QUANTITATIVE METHOD FOR ESTIMATING TOTAL ORGANIC CARBON … · 2014-12-11 · We introduce a new...
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SPWLA 52 nd Annual Logging Symposium, May 14-18, 2011 QUANTITATIVE METHOD FOR ESTIMATING TOTAL ORGANIC CARBON AND POROSITY, AND FOR DIAGNOSING MINERAL CONSTITUENTS FROM WELL LOGS IN SHALE-GAS FORMATIONS Zoya Heidari and Carlos Torres-Verdin, The University of Texas at Austin William E. Preeg, Private Consultant Copyright 2011 , he ld jointly by the Society ofpetrophys ici sts and We ll Log Analysts (S PWLA) and the submitting authors Thi s paper was prepared for presentati on at the SPWLA 52nd Annual Logging Symposium held in Colorado Springs, Co, USA, May 14-1 8, 20 II . ABSTRACT Reliable estimates of shale properties are critical for detecting perforation zones or candidates for hydro-fracturing jobs, Current methods for in-situ lithological and petrophysical assessment of organic shales are largely based on qualitative responses and empirical formulas. Even core-based measurements can be inconsistent and inaccurate when evaluating clay minerals and other grain constituents. We introduce a new method for organic-shale evaluation based on well logs to estimate total porosity, total organic carbon (TOC) and volumetric/weight concentrations of minerallfluid constituents. After detecting bed boundaries, the first step of the method is to perform separate inversion of individual well logs to estimate bed properties such as density, migration length, electrical conductivity, PEF (Photo Electric Factor), and Th (Thorium), U (Uranium), and K (Potassium) volumetric concentrations. Next, a multi-layer petrophysical model specific to organic shale is constructed with an initial guess obtained from conventional petrophysical interpretation or XRD (X-Ray Di ffraction) data; bed properties are calculated with the initiallayer-by-Iayer values. Final estimates of organic shale Q properties are obtained by progressively minimizing the difference between calculated and measured bed properties. A unique advantage of this method is the possibility of implicitly correcting for shoulder-bed effects in well logs, which are prevalent in shale-gas plays. Another advantage is the possibility of calculating accurate well-log responses for specific petrophysical, mineral, fluid, and kerogen properties. Examples are described of the successful application of the new organic-shale evaluation method in the Haynesville shale-gas formation. This formation includes complex solid compositions and thin beds where rapid depth variations of both mineral/fluid constituents are commonplace. Comparison of estimates for total porosity, total water saturation, and TOC obtained using (a) conventional commercial software, (b) our organic-shale evaluation method, and (c) core/XRD measurements, indicates an improvement of more than 50% in estimates of total porosity and water saturation when calculated with the newly developed method. The estimated TOC is also in agreement with core laboratory measurements. INTRODUCTION Evaluation of shale properties such as TOC, total porosity, gas-filled porosity, fluid saturation, and grain composition remains a technical challenge to the petroleum industry. Conventional log interpretation methods are not applicable for these unconventional reservoirs, and there exist no general guidelines for the petrophysical interpretation of organic shales. Accurate mineralogy evaluation in addition to geological knowledge can improve the evaluation of in-situ mechanical properties and, consequently, aid in the decision of perforation intervals in hydrocarbon-bearing shale. Improving estimates of volumetric concentration of mineral constituents also improves the estimation of porosity, TOC, and water saturation. Several methods have been developed to estimate or measure volumetric/weight concentration of mineral constituents, including commercial multi-mineral linear solvers, neutron-capture spectroscopy, gamma-ray spectroscopy, and core (i.e. XRD, and FTlR (Fourier Transform Infrared Transmission) spectroscopy, and XRF (X-Ray Fluorescence) measurements). Even though some of these methods are reliable in conventional reservoirs, they are not in the presence of thin beds and complex mineral compositions. Among such methods, core measurements are believed to provide the most reliable estimates of mineral concentrations. Even 1
Transcript of QUANTITATIVE METHOD FOR ESTIMATING TOTAL ORGANIC CARBON … · 2014-12-11 · We introduce a new...
