Abstract
This paper describes the petrophysical analysis resulting from operation of two independent pulsed neutron logging tools in the same cased hole well. The well was primarily carbonate and included many different subsurface formations located in the Southeast Anatolia Region of Turkey that included the Derdere, Karababa A, B, and C, Karaboğaz, Bozova, and Germav. Computing the mineralogy and saturation in these environments is challenging due to the complexity and low porosity of the formations that included mixed lithologies and organic shale.
One of the objectives of this work was to demonstrate how the spectral data from the two tools was not only consistent, but that they could be combined to create an optimal petrophysical interpretation of the lithology, detailed mineralogy, porosity, and saturation of the formations within the well. Both tools employed a pulsed neutron generator capable of emitting 2 x 108 neutrons/second into the ambient formation. One was a 4-detector, 1-11/16-inch diameter reservoir evaluation tool, and the other was a single detector, 3-1/4-inch geochemical spectroscopy tool.
In order to obtain the best possible results, a sound logging program was created that involved running the reservoir evaluation tool in 3 different modes of operation. This included the carbon/oxygen (C/O) mode, the sigma mode, and the gas mode. Stationary measurements were also obtained. The geochemical logging tool has only a single mode of operation. The resulting sigma measurements were in complete agreement. The sigma from the geochemical logging tool was corrected for the effects of diffusion. The advantage of the slim-hole reservoir evaluation tool is that the measurements from the 4th detector are diffusion-free.
Data from the 1-11/16-inch reservoir evaluation tool from the gas mode did not reveal any bypassed gas zones in the well.
Oil saturation was computed with the reservoir evaluation tool based upon three logging passes in the C/O mode. An important component of the interpretation was that it was supported by MCNP modeling that predicted the tool's response for hydrocarbon saturation. Although data from the geochemical spectroscopy tool was not used to determine saturation in this well, the resulting carbon concentration, that included kerogen as well as hydrocarbons, was completely consistent with the saturation computed from the reservoir evaluation tool.