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| ===Unconformities and subcrops=== | | ===Unconformities and subcrops=== |
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− | [[Mapping unconformities|Surfaces of unconformity]] can be especially useful [[Marker|marker horizons]] for structure contour mapping ([[:file:subsurface-maps_fig2.png|Figure 2]]). In many fields, unconformities are the location of sealing [[shale]]s and/or source rocks above reservoir pay. [[Subcrop map]]s, traces of productive zones, barriers, or marker horizons mapped on the unconformity surface are invaluable for planning well placement and for [[Field development|reservoir development]]. | + | [[Mapping unconformities|Surfaces of unconformity]] can be especially useful [[Marker|marker horizons]] for structure contour mapping ([[:file:subsurface-maps_fig2.png|Figure 2]]). In many fields, [[Unconformity|unconformities]] are the location of sealing [[shale]]s and/or source rocks above reservoir pay. [[Subcrop map]]s, traces of productive zones, barriers, or marker horizons mapped on the unconformity surface are invaluable for planning well placement and for [[Field development|reservoir development]]. |
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| ===Pressure=== | | ===Pressure=== |
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| ===Isopach=== | | ===Isopach=== |
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− | A contour map of equal values of true stratigraphic thickness is an ''isopach map'' ([[:file:subsurface-maps_fig4.png|Figure 4]]). Except for vertical wells in horizontal beds, corrections for [[Wellbore trajectory|wellbore deviation]] and formation [[dip]] are needed to make isopach maps. | + | A [[contour]] map of equal values of true stratigraphic thickness is an ''isopach map'' ([[:file:subsurface-maps_fig4.png|Figure 4]]). Except for vertical wells in horizontal beds, corrections for [[Wellbore trajectory|wellbore deviation]] and formation [[dip]] are needed to make isopach maps. |
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| ===Isochore=== | | ===Isochore=== |
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| ===Isochron=== | | ===Isochron=== |
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− | An ''[[Mapping with two-dimensional seismic data#Time interval maps|isochron map]]'' is a contour map of equal values of seismic traveltime between selected events.<ref name=pt06r141 /> Isochron maps are the seismic analog of isochore maps and, as such, are intended to derive thickness information from seismic data. Isochroning between events above and below a pay horizon, for example, would estimate pay thickness. Renick and Gunn<ref name=pt06r109>Renick, H. Jr., Gunn, R. D., 1989, Triangle Ranch Headquarters field development using shallow core holes and high-resolution seismic data: Geophysics, v. 54, n. 11, p. 1384–1396, DOI: [http://library.seg.org/doi/abs/10.1190/1.1442602 10.1190/1.1442602].</ref> present a good case history of using isochron and time-structure maps to generate “isopach” and elevation-structure maps. Their isochron-isopach approach delineated reef trends for further development drilling and used well penetrations through a shallow horizon for depth control on a deeper horizon. Phipps<ref name=pt06r99>Phipps, G. G., 1989, Exploring for dolomitized Slave Point carbonates in northeastern British Columbia: Geophysics, v. 54, n. 7, p. 806–814, DOI: [http://library.seg.org/doi/abs/10.1190/1.1442709 10.1190/1.1442709].</ref> documents the pros and cons of using isochron thins and structural highs as exploration drilling criteria for dolomitized Devonian limestones. | + | An ''[[Mapping with two-dimensional seismic data#Time interval maps|isochron map]]'' is a contour map of equal values of seismic traveltime between selected events.<ref name=pt06r141 /> [[Isochron]] maps are the seismic analog of isochore maps and, as such, are intended to derive thickness information from seismic data. Isochroning between events above and below a pay horizon, for example, would estimate pay thickness. Renick and Gunn<ref name=pt06r109>Renick, H. Jr., Gunn, R. D., 1989, Triangle Ranch Headquarters field development using shallow core holes and high-resolution seismic data: Geophysics, v. 54, n. 11, p. 1384–1396, DOI: [http://library.seg.org/doi/abs/10.1190/1.1442602 10.1190/1.1442602].</ref> present a good case history of using isochron and time-structure maps to generate “isopach” and elevation-structure maps. Their isochron-isopach approach delineated reef trends for further development drilling and used well penetrations through a shallow horizon for depth control on a deeper horizon. Phipps<ref name=pt06r99>Phipps, G. G., 1989, Exploring for dolomitized Slave Point carbonates in northeastern British Columbia: Geophysics, v. 54, n. 7, p. 806–814, DOI: [http://library.seg.org/doi/abs/10.1190/1.1442709 10.1190/1.1442709].</ref> documents the pros and cons of using isochron thins and structural highs as exploration drilling criteria for dolomitized Devonian limestones. |
