Estimation of pore‐pressure change in a compacting reservoir from time‐lapse seismic data

Abstract

A B S T R A C TAn approach is developed to estimate pore-pressure changes in a compacting chalk reservoir directly from time-lapse seismic attributes. It is applied to data from the south-east flank of the Valhall field. The time-lapse seismic signal of the reservoir in this area is complex, despite the fact that saturation changes do not have an influence. This complexity reflects a combination of pressure depletion, compaction and stress re-distribution throughout the reservoir and into the surrounding rocks. A simple relation is found to link the time-lapse amplitude and time-shift attributes to variations in the key controlling parameter of initial porosity. This relation is sufficient for an accurate estimation of pore-pressure change in the inter-well space. Although the time-lapse seismic estimates mostly agree with reservoir simulation, unexplained mismatches are apparent at a small number of locations with lower porosities (less than 38%). The areas of difference between the observations and predictions suggest possibilities for simulation model updating or a better understanding of the physics of the reservoir.

An estimation method for effective stress changes in a reservoir from 4D seismics data

“…Such uncertainties may be particularly large around the faults due to possible reactivation movement. Similarly, the next step from effective stress to pressure carries an error as this requires knowledge of the stress arching ratios and the Biot‐Willis coefficient (Corzo, MacBeth and Barkved 2011), the former of which can be specified by running geomechanical simulations and the latter of which may be conditioned through laboratory experiment (Fjær et al . 2008).…”

Engineering Consistent Constraints for the Inversion of Changes in Pressure and Saturation on Ekofisk

“…This is a continued effort from Corzo et al (2013) where initial porosity was considered as an important factor in inverting for pressure depletion in the Valhall field. In the usual way, impedances are modelled by a petro-elastic model to convert dynamic parameters from the simulation model.…”

Time-shifts Interpretation of Legacy and Frequent Repeat Seismic Data in a Compacting Chalk Reservoir

“…The attribute we will employ in our analysis is the reservoir time-shift, defined as the difference of top and base reservoir time shift. This was first analyzed in the Valhall field by Corzo (2012), with proven success. A positive reservoir time-shift is a speed-up attributed to compaction or impedance hardening.…”