Microresistivity Curve Extraction from Borehole Microimager Data
- Alexandra Roslin (University of Queensland)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2015
- Document Type
- Journal Paper
- 140 - 146
- 2015. Society of Petrophysicists & Well Log Analysts
- 0 in the last 30 days
- 145 since 2007
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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 identification 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.
Although resistivity tools are commonly used in the petroleum exploration, they are not as common in the coal industry. Moreover, the vertical resolution of conventional resistivity tools might exceed several times the thickness of individual coal seams and cannot reliably be used for coal-properties characterization due to this drawback. Microresistivity tools might be of interest in that case but the problem is that these devices are even more rarely exploited in coal studies than conventional resistivity tools.In contrast to microresistivity sondes, high-resolution microresistivity imaging tools are widely used in petroleum exploration, e.g., for formation textural features interpretation and dip determination (Ye et al., 1997; Ye et al., 1998). However, these data are presented as an image (graphical object). The transformation of imaging data into a single microresistivity curve might provide resistivity data with perfect vertical resolution (5 mm). For unconventional reservoirs in general, and coal seams in particular, this level of resolution would enhance the identification of laminations and banding properties used for characterization.
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