10,323
edits
Changes
Jump to navigation
Jump to search
Line 86:
Line 86: + + + Line 93:
Line 96: − +
→Carbonate reservoirs
==Carbonate reservoirs==
==Carbonate reservoirs==
<gallery mode=packed heights=200px widths=200px>
thin-section-analysis_fig2.png|{{figure number|2}}Carbonate classification schemes of (a) Folk<ref name=pt05r56 /> and (b) Dunham<ref name=pt05r50 />, both based on textures observed in hand specimen or thin section. In Folk's scheme, the black pattern represents lime mud matrix, the lined pattern represents sparry calcite cement, and the white objects represent various carbonate grains.
Porosity_fig3.png|{{figure number|3}}
Petrographic analysis of carbonate reservoirs provides description of depositional facies, reconstruction of diagenetic history, and documentation of the porosity system.
Petrographic analysis of carbonate reservoirs provides description of depositional facies, reconstruction of diagenetic history, and documentation of the porosity system.
Diagenetic history of carbonate reservoir rocks is important to reconstruct because it influences the volume, size, shape, and distribution of pores. Diagenesis may involve porosity-reducing cementation, porosity-enhancing dissolution, and recrystallization, which may result in either reduction or enhancement of porosity. An important goal of carbonate petrography is to establish the sequence of such events, or paragenesis, of the reservoir. Careful reconstruction of reservoir paragenesis can provide a perspective of the porosity system at the time of hydrocarbon accumulation, thereby enhancing the geologist's understanding of how reserves may be distributed relative to diagenetic facies.
Diagenetic history of carbonate reservoir rocks is important to reconstruct because it influences the volume, size, shape, and distribution of pores. Diagenesis may involve porosity-reducing cementation, porosity-enhancing dissolution, and recrystallization, which may result in either reduction or enhancement of porosity. An important goal of carbonate petrography is to establish the sequence of such events, or paragenesis, of the reservoir. Careful reconstruction of reservoir paragenesis can provide a perspective of the porosity system at the time of hydrocarbon accumulation, thereby enhancing the geologist's understanding of how reserves may be distributed relative to diagenetic facies.
Documentation of the porosity system within a carbonate reservoir provides a clear understanding of the origin and three dimensional distribution of pores. This information is typically collected by classifying individual pores into discrete categories<ref name=pt05r34>Choquette, P. W., Pray, L. C., 1970, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0054/0002/0200/0207.htm Geological nomenclature and classification of porosity in sedimentary carbonates]: AAPG Bulletin, v. 54, p. 207–250.</ref> and by evaluating the degree to which the various pore types are interconnected. (For more on carbonate porosity types, see [[Porosity#Carbonate pore systems|Table 1]] and [[:file:porosity_fig3.png|Figure 3]] in the article on [[Porosity]], as well as [[Carbonate reservoir models: facies, diagenesis, and flow characterization]].)
Documentation of the porosity system within a carbonate reservoir provides a clear understanding of the origin and three dimensional distribution of pores. This information is typically collected by classifying individual pores into discrete categories<ref name=pt05r34>Choquette, P. W., Pray, L. C., 1970, [http://archives.datapages.com/data/bulletns/1968-70/data/pg/0054/0002/0200/0207.htm Geological nomenclature and classification of porosity in sedimentary carbonates]: AAPG Bulletin, v. 54, p. 207–250.</ref> and by evaluating the degree to which the various pore types are interconnected. (For more on carbonate porosity types, see [[Porosity#Carbonate pore systems|Table 1]] and [[:file:porosity_fig3.png|Figure 3]].)
This analysis results in a conceptualization of the three-dimensional pathways that hydrocarbons must follow from their original location in the virgin reservoir to the wellbore. Knowing, for example, that porosity in a particular reservoir is selective to a specific depositional facies would allow a geologist to plan enhanced recovery by siting injection and withdrawal locations on the basis of facies distribution. In contrast, knowing that porosity is mostly not fabric selective (e.g., a combination of fracture and vuggy) would likely result in a very different plan for siting injection and withdrawal locations. Documentation of the porosity system also provides information that is fundamental to planning optimum reservoir stimulation procedures.
This analysis results in a conceptualization of the three-dimensional pathways that hydrocarbons must follow from their original location in the virgin reservoir to the wellbore. Knowing, for example, that porosity in a particular reservoir is selective to a specific depositional facies would allow a geologist to plan enhanced recovery by siting injection and withdrawal locations on the basis of facies distribution. In contrast, knowing that porosity is mostly not fabric selective (e.g., a combination of fracture and vuggy) would likely result in a very different plan for siting injection and withdrawal locations. Documentation of the porosity system also provides information that is fundamental to planning optimum reservoir stimulation procedures.