Conductivity Derived Porosity: A Log Supplement For Simplified Wellsite Formation Evaluation
Authors: Fons Lloyd 
Published: December 2007

American Institute of Mining, Metallurgical, and Petroleum Engineers, Inc.

This paper was prepared for the 43rd Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Houston, Tex., Sept. 29-Oct. 2, 1968. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere after publication in the JOURNAL paper is presented. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made. provided agreement to give proper credit is made. Discussion of this paper is invited. Three copies of any discussion should be sent to the Society of Petroleum Engineers office. Such discussion may be presented at the above meeting and, with the paper, may be considered for publication in one of the two SPE magazines.

A logging truck-mounted, conductivity-to-porosity analog computer has been developed to facilitate rapid wellsite formation evaluation. The computer is miniaturized so as to fit within present logging panels. It converts formation conductivity to formation porosity occupied by water which is simultaneously recorded as a supplemental well log curve. This is accomplished by a continuous solution of the classic Archie formula. Relative to other porosity curves, the conductivity-derived values are greatly affected by formation hydrocarbon content. A simple overlay of these water-filled porosity curves upon any computed porosity curve, as obtained from a device measuring total porosity, will lead to a reasonably accurate and immediate wellsite formation evaluation.

This paper describes the wellsite recording of conductivity-derived porosity [CDP] and its use in formation evaluation. It derives the analog porosity equation and presents examples showing the identification of hydrocarbons and the calculation of formation hydrocarbon content, movable oil, water saturation, and other useful formation parameters.

Introduction

A prime concern of petroleum industry well logging is the detection and evaluation of hydrocarbon bearing formations penetrated by the wellbore. The need for a rapid appraisal of each newly drilled hole is inescapable. Delays in formation evaluation after the well has reached total depth may be expensive in terms of lost rig time, idled men or increased frequency of hole trouble.

Ideally, well log interpretation should be inexpensively accomplished immediately upon completion of the logging operation and without the need for additional logging runs or additional logs. The interpretation readout should be in terms of the parameters required with no need for the complex conversion of values to put the readout in a usable or more meaningful form. At the conclusion of logging, it is desirable to estimate the volume of hydrocarbons in place, movable hydrocarbons and formation porosity. The identification of permeable and productive porosity. The identification of permeable and productive intervals will be coincidental with the establishment of movable hydrocarbons.