Frontiering Ultra-Deep Water Gas Field Development, Offshore Black Sea - Turkey: Solutions to Complex Well Testing Challenges and Proving Production Potential
Authors: Ayan C. , Aktepe S. , Cig K. , Gokmen M. , Ceyhan A. , Tugan M. , Shumakov Y. , Dolu A. , Theuveny B. 
Published: October 2023

Increasing demand on reliable energy resources have led to an increased exploration activity for untapped hydrocarbon resources in deep-water. The recently discovered, but fast-tracked Turkey's Sakarya offshore natural gas field development is also a result of the country's commitment to energy independence. This paper describes the dynamic reservoir characterization considerations, challenges, and engineering solutions to de-risk field development decisions, confirmed by a well test campaign in a complex setting, with no tolerance to failure.

In Sakarya field, a live field development planning approach was applied, where the development plans were updated rapidly, in parallel with the dynamic reservoir characterization process. Therefore, a strong link between static modelling, advanced logging and dynamic well behavior analysis had to be established. In addition, proof of concept for the well completion design had to be validated. Following an unprecedented, detailed formation evaluation, fine-scale reservoir and transient wellbore simulations, five well tests were designed and executed. The design considerations and execution challenges included the completion type, big fluid losses and high risk of hydrate formation in the deep-water environment.

Five successful well tests were completed in ultra-deep water and led to the initiation of the first ultra-deep water natural gas field development in Turkey. The detailed formation testing campaign played a key role in selecting production intervals and optimizing well completion. In light of the high-resolution vertical formation evaluation, well tests were designed to prove reservoir extent, connectivity and long-term production potential of the field. Completion design and the actual conditions observed during the execution were compiled and simulated using fine-scale reservoir modeling and transient wellbore simulations to assess all potential risks during well test. The tests were executed successfully, revealing critical well deliverability and reservoir characterization information. Completion brine losses into the formation, hydrate formation risks at low subsea and surface temperatures, completion and formation differential pressure considerations were evaluated with real-time data analysis. Well test execution plan was updated real-time to achieve critical reservoir information. This closely integrated characterization and field development planning approach led to keeping the tested wells as production wells, thus improved efficiency, minimized cost, minimized environmental impact and accelerated time to first production.

Many technical challenges and time limitations were overcome during this work. Application of detailed formation testing practices, cased hole gravel pack completion in an offshore environment with hydrate risks and closely integrating the observations with the well test design by a multi-skilled team led to accurate well test simulations, correct test design and successful execution with excellent quality information. This paper allows readers to experience technical considerations in the design and execution steps for successful well test.