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Line 52: − + − Faults must be located in wellbores by omission (extension fault) or repetition (reverse fault) of stratigraphic section.+ − [[File:Hossack_etal__evaluating-structurally-complex-reservoirs__Fig_3.png|thumb|{{figure_number|3}}Cross section through an asymmetric ramp anticline, whitney canyon field, Wyoming, with scat and isogon data superimposed. Unconformities, axial planes and inflection surfaces have been identified from the dipmeter data and projected away from the wellbore. Isogons are contours of equal dip (see Ramsay, 1967)<ref name=Ramsay_1967 /> and can constrain the shapes of folds in section. (From Lammerson, 1982)<ref name=Lammerson_1982>Lammerson, P. R., 1982, The Fossil basin and its relationship to the Absaroka thrust system, Wyoming and Utah, in R. B. Powers, ed., Geological Studies of the Cordilleran Thrust Belt: Rocky Mountain Association of Geologists, p. 279-340.</ref>. ]]+ − [[File:Hossack_etal__evaluating-structurally-complex-reservoirs__Fig_4.png|thumb|{{figure_number|4}}Modeling extensional fault shapes from the rollover geometry. (a) the groshong (1989b)<ref>Groshong, R. H., 1989b, Structural style and balanced cross sections in extensional terranes: Houston Geological Society Short Course Notes, Feb. 24-25, 128 p.</ref> method uses oblique simple shear with a reference grid constructed with a spacing equal to the fault heave. Distance 2 from the rollover up to regional elevation of the same reference bed is transferred to 2′; likewise, 2′ + 4 is transferred to 4′ and so on to complete the fault trajectory. Interpolation between these points is carried out using a half grid spacing. (b) fault trajectory reconstruction by the groshong (1989b)<ref>Groshong, R. H., 1989b, Structural style and balanced cross sections in extensional terranes: Houston Geological Society Short Course Notes, Feb. 24-25, 128 p.</ref> method uses simultaneous modeling of three horizons. Dashed trajectories are individual solutions; solid lines are the preferred solution. (From Hossack, unpubl. Data, 1988). ]] + − − [[File:Hossack_etal__evaluating-structurally-complex-reservoirs__Fig_5.png|thumb|{{figure_number|5}}Example of a balanced section through a complex thrust ramp structure showing both the deformed and undeformed sections. (From Mitra, 1986)<ref name=Mitra_1986>Mitra, S., 1986, Duplex structures and imbricate thrust systems--geometry, structural position, and hydrocarbon potential: AAPG Bulletin, v. 70, p. 1087-1112.</ref>. ]] − − These are defined on the electric logs by repetition or omission of parts of the SP and gamma ray signatures compared to a reference well that is believed to show an unfaulted section. Fault map trends and dip direction can also be defined by SCAT dipmeter analysis or on the stacked three-dimensional seiscrop sections. Generally, fault cuts have to be correlated from well to well to define the dip and curvature of the fault. Once these are estimated, fault contour maps can be generated by contouring the subsurface elevations of the fault cuts or, more directly, on the seismic workstation by stacking the seiscrop sections (Brown, 1986). The faults will offset the reference beds, and the amount of offset in section and map view must be estimated. Once the separation is known, a separatin surface can be projected along the fault retaining the same trend, but adjusted in value by an amount appropriate for the offset on the fault (see Figure 6a). − −
Structurally complex reservoirs: evaluation (view source)
Revision as of 20:43, 8 January 2014
, 20:43, 8 January 2014→Structure contour maps
==Map construction==
==Map construction==
===Structure contour maps===
===Structure contour maps===
The geometry of the field is defined by a series of structure contour maps of key reservoir horizons (Figure 6a). The maps, showing several levels through the prospect or reservoir, are generated from well elevations of reference beds or depth-converted seismic sections (see [[Subsurface maps]]). Workstations for three-dimensional [[seismic interpretation]] considerably aid the process because the shapes of the structure contours and the faults are readily observable on horizontal seiscrop sections generated by the workstation (Brown, 1986) (see Part 8). Contour maps can be quickly generated from stacked seiscrop sections.
The geometry of the field is defined by a series of structure contour maps of key reservoir horizons ([[:Image:Drive-mechanisms-and-recovery_fig3.png|Figure 6a]]). The maps, showing several levels through the prospect or reservoir, are generated from well elevations of reference beds or depth-converted seismic sections (see [[Subsurface maps]]). Workstations for three-dimensional [[seismic interpretation]] considerably aid the process because the shapes of the structure contours and the faults are readily observable on horizontal seiscrop sections generated by the workstation (Brown, 1986). Contour maps can be quickly generated from stacked seiscrop sections.
[[File:Drive-mechanisms-and-recovery fig3.png|thumbnail|'''Figure 6.''']]
Faults must be located in wellbores by omission (extension fault) or repetition (reverse fault) of stratigraphic section. These are defined on the electric logs by repetition or omission of parts of the SP and gamma ray signatures compared to a reference well that is believed to show an unfaulted section. Fault map trends and dip direction can also be defined by SCAT dipmeter analysis or on the stacked three-dimensional seiscrop sections. Generally, fault cuts have to be correlated from well to well to define the dip and curvature of the fault. Once these are estimated, fault contour maps can be generated by contouring the subsurface elevations of the fault cuts or, more directly, on the seismic workstation by stacking the seiscrop sections (Brown, 1986). The faults will offset the reference beds, and the amount of offset in section and map view must be estimated. Once the separation is known, a separatin surface can be projected along the fault retaining the same trend, but adjusted in value by an amount appropriate for the offset on the fault (see [[:Image:Drive-mechanisms-and-recovery_fig3.png|Figure 6a]]).
Bed contours and fault contours have to be combined in a series of overlays to generate the structure map. Initially, individual fault blocks bounded on all sides by faults have to be contoured separately<ref name=Dickinson_1954>Dickinson, G., 1954, Subsurface interpretation of intersecting faults and their effect upon stratigraphic horizons. AAPG Bulletin, v. 38, n. 5, p. 854-877.</ref> (Brown, 1986). The intersections between the bed and the fault contours of equivalent elevation value have to be identified to define the line of intersection of the bed and the fault. These lines are the fault cutoffs of the beds. There are two on each fault, one in the hanging wall and the other in the footwall. For extensional faults, there is a gap between the cutoffs where the key reference bed is omitted, and the gap in map view defines the heave across the fault.
Bed contours and fault contours have to be combined in a series of overlays to generate the structure map. Initially, individual fault blocks bounded on all sides by faults have to be contoured separately (Dickinson, 1954<ref name=Dickinson_1954>Dickinson, G., 1954, Subsurface interpretation of intersecting faults and their effect upon stratigraphic horizons. AAPG Bulletin, v. 38, n. 5, p. 854-877.</ref>; Brown, 1986). The intersections between the bed and the fault contours of equivalent elevation value have to be identified to define the line of intersection of the bed and the fault. These lines are the fault cutoffs of the beds. There are two on each fault, one in the hanging wall and the other in the footwall. For extensional faults, there is a gap between the cutoffs where the key reference bed is omitted, and the gap in map view defines the heave across the fault.
===Map restorations===
===Map restorations===