Reservoir Characterization of Clastic Rocks by Sedimentological Methods

8/12/2019 Reservoir Characterization of Clastic Rocks by Sedimentological Methods

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Presented By :Satyam Mehta

B.Tech-Geoscience

R280308031

Clastic Reservoir Characterization by

Sedimentological Methods


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Aim of the study The Gulf Coast region of the United States accounts for approx. 16 %

of the U.S. annual carbon dioxide (CO2) emissions from fossil fuels .The burning of fossil fuels has increased the amount of carbon dioxide

released into the Earths atmosphere.

Major steps have been taken to develop a method for CO2 storage.

Geologic sequestration involves the capturing of CO2 emissionsfollowed by injection into subsurface geologic formations such assaline aquifers and hydrocarbon reservoirs.

For an accurate assessment of geologic formations in response to CO2sequestration in 2004, the GCCC conducted the Frio Pilot

Experiment to test the feasibility of the Oligocene Frio Formation bystudying its characteristic reservoir properties including permeabilityand porosity, framework mineralogy, diagenesis and authegenicmineralogy, etc.


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Conte nts :-Previous petrographic analysis

Framework mineralogy

Diagenesis and authegenic mineralogy

FRIO Pilot study

Results

Framework mineralogy of the upper Frio formation

Diagenesis and authigenic mineralogy

Conclusion


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Previous petrographic analysis

Framework Mineralogy

have a wide range of mineral composition geographically separating thesouthern or lower, middle or central, and northern or upper units.

The southern Frio sandstones as poorly-sorted, fine-grained, feldspathiclitharenites, sub-litharenites to lithic arkoses with an abundance of volcanicrock fragments.

The central Frio sandstones are considered moderately to well-sorted, fine-grained, quartzose lithic arkoses with abundant metamorphic rockfragments .

The northern Frio, is considered a poorly-sorted, fine-grained, quartzose

lithic arkose to subarkose rock fragments, mainly volcanic. Thisclassification is displayed in the Folk diagram,


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Diagenesis and authigenic mineralogy

Two main episodes of diagenesis identified as syndepositional diagenesis andburial diagenesis. Burial-diagenetic modification of Frio sandstones occurs atdepths shallower than 8,000 ft.

Cementation, associated with the presence of quartz overgrowths, calcite,and clays (kaolinite) is considered to predate the formation of secondaryporosity, usually with quartz preceding all other diagenetic phases.

Secondary porosity is associated with the dissolution of detrital feldspars,rock fragments, and some authigenic calcite, and is considered to be the lastporosity-affecting diagenetic event to occur in the Frio .


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Frio Pilot Stu dySite Selection :-The experiment took place in the sandstone formation of

eastern Texas to assess field methods and measuring techniques to assist inunderstanding geochemical reactions and trapping capabilities of the Frio.

Well location & Installation :

The Pilot Experiment site is located in Liberty County, Texas, flanking theSouth Liberty oil field and salt dome, 5.5 miles south of Liberty, Texas.

Cored samples were collected in aluminum barrels, frozen with dry ice, andslabbed before transportation to the BEGs Houston Core Research Centerwhere they remain frozen.

Porosity and permeability values for the injection zone were determinedfrom core analyses of the new well.

To examine the mineralogy, cement/ matrix, and pore geometries of thesite,conventional core analysis, XRD investigation, and thin section analyseswere completed.


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Location map of well site


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ResultsFramework mineralogy of the upper Frio formation:

Petrographic analysis identifies the upper Frio sandstone as a very fineto fine-grained, poorly cemented, subangular to subrounded withmean composition of Q70F24L6(fig.3).

Detrital quartz is predominantly monocrystalline (31% 10) with

polycrystalline quartz less abundant 6% (3) (Figures 4 & 5).

Feldspar is dominated by orthoclase 8% (5) (Fig. 6) followed byplagioclase 4% (2) (Fig. 7) and trace amounts of microcline.

Feldspar grains are mostly unaltered although a small percentage ofgrains show signs of sericitization and dissolution.


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Fig.3:Ternary plot of Frio Formation samples, based on FolksClassification system (1974). Photomicrograph image illustrating

typical Frio sandstone composition.


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Fig.4: Photomicrograph displaying dominant detrital grains:quartz (Q), feldspar (F), and volcanicrock fragments (VRF). Arrows indicate point-

contacts.

Fig. 5: Photomicrograph of detrital quartz grains


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Fig.6: Photomicrograph displaying an orthoclase feldspar grain; photo width ~200m.

Fig.7:Photomicrograph displaying dominantdetrital grains: quartz (Q), plagioclase (P), K-feldspar (K-Spar), and volcanic rock fragments(VRF). Arrows indicate point-contacts.


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D ia genesis a nd a uth igen ic m ine ralogy : Cementation in the upper Frio samples is minor, with authigenic phases

dominated by clay (I/ S) and pyrite, followed by minor quartz and feldspar

overgrowths and calcite occurring late in diagenesis (Fig.8). The following sectionswill describe the diagenesis and authigenic mineralogy of the upper Frio Csandstone at Liberty field, Texas.

Fig.8:Diagenetic reactions occurring in the upper Frio Formation sandstones at Liberty oil

field, Liberty County, Texas.


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Clays :-

Clay is the dominant authigenic phase in the upper Frio sandstone .Illite/ smectite (I/ S) was identified by XRD and SEM as the principal

clay, occurring as thin grain-coats, with minor amounts of kaolinite .Illite/ smectite formed following compaction of the unit.

Geochemical analyses of upper Frio clay coats by EDAX identified

indicative of I/ S and kaolinite composition .


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Conclusions:

Essential to reservoir characterization, petrographic analysis identifiesthe upper Frio sandstone, along the northern Texas Gulf Coast, assubarkose.

Subarkose classification contrasts from the Frio sandstones of the

central and southern Texas Gulf Coast that are typically moreenriched in rock fragments (volcanic) and plagioclase indicating achange in the units composition from the southern Texas Gulf Coastto the upper formation .


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Fig.9:Ternary diagram displaying upper Frio sandstones at Liberty County(), compared to Middle Frio sandstones (X)

The diagenetic history of the upper Frio at the South Liberty oil field hasproduced mineralogical and reservoir characteristics unlike the southernand central Frio units along the Texas Gulf Coast. The same diagenetichistory that makes the formation (at this location) an ideal reservoir has alsointroduced secondary minerals which may alter reservoir conditions .


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Reservoir Characterization of Clastic Rocks by Sedimentological Methods