Changes

A large amount of data is available to the production geologist for reservoir evaluation. Much of the data will have been expensive to acquire, particularly if obtained from wells offshore. For instance, core taken from a drilling operation on an offshore drilling rig may have cost more than a million dollars to recover. There is an obligation to take good care of the data and to make sure that the information is accessible, either as well-organized paper data files or as data on a computer shared drive. Data files stored on a computer should be labeled with the originator's initials, a date, and some idea of the significance of the data, e.g., "MS August 31, 2008, final top reservoir depth map." Well files should be compiled with all the available data collected on a well-by-well basis. Good data management can make all the difference between a project that is well organized and effective, and one that is disorganized and inefficient.

A large amount of data is available to the production geologist for reservoir evaluation. Much of the data will have been expensive to acquire, particularly if obtained from wells offshore. For instance, core taken from a drilling operation on an offshore drilling rig may have cost more than a million dollars to recover. There is an obligation to take good care of the data and to make sure that the information is accessible, either as well-organized paper data files or as data on a computer shared drive. Data files stored on a computer should be labeled with the originator's initials, a date, and some idea of the significance of the data, e.g., "MS August 31, 2008, final top reservoir depth map." Well files should be compiled with all the available data collected on a well-by-well basis. Good data management can make all the difference between a project that is well organized and effective, and one that is disorganized and inefficient.

Obtaining data in an oil field environment is expensive; therefore, it is necessary to justify the economics of gathering the information. In the early stage of field life, the value of information is enormous; the data are essential for reservoir evaluation. Later on in field life, it becomes more important to justify the expense of the data. The new information should be gathered on the basis that it significantly improves the project value and reduces the company's investment risk (Gerhardt and Haldorsen, 1989).

Obtaining data in an oil field environment is expensive; therefore, it is necessary to justify the economics of gathering the information. In the early stage of field life, the value of information is enormous; the data are essential for reservoir evaluation. Later on in field life, it becomes more important to justify the expense of the data. The new information should be gathered on the basis that it significantly improves the project value and reduces the company's investment risk.<ref name=Gerhardtandhaldorsen_1989>Gerhardt, J. H., and H. H. Haldorsen, 1989, On the value of information: Presented at Offshore Europe, Society of Petroleum Engineers, September 5–8, Aberdeen, United Kingdom, [https://www.onepetro.org/conference-paper/SPE-19291-MS SPE Paper 19291], 11 p.</ref>

==Types of data==

==Types of data==

The mud loggers on the rig site will monitor the drilling parameters during the well operation, and these are summarized graphically as a mud log. The mud log will include a lithology log. This is a depth plot showing in graphical form the percentage of the various lithologies in each cutting sample recovered while drilling the wellbore. A written description will be made for the lithology of the drill cuttings. Accompanying the lithology log is a record of the rate of penetration of the drill bit. This is an indication of lithology; sandstone is normally drilled faster than shale for instance. Any drilling problems encountered or changes in the drilling parameters will be reported in the margins of the mud log. The presence of oil shows will be noted. The gas returns and gas chromatography analysis are monitored and graphed against depth. High gas returns are a sign that a hydrocarbon reservoir may have been drilled. Significant concentrations of the higher alkanes on the gas chromatograph can indicate that an oil zone has been penetrated. The mud log is used as a first pass, qualitative indication of reservoir presence and quality. A more detailed and accurate representation will be available once wireline logs have been run and interpreted.

The mud loggers on the rig site will monitor the drilling parameters during the well operation, and these are summarized graphically as a mud log. The mud log will include a lithology log. This is a depth plot showing in graphical form the percentage of the various lithologies in each cutting sample recovered while drilling the wellbore. A written description will be made for the lithology of the drill cuttings. Accompanying the lithology log is a record of the rate of penetration of the drill bit. This is an indication of lithology; sandstone is normally drilled faster than shale for instance. Any drilling problems encountered or changes in the drilling parameters will be reported in the margins of the mud log. The presence of oil shows will be noted. The gas returns and gas chromatography analysis are monitored and graphed against depth. High gas returns are a sign that a hydrocarbon reservoir may have been drilled. Significant concentrations of the higher alkanes on the gas chromatograph can indicate that an oil zone has been penetrated. The mud log is used as a first pass, qualitative indication of reservoir presence and quality. A more detailed and accurate representation will be available once wireline logs have been run and interpreted.

