Reservoir Characterization as a Tool to Identify Opportunities for EOR

Carrizo, Nicolas R.¹ and Schiuma, Mario
¹[email protected]

The purpose of this work is to analyze the conglomerates reservoir of the Quintuco Fm in the "El Medanito" field which has been producing oil for over 50 years.

Despite the waterflood campaign, the recovery factor was low. The description of core from new wells shows that conglomerates have porosities and oil impregnations. The resistivity logs also showed interesting values but when these layers were tested, the majority of them produced mostly low salinity water. The difficulty was the complexity of the poral system and the exogenous water of low salinity due to the secondary recovery and inflow of water due to damage in the casing.

The cross plots Phi/K/Facies shows that the few centimetres thick grain support conglomerates with permeabilities of several Darcys was cyclically alternated with thicker levels of less permeability.

A linking between the rock quality, facies and mineral content confirmed that the lower the carbonate content, the higher the rock quality.

The best poral model was Pitman 10, reinforcing the idea that the hydraulic capacity of the reservoir was controlled by a small portion of it.

The Rock Types identified was
1) High perm: Phie>0.12; K> 1000mD; pore throats diameter: 90microns. Conglomerate grain-support
2) Phie: 0.1 to 0.12 and K: 20 to 200mD; pore throats diameter: 30microns. Conglomerate grain to matrix-support
3) High-risk: Phie: 0.8 to 0.1 and K: 3 to 50mD; Conglomerate matrix-support
4) No Reservoir: Phie<0.1, except for the rock type 3. Calcarenites and limestone

The differentiation of the rock type using logs was done on the basis that the reservoir quality is directly related to the abundance of clastic content, given that it has a high potassium content and low density. Because of high channels are usually thin, not always can they be well identified. In order to know the cyclicity pattern of these, systematic permeability measurements were done and textural interpretation of images.

Thus, these reservoirs have an alternance between the high permeability channels and other less permeable reservoirs. Flow capacity is dominated by the rock type 1. However the lower permeability reservoir significantly thicker than those with high permeability are a lot less drained. This fact allowed explaining the apparent contradiction between the log analysis results and the well test results. It was also established that there is an important volume of remainder oil and it makes attractive for some EOR system.

AAPG Search and Discovery Article #90166©2013 AAPG International Conference & Exhibition, Cartagena, Colombia, 8-11 September 2013