Formation Evaluation From Conventional Well Logs in the Gulf Coast Area
Authors: Sanyal S.K. 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nev., Sept. 30-Oct. 3, 1973. 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 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.

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.

This paper gathers some existing, but often overlooked, techniques of estimating water saturation, residual fluid saturation, anticipated water-cut and primary hydrocarbon reserve from conventional well logs and sidewall core data. Successful applications of these techniques for Pliocene and Miocene sands of the Louisiana Gulf Coast area are presented. Water saturation is obtained by a resistivity-porosity cross. plotting technique. The other reservoir plotting technique. The other reservoir properties are estimated from existing properties are estimated from existing correlations utilizing logs, sidewall core data and local experience.

On the basis of these techniques, a practical and systematic formation evaluation scheme is presented for the Gulf Coast area. This approach provides estimates of the basic petrophysical parameters and reservoir properties. parameters and reservoir properties. Field engineers and geologists can use this procedure for an "on-the-rig" evaluation of a newly drilled well or a proposed workover completion. This proposed workover completion. This simplified formation evaluation approach is very useful for wells or reservoirs where operational or economic considerations preclude more sophisticated formation evaluation.

Introduction

The availability of many sophisticated logging devices and the ever-increasing use of digital computers have brought forth various detailed and accurate formation evaluation techniques. Lithology and porosity can be determined accurately from a suite of sonic, neutron, and density logs, while watersaturation can be calculated with accuracy from a pulsed-neutron log. However, the usual methods of determining Sw from resistivity logs still have drawbacks because they need one or more of the following:knowledge of Rw,an assumed F - 0 relationship,an empirical correlationbetween Sxo and Sw, andestimates of di and Sor.

Hence, it was decided to try an often overlooked technique, which does not have such drawbacks, for routine calculation of Sw in the Louisiana Gulf Coast area. This technique is resistivity-porosity cross plotting on log-log paper, introduced by Pickett. This method does not require micro-resistivity, lateral or dual induction logs, which are not often run in development wells; a conventional electrical or induction log suffices.