika Gambus for her tireless efforts to locate, provide access to, and assist in the analysis of performance data. Finally, we thank Gabriel Diaz, Jorge Chirinos, Luis Acosta, Alán Gonzalez, and the all the other former Maraven staff who often took time out of their busy schedules to make this study a success. Fruitful and constructive reviews were provided by Susan M. Agar, Peter A. Bentham, Charles Kluth, Steven Laubach, and William Belfield. Their input significantly improved this manuscript.
ABSTRACT
La Paz oil field is one of the most famous, well-documented
fractured
reservoirs in the world. Since 1945 it has produced more than 830 million bbl of
oil from both low porosity Cretaceous limestones and underlying granitic basement. The
field is situated on a large inversion structure, partially uplifted in the late Eocene,
having the majority of the inversion occurring in the MiocenePliocene. Fracture
distributions, initial rate and cumulative production distributions, and trends in
formation water chemistry all suggest that reservoir quality and reserves are controlled
by natural fractures associated with MiocenePliocene and younger strike-slip faults
and possibly by secondary microporosity related to the geometry of the earlier Eocene
block uplift. Production levels within the area of Eocene uplift are anomalously high,
with one well producing 59 million bbl of oil. Typical wells in other parts of the field
produce 1 million bbl of oil. Analysis of the distributions cited previously suggests that
production has occurred from highly elliptical to linear drainage areas surrounding
faults. These restricted zones of fault-related fractures allow for communication of
hydrocarbons stored in the low porosity rock carbonate matrix to the wellbore. In
addition, diagenetic microporosity may be an important component in matrix storage in the
carbonates and may be due to local subaerial exposure during the Eocene uplift.
This article shows that analysis of the natural fracture system with respect to the production characteristics in even old fields can give rise to new reservoir models, leading to new infill locations within the field limits or additional exploration opportunities in the area.
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