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| ==Core and well log analysis== | | ==Core and well log analysis== |
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| + | [[file:evaluating-fractured-reservoirs_fig2.png|thumb|{{figure number|2}}Schematic of typical features to measure and record in core analysis. © van Golf-Racht, 1982; courtesy of Elsevier. Typical recording format from <ref name=pt06r108>Reiss, L. H., 1980, The reservoir engineering aspects of fractured formations: Houston, TX, Gulf Publishing Company, 108 p.</ref>; courtesy of Gulf Publishing Co.]] |
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| The following procedures have proven useful in fracture analyses of core (after <ref name=pt06r95 />): | | The following procedures have proven useful in fracture analyses of core (after <ref name=pt06r95 />): |
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| * Create the fracture stratigraphy (involves steps 5 through 16). | | * Create the fracture stratigraphy (involves steps 5 through 16). |
| * Construct a core deformation strip log at a relevant scale that includes the positioning of major lithology and formation breaks, lost core and noncored intervals, oil-water or gas-water contacts (if available), fractures, and stylolites. Hairline fractures in the core are often difficult to see. These can be enhanced by painting the core with a volatile liquid and observing the drying pattern. Overlooked fractures may “jump out” at the observer by persistence of wetting along hairline fractures reaching the core surface. Additional characterization of hairline or larger fractures internal to the core can be accomplished by core X-radiographs or core computer tomography scans. | | * Construct a core deformation strip log at a relevant scale that includes the positioning of major lithology and formation breaks, lost core and noncored intervals, oil-water or gas-water contacts (if available), fractures, and stylolites. Hairline fractures in the core are often difficult to see. These can be enhanced by painting the core with a volatile liquid and observing the drying pattern. Overlooked fractures may “jump out” at the observer by persistence of wetting along hairline fractures reaching the core surface. Additional characterization of hairline or larger fractures internal to the core can be accomplished by core X-radiographs or core computer tomography scans. |
− | * Record the fracture distribution with depth (Figure 2). (Recording of this and all following data could be done in a tabular format compatible with computer entry to facilitate output compatible with other strip and well logs.) | + | * Record the fracture distribution with depth ([[:file:evaluating-fractured-reservoirs_fig2.png|Figure 2]]). (Recording of this and all following data could be done in a tabular format compatible with computer entry to facilitate output compatible with other strip and well logs.) |
| * Relate fracture distribution to rock type. | | * Relate fracture distribution to rock type. |
| * Record the dip of fractures either real or apparent. | | * Record the dip of fractures either real or apparent. |
| * Back up core observations with appropriate logs from the same zones as core from the well for effective extrapolation to uncored wells (see [[Formation evaluation of naturally fractured reservoirs]]). Record the strike of features if the core is oriented core or if it is locally oriented either mechanically or by oriented logs such as the Borehole Televiewer, Formation MicroScanner, or high resolution dipmeter.<ref name=pt06r101>Plumb, R. A., Luthi, S. M., 1986, Application of borehole images to geologic modeling of an eolian reservoir: 61st Annual Technical Conference of the Society of Petroleum Engineers, New Orleans, LA, Oct. 5–8, SPE 15487, 11. p.</ref> (For more on these methods, see [[Core orientation]], [[Borehole imaging devices]], and [[Dipmeters]].) | | * Back up core observations with appropriate logs from the same zones as core from the well for effective extrapolation to uncored wells (see [[Formation evaluation of naturally fractured reservoirs]]). Record the strike of features if the core is oriented core or if it is locally oriented either mechanically or by oriented logs such as the Borehole Televiewer, Formation MicroScanner, or high resolution dipmeter.<ref name=pt06r101>Plumb, R. A., Luthi, S. M., 1986, Application of borehole images to geologic modeling of an eolian reservoir: 61st Annual Technical Conference of the Society of Petroleum Engineers, New Orleans, LA, Oct. 5–8, SPE 15487, 11. p.</ref> (For more on these methods, see [[Core orientation]], [[Borehole imaging devices]], and [[Dipmeters]].) |
− | * Look for intersection angles of fractures as expressed on the outside surface of the core or on the ends of the samples and record the true or apparent angles (Figure 2). | + | * Look for intersection angles of fractures as expressed on the outside surface of the core or on the ends of the samples and record the true or apparent angles ([[:file:evaluating-fractured-reservoirs_fig2.png|Figure 2]]). |
| * Determine which of the fractures in the core are natural or induced.<ref name=pt06r69>Kulander, B. R., Dean, S. L., 1985, Hackle plume geometry and joint propagation dynamics, in Stephansson, O. ed., Fundamentals of Rock Joints: Proceedings of the International Symposium, Bjorkliden, Sept. 15–20, p. 85–94.</ref> | | * Determine which of the fractures in the core are natural or induced.<ref name=pt06r69>Kulander, B. R., Dean, S. L., 1985, Hackle plume geometry and joint propagation dynamics, in Stephansson, O. ed., Fundamentals of Rock Joints: Proceedings of the International Symposium, Bjorkliden, Sept. 15–20, p. 85–94.</ref> |
| * Describe stylolite distribution (position, rock type, and postulated σ<sub>1</sub>.<ref name=pt06r95 /><ref name=pt06r145 /> | | * Describe stylolite distribution (position, rock type, and postulated σ<sub>1</sub>.<ref name=pt06r95 /><ref name=pt06r145 /> |
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| * Photograph important relationships shown in the core for documentation in reports, if needed. | | * Photograph important relationships shown in the core for documentation in reports, if needed. |
| * Select samples for mechanical testing, if appropriate. | | * Select samples for mechanical testing, if appropriate. |
− | * If needed, set up a checklist of important parameters and document as many parameters as needed on a foot-by-foot basis (on each whole core piece is ideal). Such a checklist should be compatible with direct computer input of the tabular data (see Figure 2). | + | * If needed, set up a checklist of important parameters and document as many parameters as needed on a foot-by-foot basis (on each whole core piece is ideal). Such a checklist should be compatible with direct computer input of the tabular data (see [[:file:evaluating-fractured-reservoirs_fig2.png|Figure 2]]). |
| * Write down impressions and conclusions arrived at before leaving the core. Include thoughts on the relative importance of fractures to production and flow, the permeability of the fractures present, fracture porosity (qualitative), fracture fill and relative compressibility of the fractures, fracture origin and continuity in the reservoir, the percentage of real versus induced fractures, and the fractured reservoir type. | | * Write down impressions and conclusions arrived at before leaving the core. Include thoughts on the relative importance of fractures to production and flow, the permeability of the fractures present, fracture porosity (qualitative), fracture fill and relative compressibility of the fractures, fracture origin and continuity in the reservoir, the percentage of real versus induced fractures, and the fractured reservoir type. |
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− | [[file:evaluating-fractured-reservoirs_fig2.png|thumb|{{figure number|2}}Schematic of typical features to measure and record in core analysis. © van Golf-Racht, 1982; courtesy of Elsevier. Typical recording format from <ref name=pt06r108>Reiss, L. H., 1980, The reservoir engineering aspects of fractured formations: Houston, TX, Gulf Publishing Company, 108 p.</ref>; courtesy of Gulf Publishing Co.]]
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| ==Outcrop analysis== | | ==Outcrop analysis== |