Abstract

Though there are many proven ways of predicting productivity in hydraulically fractured wells in medium-permeability oil reservoirs, there is still no simple, practical production forecasting methodology for hydraulically propped fracturing stimulations for the gas and gas-condensate wells in the Western Siberian Arctic sector.

The candidate selection process, including production prediction, is at an infant development stage and is additionally hampered by the lack of, or ambiguity in, the reservoir and production data.

This is particularly true for the Yamburgskoe gas condensate field, where the wells are completed in a series of medium- and low-permeability reservoirs. Some wells cannot maintain stable production rates and have either been shut-in or are on intermittent production. Factors may include low reservoir quality, reservoir pressure, and specific production conditions. A reliable methodology for selection of candidate wells for stimulation treatments was clearly needed.

This paper describes the comprehensive methodology derived from integrated analysis of the fracturing treatments performed between 2003 and 2005 in the Yamburgskoe gas-condensate field.

The analysis revealed a series of correlations and elaborated an engineering approach that reduced the assumptions in the estimation of hydraulic fracturing efficiency, particularly for the wells that were completed but were unable to maintain stable production. Although the certainty of the final, stabilized production rate remains a challenge for the production and stimulation engineer, recent production results showed that hydraulic propped fracturing can bring many wells to economical production.

Introduction

Candidate selection and accurate post-fracturing productivity prediction was a main challenge in the recent stimulation campaigns of the Neocomian formation (Fig. 1) in the Yamburgskoe gas condensate field.

This crucial process is difficult and time consuming. In this case it was further complicated because the main pool of preselected candidate wells included wells that were either never completed after drilling, or were shut-in for a long period of time; therefore no recent production history or recent measurements of reservoir pressure and other crucial parameters were available. Therefore the method envisioned had to be based on frequently available information---the openhole logs that are commonly used in the Russian oil field, i.e., the spontaneous potential, gamma-ray, neutron and resistivity, and information from common well testing. In most cases, these were the only data available in any significant quantity, and therefore a thorough analysis of the available testing practices was necessary. Also, the methods of determining reservoir pressure, fluid composition, and production prediction that have been historically applied in the field had to be compared to understand the possible discrepancies in prediction results. The range of application of the various inflow equations also had to be determined.

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