Abstract

Since 1996, International Reservoir Technologies (IRT) and Petroleos de Venezuela, SA (PDVSA) have completed four (4) integrated studies within Block V Lamar, Block VI Lamar, Block V Centro, and Centro Sur Lago Areas of Lake Maracaibo, Venezuela. These studies have identified four major and numerous minor "positive flower" structures along confining bends of three major strike slip faults. These flower features provide the structural trap that has accounted for some 623 MMstb of oil production from the Eocene Misoa B and C sands.

Positive flower structures are often dismissed as non-existent and are often interpreted as reactivated normal faults with reverse movement. Although the normal displacement is true on the examples shown in this paper, we will show several examples of bounding arcuate reverse faults that coalesce into a single fault at depth commonly referred to as "Positive Flower" structures.

3D seismic, in conjunction with dipmeters, logs, fluid contacts, engineering tests and production data provided the necessary information to build a detailed, comprehensive and consistent 3D geologic model of these structures. The integration and use of all possible data sources was key to accurately mapping the associated reservoirs.

The studies have led to improved knowledge of the timing and development of flower structures with respect to hydrocarbon migration and trapping. Production continues in these structures and development drilling continues both within the flower structures and to drain oil that has been trapped on the underside of bounding reverse faults. The integrated study approach has lead to optimized development of these complex "Positive Flower" structures, but is also applicable to other structural and stratigraphic regimes.

Introduction

Positive flower structures develop along restraining or convergent bends in a strike-slip fault (Harding, 1985), where the change in the direction of the trace of the fault is opposed to the sense of the offset. The result is an en echelon series of uplifted blocks and folded structures that are separated by reverse faults that steepen and root into a main strike-slip fault. The first mention of these faults is reported to be by Rod (1956) at outcrops along the Oca Fault, Venezuela. Since that time numerous others have reported the existence of positive flower structures, (Harding, et al, 1983), (Schlische and Ackermann, 1995), (Robb, et al, 2002), (Lindenbeck, et al, 1997), (Sylvester and Smith, 1976), (Edwards and Kidd, 1996), (Holdsworth, 1989), and (Stea, 1995). Pull-apart structures along releasing bends in strike-slip faults generate negative flower structures, (Litak, et al, 1998), (Aksu, et al, 2000), (Nemoek and Nemoek, 1998).

In the Maracaibo Basin area of northern Venezuela a series of strike-slip faults developed near the end of the Eocene as the South American plate continued a north and west migration and interacted with the Caribbean plate. Major strike-slip faults that developed are shown in Figure 1 and are from west to east, respectively, the Tigre, Icotea, Pueblo Viejo and Valera faults (Lugo, 1991). These faults are believed to have originated as normal faults during the Jurassic extensional phase and were periodically reactivated from Jurassic through Early Miocene time. Displacement along some of these major faults, including the Icotea Fault that passes just west of Block V Centro and Block VI Lamar, changed from extensional to left-lateral strike-slip sometime during Middle to Late Eocene time as oblique compression occurred between the Caribbean and South American plates (Pindell et al, 1998). Several of these strike-slip faults have formed "pop-up" features along the location where the rooted fault changes direction. The following discussion details the integrated methodology used to map these features.

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