Nuclear Techniques for Subsurface Geology

Ellis, Darwin V.; Schweitzer, J.S.; Ullo, J.J.

doi:10.1146/annurev.ns.37.120187.001241

Cited by 22 publications

(4 citation statements)

References 32 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In a dual porosity tool the basic measurement is the ratio (R) of counting rates at the near (N) and far (F) epithermal and thermal detectors (Figure 2). Unlike thermal neutrons, epithermal neutrons are less sensitive to neutron absorbers in the formation, and therefore they reflect more accurately the effective porosity of the rock [Ellis, 1987a;Ellis et al, 1987b]. In both cases the measured ratio is converted into porosity units, based on laboratory calibrations.…”

Section: Prediction Of the Neutron Response In Basalts As A Function mentioning

confidence: 99%

“…Present neutron porosity tools employ a chemical source (Am-Be or Pu-Be) to bombard the borehole and the formation with fast neutrons, and two or four sensors at a certain distance from the source to detect the neutrons in the epithermal and thermal energy ranges. During the scattering process the neutrons interact elastically with the nuclei in the formation, losing part of their kinetic energy at each collision; eventually, they reach the thermal energy level at which they can be absorbed by the surrounding nuclei [Ellis, 1987a;Ellis et al, 1987b]. The entire process is controlled mainly by the hydrogen content of the formation; in fact, because their mass is equal to that of the bombarding neutrons, hydrogen nuclei are the most efficient in slowing them down.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Broglia¹,

Ellis²

1990

J. Geophys. Res.

View full text Add to dashboard Cite

DARWIN ELLIS Schlumberger-Doll Research, Ridgefield, ConnecticutThis study focuses on the effects of hydrous alteration minerals, formation absorption, and standoff on the response of the thermal neutron porosity log in the basaltic and gabbroic rocks logged at sites 395,418,504, 642, and 735 during the Ocean Drilling Program. The concentration of hydrogen present in the rocks in the form of free water (pore space) and bound water (hydrous minerals) is the primary factor controlling the neutron elastic scattering process, while the presence of other elements, such as chlorine, gadolinium, boron, lithium, and samarium in the fluids and in the rock matrix can largely affect the thermal diffusion phase. These neutron absorbers cause an increase of the capture cross section, and in turn of the apparent thermal porosity. Further perturbations occur when the recording conditions depart from those under which the tool has been calibrated; a large and irregular hole diameter and a lack of eccentralization both produce erroneous porosity readings. The effect of hydrous alteration minerals on the thermal neutron porosity log has been estimated from 922 core oxide measurements using an analysis program that calculates the slowing-down length and converts it into apparent porosity. The results show that the computed apparent porosity ranges from less than 1% in fresh basalts and gabbros to about 30% in highly altered units. Depending on the alteration mineral assemblage, natural gamma ray, capture cross section, or hydrogen logs have been used to continuously predict the effect of bound hydrogen at each site. Corrected porosities generally show excellent agreement with core data for massive units, whereas they are higher for pillow basalts and fractured zones. The discrepancy is interpreted as the result of (1) difference in the volume of rock investigated (core specimens do not sample large vugs and fractures) and (2) frequent variations in the hole size and lack of tool contact with the borehole wall (standoff), not completely accounted for in the corrections. High capture cross section values measured on selected basalt samples seem to be associated with more altered basalts, suggesting a larger concentration of strong neutron absorbers in secondary minerals. The concentrations of elements with large capture cross section (E) measured at three of the five sites studied yield a maximum increase of 1% in the apparent neutron porosity. This is too low to explain the porosity values, some greater than 7%, observed in some of the fresh and unfractured massive units. A 1-to 2-inch standoff due to the lack of eccentralization of the tool string used in the Ocean Drilling Program is considered the most probable cause of such discrepancy. This interpretation is confirmed by the neutron porosity values recorded at site 735, where the nuclear string was for the first time fully eccentralized, and only a correction for borehole size and the presence of hydrous minerals has been applied. and Chiaromonte, 1983; Gilchrist et al.scientif...

show abstract

Section: Prediction Of the Neutron Response In Basalts As A Function mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Broglia¹,

Ellis²

1990

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…by Gorschkow (1960) and applied to downhole logging e.g. by Hallenburg (1973), Ellis et al (1987), Rider (2002), and Serra and Serra (2004). The method of simple (or 'total-count') gamma-ray borehole logging is often abbreviated to different mnemonics (Heise, 1993;Zscherpe and Steinbrecher, 1997;ODP, 2004;SPWLA, 2007;IODP, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…The amount of registered counts is influenced by the size and efficiency of the used detector (Ellis et al, 1987), and thus needs to be normalised and calibrated. Physically, the respective count rate represents a specific activity and, for a defined radiation energy level, a dose rate.…”

Section: Introductionmentioning

confidence: 99%

Environmental corrections to gamma-ray log data: Strategies for geophysical logging with geological and technical drilling

Lehmann

2010

Journal of Applied Geophysics

View full text Add to dashboard Cite

Scattering and Absorption of γ‐Rays and Thermalization and Disappearance of Neutrons

Borşaru

2000

Encyclopedia of Analytical Chemistry

View full text Add to dashboard Cite

Nuclear techniques are widely used in geological and mineral applications. Owing to the high penetration of γ‐radiation and neutrons, nuclear techniques have found many applications, including well logging, bulk analysis and on‐stream analysis. The first part of this article presents the physics of the interaction of γ‐rays and neutrons with matter. Applications based on these interactions to well logging for oil, uranium, coal and iron ore are presented in the second part of the article. Applications based on the natural radioactivity of rocks are also covered.

show abstract

Nuclear Techniques for Subsurface Geology

Cited by 22 publications

References 32 publications

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Effect of alteration, formation absorption, and standoff on the response of the thermal neutron porosity log in gabbros and basalts: Examples from Deep Sea Drilling Project‐Ocean Drilling Program Sites

Environmental corrections to gamma-ray log data: Strategies for geophysical logging with geological and technical drilling

Scattering and Absorption of γ‐Rays and Thermalization and Disappearance of Neutrons

Contact Info

Product

Resources

About