The porosity response of four proposed generator-based neutron tool concepts is studied using Monte Carlo simulation of the radiation transport. The objective is to examine, at a fundamental level, the potential of these sources to replace americium-beryllium (Am-Be) sources primarily in openhole applications and, briefly, in a through-casing application of interest to a number of operators. The accelerator-based sources include a dense-plasma focus (DPF) alpha-particle accelerator and deuterium-tritium (DT), deuterium-deuterium (D-D), and deuterium-lithium (D-7Li) neutron generators. The DPF uses the (a-Be) reaction to generate a neutron spectrum that is nearly identical to that from an Am-Be source. D-T and D-D neutron generators use compact linear accelerators and produce, respectively, 14.1 and 2.45 MeV neutrons. The D-7Li neutron spectrum resembles the Am-Be spectrum at lower energies, and has a neutron peak at 13.3 MeV
Simple spherical-geometry models that do not include tool and borehole are used to explore the basic physics. An openhole tool-borehole-formation configuration is used to explore key observations from the simpler model. In both models, the responses at various detectors are examined to understand the behavior of the ratios constructed. Sensitivity to formation conditions, such as lithology, presence of gas, low porosity and presence of thermal absorbers, and operational conditions, such as tool standoff, are examined. A casedhole configuration is also analyzed where neutron counts are the only method for zonal correlation.
The state of neutron-generator technology is discussed in terms of neutron yield, target properties, power demands etc., which are important considerations for implementing such generators in nuclear logging tools.
Basics of ratio-based porosity response of four proposed generator-based neutron tools are studied using Monte Carlo simulation of the radiation transport to examine, at a fundamental level, their potential to replace Americium-Beryllium (Am-Be) sources. Accelerator-based sources considered include a dense plasma focus (DPF) alpha-particle accelerator, Deuterium-Tritium (D-T), Deuterium-Deuterium (D-D), and Deuterium–Lithium (D-Li7) neutron generators. The DPF alpha-particle accelerator utilizes the (α-Be) reaction generating a neutron spectrum that is nearly identical to that from an Am-Be source. D-T and D-D neutron generators utilize compact linear accelerators and emit, respectively, 14.1 and 2.45 MeV neutrons. The D-Li7 neutron spectrum resembles the Am-Be spectrum at lower energies, and has a neutron peak at 13.3 MeV.
In the present work, simple spherical geometry models that do not include tool and borehole are first used to explore the basic physics. A tool-borehole-formation configuration is then utilized to briefly explore key observations from the simpler model. In both models, the responses at various detectors are examined to understand the behavior of the ratios constructed. Sensitivity to formation conditions such as low porosity and presence of thermal absorbers, and operational conditions, such as tool standoff are examined. The state of neutron generator technology is also discussed in terms of neutron yield, target properties, power demands, etc., which would be important considerations in actually utilizing generators in nuclear logging tools.
For over fifty years, down-hole devices using radioisotopes Cs-137 and Am-241, have been utilized, together with electrical resistivity/induction, to map the subsurface in open holes.1 [Ellis, 1987] The 662-keV gamma rays produced by Cs-137 are utilized in 2-3 detector tools to determine the formation bulk density which then provides the most accurate measure of porosity. In an Am-Be source, alpha particles (4He) emitted by Am-241 impinge on beryllium to produce a broad spectrum of source neutrons which can then be utilized to compute the neutron porosity. The neutron porosity, often in conjunction with the density, is used to determine lithology and locate gas. Recently, Am-Be (n-gamma) capture spectroscopy tools were developed to determine mineralogical information. [Herron and Herron 1996; Galford et al 2009] In addition, acoustic devices to measure porosity are often included in the suite of logging measurements. In special cases, nuclear magnetic resonance (NMR)-based techniques are also used to compute the porosity. [Ellis and Singer 2007] It should be noted that radionuclide tools are used for data acquisition both in the wireline mode where tools are inserted in the well-bore post-drilling and during logging-while-drilling (LWD).