The mud loggers also collect bags of rock cutting samples at regular intervals while the well is being drilled. These may be used later for biostratigraphic and lithological analysis (Whittaker, 1992).

The mud loggers also collect bags of rock cutting samples at regular intervals while the well is being drilled. These may be used later for biostratigraphic and lithological analysis.<ref name=Whittaker_1992>Whittaker, A., 1992, [[Mudlogging]]: The mudlog, in D. Morton-Thompson and A. M. Woods, eds., [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Development geology reference manual]: AAPG Methods in Exploration Series 10, p. 101–103.</ref>

==Core data==

==Core data==

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[[File:M91Ch6FG41.JPG|thumb|300px|{{figure number|2}}Example of a core photograph. The photograph shows the channel margin facies association from deep-water sediments of the Nelson field, UK North Sea (from Kunka et al., 2003). Reprinted with permission from the Geological Society of London, whose permission is required for additional use.]]

[[File:M91Ch6FG41.JPG|thumb|300px|{{figure number|2}}Example of a core photograph. The photograph shows the channel margin facies association from deep-water sediments of the Nelson field, UK North Sea (from Kunka et al.<ref name=Kunkaetal_2003>Kunka, J. M., G. Williams, B. Cullen, J. Boyd-Gorst, G. R. Dyer, J. A. Garnham, A. Warnock, A. Davis, and P. Lynes, 2003, The Nelson field, Blocks 22/11, 22/6a, 22/7, 22/12a, UK North Sea, in J. G. Gluyas and M. H. Hichens, eds., United Kingdom oil and gas fields, commemorative millennium volume: Geological Society (London) Memoir 20, p. 617–646.</ref>). Reprinted with permission from the Geological Society of London, whose permission is required for additional use.]]

{| class = "wikitable"

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| 12 || 2250.42 || 672.00 || - || 15.3 || 51.30 || 1.2 || 2.65

| 12 || 2250.42 || 672.00 || - || 15.3 || 51.30 || 1.2 || 2.65

|-

|-

| 13 || 2250.75 || colspan = 6|Preserved sample

| 13 || 2250.75 || style="text-align:center" colspan = 6|Preserved sample

|-

|-

| 14 || 2300.00 || 76.30 || - || 9.5 || 47.90 || 5.6 || 2.54

| 14 || 2300.00 || 76.30 || - || 9.5 || 47.90 || 5.6 || 2.54

''^{1 = horizontal permeability to air (md.) 2 = vertical permeability to air (md). 3 = core porosity (%). 4 = core oil saturation (%). 5 = core water saturation (%). 6 = grain density (g/cm³).}''

''^{1 = horizontal permeability to air (md.) 2 = vertical permeability to air (md). 3 = core porosity (%). 4 = core oil saturation (%). 5 = core water saturation (%). 6 = grain density (g/cm³).}''

The depths at which preserved core samples have been picked will also be listed. These are selected pieces of core that are kept to preserve the conditions of the rock as close to those in the reservoir as possible. They may be required for special core analysis such as wettability studies (Bajsarowicz, 1992). One preservation method is to store the samples in sealed jars containing simulated formation brine.

The depths at which preserved core samples have been picked will also be listed. These are selected pieces of core that are kept to preserve the conditions of the rock as close to those in the reservoir as possible. They may be required for special core analysis such as wettability studies.<ref name=Bajsarowicz_1992>Bajsarowicz, C. J., 1992, [[Core alteration and preservation]], in D. Morton-Thompson and A. M. Woods, eds., [http://archives.datapages.com/data/alt-browse/aapg-special-volumes/me10.htm Development geology reference manual]: AAPG Methods in Exploration Series  10, p. 127–130.</ref> One preservation method is to store the samples in sealed jars containing simulated formation brine.

A core gamma log will also be included in a core analysis report. The gamma-ray response is measured along the length of the core in the laboratory. It is used to match up the core depths to the depths on the wireline gamma-ray log run over the cored interval in the reservoir. These can differ from about half a meter to sometimes more than 6 m (18 ft). This is because over a distance of 2000 or 3000 m (6500 or 10,000 ft) within the borehole, the drill string to which the core barrel is attached will stretch under tension a few meters more or less than the wireline to which the log is attached. Also, incomplete recovery of core, particularly unconsolidated core, can lead to discrepancies in the core log. Comparison of the core gamma with the wireline gamma log allows the core-to-log shift to be determined. This is important for matching features in the core to the equivalent log response.

