Time-lapse (4D) seismic has been proven as a reservoir management tool. By acquiring successive seismic images on the same producing field, geophysicists can identify by-passed oil, optimize exploitation drilling investments, and better manage injection programs.
To date, the majority of 4D programs have been undertaken in the marine environment, primarily in the North Sea and using towed streamer acquisition systems. However, the basic concepts of 4D seismic apply on land; in many cases, time-lapse monitoring could actually be better suited to onshore applications.
The primary factor that affects time-lapse seismic programs is repeatability – making sure that there is as little variance in the ‘environmental factors’ from one time-lapse survey to the next. Repeatability is often difficult to assure in the offshore environment, where typical streamer-based deployment methods are influenced by unpredictable tidal or sea-state conditions. Onshore, however, environmental conditions and source and receiver positioning can be better controlled from one survey to the next.
Additionally, full-wave seismic data is often better suited to monitoring pressure and saturation changes within the reservoir than conventional, P-wave-only data. ION's award-winning full-wave sensor, VectorSeis, gives geophysicists a natural advantage in detecting pressure and saturation changes and monitoring fluid and gas movements during time-lapse seismic programs.
One traditional drawback of onshore 4D programs has been the challenge imposed by the weathering layer, and other near-surface conditions, which can cause seismic wave fields to scatter unpredictably. Not only is VectorSeis well suited to measuring, and compensating for, these near-surface effects, but this gravity-detecting sensor is also uniquely capable of being buried for extended periods. By burying VectorSeis sensors below the weathering layer, geophysicists are able to mitigate some of the adverse impacts the near-surface has traditionally presented.
A second drawback often sited for onshore 4D has been the cost, environmental impact, and general impracticality of burying cables to connect the sensor grids in a producing oil & gas field. However, FireFly changes all that. With its cableless architecture, FireFly is capable of being easily moved into identical, pre-determined positions when acquisition operations are underway. Once acquisition is complete, FireFly can be removed and stored or, in the application that several of our customers are considering, moved to a nearby field for acquisition as part of a multi-field, rotational time-lapse monitoring program.
Completing the ION 4D toolkit are the advanced imaging tools available from our subsidiary, GX Technology. With expertise in areas like statics and data conditioning, noise removal, azimuthal and tomographic velocity modeling, PreSTM and PreSDM, and converted wave processing, GXT is the company to turn to when the imaging challenges are at their most extreme.
Given our toolkit and experience, the ION family of companies is rapidly becoming the partner-of-choice for designing and executing critical 4D programs in the onshore environment.
