Efficient Seismic Monitoring Of Hydrocarbon Reservoirs Using Multiple Shooting Vessels
Authors: Ayeni Gboyega Olaoye , Tang Yaxun , Biondi BIondo 
Published: July 2010

Abstract
We propose an efficient reservoir monitoring method that utilizes data from multiple seismic sources. Because this technique reduces acquisition time and cost, seismic data sets can be recorded cheaply at short, regular intervals. Although, in many cases, the recorded multiplexed data can be separated into independent records, we choose to leverage the efficiency of direct imaging of such data sets. However, direct imaging with a migration algorithm introduces cross-talk artifacts and does not account for differences in acquisition geometry and relative shot-timing between surveys. We propose a joint least-squares migration/inversion approach that attenuates artifacts caused by imaging cross-talk and by acquisition discrepancies in the recorded data sets. By incorporating spatial and temporal regularization in our inversion algorithm, we ensure that the resulting time-lapse images are geologically plausible. Using a 2D numerical model, we show that our method can give results of comparable quality to migrated single-source data sets.

Introduction
Conventional seismic data acquisition involves a single seismic source and a recording array of receivers. Although not a new idea (Womack et al. 1990), recent advances in acquisition technology enables seismic acquisition with multiple sources (e.g., Hampson et al. (2008); Beasley (2008)). This acquisition approach, also called simultaneous-shooting (or multi-shooting, or blended acquisition), can be used to achieve longer offsets, better shot-sampling, and improved time and cost efficiency (van Mastrigt et al. 2002; Berkhout et al. 2008; Howe et al. 2009). The recorded data can be separated into independent shot records and then imaged with conventional methods (e.g. Hampson et al. (2008); Spitz et al. (2008)), or they can be imaged directly (e.g., Berkhout et al. (2008); Tang and Biondi (2009)).
Although time-lapse (4D) seismic is an established technology for monitoring hydrocarbon reservoirs (Rickett and Lumley 2001; Whitcombe et al. 2004; Zou et al. 2006; Ebaid et al. 2009), it still has several limitations. First, because of the high cost of conventional (single-source) acquisition, it is impractical to acquire seismic data sets at short time intervals. Therefore, typical monitoring survey intervals may be too large to measure production-related, short-period variations in reservoir properties. Because of the large time intervals between seismic surveys, it may be difficult to match time-lapse seismic signatures to reservoir property changes derived from well-sampled sources (e.g. production history matching). Secondly, in many time-lapse seismic applications, inaccuracies in the replication of acquisition geometries for different surveys (nonrepeatability) are a recurring problem. Although modern acquisition techniques can improve repeatability of shot-receiver geometries, field conditions usually prevent perfect repetition. In order to isolate differences caused by changes in reservoir properties, non-repeatability effects must be removed from time-lapse data sets. Furthermore, because of operational, climatic, and other limitations, the acquisition time-window may be too small for conventional seismic data acquisition. In such cases, it would be difficult to acquire conventional seismic data sets at desirable intervals.