A core gamma log will also be included in a core analysis report. The gamma-ray response is measured along the length of the core in the laboratory. It is used to match up the core depths to the depths on the wireline gamma-ray log run over the cored interval in the reservoir. These can differ from about half a meter to sometimes more than 6 m (18 ft). This is because over a distance of 2000 or 3000 m (6500 or 10,000 ft) within the borehole, the drill string to which the core barrel is attached will stretch under tension a few meters more or less than the wireline to which the log is attached. Also, incomplete recovery of core, particularly unconsolidated core, can lead to discrepancies in the core log. Comparison of the core gamma with the wireline gamma log allows the core-to-log shift to be determined. This is important for matching features in the core to the equivalent log response.

The second report received is the core photography report ([[:file:M91Ch6FG41.JPG|Figure 2]]). This is a set of color photographs of the slabbed core. The geologist can keep this in the office as a substitute for a trip to the core storage location to see the actual rock. If any oil is present in the core, the core will also be photographed under ultraviolet light. Any oil-saturated intervals will show up as fluorescent patches on the photographs.

The second report received is the core photography report ([[:file:M91Ch6FG41.JPG|Figure 2]]). This is a set of color photographs of the slabbed core. The geologist can keep this in the office as a substitute for a trip to the core storage location to see the actual rock. If any oil is present in the core, the core will also be photographed under ultraviolet light. Any oil-saturated intervals will show up as fluorescent patches on the photographs.

[[File:M91Ch6FG42.JPG|thumb|300px|{{figure number|3}}Example of a sedimentological core log, Well d-2-C/94a-16, Peejay field, Canada (after Caplan and Moslow, 1999).]]

[[File:M91Ch6FG42.JPG|thumb|300px|{{figure number|3}}Example of a sedimentological core log, Well d-2-C/94a-16, Peejay field, Canada (after Caplan and Moslow<ref name=Caplanandmoslow_1999>Caplan, M. L., and T. F. Moslow, 1999, [http://archives.datapages.com/data/bulletns/1999/01jan/0128/0128.htm Depositional origin and facies variability of a Middle Triassic barrier island complex, Peejay field, northeastern British Columbia]: AAPG Bulletin, v. 83, no. 1, p. 128–154.</ref>).]]

==The sedimentology report==

==The sedimentology report==

It is good practice to call in an expert sedimentologist to look at the core and to provide a detailed sedimentological report. The report will include a sedimentological log with a detailed description of all the sedimentological features seen in the core ([[:file:M91Ch6FG42.JPG|Figure 3]]). Various details will be noted (Blackbourn, 1990).

It is good practice to call in an expert sedimentologist to look at the core and to provide a detailed sedimentological report. The report will include a sedimentological log with a detailed description of all the sedimentological features seen in the core ([[:file:M91Ch6FG42.JPG|Figure 3]]). Various details will be noted.<ref name=Blackbourn_1990>Blackbourn, G. A., 1990, Cores and core logging for geologists: Caithness, Whittles Publishing, 120 p.</ref>

These include:

These include:

==Wireline and LWD logs==

==Wireline and LWD logs==

Wireline logs are run in wells to determine the physical properties of the rock and fluids in the borehole (Table 3). From this, a detailed interpretation can be made of the geology and fluid saturations in the reservoir interval. A brief summary of these logs is provided here. For more details, the textbooks by Serra (1984), Rider (1996), and Luthi (2001) can be consulted.

Wireline logs are run in wells to determine the physical properties of the rock and fluids in the borehole (Table 3). From this, a detailed interpretation can be made of the geology and fluid saturations in the reservoir interval. A brief summary of these logs is provided here. For more details, the textbooks by Serra,<ref name=Serra_1984>Serra, O., 1984, Fundamentals of well-log interpretation: 1. The acquisition of logging data: Amsterdam, Elsevier, 423 p.</ref> Rider,<ref name=Rider_1996>Rider, M. H., 1996, The geological interpretation of well logs: Caithness, Whittles Publishing, 300 p.</ref> and Luthi<ref name=Luthi_2001>Luthi, S. M., 2001, Geological well logs: Their use in reservoir modelling: Berlin, Springer-Verlag, 373 p.</ref> can be consulted.

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