Changes

==Reservoir description methodology==

==Reservoir description methodology==

A schematic diagram illustrating the basic stages of reservoir description in a diagenetically complex reservoir is shown in Figure 2. Geological activities follow the stages of well data analysis and core analysis, which constitute basic input to the geological phase of the analysis.

[[file:evaluating-diagenetically-complex-reservoirs_fig2.png|thumb|{{figure number|2}}Stages In the generation of an Integrated geological reservoir model.]]

[[file:evaluating-diagenetically-complex-reservoirs_fig2.png|thumb|{{figure number|2}}Stages In the generation of an Integrated geological reservoir model.]]

A schematic diagram illustrating the basic stages of reservoir description in a diagenetically complex reservoir is shown in [[:file:evaluating-diagenetically-complex-reservoirs_fig2.png|Figure 2]]. Geological activities follow the stages of well data analysis and core analysis, which constitute basic input to the geological phase of the analysis.

===Stage 1. Construction of a regional geological framework===

===Stage 1. Construction of a regional geological framework===

|}

|}

Sample sites for petrographic analysis are best selected on the basis of low magnification rock descriptions generated in step 1 and through examination of semilog porosity-permeability crossplots (Figure 3) with values keyed to major categories of size, sorting, matrix content, cement content, or pore type, depending on their relative importance in a particular reservoir. Samples should be selected to span a wide range of porosities and permeabilities for each major type of reservoir rock (for example, sandstones that are dolomite cemented, anhydrite cemented, quartz-overgrowth cemented, or argillaceous).

[[file:evaluating-diagenetically-complex-reservoirs_fig3.png|thumb|left|{{figure number|3}}[[Porosity]]-permeability semilog crosspiot with samples coded according to grain size, clay content, and dominant agent of cementation.]]

[[file:evaluating-diagenetically-complex-reservoirs_fig3.png|thumb|{{figure number|3}}[[Porosity]]-permeability semilog crosspiot with samples coded according to grain size, clay content, and dominant agent of cementation.]]

Sample sites for petrographic analysis are best selected on the basis of low magnification rock descriptions generated in step 1 and through examination of semilog porosity-permeability cross plots ([[:file:evaluating-diagenetically-complex-reservoirs_fig3.png|Figure 3]]) with values keyed to major categories of size, sorting, matrix content, cement content, or pore type, depending on their relative importance in a particular reservoir. Samples should be selected to span a wide range of porosities and permeabilities for each major type of reservoir rock (for example, sandstones that are dolomite cemented, anhydrite cemented, quartz-overgrowth cemented, or argillaceous).

Use of plug ends from homogeneous horizontal core analysis plugs for thin section, XRD, or SEM sample preparation allows for the development of quantitative relationships between data from these analyses and data from core analysis measurements. Plugs containing significant inhomogeneities, such as laminae of distinctly different grain size or degrees of cementation, should be avoided or else erroneous variance in the data set will tend to blur what otherwise might be easily recognizable clear-cut relationships.

Use of plug ends from homogeneous horizontal core analysis plugs for thin section, XRD, or SEM sample preparation allows for the development of quantitative relationships between data from these analyses and data from core analysis measurements. Plugs containing significant inhomogeneities, such as laminae of distinctly different grain size or degrees of cementation, should be avoided or else erroneous variance in the data set will tend to blur what otherwise might be easily recognizable clear-cut relationships.

If continuous core is available, analysis can proceed directly to the preparation and correlation of vertical component profiles (steps 4 and 5). However, in many reservoirs, particularly those with thick gross pay intervals, core or sidewall core coverage is limited to only a few wells or intervals. To complete the lithological analysis, the geologist must resort to cuttings descriptions or log analysis (see [[Quick-look lithology from logs]]). Commonly, the degree of detail that can be extracted from cuttings samples is not adequate for the objectives of the study, so the geologist must attempt to correlate log response with lithological data from intervals containing full diameter or sidewall cores and then apply these correlations to uncored intervals.

If continuous core is available, analysis can proceed directly to the preparation and correlation of vertical component profiles (steps 4 and 5). However, in many reservoirs, particularly those with thick gross pay intervals, core or sidewall core coverage is limited to only a few wells or intervals. To complete the lithological analysis, the geologist must resort to cuttings descriptions or log analysis (see [[Quick-look lithology from logs]]). Commonly, the degree of detail that can be extracted from cuttings samples is not adequate for the objectives of the study, so the geologist must attempt to correlate log response with lithological data from intervals containing full diameter or sidewall cores and then apply these correlations to uncored intervals.

===Step 4. Diagenetic profile construction===

===Step 4. Diagenetic profile construction===

Once the lithological data for all wells involved in the study have been gathered, vertical profiles of diagenetic component abundance should be prepared. Only components having a significant effect on reservoir quality should be profiled. In some instances, components measured separately but having similar overall effects on reservoir properties can be combined to form one profile.

Once the lithological data for all wells involved in the study have been gathered, vertical profiles of diagenetic component abundance should be prepared. Only components having a significant effect on reservoir quality should be profiled. In some instances, components measured separately but having similar overall effects on reservoir properties can be combined to form one profile.

If the abundances of the major diagenetic components are based strictly on visual estimation using a binocular microscope, qualitative (very minor, minor, moderate, or abundant) or semiquantitative (0–5%, 5–10%, or 10–15%) bar profiles can be prepared displaying sedimentological and petrophysical data (Figure 4). Where quantitative petrographic data are collected, they can replace the original bar profile data.

If the abundances of the major diagenetic components are based strictly on visual estimation using a binocular microscope, qualitative (very minor, minor, moderate, or abundant) or semiquantitative (0–5%, 5–10%, or 10–15%) bar profiles can be prepared displaying sedimentological and petrophysical data ([[:file:evaluating-diagenetically-complex-reservoirs_fig4.png|Figure 4]]). Where quantitative petrographic data are collected, they can replace the original bar profile data.

 

===Step 5. Continuity analysis===

===Step 5. Continuity analysis===