Seafloor 4D gravity is used to monitor changes in the distribution of density within producing reservoirs. The highest sensitivity is obtained when tracking contacts between fluids with high density contrast, like gas-water, gas-oil, or CO-water in injection sites. The detection of fluid movements provides valuable information on aquifer strengths, lateral compartmentalization and permeability.

Seafloor subsidence is monitored in gravity surveys by means of an elaborate processing of seafloor pressure measurements. Subsidence is a required correction for the interpretation of gravity results, but it is in itself a valuable monitoring tool, sensitive to important reservoir and overburden properties. It directly relates to pressure depletion and lateral compartmentalization, and in some cases, it is a key factor for the safety of the installations.

When combined, simultaneous measurements of 4D gravity and subsidence provide valuable information from the areas of the field far away from monitoring and production wells.

A key step in the processing of both gravity and pressure data is correcting for ocean tides. Tides are monitored during the surveys by means of tide gauges, which are pressure sensors deployed at stable locations on the seafloor during the survey.

In this study, we first introduce the principles of the technology utilized in offshore gravity and subsidence monitoring surveys. Secondly, we review a few published field cases from fields on the Norwegian continental shelf. We then discuss the possibility of using an alternative sensor technology for tide gauges with a potential positive impact in data quality.

Presentation Date: Wednesday, October 19, 2016

Start Time: 2:45:00 PM

Location: 156

Presentation Type: ORAL

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