PAXTON, STANLEY T., Exxon Production Research Co.; GARY C. STONE, Exxon Corp.; B.L. FAULKNER, Exxon Production Research Co.

Abstract: Regional Distribution of Reservoir Quality, Venezuela

The re-opening of Venezuela to exploration by the international industry has focused on generally unproved areas. Early reconnaissance of the ten blocks tendered in Exploration Round 1 indicated that reservoir quality (RQ) was likely to be a primary risk. For many of the blocks, reservoirs were expected to contain finer-grained facies, to be derived from diverse sediment-source areas (provenances), and to be situated in areas of deep and complex burial. Exxon's analyses suggest that regional variations in the quality of Venezuelan sandstone reservoirs are due primarily to regional differences in sediment provenance, burial temperatures, and, in some cases, fracture susceptibility.The data also suggest that through time there is a clear regional segregation of provenances and burial temperatures that reflect the tectonic evolution of northern South America. Consequently, the major clastic reservoir intervals are divisible into broad sandstone groups that have responded quite differently to burial compaction, burial temperature, and tectonic stress.

Toward an understanding of the regional RQ in Venezuela, this poster presentation will review the 1) methodology used to evaluate and map regional RQ, and 2) discuss implications of the RQ findings to future round evaluations.

Methodology

RQ in any basin is governed by a finite number of factors that are both quantifiable and mappable within the context of the regional geology (Figure 1). These factors, or controls, include burial temperature, fluid pressure, fluid types/chemistry, provenance, sandstone grain size/sorting, depositional matrix, and fracture susceptibility. Data pertaining to each of these controls were collected, posted, and mapped by the project teams. A single composite map was constructed for each of the major reservoir intervals. Each "sweet spot" map shows the geographic distribution of where in the basin, due to coincidence of favorable conditions, optimum RQ should be preserved (Figure 2).

Future Evaluations

Assuming sand presence, regional world class RQ potential exists in areas broadly defined by favorable provenance and/or short effective heating time.These areas include the a) Upper Miocene/Pliocene intervals in far eastern Venezuela, b) Miocene of the Lake Maracaibo area, and c) shallow to intermediate depth intervals east of the Oficina area, in eastern Venezuela. In addition to these broadly defined areas, excellent RQ potential exists locally within areas predicted to be at risk regionally. However, locating occurrence of producible reservoir within these areas of complex burial history requires prospect-scale detail, with attention paid to rapid, local changes in the tectonic and thermal history.
 
 

Figure 1. Scale-dependent hierarchy of reservoir-quality and -performance controls.

Figure 2. Approach to recognizing reservoir-performance fairways.

AAPG Search and Discovery Article #90923@1999 International Conference and Exhibition, Birmingham, England