Geological Evaluation of San Diego Norte Pilot Project, Zuata Area, Orinoco Oil Belt, Venezuela

Abstract

The San Diego Norte Pilot Project consists of twelve inclined wells (7 producing wells 300 m (984 ft) apart, plus 5 observation wells) drilled from a cluster, to study the production and compaction behavior under steam soak (huff and puff) of the Tertiary heavy crude oil reservoirs of the Zuata area. This area is located within the Orinoco Heavy Oil belt of Venezuela. A geological model was needed as a base for the reservoir studies and to understand the geological setting. This model was constructed from extensive log information, seismic lines, well samples, and cores. The reservoir sands are friable with an average porosity of 34% and permeabilities ranging from 1 to 7 µm2 (1 to 7 darcys). The sands were deposited in meander belts that stacked up forming multistory bodies. Point bars and channel fills account for 80-90% of the total sand. These sands are internally heterogeneous, sinuous and elongated, and larger than the 1 km2 area covered by the project. The topmost two productive sands, which together average 22 m (72 ft), show the best porosities and permeabilities and are isolated by thick clays that make them suitable for selective steam injection. In the project, the oil has a density of about 1.0 g/cm3 (10° API) and fills all the sands down to the oil-water contact. The depth of this contact is controlled by regional faults. Based on core compressibility tests, compaction is expected to be the principal production mechanism that could increase the expected primary recovery of 4 to 12% by huff and puff steam injection, leading to a possible recovery of 0.64 × 106 m3 (4 million bbl) in six years with four cycles of steam injection.