Abstract: A Statistical Approach to Estimation of Bitumen Distribution in the Tengiz Reservoir, Kazakhstan
William S. Hallager, Ben Robertson, Kevin Chambers, Feitze Papa, Bill Wood, Kubentai Suyesinov, Ray Garber
Solid bitumen occludes approximately two porosity units of Tengiz reservoir porosity. Neutron, density and sonic logs overestimate porosity at Tengiz because they do not adequately distinguish solid bitumen from movable oil. It has, therefore, been necessary to estimate the amount and distribution of bitumen in order to correct for its impact on field reserves. The origin of the solid bitumen has not yet been resolved. We have therefore taken a statistical approach to bitumen distribution.
Several hundred bitumen analyses indicate an inhomogeneous distribution of bitumen at Tengiz. Higher volume percentages are present in the Bashkirian and Serpukhovian age carbonates near the top of the reservoir. Although core descriptions and chemical analyses show some lateral variation in bitumen abundance across the field, there is no recognizable pattern to that variation.
Based on bitumen analytical data we have subdivided the reservoir into three statistically distinct groups of formations. We used bitumen and porosity analyses obtained by VolgogradNIPIneft on individual core plugs to calculate an expected log response for those samples. The results were used to build a log porosity to effective porosity cloud transform. Sequential Indicator Simulation was then applied to the digitized log data to develop a 3-D porosity cube for Tengiz. Our cloud transform was applied to that cube to predict effective porosities fieldwide.
AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France