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Utilization of CT Scan Technique to Manipulate the Heterogeneity Effect
in Reservoir Rock Properties Determination

Salehi, Maryam | 2016

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 49192 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Ayatollahi, Shahabodin; Fazel Abdol Abadi, Babak; Nematzadeh, Mostafa
  7. Abstract:
  8. Petrophysical properties of reservoir rocks are of the most important parameters in fluid flow simulation and reservoir characterization. Although in core laboratories some well-known procedures for determination of these parameters are applied, in almost all of them the rocks are assumed to be homogeneous and their properties are taken up as identical in all directions. To eliminate these unrealistic assumptions, an accurate, non-destructive technique with appropriate degree of resolution is required for recognition of internal heterogeneity of cores. Medical “CT Scanner” is one of these techniques whose information in conjunction of conventional experiments could reduce their limitations and with respect to other non-destructive methods it produces cheaper and faster results with appropriate accuracy. In this research, three salient objectives are prospered by utilization of CT scan technique: A. a dedication of quantitative criterion for rock’s heterogeneity analogy, B. Feasibility of employment of basic information in conjunction of CT scan data for estimation of more advanced parameters, and C. delving the efficacy of heterogeneity in determination of rock properties and proposing a novel procedure for ascertaining parameters in radial direction. In this regard, some vertical core plugs in different rock types were chosen and then the presence of probable geological phenomena were investigated intuitively with the aid of CT scan images. Afterwards, by analyzing CT number variations through the core plug region and proposing quantitative criteria, the samples have been evaluated from the heterogeneity viewpoint. Subsequently, the effect of various factors on calculated representative elementary area have been investigated and the correlation between representative elementary volume and heterogeneity index have been probed. Then by having the CT number in each voxel and proposing a linear relation, the porosity distribution within the sample have been estimated. To ascertain each voxel’s permeability, this parameter have been supposed as a function of porosity and the coefficients of each permeability models (analytical, empirical and semi-empirical) have been optimized utilizing PSO algorithm. Simulation results for each rock type have been validated by a control sample with known experimental permeability and then the best describing models have been selected in each group. Finally by applying the obtained permeability distribution and changing the flow direction from longitudinal to radial, the amount of radial permeability was calculated for all samples and compared with their vertical permeabilities. As the results indicate, factors such as trigger point and scheme of element growing, applied criterion and heterogeneity intensity have perceptible efficacy on calculated REA. Additionally, by comparing REV and heterogeneity index values an increase in REV is observable as heterogeneity increase. In permeability optimization section, the excellence of Carman-Kozeny model is evident in overtaking minimum cost in all groups as well as best prognostication of control sample’s permeability. Also, findings show that the application of CT scan data in approximation of target parameter (permeability in this work) attain an acceptable result in a way that the maximum relative error is less than 5.4% in all studied rock types. One of the salient achievement of this research is to proffer a novel scheme for determination of radial permeability which is unmeasurable in conventional core laboratories. Calculated radial permeabilities indicate a 20%-90% excess with respect to vertical permeabilities
  9. Keywords:
  10. Optimization ; Representative Volume Element ; CT Scan ; Permeability ; Radial Heterogeneity ; Porosity Distribution ; Radial Permeability

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