Why Time Lapse Seismic (4-D) Works Better than Expected

Karl Berteussen¹*, Yuefeng Sun², Akmal Sultan³, Hamad BuAlRougha³, and Sandra Vega^1
1The Petroleum Institute, UAE
²Texas A&M University, USA
³ZADCO
*[email protected]

Time-lapse seismic (4-D) has become a standard and highly valued tool in production optimalization in areas like the North Sea and the Gulf of Mexico. The basic principle is to acquire two 3-D seismic surveys some time apart, and process them with the aim of estimating the difference caused by the reservoir production activity. This technique has generally not become a standard tool in carbonate reservoirs. A main reason for this is that feasibility studies generally have concluded that the time-lapse effect is too weak to be detectable by seismic methods. There are obvious reasons for that. However, one experience from the clastic reservoirs, where this has been routinely used for some time, is that the observed 4-D effects are larger than predicted. In feasibility studies one typically estimates fluid content at the initial survey time and at the final survey time. Then the seismic response for each model is calculated and the difference estimated. This is done for the existing, typically very homogeneous reservoir model. When the method is being used one is, however, looking for the anomalies, typically barriers to flow or high permeability zones, which in their nature will have more extreme 4-D effects than the modeled ones. The general effect is that one systematically underestimates the 4-D signal. In this presentation we discuss and illustrate some of the reasons why that is the case. These arguments are important to bear in mind, because if one does not take these effects into account one might underutilize a tool, which could be of great commercial value for the reservoir production strategy.

AAPG Search and Discovery Article #90077©2008 GEO 2008 Middle East Conference and Exhibition, Manama, Bahrain