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.

Introduction

The first known methods of obtaining oil in Russia came from the gathering of oil seeps from riverbeds. This method of oil gathering produced the first deliveries of oil to Moscow from the Ukhta River in 1567. Oil and gas seeps were also recorded on the western shores of the Caspian Sea in Baku near were the world's first oil well was drilled at Bibi-Aybat in 1846, a decade before the first well was drilled in the United States. This marked the birth of the modern oil industry. Newer fields were under development in the Volga Urals from the 1930s and by the 1960s the Soviet Union had replaced Venezuela as the second largest oil producer in the world. The 1960s saw the first major discoveries of oil in Western Siberia, culminating in the discovery of super-giant Samotlor field in 1965. In 1975 Kholomogorskoye began production from the most northern oilfield at the time, which in 1981 became part of Noyabrskneftegaz. By 1988, largely because of the investment in the development of fields in western Siberia, the Soviet Union had become the largest oil producer in the world at that point in time, with production of 11.4 million BOPD.

Poor reservoir management techniques and old-fashioned technology, along with the post-Soviet Union economic crisis that halted spending in new exploration and drilling, caused a collapse in the beginning of the 1990s where Russian oil production dropped to almost one-half its peak by 1997. This was despite major investments in the mid 1990s that yielded only marginal improvements.

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