Modeling Formation Damage and Completion Geometry in an old Well Enables Better Planning for new Wells - Gyda Development Case Study

Byrne, M. (Senergy ) | Rojas, E. (Senergy) | Holst, V. B. (Talisman Energy Norge AS)


Gyda is a mature oil development in the Norwegian sector of the North Sea. The first production wells were drilled more than twenty years ago. This study focuses on wells drilled in the porer reservoir quality areas of the Gyda reservoir. Some recent production wells have significantly underperformed relative to equivalent initial wells. In particular, a sidetrack to an early successful well, had very poor performance on initial start-up.
The geometry of the original well and the sidetrack were simulated, together with various assumptions and sensitivities to formation damage. In the original well an attempted hydraulic fracture had been assumed to have failed. This assumption was challenged in the model.
The model demonstrated that the original well must have included a successful hydraulic fracture in order to flow at the historical rates recorded. In addition for the sidetrack, that contained no fracture, there were indications that the perforation tunnels may not have fully cleaned up and that whilst the well performance may recover somewhat with time, a significant change in completion would be required in order to match the performance of the original well.
The model constructed included the completion geometry and formation damage and has enabled evaluation of old wells and more importantly, design of new wells in this mature reservoir development.

Some recent wells drilled on Gyda have not fulfilled the production objectives. A numerical 3D model was proposed in order to investigate and understand the flow dynamics and the production potential from the Gyda A19 and A19A wells. This modeling process includes a detailed numerical fluid flow simulator based on Computational Fluid Dynamics (CFD) which captures the reservoir, well and completion geometry complexity (Byrne et al, 2009 and 2010).
The CFD simulations are used to determine potential explanations for the wells performance and lead to stimulation options and development of optimum drilling and completion for future wells. The Senergy Wellscope modeling process has the stated objective of better production through better prediction. As the A-19 well is very similar to the A-19A well from Gyda, some conclusions may be derived from the present study which could support the understanding of the productivity behaviour of the A19A well.
To achieve the objective one base CFD model was constructed to represent the two wells to be evaluated (A19 and A19A). Different completion options were included, including the case of the well hydraulically fractured. Several sensitivities were carried out in order to depict the well potential.
Throughout the project, regular contact was held between the Senergy and Gyda team. These helped to frame and direct the project as well as providing necessary feedback on data gathered and model construction.