Detection of over pressure zones from seismic and well data

Projektinformationen

ID Finanzhilfevereinbarung: JOF3970036

Projekt abgeschlossen

Startdatum 1 Dezember 1997

Enddatum 30 April 2001

Finanziert unter

• Specific programme for research and technological development, including demonstration in the field of non-nuclear energy, 1994-1998

Gesamtkosten

Keine Daten

EU-Beitrag

Keine Daten

Koordiniert durch

Well Service Technology A/S
Norway

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Verwertbare Ergebnisse

Overpressure detection with seismic and well data

The main results obtained in the project can be summarised as follows: - A complete cellular geological model was created with an associated database for formations of particular practical interest in the study area. - Comprehensive set of experimental data on rock physical properties and seismic parameters derived from rock samples taken from the study area. (This work also required to further development of existing equipment, experimental methods and procedures as well as data analysis techniques.) - A fault-analysis-based flow model was developed for key reservoir sections where overpressure is observed in the study area. Fault property estimates where used to investigate the physical conditions under which over-pressure develops and may be maintained. These results are useful to assess the uncertainty of the fault distributions obtained from the seismic interpretations. Models were developed for: - Comparison of seismic attenuation as derived from sonic logs and VSP data with laboratory measurements by means of a genetic annealing algorithm. - Acoustic model for seismic velocity versus clay content, pore fluid and effective pressure. - Overburden corrections in AVO analysis for visco-elastic fine-layering. - Neural nets for estimating porosity and permeability from suites of log data (including MWD) accounting for various reservoir fluids. - Committee neural networks for porosity, permeability and saturation estimates from log data. We investigated the seismic detectability of an overpressured reservoir in the case study area by computing synthetic seismograms for different pore-pressure conditions by using an integration of the techniques described above. The results of the seismic detectability study indicate that changes in pore pressure can be detected with seismic methods under circumstances such as those of moderately deep North Sea reservoirs. In order to extend this method to obtain pore pressure in shaley sandstones, an acoustic model for seismic velocity versus clay content and effective pressure was required. Pore Pressure Prediction with Seismic Calibration of the model requires log data, porosity, clay content and sonic velocities to estimate the dry-rock modules and the effective stress coefficients as a function of depth and pore pressure. The seismic P-wave velocity, derived from seismic modelling and inversion techniques, was fitted to the theoretical velocity by using pore pressure as the fitting parameter. The method was applied to the Tune field in the Viking Graben sedimentary basin of the North Sea. We have obtained a high-resolution velocity map that reveals the sensitivity to pore pressure and fluid saturation in the Tarbert reservoir. The velocity map of Tarbert and the inverted pressure distribution agree with the structural features of the Tarbert formation and its known pressure compartments.