Abstract

A suite of conventional petrophysical methods is applied in intervals of Canyon Limestone and Fusselman Dolomite in two separate wells in the Permian Basin, for reservoir identification, hydrocarbon detection and assessment of hydrocarbon movability in each of those wells. Self-Potential provides initial indications of permeable beds and Neutron and/or Density logs provide information on reservoir porosity. Dual Induction – Laterolog resistivity log data founds many of the key analytical parameters used to identify clean, productive hydrocarbon zones and distinguish them from wet or unproductive zones.

Resistivity measurements in subsurface formations penetrated by a wellbore reflect certain characteristics of the rock-fluid properties of the formations, including the volumetric extent and geometric nature of the pore system, electrolytic properties and volume of the connate water included in the pores and any conductive properties of the rock matrix. Archie water saturation analysis, based on formation resistivity and porosity measurements, connate water resistivity, and a general assumption concerning the values of critical empirical parameters relating formation resistivity and porosity, is commonly applied in assessing the value of individual reservoir zones as potential candidates for testing as hydrocarbon producers. However, formation resistivity data can be applied further to the detection and evaluation of subsurface hydrocarbon accumulations. In the context of an invaded reservoir, examination of a series of analytical parameters developed from the formation resistivity factor, resistivity porosity, moved hydrocarbon index and ratio water saturation can provide a broader analysis of indications of hydrocarbon presence and the transmissibility properties of reservoir rock-fluid systems. This expanded petrophysical analysis is presented in a series of page-size log-format charts and enhances the ability of operators to recognize rock-fluid characteristics of a potential reservoir zone that underpin hydrocarbon productive capacity.

Results of all the petrophysical methods developed in the analysis are collected in relative frequency plots that can be used rapidly, consistently and objectively to compare and rank the hydrocarbon productive characteristics among several zones being considered for completion in a well. This enhances the ability of an operator to successfully identify zones to test.

The evaluation frequency plots are based on logical arguments developed in Excel and are intended to draw-on and systematize an interpreter’s experience with critical rock-fluid system properties in a developing field or field-analogous exploration play. Individual operators can revise the calibration of the relationship of the elements in the logical arguments to hydrocarbon productivity as necessary through their own experience or through systematic analysis of existing wells in a field completed for a range of test results from successful to P&A tight or wet.

The economic value of a well can be significantly enhanced through successful recompletions. This method anticipates that the geologist and reservoir engineer involved with planning and completing the formation evaluation program for a well are thus highly knowledgeable about the well and should identify and assess all potential reservoir zones in the well upon its completion. The frequency plots developed using this method are page-size summaries of a complete petrophysical evaluation. They can be readily included in a well file to reliably document uphole potential, good, fair, or risky, for future use when initial completions are abandoned and the technical professionals responsible for the initial success of the well are no longer involved with the project. If sufficient potential beyond the planned objective is indicated, the evaluation frequency plots could help support the need for additional drilling for new objectives.