Clays in reservoir rocks have a significant impact on formation evaluation. An important property... more Clays in reservoir rocks have a significant impact on formation evaluation. An important property of clay minerals is their ability to adsorb ions on their exposed surface, which is measured by its cation exchange capacity (CEC). This property can affect saturation calculation if not properly accounted for. Many techniques have been developed for clay characterization, but it remains a focus of frontline research to find an accurate method for quantifying clays in situ and is the main objective of this study. Extensive numerical studies have been conducted and the results have indicated that for a shaly sand formation, strong dielectric dispersions were observed for all the simulated models at frequencies below 1MHz, which allowed an equation to be established that can be used to calculate clay volume through derivatives of the permittivity dispersive curves. In deriving this equation, parameters used for the studies include water-filled porosity, formation water salinity, grain siz...
Pulsed neutron carbon-oxygen (C/O) logging is a valuable measurement for dynamic reservoir satura... more Pulsed neutron carbon-oxygen (C/O) logging is a valuable measurement for dynamic reservoir saturation monitoring, especially in mixed salinity and fresh-water environments. Currently, all C/O logs are based on apparent C/O measurements, thus responses of raw data are not comparable between different tools. Tool-specific calibrations are used to convert apparent C/O log to reservoir oil saturation; the objective of C/O logging. In this paper, a new concept of intrinsic C/O logging is introduced so that raw data from different tools can be compared for enhanced log quality control and consistency of raw data and their applications. For a given system of rock, oil, and water, intrinsic carbon (C) and oxygen (O), thus C/O ratio, are theoretically calculated. For the same system, apparent C/O ratio measured by a generic C/O logging tool is also obtained using existing apparent C/O methodology. A correlation between the two is established, enabling an intrinsic C/O log output. Eleven labo...
The interaction of surface-active species within crude oil with ions in the aqueous phase can hav... more The interaction of surface-active species within crude oil with ions in the aqueous phase can have a major influence on the interfacial tension (IFT) between these two phases. Herein, the influence of salinity on IFT is investigated systematically. Brines with different salinities, including seawater and reservoir formation water, are considered. The measurements clearly show distinct IFT trends depending on the composition and concentration of salts in the aqueous phase as well as on the crude oil chemical species, as represented by the API values. The results show that complex brine systems have a stronger effect on IFT than individual single salt brine systems. It is possible to derive distinct additive correction factors for the respective tested brine systems based on the averaged values of deviation from the respective cases in deionized water. On average for the tested 10 oils, and in comparison to measurements in DI water, IFT was reduced by 3.4 mN/m in 100 kppm CaCl2 soluti...
It is desirable to evaluate the possibility of developing a deeper dielectric permittivity based ... more It is desirable to evaluate the possibility of developing a deeper dielectric permittivity based Sw measurement for various petrophysical applications. The low frequency, (< MHz), resistivity-based method for water saturation (Sw) evaluation is the desired method in the industry due to its deepest depth of investigation (DOI, up to 8 ft). However, the method suffers from higher uncertainty when formation water is very fresh or has mixed salinity. Dielectric permittivity and conductivity dispersion have been used to estimate Sw and salinity. The current dielectric dispersion tools, however, have very shallow DOI due to their high measurement frequency up to GHz, which most likely confines the measurements within the near wellbore mud-filtrate invaded zones. In this study, effective medium-model simulations were conducted to study different electromagnetic (EM) induced-polarization effects and their relationships to rock petrophysical properties. Special attention is placed on the ...
One of the most crucial decisions in drilling operations is the choice between water-based mud (W... more One of the most crucial decisions in drilling operations is the choice between water-based mud (WBM) and oil-based mud (OBM). Although WBM is often preferred, mainly due to its low cost, OBM usage ...