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| ==Mapping to calculate reserves== | | ==Mapping to calculate reserves== |
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| The product ''A'' × ''H'' is the reservoir bulk volume, and the product ''A'' × ''H'' × ϕ is the reservoir pore volume. The general determination of bulk reservoir volume involves mapping reservoir area in plan view and mapping net pay in terms of true vertical thickness to provide a common presentation of dipping beds or deviated wells. An [[Subsurface maps#Isochore|isochore]] map of net pay should be contoured using well control points and interpolated or extrapolated using available seismic and well test data and the geologist's interpretation of [[Depositional environments|depositional]] and [[Diagenesis|diagenetic]] history. | | The product ''A'' × ''H'' is the reservoir bulk volume, and the product ''A'' × ''H'' × ϕ is the reservoir pore volume. The general determination of bulk reservoir volume involves mapping reservoir area in plan view and mapping net pay in terms of true vertical thickness to provide a common presentation of dipping beds or deviated wells. An [[Subsurface maps#Isochore|isochore]] map of net pay should be contoured using well control points and interpolated or extrapolated using available seismic and well test data and the geologist's interpretation of [[Depositional environments|depositional]] and [[Diagenesis|diagenetic]] history. |
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− | “Net” pay (see [[Effective pay determination]]) implies that some formation thickness has been excluded from consideration by either (1) occurring below an [[Fluid contacts|oil-water contact]] (or above a gas-water contact), or (2) having porosity and/or [[permeability]] values below a “cutoff” limit for productivity. Not all net pay is necessarily productive at a given well spacing. Discontinuous productive horizons between wells might be described, for example, by the concept of net pay to net connected pay ratio.<ref name=pt06r103>Poston, S. W., 1987, [https://www.onepetro.org/book/peh/spe-1987-36-peh Development plan for oil and gas reservoirs], in Bradley, H. B., ed., Petroleum Engineering Handbook: Richardson, TX, Society of Petroleum Engineers, p. 36-1–36-11.</ref> | + | “Net” pay (see [[Effective pay determination]]) implies that some formation thickness has been excluded from consideration by either (1) occurring below an [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water+contact oil-water contact] (or above a [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=gas-water+contact gas-water contact]), or (2) having porosity and/or [[permeability]] values below a “cutoff” limit for productivity. Not all net pay is necessarily productive at a given well spacing. Discontinuous productive horizons between wells might be described, for example, by the concept of net pay to net connected pay ratio.<ref name=pt06r103>Poston, S. W., 1987, [https://www.onepetro.org/book/peh/spe-1987-36-peh Development plan for oil and gas reservoirs], in Bradley, H. B., ed., Petroleum Engineering Handbook: Richardson, TX, Society of Petroleum Engineers, p. 36-1–36-11.</ref> |
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| ===Porosity=== | | ===Porosity=== |
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| ===Water saturation=== | | ===Water saturation=== |
