Production induced reservoir compaction and surface subsidence, with applications to four-dimensional seismic

Reservoir compaction due to hydrocarbon production and pore pressure depletion is common in unconsolidated reservoirs worldwide. Compaction may result in well failure, surface subsidence, and platform sinking. Surface subsidence occurs in many parts of the world, in some cases as much as tens of meters within the short period of a few decades.; Traditionally, reservoir monitoring is carried out through 4D seismic. In this path-finding study, we use InSAR to measure surface subsidence occurred in the Belridge and Lost Hills oil fields due to production, and investigate the applications and implications of reservoir compaction and surface subsidence in reservoir monitoring. We found: (1) For the traditional “Geomechanics + Flow simulation” workflow of subsidence prediction, InSAR provides massive data for validation. Previously, those types of predictions can only be validated at very few points where geodetic survey data are available. (2) InSAR can be used as a stand-alone tool for reservoir characterization and monitoring. First, the magnitude and patterns of subsidence are often good indications of reservoir shape, size and depth. They are also affected by reservoir rock and fluid properties and production history. We show how this cause-and-effect relationship may be used for reservoir monitoring. Second, subsidence pattern may also be a good indication of permeability anisotropy. We perform numerical simulations on an imaginary reservoir for different combinations of permeability anisotropy and boundary conditions, and discuss how this may be used for reservoir monitoring. (3) InSAR can also be used together with 4D seismic for reservoir monitoring. First, traditionally, 4D seismic changes are interpreted in terms of pressure and saturation changes, while porosity is assumed to be constant during production. This is often inaccurate or incorrect. By using compaction as an additional input, we can improve the accuracy of 4D seismic interpretations. Second, we show that by using 4D seismic and Geomechanics, we can predict porosity loss in a reservoir. This porosity loss is related to surface subsidence. If we know how the two are related, then the surface subsidence from InSAR can be used as an integral constraint on the 4D seismic prediction of porosity loss.