Abstract
Hydraulic fracturing in Western Siberia is continually evolving into larger and more aggressive fracture treatments to achieve higher conductivity than conventionally planned. At the same time some of the fields that have been waterflooded for 20 years or more for pressure maintenance, have become highly water-saturated. In the past, stimulation treatments were designed based on old log interpretations showing water saturation at original conditions and post-fracture water production was frequently under-estimated, while over-estimating oil production.
A comprehensive study was conducted into the water-flooding pattern of a Western Siberia oil field, and water-cut maps were generated to determine which areas of the field were more water-saturated. This study included a statistical analysis of the effect of various fracture parameters on the post-fracture water-cut. Also the relationship between nearby water injectors and post-fracture water production was analyzed. It was found that injectors in a NNW proximity to the fractured well contributed higher post-fracture water rate. Generally, fractures grow in this direction, which is the maximum principal stress orientation across much of the Western Siberian Basin. This paper presents and discusses the statistical approach we developed.
A new method of predicting post-fracture production involving a multi-phase reservoir simulator, was employed. The water and oil production match achieved using this simulator allowed us to re-calibrate the layer information from the original log interpretations, resulting in highly accurate production forecasts. A brief discussion of the simulator is also included in the paper.
The trend toward larger treatments and coarser proppant has (1) produced higher-conductivity fractures and (2) significantly improved production from fields in western Siberia. At the same time, the trend has created longer effective fractures and in some instances increased access to water through inter-well communication. This development has underlined the importance of understanding reservoir saturation and waterflood patterns, so that full advantage can be taken of the increased conductivity through gain in oil productivity.
These techniques of reservoir simulation and studying injector proximity were then employed in the field for candidate selection. The result has allowed fracturing to be performed in this field with greater confidence in predictability of post-fracture productivity. This paper presents the field study illustrating the developed methodology.
