Dual Density Acquisition in the Karachaganak Field, Aksai, Kazakhstan

摘要

This paper discusses the success of routinely acquiring dual-density measurements in the Karachaganak Field, located near Aksai in Western Kazakhstan. Karachaganak consists of a thick, carbonate reservoir with biohermal mound/inter-mound facies overlaying shallow platform carbonates. In 2002, drilling and logging activity increased. The newly-logged wells had intervals with anomalously low bulk densities. These intervals did not necessarily show increases in hole size on the density calipers. Eventually these problems were found to exist primarily in intervals of borehole breakout (as supported by borehole image data). The density tool has a tendency to 'lock' into the breakout and not maintain good borehole contact, resulting in erroneously low bulk densities. Since density measurements are fundamental to porosity/lithology calculations, a solution to this problem was required. The eventual solution was to run a dual-density configuration, with two sourced density tools on the same string, mutually oriented at 90 degrees. With this configuration, one of the axes becomes locked into the breakout, while the other maintains good borehole contact and provides a good density measurement. Since its implementation, the dual-density approach has been 100 percent successful in providing valid density data throughout the breakout intervals. As a result, there is now more confidence in the calculated porosities and lithologies.