Presentation on theme: "Geological and Petrophysical Analysis Of Reservoir Cores"— Presentation transcript:
1 Geological and Petrophysical Analysis Of Reservoir Cores Upper Spraberry FormationClaudio J. SaletaNew Mexico Petroleum Recovery Research CenterNew Mexico Institute of Mining and Technology
2 Outline1. Introduction2. Petrography and Diagenesis3. Petrophysics: Rock-Fluid Model4. Conclusions
3 1. IntroductionThe objective of this study is to develop a detailed geological characterization of reservoir and non-reservoir rocks.This investigation provides the framework for further studies:Log AnalysisCut Off values and Net Pay DeterminationReserve CalculationFluid Transfer StudiesRock-Fluid Parameters for Modeling and Simulation
4 Introduction (cont.)The outcome of this study is a rock-fluid model which, in conjunction with the fracture model found in a parallel investigation, provides a much- improved characterization of the Spraberry reservoir.Parameters under study:Matrix Composition Grain DensityCements SwRock-matrix porosity WettabilityPermeability Capillary pressure
6 SMALL SCALE LITHOFACIES Six Rock Types were observed in thin sections from Spraberry Formation core samples.Petrographic data are related to petrophysical measurements of core plugs to build a rock-fluid model.Each Rock Type possesses different:pore geometrymineralogical compositionfluid flow characteristics
7 Six Spraberry Rock Types Very Fine Sandstone and Coarse Siltstones, Reservoir Rock : Rock Type “A”V.F. Sandstones and Siltstones Slightly Shaly and/or Dolomitic : Rock Type “B”Dolomite Mudstone or “Dolostone”: Rock Type “C”Very Patchy Dolomitic Siltstones: Rock Type “D”Shales and Very Shaly Siltstones: Rock Type “E”Highly Laminated Siltstones: Rock Type “F”
8 THE SPRABERRY RESERVOIR ROCKS Very fine grained sandstones and coarse siltstonesWell sortedVery well consolidatedComposition:
9 Five factors control porosity in Spraberry Reservoir Rocks: Original rock texture: grain size and sortingCompactional effects: grain packing, deformation of ductile grainsCementation: decreases overall porosity, increases tortuosityDissolution: produces secondary porosity, improves permeabilityFabric Rigidity: quartz rich lithologies resist compaction
10 CLAYS AFFECT POROSITY AND PERMEABILITY Depositional clay occurs as dispersed clay particles or as laminae.0.125mmShaleLaminaeAuthigenic clays occur as pore linings, pore bridgings or discrete particles.CLAYS AFFECT POROSITY AND PERMEABILITY
16 Better correlation of porosity and permeability between depth 7195-7245 ft. Pay zone (5U unit) and associated rock types.More scattered points at shallower depth in same core well( ft).Rocks are shales and very shaly laminated lithofacies.
21 Correlation for Porosity-Permeability and Pore Throat Radius
22 Pore Throat Distribution for Rock Types A, C and D: RT-A shows one dominant pore throat size at 0.66 mm.
23 Patchy dolomitic siltstone (“D”) is a rock type that falls between “B” and “F”. This category shows slightly higher grain density range and lower porosity (8.0 %) than “B” due to the higher amounts of dolomite cement present.
24 4. CONCLUSIONS1. Six (6) small-scale lithofacies have beendefined based on thin section, SEM, XRD, and petrophysical measurements.2. Diagenetic processes have overprintedoriginal depositional characteristics. Originalrock composition exerts the most importantcontrol on reservoir quality.
25 3. Controls that affect reservoir quality: Quality damaging controls: CONCLUSIONS (cont.)3. Controls that affect reservoir quality:Quality damaging controls:Authigenic illite.Argillaceous laminae.Quartz cement as overgrowths and pressure solution.Carbonate cements.Initial very fine grain size.Quality ehancing controlsQuartz rich composition (arkosic to subarkosic) make reservoir rocks relatively more resistant to compression forces and chemical wearing.Dissolution of unstable grains and cements.
26 CONCLUSIONS (cont.)4. Water and oil saturation data shows a close relationship between water saturation, porosity and lithology.5. The relationship of water saturation and lithology suggests that rock type may control reservoir wettability, however this question is still unresolved.6. Lithological variability exerts control upon the different petrophysical parameters: porosity, permeability, capillary pressure, pore throat size, and water saturation.7. The knowledge obtained from the geological study is integrated with subsequent investigations to improve log interpretations, to understand the mechanical state of the rocks and to understand wettability of the rock matrix.