Smooth solid surfaces of reservoir rocks are assumed in formation evaluation, such as NMR petroph... more Smooth solid surfaces of reservoir rocks are assumed in formation evaluation, such as NMR petrophysics and reservoir wettability characterization through contact angle measurements. Measuring the degree of surface roughness, or smoothness, and evaluating its effects on formation evaluation are topics of research. In this paper, we will primarily focus on details in characterizing solid surface roughness, though its applications will also be exemplified. Surface roughness can be measured by methods of contacts and non-contacts techniques, such as stylus profilometer, atomic force microscopy, and different kinds of optical measurements. Each technique has different sensitivities, measurement artifacts, resolutions and sizes of field-of-view (FOV). Intuitively, while a finer resolution measurement provides the closest account of all surface details, the corresponding small FOV may compromise the representativeness of the measurement, which is particularly challenging for charactering h...
Abstract Usually, during oil production, water and oil flow simultaneously in the wellbore. When ... more Abstract Usually, during oil production, water and oil flow simultaneously in the wellbore. When water holdup in the borehole is small, water droplets may be dispersed into bulk oil making water breakthrough detection a challenging task. In this paper, a comprehensive engineering model of droplet dispersion is presented. Dispersion of droplets in a long vertical turbulent tubing flow is modeled by an Advection-Diffusion-Population Balance equation. The Prandtl Mixing-Length model of turbulence is used to describe the velocity profile across a tubing. The turbulence energy dissipation rate distribution across a pipe is calculated by an analytical equation. The fixed pivot method is employed for calculation of the population balance term of the governing equation. Droplet fragmentation is modeled using a recently developed droplet breakup model (Eskin et al., 2017). It is assumed that volume concentration of a dispersed phase does not exceed 10%. A computational code developed allows tracking evolution of droplet size distribution along a tubing. Model performance is illustrated by computations of the water in oil dispersion process. Effects of oil/water interfacial tension, well production rate and oil viscosity on dispersion are demonstrated.
A century after the 1918 flu pandemic, much of the world in early 2020 was experiencing the COVID... more A century after the 1918 flu pandemic, much of the world in early 2020 was experiencing the COVID-19 pandemic lockdown except a few places such as parts of Northern Europe. The reduced global demand for oil was one of the main reasons that the May futures contract for West Texas Intermediate crude fell to an unbelievable low level in late April. It was indeed an unprecedented historical moment. What has this to do with petroleum engineering in general and formation evaluation in particular? A lot. In the short term, universities would experience significantly reduced enrollments in petroleum engineering and probably geoscience majors. The industry is quickly losing experienced hands and subject-matter experts; thus, activities in innovation and new technology development would suffer. Consequently, limited numbers of professionals and fewer new business impact solutions would be available when needed in the near future when the business comes back. Therefore, we must have a longer-term vision for business planning, balancing short-term challenges with long-term perspectives. This is especially true for professional retention and development. Individually and collectively, we are currently facing undeniable difficult times. But, as has been said, challenges are also opportunities. It is a proper time for all of us to pause a bit and formulate way-forward plans that suit our needs. It is surely a good time to recharge ourselves with newly emerging skills to meet the anticipated future needs through various resources such as online training and webinars offered by service providers or from professional societies such as SPE. In any case, oil will still be an irreplaceable resource that the world needs in the foreseeable future, and formation evaluation is a critical subject-matter area that the industry cannot exist without - from resources exploration, to field development, to production, all the way to abandonment. We should sharpen our tools when we can so we will not be regretful when the time of needs comes.
Technology Focus Comprehensive formation evaluation is performed by integrating logs, cores, well... more Technology Focus Comprehensive formation evaluation is performed by integrating logs, cores, well tests, and other geoscience and engineering information. It plays a critical role in resources assessment and is equally important in well-placement development and reservoir surveillance. It is one of the technical focus areas that is fundamental across almost all upstream businesses, from initial exploration through final field abandonment. So how well are we doing in modern formation evaluation? In resources exploration, we have come a long way from the historical wireline (WL) triple combination of logging of bulk density, neutron porosity, and resistivity for reservoir lithology, porosity, and saturation, respectively. With continuing development in technologies such as acoustic, mud logging, nuclear magnetic resonance, imaging, and formation testing and sampling, we can identify fluid types and contacts; quantify viscosity, free fluid, and mobility; and characterize pore structure...
