New Frontiers in Formation Evaluation Based on Information from a New Three-Dimensional Array Induction Tool, and Geological Analysis in Fluvial-Deltaic Gas Reservoirs at Area Mayor, Anaco, Venezuela

Gomez, German¹, Karen Blanca², Felix Merchan², Mario Gomez², Carlos Minetto¹ (1) Baker Hughes, El Tigre, Venezuela (2) PDVSA Gas, Anaco, Venezuela

The Area Mayor of Anaco is located at the Eastern Venezuelan Basin. Structurally, it is formed by a sequence of linearly aligned domes (with a NE-SW direction) along a reverse fault known as “Corrimiento de Anaco”. The stratigraphic column of the Oficina Formation (lower Miocene), where the target zone is located, is composed of intercalations of sand­shale bodies in a fluvial-deltaic system.

Petrophysical evaluations, performed in the potentially productive intervals of the Area Mayor, traditionally have been based in the response of conventional logs (Resistivity and Porosity), interpretations of Isopach and Structural maps and production data from wells in the area. The greatest uncertainty is found in laminated sands, where low resistivities and the poor quality of the rock, observed in the logs, add doubts regarding the types of fluids and producibility of the reservoir.

Modern methodologies in Formation Evaluation from the new Three-dimensional resis­tivity measurements, which include Horizontal and Vertical resistivity, in combination with Stratigraphic and Sedimentological analysis, aid in the generation of volumetrically balanced models. In this manner, more realistic values of shale content and distribution (Structural, Disperse, or Laminar), porosity and water saturation are obtained and therefore, the static reservoir model is actualized. The methodology incorporates new reserves and adds exploitation plans to sands thought to be non prospective.

Examples of the results of this new methodology are presented, showing the addition of valuable reserves and gas production registered at the wells located in the areas evaluated.