Analysis and application of in situ pore pressure measurements in marine sediments

Fang, Weijiang W.; Langseth, Marcus G.; Schultheiss, Peter

doi:10.1029/93jb00153

Cited by 32 publications

(18 citation statements)

References 30 publications

(26 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…An analytical solution to is known for single‐layer systems [ Fang et al , 1993], and multiple‐layer systems [ Wang and Davis , 1996]. If the ocean tidal loading function takes the form then the solution for a single layer can be written: where …”

Section: One‐dimensional Modelmentioning

confidence: 99%

Modeling the effects of tidal loading on mid‐ocean ridge hydrothermal systems

Crone

Wilcock

2005

Geochem Geophys Geosyst

View full text Add to dashboard Cite

[1] Tidal signals are observed in numerous time-series measurements obtained from mid-ocean ridge hydrothermal systems. In some instances these tidal signals are clearly the result of ocean currents, but in other instances it appears that the signals may originate in the subseafloor formation. In order to explore the effect of ocean tidal loading on mid-ocean ridge hydrothermal systems, we apply a one-dimensional analytical model of tidal loading on a poroelastic half-space and develop a two-dimensional numerical model of tidal loading on a poroelastic convection cell. The one-dimensional models show that for a reasonable range of fluid, elastic, and hydrological properties, the loading efficiency may vary from near zero to near unity and the diffusive penetration depth for tidal pressure signals may vary from tens of meters to kilometers. The two-dimensional models demonstrate that tides may generate significant vertical and horizontal pressure gradients in mid-ocean ridge hydrothermal systems as a result of spatial variations in fluid temperatures and the elastic and hydrological properties of the crust. These continuum models predict that outflow temperature perturbations will be very small (<10 À4°C), but in real systems where the continuum hypothesis does not always apply, the perturbations may be on the order of $0.1°C. The models predict relatively large perturbations to fluid velocity at the seafloor. For high-temperature vents the outflow perturbations normalized to the mean flow velocity increase as the permeability decreases. Flow reversals at the seafloor are predicted in some regions of net low-temperature outflow and net inflow during the tidal cycle. In the subseafloor, tidally induced flow perturbations are likely to significantly enhance mixing and fluid exchange below the seafloor in regions of slow flow and in regions where there are strong gradients in temperature or in the mechanical and hydrological properties of the crust. Tidally enhanced mixing and fluid exchange may significantly influence the extent and character of microbial production in the subseafloor.

show abstract

Section: One‐dimensional Modelmentioning

confidence: 99%

Modeling the effects of tidal loading on mid‐ocean ridge hydrothermal systems

Crone

Wilcock

2005

Geochem Geophys Geosyst

View full text Add to dashboard Cite

show abstract

“…The equilibrium pressure for the PZ1‐7 piezometer is first calculated using the technique developed by Davis et al () and Fang et al (), which is by plotting the pressure record versus the reciprocal of time and extrapolated to 1/time = 0 (Fig. a).…”

Section: Resultsmentioning

confidence: 99%

A multi‐disciplinary approach to marine shallow geohazard assessment

Marsset

Thomas

Sultan

et al. 2012

Near Surface Geophysics

View full text Add to dashboard Cite

Seismic velocities together with sediment/rock compaction models are of common use in the oil industry to predict reservoir pressures and to detect and identify any potential hazard associated with over‐pressured formations. Excess pore pressure is a key parameter for geohazard assessment, nevertheless this approach is very seldom applied to shallow offshore engineering as it requires expensive ground‐truth boreholes. The simultaneous availability in the Bourcart‐Hérault canyon interfluve (Gulf of Lion – NW Mediterranean) of 1) geotechnical and sedimentological data (300 m boreholes) from the PROMESS project; 2) in situ pore pressure measurements; and 3) High Resolution (HR) seismic geophysical data showing the presence of active structures in relation to fluid circulation, allows the importance of a multi‐disciplinary approach to shallow geohazard assessment to be illustrated through a case study. The velocity field obtained from HR seismic data is interpreted in light of the neighbouring boreholes and resulting velocity anomalies are translated in terms of fluid overpressure and free gas content. Additional in situ surface geotechnical measurements (piezometers) are then taken into account and the role of these parameters is discussed.

show abstract

“…Common methods for interpretation of full dissipation are: − Extrapolation of measured pore pressure dissipation data on an inverse time scale, 1/t-method (Davis et al, 1991;Fang et al, 1993;Whittle et al, 2001;Flemings et al, 2008). In practice, offshore deployment time will be limited and recorded PPDT data will require interpretation or extrapolation for full dissipation.…”

Section: Dissipation Measurements and In-situ Pore Pressurementioning

confidence: 99%

Prediction of Formation Pore Pressures for Tophole Well Integrity

Peuchen

Klein

2011

All Days

View full text Add to dashboard Cite

Knowledge about formation pore pressures is important for planning and control of offshore well drilling operations. Particularly, a combination of unconsolidated clay/shale sediments and in-situ pore pressures exceeding hydrostatic values can create a distinctly adverse setting for tophole well integrity. If unanticipated, well completion may fail.Pore pressure prediction for the tophole section generally relies on use of multiple methods, as no single technology is available. Actual measurement of in-situ pore pressure is necessary. Pore Pressure Dissipation Testing PPDT with a push-in piezoprobe or piezocone penetrometer is currently the most efficient and accurate method for actual measurement of formation pore pressure in unconsolidated sediments. The method can be used in a pre-well site survey, during pre-setting a tophole well section or combined with well installation itself.Capabilities and limitations are highlighted for predicting and accurately measuring formation pore pressures in shallow unconsolidated clay/shale sediments. Use is made of a unique database containing more than 160 PPDT piezoprobe measurements. The database probably covers a majority of piezoprobe measurements ever completed for offshore tophole sections. It includes (1) hydrostatic pressure profiles, (2) excess pore pressures due to natural phenomena and (3) excess pore pressures due to formation damage caused by earlier well drilling. Depth coverage is up to 400 m below seafloor.Achievable accuracy for measurement of pore pressure is typically estimated at about 50 kPa (= 5 m water column) or 5% of penetration pore pressure, whichever is the greater. Difficulties are noted for establishing formation pore pressures where (1) clay/shale sediments have been affected by formation damage caused by earlier drilling and (2) clay/shale sediments include shallow gas zones. Opportunities for improvement are discussed.

show abstract

Analysis and application of in situ pore pressure measurements in marine sediments

Cited by 32 publications

References 30 publications

Modeling the effects of tidal loading on mid‐ocean ridge hydrothermal systems

Modeling the effects of tidal loading on mid‐ocean ridge hydrothermal systems

A multi‐disciplinary approach to marine shallow geohazard assessment

Prediction of Formation Pore Pressures for Tophole Well Integrity

Contact Info

Product

Resources

About