--> Characterization of Carbonates Through High Definition Borehole Images: Examples from Texas & Oklahoma (presented by D. Andjelkovic and T. Hunt)

AAPG Annual Convention and Exhibition

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Characterization of Carbonates Through High Definition Borehole Images: Examples from Texas & Oklahoma (presented by D. Andjelkovic and T. Hunt)

Abstract

The presence of heterogeneity in carbonates, pose a challenge for the characterization of such rocks. Conventional logging technologies do not have the necessary resolution to address such variabilities and the identification of textural variations, within a carbonate body, is important to highlight intervals of diagenetically altered matrix, and discover additional porosity hidden from the standard resolution measurements. Advanced techniques in borehole image analysis have been applied to carbonate data sets from Permian aged rocks from Texas and have highlighted intervals characterized by various heterogeneities which can be interpreted as developed vugs. Such heterogeneities can be additionally classified in reference to their connectivity and their intersection to fractures or to bed boundaries, always observed on the borehole image, finally exposing intervals differently characterized by vugs connected to fractures, vugs connected to bed boundaries, isolated vugs or vug to vug connected. The identification and analysis of heterogeneities in carbonates, based on borehole images, is not a novelty (Delhomme, 1992; Newberry et all, 1996; Akbar et al, 2008;) but a newly revisited workflow (Yamada et al 2013) allows for an even more detailed description of such texture. The proposed workflows starts with the creation of a full borehole image, generated using multipoint statistics, and providing a 360 degrees full borehole coverage image. From this image a matrix computation is performed on the calibrated image, allowing the extraction of the background conductivity utilized in the following step. Once the background conductivity is delineated, a series of cut offs are applied based either on the contrast or based on the resistivity values between matrix resistivity and heterogeneity resistivities. The output of this step is the delineation of conductive and resistive heterogeneities in respect to the background matrix. Superimposing the delineated heterogeneities, together with bed boundaries and natural fractures, allows the identification of vugs connected to fractures and/or vugs connected to bed boundaries or solution enlarge boundaries. A defined connectivness allows the identification of isolated vugs versus connected vugs. This methodology was applied to various carbonate data set from the Permian succession of Texas and have been helpful for the operators in characterizing the full porosity distribution in the reservoir.