Quantitative discrimination between oil and water in drilled bore cores via fast-neutron resonance transmission radiography

📝 Abstract

A novel method based on Fast Neutron Resonance Transmission Radiography is proposed for non-destructive, quantitative determination of the weight percentages of oil and water in cores taken from subterranean or underwater geological formations. The ability of the method to distinguish water from oil stems from the unambiguously-specific energy dependence of the neutron cross-sections for the principal elemental constituents. Monte-Carlo simulations and initial results of experimental investigations indicate that the technique may provide a rapid, accurate and non-destructive method for quantitative evaluation of core fluids in thick intact cores, including those of tight shales for which the use of conventional core analytical approaches appears to be questionable.

💡 Analysis

A novel method based on Fast Neutron Resonance Transmission Radiography is proposed for non-destructive, quantitative determination of the weight percentages of oil and water in cores taken from subterranean or underwater geological formations. The ability of the method to distinguish water from oil stems from the unambiguously-specific energy dependence of the neutron cross-sections for the principal elemental constituents. Monte-Carlo simulations and initial results of experimental investigations indicate that the technique may provide a rapid, accurate and non-destructive method for quantitative evaluation of core fluids in thick intact cores, including those of tight shales for which the use of conventional core analytical approaches appears to be questionable.

📄 Content

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Quantitative discrimination between oil and water in drilled bore cores via fast-neutron resonance transmission radiography+

D. Vartskya,*, M. B. Goldbergb, V. Dangendorfc, I. Israelashvilia,e, I. Mord, D. Bard, K. Tittelmeierc, M. Weierganzc, A. Breskina

a Weizmann Institute of Science, Rehovot, 76100, Israel b Herzbergstr. 20, 63584 Gründau, Germany c. Physikalisch-Technische Bundesanstalt (PTB), 38116 Braunschweig, Germany d. Soreq NRC, Yavne 81800, Israel e. Nuclear Research Center of the Negev, P.O.Box 9001, Beer Sheva, Israel

Abstract A novel method based on Fast Neutron Resonance Transmission Radiography is proposed for non-destructive, quantitative determination of the weight percentages of oil and water in cores taken from subterranean or underwater geological formations. The ability of the method to distinguish water from oil stems from the unambiguously-specific energy dependence of the neutron cross-sections for the principal elemental constituents. Monte-Carlo simulations and initial results of experimental investigations indicate that the technique may provide a rapid, accurate and non-destructive method for quantitative evaluation of core fluids in thick intact cores, including those of tight shales for which the use of conventional core analytical approaches appears to be questionable.
Keywords: Petrophysical analysis, core analysis, core fluid content, Fast Neutron Resonance Radiography,

• Corresponding author. Tel.: + 972.50.6292126; fax: + 972. 8.9342611 E-mail address: david.vartsky@weizmann.ac.il +Patent pending 2

1. Introduction When a whole drill core of reservoir rock extracted from oil or gas well enters a modern petro-physical laboratory, it may undergo several non-destructive tests, such as a gamma-ray scan which correlates core depth with log depth, or a CT scan which can provide a 3-D image of a the whole core, providing information on its internal features and fractures.
   The core is then cut into slabs, disks or plugs that subsequently undergo a procedure of cleaning and fluid extraction, to obtain samples of dry rock and the associated quantities of extracted oil and water (Andersen et al., 2013). These samples serve for determining the critical core properties required to decide whether the well in question can be economically exploited. The parameters relevant to such decision are: porosity-storage capacity for reservoir fluids, permeability-reservoir flow capacity, as well as fluid saturation-fluid type and content (American Petroleum Institute, 1998, Ubani et al., 2012).
   Nuclear geophysics is a discipline that assists oil, gas and uranium exploration, both in nuclear borehole logging and analysis of core samples (Borsaru M., 2005). Middleton et al, 2001, investigated thermal neutron radiography to estimate rock’s porosity and relative fluid saturation in 5 mm thick rock slices. The use of thermal neutrons does not permit distinguishing between water and oil, because it relies solely on the attenuation of hydrogen. De Beer et al, 2004 also used thermal-neutron radiography to provide internal structure images of rocks, in order to determine the effective porosity of the object. Nshimirimana et al, 2014 examined the precision of porosity calculations in 14-17 mm thick rock samples using thermal neutron radiography. Lanza et al, 1991 investigated thermal neutron computerized tomography to image the distribution of hydrogenous liquids (oil or water) in a 25.4 mm diameter core. As in the above-mentioned studies it cannot distinguish between oil and water either. In certain cases deuterated water is introduced into the porous media, in order to study immiscible fluid flow by thermal neutron tomography (Murison et al. 2015). A recent review (Perfect et al, 2014) of thermal-neutron imaging of hydrogen-rich fluids in geo-materials discusses the non-destructive visualization of such fluids within diverse porous media.
   In this paper we present a new method based on Fast Neutron Resonance Transmission (FNRT) radiography that can determine non-destructively and quantitatively the content of different fluids in the core.

2. Fast Neutron Resonance Transmission Radiography FNRT is a method that exploits characteristic structures (resonances) in the neutron attenuation of the analysed object constituents to determine the identity and proportions of substances within it. A typical neutron energy range is 1-10 MeV. In FNRT the inspected object is irradiated with a broad spectrum of neutrons in the above-mentioned energy range. Depending on the nature of the inspected object the transmitted neutron spectrum will exhibit dips and peaks at specific energies. 3

Therefore, the transmitted neutron spectrum carries information about the composition of the object.
FNRT has been applied in the past for detecting low-Z (light) elements, such as H,C, N, a

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