Acquisition of density data in the carbonate Karachaganak Field in Aksai, Kazakhstan can be severely affected by borehole breakout. Valid porosity determination is key in the development of the field. Breakout occurs with 180o phasing (parallel to the minimal stress direction and can be easily identified in the borehole from acoustic and resistivity imaging logs. Erroneously high density porosities across the breakout intervals on previous logs indicated that the density pad was tracking in one of the rugose breakout grooves. The initial solution to solve this problem was to run a second density device (no radiation source at the bottom of the tool string at 900 to the sourced density pad. The idea was to open the bottom caliper and lock it into the breakout groove, so that the sourced tool was reading competent rock across the breakout interval. The problem with this method became apparent when the opposite situation occurred and the sourced density pad locked into the breakout. The current solution to the breakout problem is to put radioactive sources in both tools and simultaneously record density data at 90o phasing. The result is the ability to collect valid density data from competent rock regardless of tool orientation.
After the initial dual density acquisition was performed it became apparent that other relevant information presented itself. The Karachaganak reservoir sections have some complicated porosity distribution, most notably; dolomitized sections with anhydrite plugging the porosity on one side of the well bore and open porosity on the other side of the well bore. In combination with image logs, the dual density can give better porosity estimations across these zones of lithologic anisotropy.
Examples will be presented showing the relation of the borehole images to each of the density curves. From these comparisons, the relevance and necessity of simultaneously recording density data from two density tools with 90o phase separation in the Karachaganak field will be shown.