4-D time lapse reservoir monitoring of Nelson Field, Central North Sea: Successful use of an integrated rock physics model to predict and track reservoir production

Abstract

Nelson Field, in the U.K. sector of the Central North Sea approximately 180 km east of Aberdeen in 280 ft of water, is on the Forties-Montrose ridge and forms a broad, low relief anticline with four-way dip closure (Figure 1). Figure 1. Nelson Field in relation to Forties-Montrose trend and established infrastructure. 4-D seismic data, acquired using conventional towed streamers, have been successfully applied to the Paleocene reservoirs of the North Sea. Importantly, AVO applications enhance the 4-D difference signal in this reservoir. We tested a new multivariate solution to predict shear-wave slowness against field data, and used this to establish an integrated rock physics model of the Forties Sandstone. This formed the basis for full elastic inversion of the AVO data sets. Full elastic inversion results demonstrate that quantifiable seismic differences can be detected and that they are of similar magnitude to those estimated independently from core and log data. Our study found that the predicted, simulated, drainage pattern and the actual time-lapse seismic difference signal are in good agreement. The 4-D is detecting OWC movements as small as 15–20 ft within the main sand channel fairways. 4-D seismic may provide a valuable tool to monitor reservoir drainage patterns for areas characterized by low net-to-gross sand ratios, but the method clearly works best within main sand fairways to target potential upside areas. The field was discovered in 1988. An extensive appraisal campaign by Enterprise and Shell/Esso followed. By 1990 13 appraisal wells had been drilled. The field began producing in February 1994 from eight wells. To date, 27 development wells have been drilled from a single central platform: 23 oil producers and 4 water injectors. In addition, four subsea producers exploit the southern satellite area. Plateau production was maintained during 1994–1996 at 150 000 b/d. Top Reservoir is relatively shallow at …