Quantifying the Geologic Control of Reservoir Heterogeneity in Clastic Reservoirs, Bohai Bay Basin, China

Qian Song¹, Yuefeng Sun¹, Xiangfei Che², and Li Zhuang^2
1Texas A&M University, College Station, TX
²Exploration & Development Institute, PetroChina, Panjin, China

Clastic heavy oil reservoirs of lower Tertiary age in the Bohai Bay basin, China, have been under thermal production for more than twenty years. However, production performance has remained unstable, largely due to the fact that the producing formations are highly heterogeneous. A better understanding of reservoir heterogeneity and establishment of accurate high-resolution reservoir heterogeneity models are critical to optimizing the field development.

In order to identify the reservoir heterogeneity accurately, quantitative heterogeneity levels need to be determined. The important step is to develop the relationship between a heterogeneity level and a lithofacies that is genetically related to depositional patterns and subsequent diagenesis. Heterogeneity levels are determined by calculation of permeability variation coefficient, dart coefficient and contrast coefficient. These permeability coefficients are then linked to the lithofacies model to characterize quantitatively the internal heterogeneity variations within the model. The new model with quantitative heterogeneity levels thus can be used to predict reservoir heterogeneity when lithofacies is available from well logs and cores.

This method has been successfully tested in two pilot areas in the Bohai Bay basin. The dominant heterogeneity models within different producing layers are very different, which well explains the dramatic changes of production heterogeneity inside a producing layer or between different producing layers. Based on the quantitative and better understanding of the reservoir heterogeneity, well developments optimization has been carried out, including new well patterns, horizontal wells and others. The thermal production efficiency has been greatly enhanced subsequently.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas