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Fracture Characterization and Data Analysis of the Poland Unconventional Shale Play and Relation to Other Unconventional Plays

Abstract

The purpose of this work was to understand the natural fracture characteristics, their distribution, and the controlling factors of the Silurian-Ordivician Poland shale play. The data set includes five Marathon cores, four legacy cores, and five borehole image (BHI) logs. This dataset has provided a unique opportunity to analyze basin-scale (approximately 2.3 million gross acres) tectonism and fracturing. The interpretations indicate a mix of fold-related, fault-related, and regional fractures. The data show that the best fracture characteristics (tall, planar, and open/partially open) exist in the Wenlock and Upper Caradoc intervals. Average quantitative natural fracture intensity is 10.86 fractures per meter, with an average of 76% cementation (from core analysis). Mapping in the Baltic Bain shows the highest total fracture intensity (>15 fractures/meter) is in the north Kwidzyn concession. Fracture intensity of target intervals has a positive map correlation with shear (rigidity) modulus. Orientation data from BHI logs show NW-SW fault trends, suggesting a strong relationship with the regional tectonic paleostressses of the Caledonian orogeny (~450-420Ma). Quantitative fracture counts over multiple data types (core, computed tomography (CT), core photographs, and BHI logs) allow for comparison of data sets. The CT scans resolved an average of 44% of fractures described in core, and is also useful for analysis of undisturbed core to attain natural fracture intersection angles. The BHI logs only resolved an average of 5.2% of fractures described in core, they provide qualitative unit to unit relative natural fracture intensity and bedding data, useful to determine feature orientation, fracture domains, and large-scale tectonic features. The Poland shales studied display higher quantitative natural fracture intensity and higher rigidity than five other unconventional reservoirs studied in the same manner. In addition, within the population of fold-related fractures, a strong correlation exists between the distribution of fracture intensity and rigidity. The poor correlation of fracture intensity between core and BHI is typical of all these plays in vertical wells. The best correlations between core and BHI results have occurred in horizontal wells. Across the plays studied, natural fractures in the Poland shale reservoirs could have the biggest effect on production and stimulation.