Transcript Document
AFES MEETING SPWLA Distinguished Speaker May 2012 Station Hotel, Guild Street Wednesday 16th May 2012, 6.00 PM for 6.30 PM Start A Review of the Pe Measurement and the Derivation of Accurate Pe Equations Using Computer Modeling Gordon L. Moake Halliburton SPWLA Distinguished Speaker Abstract: Over the years, several equations have been used to compute the photoelectric log of a formation (Pe). Some of these equations lack a density term, resulting in errors; this is obvious when the tool is placed in a tank of water. In addition, the lack of quality test standards or marker beds makes Pe accuracy difficult to verify in all but a few conditions. This leads to the question: what is the proper response equation for computing Pe? To answer that question for a wireline density tool, a Monte Carlo computer-modeling study was undertaken. Two features of computer modeling make it ideal for studying this problem. First, any formation can be easily simulated, so a wide variety of data points can be used to determine the response. Second, non-physical formations can be modeled, which enables the density and Pe responses of the tool to be studied independently. Because the physics behind the Pe measurement is essentially the same for all density tools, the form of the final equation should be applicable to many tools. This study used the ratio of high-energy to low-energy count rates as the primary variable for the calculation. For a given density, it is possible to obtain an accurate Pe response from 0.4 to 15 using a simple function of the ratio. As expected, the generalized equation that is appropriate for all rock densities requires a density term. Accuracy of the technique breaks down for Pe > 15. The new Pe equation is illustrated in several log examples that compare results obtained with the new algorithm to those obtained with a previous algorithm. A review of the physics and concepts behind the Pe measurement explains why the measurement breaks down when Pe > 15, and clarifies why the Pe measurement should be treated as a unitless quantity. Biography: Gordon L. Moake Gordon L. Moake is a chief scientific advisor for Formation Evaluation in the Halliburton Drilling and Evaluation division. His primary focus is the development of wireline and LWD density and neutron-porosity tools, although he sometimes works on nonnuclear projects. Before joining Halliburton in 1984, he worked four years at Baker Tubular, developing electromagnetic flaw detectors. Moake obtained BS degrees in math and in physics from the University of Wisconsin, and MS and PhD (1979) degrees in physics from Purdue University. A member of SPWLA and SPE, he holds 18 U.S. patents related to the oil and gas industry. Aberdeen Formation Evaluation Society is a registered Scottish Charity. Charity number SC039526.