Abstract

Current offshore operations are extremely expensive because of the operational environment and the necessary infrastructure. In this environment, emphasis is placed on high-efficiency operations based on specially tailored solutions combining available resources with new technologies.

To introduce greater efficiencies in offshore operations, a horizontal openhole candidate well was selected to be equipped with a permanent completion system that would enable multiple fracturing treatments. Later, it was determined that by using a novel viscoelastic polymer-free surfactant-based fluid, the entire operation could be performed in a single pumping operation, improving efficiency and adding additional savings to the process.

Because a specialized fracturing vessel tailored for operations in the Black Sea was not available, a supply vessel was used. The vessel had all required fracturing equipment rigged up and secured on decks.

To enable sufficient fracturing fluid volume for placing three propped fracturing treatments in a single pumping operation, a polymer-free fracturing fluid was formulated and mixed with seawater continuously.

This novel multistage fracturing system combined with polymer-free viscoelastic surfactant fluid system prepared with seawater was applied in the World for the first time. Results indicate a sustained increased production.

Introduction

The Lebada Vest field was discovered in 1984 and put on production nine years later. This field is situated in the Black Sea, ~95 km offshore Romania. Since then, numerous vertical oil and gas wells were drilled and completed. The wells were produced initially in natural flow and later equipped with gas lift to enhance ultimate hydrocarbon recovery.

The target reservoir is a Cretaceous-age formation located at depths of ~1,900-m true vertical depth (TVD) composed of varying shale, sandstone, and carbonate content layers. The laminated pay zone is generally formed by streaks with average permeability of 0.8 md. Reservoir rock porosity ranges between 15% and 22%. Bottomhole static temperature (BHST) is 93°C and bottomhole static pressure (BHSP) at ~1,850 m true vertical depth sub sea (TVDSS) is ~220 bars.

To increase the hydrocarbons recovery, operating company decided to drill a horizontal well and target an un-drained part of the reservoir. Furthermore, to achieve greater efficiency in offshore operations and after evaluating completion options, including open hole, cemented liner with perforations, and slotted liner, Operating company decided to complete the well openhole and equip it with a permanent completion system that enabled the placement of multiple fracturing treatments (Barba and Shook 2004). Later, it was also determined that by using a novel Visco-Elastic Surfactant-based (VES) fluid, the entire operation could be performed in a single sequence, achieving additional savings in time and related costs.

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