Time-lapse seismic surveys in the North Sea and their business impact

Abstract

In a time-lapse 3-D seismic (TL3D) project, a “monitor” seismic survey is compared to a “base” survey. Ideally, the base survey is a 3-D data set 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: In this article, we will answer these questions and illustrate our solutions with two examples. ### What field information might technically be obtained? 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 behavior 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 may be used to optimize the number and location of infill wells to access untapped reserves or to accelerate production. Ideally, this will minimize infill costs and maximize recovery. It may also indicate the need to shut off thief zones to avoid premature water or gas breakthrough. It will …