Clays in reservoir rocks have a significant impact on formation evaluation. An important property... more Clays in reservoir rocks have a significant impact on formation evaluation. An important property of clay minerals is their ability to adsorb ions on their exposed surface, which is measured by its cation exchange capacity (CEC). This property can affect saturation calculation if not properly accounted for. Many techniques have been developed for clay characterization, but it remains a focus of frontline research to find an accurate method for quantifying clays in situ and is the main objective of this study. Extensive numerical studies have been conducted and the results have indicated that for a shaly sand formation, strong dielectric dispersions were observed for all the simulated models at frequencies below 1MHz, which allowed an equation to be established that can be used to calculate clay volume through derivatives of the permittivity dispersive curves. In deriving this equation, parameters used for the studies include water-filled porosity, formation water salinity, grain siz...
Pulsed neutron carbon-oxygen (C/O) logging is a valuable measurement for dynamic reservoir satura... more Pulsed neutron carbon-oxygen (C/O) logging is a valuable measurement for dynamic reservoir saturation monitoring, especially in mixed salinity and fresh-water environments. Currently, all C/O logs are based on apparent C/O measurements, thus responses of raw data are not comparable between different tools. Tool-specific calibrations are used to convert apparent C/O log to reservoir oil saturation; the objective of C/O logging. In this paper, a new concept of intrinsic C/O logging is introduced so that raw data from different tools can be compared for enhanced log quality control and consistency of raw data and their applications. For a given system of rock, oil, and water, intrinsic carbon (C) and oxygen (O), thus C/O ratio, are theoretically calculated. For the same system, apparent C/O ratio measured by a generic C/O logging tool is also obtained using existing apparent C/O methodology. A correlation between the two is established, enabling an intrinsic C/O log output. Eleven labo...
The interaction of surface-active species within crude oil with ions in the aqueous phase can hav... more The interaction of surface-active species within crude oil with ions in the aqueous phase can have a major influence on the interfacial tension (IFT) between these two phases. Herein, the influence of salinity on IFT is investigated systematically. Brines with different salinities, including seawater and reservoir formation water, are considered. The measurements clearly show distinct IFT trends depending on the composition and concentration of salts in the aqueous phase as well as on the crude oil chemical species, as represented by the API values. The results show that complex brine systems have a stronger effect on IFT than individual single salt brine systems. It is possible to derive distinct additive correction factors for the respective tested brine systems based on the averaged values of deviation from the respective cases in deionized water. On average for the tested 10 oils, and in comparison to measurements in DI water, IFT was reduced by 3.4 mN/m in 100 kppm CaCl2 soluti...
It is desirable to evaluate the possibility of developing a deeper dielectric permittivity based ... more It is desirable to evaluate the possibility of developing a deeper dielectric permittivity based Sw measurement for various petrophysical applications. The low frequency, (< MHz), resistivity-based method for water saturation (Sw) evaluation is the desired method in the industry due to its deepest depth of investigation (DOI, up to 8 ft). However, the method suffers from higher uncertainty when formation water is very fresh or has mixed salinity. Dielectric permittivity and conductivity dispersion have been used to estimate Sw and salinity. The current dielectric dispersion tools, however, have very shallow DOI due to their high measurement frequency up to GHz, which most likely confines the measurements within the near wellbore mud-filtrate invaded zones. In this study, effective medium-model simulations were conducted to study different electromagnetic (EM) induced-polarization effects and their relationships to rock petrophysical properties. Special attention is placed on the ...
One of the most crucial decisions in drilling operations is the choice between water-based mud (W... more One of the most crucial decisions in drilling operations is the choice between water-based mud (WBM) and oil-based mud (OBM). Although WBM is often preferred, mainly due to its low cost, OBM usage ...
