A Method for Neutron Derived Porosity Determination for Thin Beds
- J.M. Edwards (McCullough Tool Co.) | A.L. Simpson (McCullough Tool Co.)
- Document ID
- Society of Petroleum Engineers
- Transactions of the AIME
- Publication Date
- December 1955
- Document Type
- Journal Paper
- 132 - 136
- 1955. Original copyright American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc. Copyright has expired.
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Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 132-136.
The application of the Scintillometer to radioactivity surveys in boreholes of oil wells has made it possible to determine bed thickness with a high degree of accuracy. This fact, combined with known relation of logging variables, makes thin bed porosity determination practical.
With the use of the Scintillometer a method has been derived whereby the apparent level of radiactivity, as recorded on radiation logs, may be converted to the true level. The true level of radioactivity is that level to which the recording pen would have traveled had the detector remained at a given depth for an infinitely long period of time.
This method depends entirely on accurate measurement of bed thickness and drag. A thorough discussion of the concept of time constant and logging speed as related to drag is undertaken.
Neutron curve interpretation has become one of the accepted methods for porosity determination in oil field practices. A great deal of literature has been published about neutron derived porosities, but this has been concerned with thick beds, or possibly even averaging of a series of thin beds as a single unit. There has been a lack of written information on methods whereby porosity can be evaluated for beds less than 10ft in thickness.
In certain areas, production is derived from relatively thin formations. The importance of thin bed evaluation, the fact that the Scintillometer is an adequate tool for this application, and the general lack of published information concerning neutron porosity for thin beds are the fundamental reasons for presenting this method of porosity determination. This concept is not put forth with the idea of discounting existing methods, but is merely suggested as a modification of other accepted methods of porosity determination which makes no allowance for quantitative evaluation of thin beds.
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