Ineffective electric-log interpretations and complex completion problems have discouraged much of the possible development of the Delaware Mountain Group of the Delaware basin of west Texas and New Mexico for over 40 years. During the early days of exploration and development, many producible horizons in the Bell Canyon, Cherry Canyon, and Brushy Canyon Formations were eliminated from future consideration because of faulty oil/water ratio and permeability estimates based primarily on resistivity logs, and the subsequent difficulties in completing wells using this information. Along with inefficient water shutoffs, and complicated cementing techniques, wells drilled during this period were further handicapped by a $2 per bbl or less market price.

In the 1980s, with the price of oil at or near the $30 per bbl level, many DMG prospects that originally were marginal, or even submarginal, are now being considered for prime exploitation programs because of the tremendous amount of acreage in the Delaware basin that has been either passed over as “nonproducible” or has not been investigated or drilled at all. New electric-log presentations, although markedly improved by computer-enhanced parameters, are still less than decisive in too many situations, leading to continued completion problems.

This paper describes a possible solution to many of the problems presently restraining more economical development within the Delaware basin and other areas with similar complex formations. An example of a typical oil/water inversion commonly found in the DMG is given along with references explaining the creative mechanism. This reservoir type is matched with a “textbook” type reservoir of the same formation and the methods used to analyze and identify each. The instruments and techniques required to accomplish an accurate determination of reservoir oil/water ratios are given along with documentation.

The benefits of this system of reservoir analysis during the drilling process are (1) elimination of testing and/or completing salt water or other non-producible zones; (2) augmentation or elimination of coring programs; (3) as an aid to a selective frac and/or acidizing program; and (4) a maximum production potential indicator when used with only neutron or sonic porosity logs.

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