Reservoir monitoring of the Draugen field through time-lapse seismic and it's business impact

Abstract

In a time-lapse 3D seismic (TL3D) project a 'monitor' seismic survey is compared to a 'base' survey. Ideally, the base survey is a 3D dataset acquired before production from the field started. Normally, the monitor survey is acquired after several years of production. The observed differences between the base and the monitor survey can be interpreted in terms of changes in fluid saturation and pressure.When embarking on a seismic monitoring project it is important to keep the following questions in mind:!What field information might technically be obtained? !What impact will it have on reservoir management? !What is the optimal timing with respect to the drilling sequence and development decisions?!What is the probability of successfully obtaining that information from TL3D? In this article we will work these questions out and illustrate them with an example. What field information might technically be obtained?The fluid drainage information from TL3D may be used directly to locate fluid fronts in each major flow unit. It may also be used to derive lateral variations in permeability of the reservoir and sealing-capacity of faults. These variations can cause areas of bypassed oil and blocks that are not being drained. In general, it will help to understand the observed production from the field. It is a very powerful method to map production related changes in reservoir fluid saturation and pressure away from the wells. Tl3D very often reveals some flow behaviour that had not been predicted, even by history-matched flow models. This information can be critical to future reservoir development. What impact will it have on reservoir management?Time-lapse seismic results may be used to optimise the number and location of in-fill wells to access untapped reserves or to accelerate production. In this way it will minimise the in-fill well costs and maximise the recovery. It may also indicate the need to shut off thief zones to avoid premature water or gas break-through. It will possibly lead to adjustments in the production and injection rates for maximum recovery. Finally, by matching the dynamic knowledge of the true communication path would allow optimisation of the field production strategy. model to both the time-lapse seismic data (seismic history) and the production history, the dynamic model will be refined and production forecasts will be improved. What is the optimal timing with respect to the drilling sequence and development decisions?Time-lapse seismic should be considered an integral part of the field development plan to ensure the availability of capital and the flexibility to influence field development. To maximise the value of time-lapse information, results should be obtained before any major investment decision in the field's development. TL3D should be avoided if the benefits are small because the information comes too late, extra wells are too expensive, or the remaining reserves are too small. What is the probability of successfully obtaining that information from TL3D?The main technical risk when ...