This paper describes a new automatic processing methodology for extracting microresistivity curves from electrical borehole images in unconventional reservoirs. Real wireline geophysical data were used to develop the technique.
Resistivity curves are mostly used for reservoir identifcation when the separation between shallow and deep readings is interpreted as a sign of permeable layer. Being true for the conventional reservoirs, this rule does not work for the unconventional ones, the coal-seam-gas reservoir is among them. The latter is described by more complex relationships between its formation properties and most of them are still to be established.
Coal-seam reservoirs are commonly characterized by their density and fracture distribution, which, in turn, affects wireline geophysical-log response. Both of the former mentioned properties are related to the lithotype layering, or brightness, and the thermal-maturity rate and this study investigates the use of microresistivity data for their determination.
Borehole electrical images have been chosen as a source of microresistivity data and an algorithm for extraction of these data from microresistivity images has been created.
Data from a specific commercial microresistivity imaging tool data were used with this algorithm, which may require some adjustment to be used with other microimagers. It should be noticed that raw data from the microimager were used prior to any static or dynamic processing.