Permanent Reservoir Monitoring with Onshore Surface Seismic

Abstract

Many of the arguments that are used for permanent seismic monitoring for offshore reservoirs also apply to onshore monitoring, but there are also differences. A permanent installation removes at least one source of repeatability problems, because there will be no receiver position differences between base and monitor surveys. For land surveys (and for Ocean Bottom Node surveys) receiver and shot position differences can be nearly avoided with careful acquisition, while for streamer surveys the unpredictable currents will always lead to some position differences, although tidal shooting and steerable streamers can reduce that problem. However, even perfect repositioning of sources and receivers will not solve all repeatability problems for land surveys because of the changing nearsurface between base and monitor survey. The use of buried sources and receivers will improve that situation, but even then careful acquisition and processing is required to remove, for instance, seasonally-changing source and receiver ghosts. This can be done successfully, as demonstrated in a permanent seismic monitoring trial of thermal EOR, in Schoonebeek, The Netherlands, where a seismic monitor surveys was acquired on a daily basis. The progress of the steam front could be monitored with surprising detail. Another similarity for offshore and onshore monitoring is that the economic benefits of a permanent installation, compared to surveys with retrievable equipment, materialize only after a number of monitor surveys have been acquired due to the upfront installation costs of the permanent system. If the changes in the reservoir are not very rapid, or if the operator of the field has no options to react with well management based on the rapid reservoir changes, then it becomes more difficult to make a business case for a permanent installation. The magnitude of the problem is more acute for onshore than for offshore applications, because onshore wells are typically significantly less costly than offshore wells. In this paper we give an overview of the results of the permanent onshore seismic monitoring trial at Schoonebeek and discuss the options to reduce the costs while maintaining the required accuracy of the monitoring results.