Abstract

In the harsh drilling environments of Siberia where logistics are difficult and expensive, a process of design optimization has led to successful application of PDC bits in the intermediate hole section of development wells, reducing costs and resulting in a record footage performance of 13944 meters - and counting - by a single 11–5/8″ PDC bit.

To control costs in the remote Ust-Vakh area of the Samotlor Field of Siberia, bits and equipment must perform at an optimum level. Typically drilled using roller cone bits and turbine motors, the application requires sufficiently rugged equipment to efficiently drill sand/shale formations without costly and time-consuming trips for repair or replacement.

This paper describes the practical evolution from use of roller cone bits and turbine motors in the intermediate hole section of these wells, to use of fixed cutter PDC bits and positive displacement motors (PDMs). The resulting performance improvements are documented, including a world footage record of 13944 meters. To facilitate rapid deployment of application-specific bit technology despite the remote location, an in-house bit specialist was located at the field operations base, collaborating with the drilling department in implementing the optimization process. Focusing on the intermediate hole section from approximately 430m to 1100m depth, areas of potential improvement were identified, and solutions proposed.

Based on success in similar applications, fixed cutter bits were recommended that incorporated steel body designs with advanced hydraulics, while analysis of various bit/BHA combinations identified the most efficient configurations for this application.

Ultimately, large diameter roller cone bits with an expected life of one or two runs were replaced by steel body PDC bits that have been re-run as many as a 20 times or more, with average days per drilling in intermediate section reduced from five to just four days.

The paper summarizes savings realized, and describes additional design changes now under investigation.

Introduction

Western Siberia is the dominant petroleum basin in Russia, producing 75% of all Russian oil and gas. It's the second richest basin in the world, second only to the Middle East, with huge reserves and substantial undiscovered resources. Samotlor Field, subject of this paper, is located at Lake Samotlor in the Urals Federal District. One of seven federal districts, it is the westernmost of the three Asian districts. (Figure 1)

Discovered in 1965, the Samotlor Field is one of the largest in the world. Initially more than 16,700 wells were drilled, from which more than 2.3 billion tons of oil was produced, with production peaking in the 1980s. By 1988, intensive development had depleted reserves, a decline exacerbated by extensive water injection resulting in water mixing with the oil. Only 16.74 million tons of oil was produced in 1996. With introduction of new technology at the turn of the century however, the field is being revived.

The Samotlor Field extension at Ust-Vakh to the south is a good example of an existing mature field in Russia where the combination of Russian expertise and advanced Western technologies has resulted in improved efficiencies. Production rates there have increased by more than 40 % since 2002.

Originally revived through directional drilling, the current phase of development incorporates use of drilling techniques requiring advanced bit technology capable of achieving well objectives. In the on-going effort to improve drilling efficiencies and reduce costs, an optimization process was utilized successfully to introduce and refine application of fixed cutter PDC bit designs in the Ust-Vakh wells.

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