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− | The [[water saturation]] (S<sub>w</sub>) within the net pay interval is typically estimated from well logs. Water saturations can also be derived from [[capillary pressure]] testing of cores to determine the relationship of water saturation versus height above the [[Fluid contacts|oil-water contact]]. Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring ([[:file:subsurface-maps_fig5.png|Figure 5]]). The averages should be weighted by porosity. | + | The [[water saturation]] (S<sub>w</sub>) within the net pay interval is typically estimated from well logs. Water saturations can also be derived from [[capillary pressure]] testing of cores to determine the relationship of water saturation versus height above the [http://www.glossary.oilfield.slb.com/en/Terms.aspx?LookIn=term%20name&filter=oil-water%20contact oil-water contact]. Like porosity, the water saturation data in an individual well within the net pay interval can be averaged arithmetically and posted on a map for contouring ([[:file:subsurface-maps_fig5.png|Figure 5]]). The averages should be weighted by porosity. |
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| ===Oil saturation=== | | ===Oil saturation=== |
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| ===Permeability=== | | ===Permeability=== |
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− | [[Permeability]] (''k'') can also be mapped and contoured (see [[Core-log transformations and porosity-permeability relationships]]). As for [[Water saturation|saturation]] values, some care must be exercised in mapping permeability because values must be derived from indirect measurements. Typically, permeabilities are derived from wireline log [[Porosity|porosities]] transformed on the basis of core permeability versus porosity cross plots. Permeabilities can be reported at ambient laboratory conditions of pressure or adjusted to reservoir conditions of [[confining pressure]]. Similarly, permeabilities can be [[Absolute permeability|absolute permeabilities]] to air (nitrogen) or liquid or [[Effective permeability|effective permeabilities]] to oil in the presence of [[irreducible water]]. Permeability values in an individual well are thickness weighted and typically [[Averaging|averaged harmonically, arithmetically, or geometrically]], depending on [[flow geometry]]. Alternatively, [[flow capacity]] (''kH'') values derived from [[pressure transient testing]] can be divided by net pay thickness (''H'') to yield a liquid permeability value for a well. | + | [[Permeability]] (''k'') can also be mapped and contoured (see [[Core-log transformations and porosity-permeability relationships]]). As for [[Water saturation|saturation]] values, some care must be exercised in mapping permeability because values must be derived from indirect measurements. Typically, permeabilities are derived from wireline log [[Porosity|porosities]] transformed on the basis of core permeability versus porosity cross plots. Permeabilities can be reported at ambient laboratory conditions of pressure or adjusted to reservoir conditions of [[confining pressure]]. Similarly, permeabilities can be absolute permeabilities to air (nitrogen) or liquid or effective permeabilities]] to oil in the presence of [http://petrowiki.org/Glossary%3AIrreducible_water_saturation irreducible water]. Permeability values in an individual well are thickness weighted and typically [[Averaging|averaged harmonically, arithmetically, or geometrically]], depending on [[flow geometry]]. Alternatively, [[flow capacity]] (''kH'') values derived from [[pressure transient testing]] can be divided by net pay thickness (''H'') to yield a liquid permeability value for a well. |
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| ===Porosity thickness=== | | ===Porosity thickness=== |
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| ==Other maps== | | ==Other maps== |
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− | A variety of other maps can come into play during the development of a specific reservoir. Maps of facies, facies architecture(for more information, see [[Lithofacies and environmental analysis of clastic depositional systems#Clastic depositional lithofacies and environments|Clastic lithofacies]] and [[Carbonate reservoir models: facies, diagenesis, and flow characterization#Carbonate sediments and environments|Carbonate lithofacies]]), paleoenvironment, and isolithology might be particularly important in selecting [[stepout well location]]s and planning reservoir development strategy. Other reservoir properties such as [[Reservoir temperature|temperature]] can have value for specific reservoir engineering applications, particularly where potentially temperature-sensitive chemical [[stimulation]], production, or recovery technology might be involved. | + | A variety of other maps can come into play during the development of a specific reservoir. Maps of facies, facies architecture for more information, see [[Lithofacies and environmental analysis of clastic depositional systems]] and [[Carbonate reservoir models: facies, diagenesis, and flow characterization]]), paleoenvironment, and isolithology might be particularly important in selecting [[stepout well location]]s and planning reservoir development strategy. Other reservoir properties such as [[Wikipedia:Temperature|temperature]] can have value for specific reservoir engineering applications, particularly where potentially temperature-sensitive chemical [[stimulation]], production, or recovery technology might be involved. |
| + | |
| + | ==Examples of use== |
| + | |
| + | * Bally, A. W., Gordy, P. L., Stewart, G. A., 1966, Structure, seismic data and orogenic evolution of southern Canadian Rocky Mountains: Bulletin of Canadian Petroleum Geology, vol. 4, p. 337–381. |
| + | * Bally, A. W., Burbi, L., Cooper, C., Ghelardoni, R., 1986, Balanced sections and seismic reflection profiles across the central Apennines: Memorie della Societa Geologica Italiana, vol. 35, p. 257–310. |
| + | * Dixon, J. S., 1982, [http://archives.datapages.com/data/bulletns/1982-83/data/pg/0066/0010/1550/1560.htm Regional structural synthesis, Wyoming salient of the Western over-thrust belt]: AAPG Bulletin, vol. 66, p. 1560–1580. |
| + | * Dunn, J. F., Hartshorn, K. G., Hartshorn, P. W., 1995, [http://archives.datapages.com/data/specpubs/memoir62/27dunn/0523.htm Structural styles and hydrocarbon potential of the Sub-Andean thrust belt of southern Bolivia], in Tankard, A. J., Suarez, R. S., Welsink, H. J., eds., Petroleum Basins of South America: [http://store.aapg.org/detail.aspx?id=476 AAPG Memoir 62], p. 523–543. |
| + | * Dutton, S. P., Goldstein, A. G., Ruppel, S. C., 1982, Petroleum potential of the Palo Duro basin, Texas Panhandle: University of Texas at Austin Bureau of Economic Geology Report of Investigations 123, 87 p. |
| + | * Picha, F. J., 1996, [http://archives.datapages.com/data/bulletns/1994-96/data/pg/0080/0010/1500/1547.htm Exploring for hydrocarbons under thrust belts—a challenging new frontier in the Carpathians and elsewhere]: AAPG Bulletin, vol. 80, p. 1547–1564. |
| + | * Roure, F., Carnevali, J. O., Gou, Y., Subieta, T., 1994, Geometry and kinematics of the north Monagas thrust belt (Venezuela): Marine and Petroleum Geology, vol. 11, p. 347–362., 10., 1016/0264-8172(94)90054-X |
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| ==See also== | | ==See also== |
| * [[Introduction to geological methods]] | | * [[Introduction to geological methods]] |
| * [[Lithofacies and environmental analysis of clastic depositional systems]] | | * [[Lithofacies and environmental analysis of clastic depositional systems]] |
− | * [[Monte Carlo and stochastic simulation methods]]
| |
| * [[Flow units for reservoir characterization]] | | * [[Flow units for reservoir characterization]] |
| * [[Effective pay determination]] | | * [[Effective pay determination]] |
− | * [[Multivariate data analysis]] | + | * [[Cross section]] |
− | * [[Geological cross sections]]
| |
| * [[Evaluating structurally complex reservoirs]] | | * [[Evaluating structurally complex reservoirs]] |
| * [[Conversion of well log data to subsurface stratigraphic and structural information]] | | * [[Conversion of well log data to subsurface stratigraphic and structural information]] |
| * [[Evaluating tight gas reservoirs]] | | * [[Evaluating tight gas reservoirs]] |
− | * [[Correlation and regression analysis]]
| |
| * [[Reservoir quality]] | | * [[Reservoir quality]] |
| * [[Carbonate reservoir models: facies, diagenesis, and flow characterization]] | | * [[Carbonate reservoir models: facies, diagenesis, and flow characterization]] |
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| * [[Evaluating stratigraphically complex fields]] | | * [[Evaluating stratigraphically complex fields]] |
| * [[Evaluating diagenetically complex reservoirs]] | | * [[Evaluating diagenetically complex reservoirs]] |
− | * [[Statistics overview]]
| |
| | | |
| ==References== | | ==References== |
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| | | |
| [[Category:Geological methods]] | | [[Category:Geological methods]] |
| + | [[Category:Methods in Exploration 10]] |