SPWLA 52nd Annual Logging Symposium, May 14-18, 2011
QUANTITATIVE METHOD FOR ESTIMATING TOTAL ORGANIC CARBON AND POROSITY, AND FOR DIAGNOSING MINERAL
CONSTITUENTS FROM WELL LOGS IN SHALE-GAS FORMATIONS
Zoya Heidari and Carlos Torres-Verdin, The University of Texas at Austin William E. Preeg, Private Consultant
Copyright 2011 , held jointly by the Society ofpetrophysicists and Well Log Analysts (S PWLA) and the submitting authors
This paper was prepared for presentation at the SPWLA 52nd Annual Logging Symposium held in Colorado Springs, Co, USA, May 14-1 8, 20 II .
ABSTRACT
Reliable estimates of shale properties are critical for detecting perforation zones or candidates for hydro-fracturing jobs, Current methods for in-situ lithological and petrophysical assessment of organic shales are largely based on qualitative responses and empirical formulas . Even core-based measurements can be inconsistent and inaccurate when evaluating clay minerals and other grain constituents.
We introduce a new method for organic-shale evaluation based on well logs to estimate total porosity, total organic carbon (TOC) and volumetric/weight concentrations of minerallfluid constituents. After detecting bed boundaries, the first step of the method is to perform separate inversion of individual well logs to estimate bed properties such as density, migration length, electrical conductivity, PEF (Photo Electric Factor), and Th (Thorium), U (Uranium), and K (Potassium) volumetric concentrations. Next, a multi-layer petrophysical model specific to organic shale is constructed with an initial guess obtained from conventional petrophysical interpretation or XRD (X-Ray Diffraction) data; bed properties are calculated with the initiallayer-by-Iayer values. Final estimates of organic shale Q properties are obtained by progressively minimizing the difference between calculated and measured bed properties. A unique advantage of this method is the possibility of implicitly correcting for shoulder-bed effects in well logs, which are prevalent in shale-gas plays. Another advantage is the possibility of calculating accurate well-log responses for specific petrophysical, mineral, fluid, and kerogen properties.
Examples are described of the successful application of the new organic-shale evaluation method in the Haynesville shale-gas formation. This formation includes complex solid compositions and thin beds where rapid depth variations of both mineral/fluid constituents are commonplace. Comparison of estimates for total porosity, total water saturation, and TOC obtained using (a) conventional commercial software, (b) our organic-shale evaluation method, and (c) core/XRD measurements, indicates an improvement of more than 50% in estimates of total porosity and water saturation when calculated with the newly developed method. The estimated TOC is also in agreement with core laboratory measurements.
INTRODUCTION
Evaluation of shale properties such as TOC, total porosity, gas-filled porosity, fluid saturation, and grain composition remains a technical challenge to the petroleum industry. Conventional log interpretation methods are not applicable for these unconventional reservoirs, and there exist no general guidelines for the petrophysical interpretation of organic shales.
Accurate mineralogy evaluation in addition to geological knowledge can improve the evaluation of in-situ mechanical properties and, consequently, aid in the decision of perforation intervals in hydrocarbon-bearing shale. Improving estimates of volumetric concentration of mineral constituents also improves the estimation of porosity, TOC, and water saturation. Several methods have been developed to estimate or measure volumetric/weight concentration of mineral constituents, including commercial multi-mineral linear solvers, neutron-capture spectroscopy, gamma-ray spectroscopy, and core (i.e. XRD, and FTlR (Fourier Transform Infrared Transmission) spectroscopy, and XRF (X-Ray Fluorescence) measurements). Even though some of these methods are reliable in conventional reservoirs, they are not in the presence of thin beds and complex mineral compositions. Among such methods, core measurements are believed to provide the most reliable estimates of mineral concentrations. Even
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