D. M. Gwinner, L. S. Laude
Mobil Exploration and Producing U. S. (Denver)
J. L. Olmos
Mobil Exploration and Producing U. S. (Midland)
J. A. Quirein
Mobil Exploration and Producing Services Inc. (Dallas)
L. J. Reimer
Mobil Exploration and Producing U. S. (Liberal)
ABSTRACT
Hugoton field is located in Southwestern Kansas in the Hugoton embayrnent. The reservoir is in the Council Grove and Chase Groups, which are both of Permian age and consist of a mixture of limestone, dolomite, sandstones and cherts, and some evaporites. The field was discovered in the early 1900’s but is still a significant producer with considerable reserves.
The complex lithologic nature of the field makes porosity calculations from log data difficult to perform for the following reasons. Single-tool calculations are not feasible because of the extreme variations in mineralogy; standard density neutron crossplot porosity is misleading because of the presence of evaporites; and porosity estimations are complicated by the presence of gas in the reservoir.
Geologic input on the facies trends in the region and in the field provided insight into the nature of the formations. Detailed core descriptions of the facies enhanced the solutions and provided a framework for modeling. Over 300 wells were processed using two different methods.
· The first method used core porosity data from a statistically significant subset of wells. Linear regression was performed using the density, neutron, spontaneous potential, and resistivity measurements.
· The second method was based upon a system of tool response equations for the density, neutron, photoelectric factor and sonic data. The system was then solved for porosity and lithology.
Both methods addressed the complex nature of the reservoir and the effect of gas on the log data. The laboratory-measured porosities were used to evaluate the success of the log-derived porosity calculations.