Well Testing Characterization of Heavy-Oil Naturally Fractured Vuggy Reservoirs

Abstract

This paper presents the advances on the characterization of Naturally Fractured Vuggy Reservoirs (NFVR) located in the South East Gulf of Mexico. Halos, fractures and vugs were characterized through well tests using the triple porosity–double permeability (3φ-2k) model. Through the analysis of well and imagelogs was determined the predominance of high vuggyporosity producing intervals, so that the pressure data were analyzed using a triple porosity-double permeability (3φ -2k) approach, with total and partial penetration. These NFVRs have vuggy and fracture porosity, with triple porosity, matrix, fractures, and vugs, or matrix, vugs with their halos. In both cases, the 3φ-2k model is appropriate to characterize these fields. These models, recently presented involve the determination of 9 and 13 parameters, for total and partial penetration, respectively, which implies challenges in terms of the uniqueness of the results. In this way, it is suggested to consider information from other sources like cores, well logs, and image logs, in order to select characteristic values for some of the parameters of the model of interpretation, specifically the storage ratios for vugs and fractures, ωv and ωf, and in this way to eliminate the non-uniqueness problem. Thus, the integration of static and dynamic information is a key element for a complete description of NFVR. The 3φ-2k model allows better data fits than the classical dual-porosity model, obtaining more information related to the interactions of the three different media. The sum of vuggy and fracture porosity obtained from 3φ-2k model is not equal to the secondary porosity obtained from the dual-porosity model. If partial penetration effects are present, it is recommended to perform the analysis taking into account these effects because information on the vertical communication of vugs and fractures can be obtained with the 3φ-2k model. It is confirmed through the analysis of well-tests with partial penetration that the vertical communication of vugs can be more important than the horizontal communication. It is crucial to obtain fracture and vug connectivity in both horizontal and vertical direction, mainly because these reservoirs are sharing a common aquifer. The objective of this work is to demonstrate the application of a 3φ-2k model to determine several parameters related to reserves and productivity of NFVR. Vertical connectivity of both vugs and fractures are important parameters when an aquifer is underlying heavy oil NFVR, because these areas could establish preferential routes for the advancement of water.

Quasi-Analytical Model of the Transient Behavior Pressure in an Oil Reservoir Made Up of Three Porous Media Considering the Fractional Time Derivative

“…Some variants made in order to make the existing models more robust were made, such as Camacho-Velazquez et al [15], who resumed their proposed model for fully and partially penetrated deposits incorporating information from pressure tests, imagelogs, cores, well logs, among others. In this work, they concluded that vertical communication between vugs may be more important than their horizontal communication in partially penetrated wells.…”