Copyright 2014, held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors. This paper was prepared for presentation at the SPWLA 55th Annual Logging Symposium held in Abu Dhabi, United Arab Emirates, May 18-22, 2014. ABSTRACT Key physics aspects of two proposed safer alternatives to Cs-137-based gamma-gamma density (GGD) concept and their interpretation and tool design implications are examined using Monte Carlo simulation of the attendant radiation transport. The other injects neutrons from a 14-Mev neutron generator and utilizes gamma-rays produced from inelastic scattering of high energy neutrons. Each has exhibited unique challenges in interpreting the bulk density thereby requiring complex design choices, corrections, or both. The paper studies the basic causes of these based on the physics, and explore the question: can these alternatives indeed replace the Cs-137 based gamma-gamma density? INTRODUCTION Down-hole instruments with radionuclide sources are a key part of the suite of measurements that are utilized in hydrocarbon exploration and production. The Cs-137 based density provides the most accurate estimate of formation porosity while Am-Be source tools provide lithological information and show the classical gas/liquid differentiation. Although the petroleum industry has in place welldefined safety protocols to handle these sources, three recent incidents, a lost source, a breached source and a stolen source, respectively [Guardian, 2003; NRC, 2006; Badruzzaman et al, 2009; Rhoades, 2010], have heightened already existing security and 1 safety concerns from using such sources. Although well logging sources contain much lower radioactivity relative to radionuclides used in other industries, such sources are small, mobile, and often utilized in unstable regions of the world, and thus pose unique risks. Consequently, enhancing the safety of these sources and ultimately, replacing them with alternative nuclear sources to reduce the threat of radiological dispersal devices (RDD) has been of interest to governments and agencies for some time. The US National Academy Sciences in its 2008 report to Congress on industrial use of radioisotopes suggested that the Am-Be source used in the petroleum industry be replaced either with a neutron generator or Cf-252. It is a lower risk-category source and at the time there appeared to be no viable commercial or near-commercial alternatives. Independent of government and agency urgings, the petroleum industry has considered source replacement at its own initiative for over two decades. Two D-T neutron generator based neutron porosity devices, one for wireline (Mills et al, 1988; Flanagan et al, 1991) and the other for LWD, (Evans et al, 2000) have been marketed. One, proposed in mid-1980s for open-hole configurations, utilized Bremsstrahlung X-rays from an electron linear accelerator (LINAC).
Radioactive sources utilized in many industries, including the petroleum industry, have raised security, safety and environmental concerns. Oilfield sources are highly mobile, transported across the world and often used in remote locations. Despite safeguards and regulations, such sources have been lost, stuck down-hole, or breached. Concerns have been raised on sources being used in a radiological dispersal device (RDD). The US National Academy of Sciences, being concerned primarily with RDD, recently recommended replacing radioactive sources used in several industries with alternative sources. These include replacing Am-Be neutron sources used in porosity devices with either neutron generators which are switchable or with Cf-252 which emits lower amounts of radioactivity. The lower risk Cs-137 source used in measuring density was spared at this time. However, a breached Cs-137 density source down-hole recently necessitated the setting up of a very long-term, elaborate monitoring program and thus such sources are of concern too.
This paper discusses the critical role of radioactive sources in petroleum exploration and production, protocols prescribed by regulators and the International Atomic Energy Agency for their safe use, concerns about their RDD potential, and lessons learned from a recent breached radioactive source incident in the field. The paper identifies additional procedures the oil industry needs to consider to use radioactive sources safely and securely, reviews the NAS recommendations and their potential impact on the industry, and describes alternatives to current chemical sources the industry is considering and the challenges which have arisen in making the transition.
Devices with radioactive sources are used for a wide range of beneficial applications. These include cancer therapy, irradiation of blood for transplant patients, sterilization of medical equipment, non-destructive testing of structures, and petroleum exploration and production. In the petroleum industry, such sources are used in applications ranging from radiography of platform and flow equipment to flow monitoring to down-hole measurements for reserves estimation. In addition, naturally occurring radioactive material (NORM) containing potassium, thorium and uranium can deposit on walls of pipes carrying fluids from the reservoir and have to be disposed off.
Despite the strict protocols mandated in utilizing radioactive sources in petroleum and other industries, radiation contamination from industrial use of sources has caused serious health effects and even death [IAEA, 1988]. Following the tragedy of September 11, 2001, concerns have been heightened on potential use of industrial radioactive sources in radiological dispersal devices (RDD's). According to the International Atomic Energy Agency [IAEA], millions of sources have been distributed in the past 50 years for the variety of applications cited, but they were not well-catalogued. Citing the United States (US) Nuclear Regulatory Commission (NRC), the IAEA noted that US companies have lost track of nearly 1,500 radioactive sources within the country since 1996 with more than half of these never recovered [IAEA, 2002]. The same IAEA report cites a European Union (EU) study which estimated that up to 70 sources are lost per year from regulatory control in the EU. Most sources contain low-level radioactivity and thus are unlikely to cause harm. However, according to the IAEA, there are over 20,000 operators of sources with significant radioactivity [IAEA, 2002].
