R. Strickland, R. Chemali, S.M. Su, and S. Gianzero
Halliburton Logging Services Austin
J. Klein and S. Sakurai
ARCO Oil and Gas Company
M. Walker
Halliburton Logging Services, Anchorage
ABSTRACT
A new deconvolution algorithm has been developed for High Resolution Induction logs to further improve their response under nearly all logging conditions. While logs run in recent years have confirmed the overall capability of HRI to produce a deep, sharp and well resolved induction measurement, the original deconvolution algorithm is sometimes inadequate in the presence of caved boreholes or magnetic formations.
A detailed analysis of the HRI logs under those adverse conditions was conducted using the elementary in-phase and quadrature components of the signal (also called R and X-signals respectively). Conductive caves showed characteristic responses on the R-signal, while magnetic muds or formations affected primarily the X-signal. All observations were confirmed and quantified by mathematical modeling. The analysis lead to the development of a new adaptive deconvolution algorithm, including an optional cave correction, that deals successfully with all the above situations.
A demonstration of the new deconvolution is given on simulated logs as well as actual field logs. The overall performance of the tool is preserved for normal conditions and vastly improved in the adverse situations cited above. Only a small degradation of the vertical resolution is observed in conductive borehole wash-outs. With the new deconvolution, magnetic minerals such as hematite or siderite do not affect appreciably the HRI conductivity log. Furthermore, the primary X-signal delineates thin siderite intervals with vertical resolution similar to the conventional spectral (litho)-density log.
M,I. Javalagi, S.L. Morriss, and M.E. Chenevert
The University of Texas at Austin
Abstract
An experimental study was made of the change in resistivity as a function of time and distance in a shale sample exposed to a liquid at one end. Two distinct shales were used in the study, Pierre and Wellington. The liquids used included KCl and NaCl solutions as well as deionized water. Resistivity was measured at three distances from the exposed end of the core samples using a six-electrode configuration. Simultaneous measurements of the swelling of the sample were used to calculate water content changes at the same three positions. The mineralogical composition of the shales was determined by x-ray diffraction analysis, resulting in a reasonably good estimate of the amount and type of clay present. Atomic absorption measurements were made on selected samples and the brine to which they were exposed in order to quantify ion movement. The results of this study give some insight into the changes in those properties of a swelling shale which influence resistivity, neutron, and density logs, and the time scale involved in the propagation of those changes away from the wellbore into the formation. While resistivity exhibits the largest relative change of the properties measured, it appears that the depth of investigation of a logging tool must be quite small for the changes to be detectable, for example.