Lessons learned from 4D projects

Time-lapse three-dimensional, or four-dimensional (4D), seismic has been un der consideration by the industry for reservoir monitoring for more than a decade. It offers the possibility of identifying the interwell distribution of bypassed and untapped oil, of monitoring displacement heterogeneity, an d of detecting uneven pressure depletion away from wells. If obtained, thes e detailed observations could be used to increase ultimate recovery, reduce production costs, and prevent surprises such as unexpectedly early breakth rough. But these benefits are not easily obtained, and are certainly not guarantee d. There are a number of factors that impact whether a 4D project will be s uccessful, and a careful study of these is required to give a realistic exp ectation of what 4D can do for a specific reservoir. Numerous 4D seismic pr ojects have been active over oil fields world wide, and successes, relative to each project's objectives, have been realized by field operators using a wide variety of data acquisition techniques (land, streamer, and seabed m ethods), and over a variety of field types, including both clastics and car bonates. This paper draws from this experience to present a generalized 4D project w orkflow, and reviews results from some of these recent projects as illustra tions. In general, sufficient software tools, rock physics data, and experi ence now exist to conclude that 4D is a low-risk/high-benefit reservoir man agement tool. The key to a successful project, however, is determining what 4D can do in a specific field, which requires a careful feasibility study, clear reservoir management objectives, and high-quality and experienced se ismic processing and interpretation.