Nuclear energy is typically used to supply electricity, but a new generation of novel, inherently safer reactors can supply high-temperature steam for a number of petroleum, coal and chemical industry applications. Potential applications include recovery from unconventional petroleum sources such as oil sands and heavy oil, coal-to-liquids conversion, and production of hydrogen for refineries, chemical industries and possibly future transportation. Currently, natural gas is the typical source of the process heat and its use in these applications is likely to increase, as a greater reliance is placed on these resources to meet the projected growth in energy demand. This will increase greenhouse emissions from fossil fuel use. Techniques, such as carbon dioxide capture and sequestration, proposed to mitigate greenhouse gas emission from fossil-fuel based power and heat generation are in early stages of development and face technical and economic challenges. Nuclear power and heat generation emits almost no greenhouse gases. In addition,use of nuclear energy can free-up fossil fuels for other unique applications. These advantages, together with energy security concerns, improved safety and reliability, and reduced cost of nuclear plants, have renewed interest in this technology.
The paper explores the potential benefits and challenges of using nuclear energy in enhanced recovery from unconventional fossil-fuel resources. The associated economics and corresponding potential reduction in CO2 emission are examined. Both appear substantial in some applications, such as production from heavy oil reservoirs and oil sands. Economic benefits are more questionable in other applications such as in hydrogen production, and would require technological breakthroughs. Challenges facing nuclear energy include concerns of proliferation, waste disposal, public perception, demands on various resources, and licensing of novel high-temperature reactors. Resolution of power and temperature rating compatibility issues and siting constraints which may arise in some of the unconventional recovery operations will be additional challenges. However, these challenges may be less inhibiting than previously thought. The paper also briefly summarizes government-industry initiatives being discussed in the US to develop novel nuclear reactor concepts for these uses.
We discuss our experience to date with the Carbon/Oxygen logging technique to determine vertical sweep in Belridge Diatomite in the Lost Hills Field. We
describe early interpretation challenges with overly optimistic saturation estimation. This required in-house Monte Carlo modeling to understand the tool response in very high porosity reservoirs. A newer vendor algorithm, however, underestimated the oil saturation. In-house test algorithms were then developed with significantly more accurate estimation of the oil saturation from a centralized-detector C/O tool in water-filled boreholes; results reported here are primarily for this tool. The C/O technique is also being tested in producers using the corresponding focused tool; we include an example of a
successful test of the tool in an unperforated well. The paper identifies further development needed to use C/O techniques, especially the focused tool, optimally in either monitor or producer wells in diatomite.
Badruzzaman, Ahmed (Chevron ETC) | Crowe, John (Chevron) | Bean, Clarke (Chevron Asia South) | Logan, James P. (PT Caltex Pacific Indonesia) | Zalan, Thomas Anthony (Pearl Oil Thailand Ltd) | Platt, Christopher J. (Chevron Indo Asia BU) | Adeyemo, Adedapo
Pulsed neutron measurements are commonly used to locate gas behind casing and quantify steam saturation, but do not always yield desired results. Several parameters are utilized to identify gas and one parameter, the thermal neutron capture cross section, Sigma, is used to compute steam saturation. In the paper we report a mixed experience in identifying gas with these techniques, across fields, tools and vendors. Some parameters have worked well in some cases but have performed poorly in others. The uncertainty in steam saturation, computed using Sigma, is greater than those previously reported elsewhere. Modeling offers insight into the mixed results. It appears that in some cases the PNC-derived Sigma may yield erroneous steam saturation for a variety of reasons, including uncertainties in the input parameters and possibly an inherent nonlinear transport effect that increases as steam saturation increases. An alternative approach based on PNC pseudo-porosity is explored. Calibration of cased-hole tools in gas reservoirs, generic and local, open-hole baseline data and core analysis of complex rocks are essential. Currently, these are either nonexistent or infrequent.
The paper describes three examples from the author's experience of technology transfer in the E&P industry and examines a number of critical elements, beyond those normally found in the literature, that need to be accounted for to bring about a successful and durable transfer of a technology. These include meticulous planning, determination of appropriateness, recipient buy-in, an early demonstration of benefits, at least a nascent technology base and awareness, continuous mentoring and monitoring, and finally evolution into a culture of technology utilization and management.
Zalan, Thomas A. (PT Caltex Pacific Indonesia) | Badruzzaman, Ahmed (ChevronTexaco Energy Technology Co.) | Julander, Dale (ChevronTexaco North America Exploration & Production Co.) | Whittlesey, Karen (ChevronTexaco North America Exploration & Production Co.)
ChevronTexaco has developed leading edge data acquisition and interpretation strategies to monitor steamfloods in Sumatra, Indonesia and San Joaquin Valley, California. This paper reviews ChevronTexaco's current steamflood surveillance techniques, and how learnings from San Joaquin Valley are adapted to operations in Sumatra.
Badruzzaman, Ahmed (Chevron Petroleum Technology Co.) | Skillin, Robert H. (Chevron North America Exploration & Production) | Zalan, Thomas A. (Chevron North America Exploration & Production) | Badruzzaman, Tahmina (Pacific Consultants & Engineers) | Nguyen, Phuong T. (Chevron Petroleum Technology Co.)