Abstract: Porosity Determination in the Tengiz Oil Field, Kazakhstan

Feitze Papa, Kamal Osman

The thick carbonate reservoir of the Tengiz oil field in Western Kazakhstan consists primarily of clean limestone. Ninety-three wells were drilled in this field, but only 74 of these wells have penetrated the reservoir. None of the wells in the field have been drilled completely through the reservoir, nor have any definite fluid contacts been encountered yet.

Log information obtained in the field varies widely from well to well. The most frequently available logs are the GR and NGR logs, which, by themselves, offer very little concrete numerical information about the reservoir.

Most of the porosity data collected over the Tengiz reservoir was obtained with Russian logging tools. A normalization process, based on available Western log data, was applied to all the porosity log information. This standardized all these data, thus eliminating any digitizing and tool calibration errors. The normalization follows a one point conformity process, thereby preserving the original distribution integrity of the data.

Based on maximum tool availability and using the normalized Russian log data, porosity was then determined for the carbonate reservoir. A visual screening method was used to check for errant tool behavior in order to eliminate any obviously incorrect porosity readings.

As a final phase in the project, possible ranges of the calculated porosity values were established for probabilistic reserve calculations. These lower and upper range values could then be applied to determine high and low probability cases.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France