Dennis J Pittman

US Patent:

6891377, May 10, 2005

Filed:

Mar 29, 2001

Appl. No.:

10/240639

Inventors:

Philip Cheung - Montesson, FR
Andrew Hayman - Voisins-le-Bretonneux, FR
Dennis Pittman - Lawrenceville NJ, US

Assignee:

Schlumberger Technology Corporation - Sugar Land TX

International Classification:

G01V003/18

US Classification:

324374, 324367

Abstract:

The present invention relates to apparatus for a tool for investigating the wall of a borehole in a geological formation, the apparatus comprising: a non-conductive pad having an inside face and an outside face for pressing against the wall; a set of measurement electrodes mounted on the outside face of the pad and means for measuring the potential difference between two measurement electrodes; and both a source electrode adapted to inject current into the geological formation and a return electrode, the set of measurement electrodes being situated between the source electrode and the return electrode for the current; the apparatus being characterized in that the pad comprises an electrically conductive portion covering the entire measurement electrode zone and electrically insulated from the measurement electrodes.

US Patent:

20030173968, Sep 18, 2003

Filed:

Feb 24, 2003

Appl. No.:

10/240646

Inventors:

Philip Cheung - Montesson, FR
Andrew Hayman - Voisins-le-Bretonneux, FR
Dennis Pittman - Lawrenceville NJ, US
Abdurrahman Sezginer - Los Gatos CA, US

International Classification:

G01V003/18

US Classification:

324/374000, 324/367000

Abstract:

The present invention relates to a method of investigating the wall () of a borehole in a geological formation by means of two injectors () with a potential V being applied between them and in measuring the potential difference V between two electrically isolated measurement electrodes () situated between the two injectors () and spaced apart from the formation by an insulating layer (), in which the resistivity of the formation is obtained from the measured values of V, V and I, with corrections being made for the effects due to the nature and the thickness of the insulating layer (). In a first variant these corrections are based on a correction factor obtained from curves of K=Rt.I/ V as a function of the impedance V/I of the injector. In a second variant these corrections are obtained by estimating the current Iactually injected into the formation while taking account of leakage current I, and calculating the resistivity of the formation from the equation (I). The invention also provides an investigation device enabling the values of Iand/or Ito be estimated.