| 摘要 |
<p>The invention concerns a method for determining the porosity of earth formation penetrated by a borehole, the method comprising conveying a tool along said borehole, wherein said tool comprises a source (7) of neutron radiation and at least two detectors (11,13) axially spaced from said source at least two different spacings; generating detector responses for each said at least two detectors which are indicative of neutron radiation from said source interacting with said formation; selecting from said at least two detectors (11,13) a set of detectors comprising at least one near detector (11) and at least one far detector (13); using said near detector response and said far detector response in order to obtain a near apparent porosity and a far apparent porosity; computing a correction, said correction being obtained from a mathematical function comprising the difference between said near apparent porosity and said far apparent porosity; and coefficients that have been determined from modeled and measured responses of the tool for a known formation porosity, a known tool standoff from the borehole wall and a known borehole size; and determining the porosity of the earth formation by correcting the far detector porosity with the computed correction.</p> |