Smooth solid surfaces of reservoir rocks are assumed in formation evaluation, such as NMR petroph... more Smooth solid surfaces of reservoir rocks are assumed in formation evaluation, such as NMR petrophysics and reservoir wettability characterization through contact angle measurements. Measuring the degree of surface roughness, or smoothness, and evaluating its effects on formation evaluation are topics of research. In this paper, we will primarily focus on details in characterizing solid surface roughness, though its applications will also be exemplified. Surface roughness can be measured by methods of contacts and non-contacts techniques, such as stylus profilometer, atomic force microscopy, and different kinds of optical measurements. Each technique has different sensitivities, measurement artifacts, resolutions and sizes of field-of-view (FOV). Intuitively, while a finer resolution measurement provides the closest account of all surface details, the corresponding small FOV may compromise the representativeness of the measurement, which is particularly challenging for charactering h...
Abstract Usually, during oil production, water and oil flow simultaneously in the wellbore. When ... more Abstract Usually, during oil production, water and oil flow simultaneously in the wellbore. When water holdup in the borehole is small, water droplets may be dispersed into bulk oil making water breakthrough detection a challenging task. In this paper, a comprehensive engineering model of droplet dispersion is presented. Dispersion of droplets in a long vertical turbulent tubing flow is modeled by an Advection-Diffusion-Population Balance equation. The Prandtl Mixing-Length model of turbulence is used to describe the velocity profile across a tubing. The turbulence energy dissipation rate distribution across a pipe is calculated by an analytical equation. The fixed pivot method is employed for calculation of the population balance term of the governing equation. Droplet fragmentation is modeled using a recently developed droplet breakup model (Eskin et al., 2017). It is assumed that volume concentration of a dispersed phase does not exceed 10%. A computational code developed allows tracking evolution of droplet size distribution along a tubing. Model performance is illustrated by computations of the water in oil dispersion process. Effects of oil/water interfacial tension, well production rate and oil viscosity on dispersion are demonstrated.
A century after the 1918 flu pandemic, much of the world in early 2020 was experiencing the COVID... more A century after the 1918 flu pandemic, much of the world in early 2020 was experiencing the COVID-19 pandemic lockdown except a few places such as parts of Northern Europe. The reduced global demand for oil was one of the main reasons that the May futures contract for West Texas Intermediate crude fell to an unbelievable low level in late April. It was indeed an unprecedented historical moment. What has this to do with petroleum engineering in general and formation evaluation in particular? A lot. In the short term, universities would experience significantly reduced enrollments in petroleum engineering and probably geoscience majors. The industry is quickly losing experienced hands and subject-matter experts; thus, activities in innovation and new technology development would suffer. Consequently, limited numbers of professionals and fewer new business impact solutions would be available when needed in the near future when the business comes back. Therefore, we must have a longer-term vision for business planning, balancing short-term challenges with long-term perspectives. This is especially true for professional retention and development. Individually and collectively, we are currently facing undeniable difficult times. But, as has been said, challenges are also opportunities. It is a proper time for all of us to pause a bit and formulate way-forward plans that suit our needs. It is surely a good time to recharge ourselves with newly emerging skills to meet the anticipated future needs through various resources such as online training and webinars offered by service providers or from professional societies such as SPE. In any case, oil will still be an irreplaceable resource that the world needs in the foreseeable future, and formation evaluation is a critical subject-matter area that the industry cannot exist without - from resources exploration, to field development, to production, all the way to abandonment. We should sharpen our tools when we can so we will not be regretful when the time of needs comes.
Technology Focus Comprehensive formation evaluation is performed by integrating logs, cores, well... more Technology Focus Comprehensive formation evaluation is performed by integrating logs, cores, well tests, and other geoscience and engineering information. It plays a critical role in resources assessment and is equally important in well-placement development and reservoir surveillance. It is one of the technical focus areas that is fundamental across almost all upstream businesses, from initial exploration through final field abandonment. So how well are we doing in modern formation evaluation? In resources exploration, we have come a long way from the historical wireline (WL) triple combination of logging of bulk density, neutron porosity, and resistivity for reservoir lithology, porosity, and saturation, respectively. With continuing development in technologies such as acoustic, mud logging, nuclear magnetic resonance, imaging, and formation testing and sampling, we can identify fluid types and contacts; quantify viscosity, free fluid, and mobility; and characterize pore structure...
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