An Interpretative Model For Naturally Fractured Reservoirs Using Borehole Electrical Images

Structural features in a borehole have been target of<br>reservoir analysts for over many years. Features such<br>as naturally open fractures help interpreters not only<br>to delineate the main structural characteristics of a<br>reservoir, but can also help the interpretation of the<br>main flow patterns during its characterisation.<br>Fractured sandstones are producing reservoirs in<br>many giant oil and gas fields around the world.<br>Recent hydrocarbon discoveries have evidenced that<br>these features can create a producing reservoir even in<br>rocks with very low primary porosity.<br>Detailed analysis of naturally fractured reservoirs<br>shows that most of those reservoir rocks have<br>anisotropic nature with regard to the fracture patterns.<br>This may be due to different stress regimes suffered<br>during deposition or after that. Mapping and<br>quantifying these heterogeneities are critical for<br>precise reservoir characterisation.<br>Most open-hole logs can indicate fractures, but do not<br>provide any in-depth quantitative analysis in terms of<br>their geometrical and petrophysical aspects. In the<br>past, standard logging tools were able to identify<br>some of these structural features, based mainly in the<br>dipmeter and sonic log curves. Today, a complete<br>characterization of these features can be obtained by<br>borehole electrical devices. This article shows the use<br>of this tool and discusses a tentative interpretative<br>model for naturally fractured reservoirs with the<br>quantification of the main reservoir geometrical and<br>petrophysical parameters.