Pressure and Physical Property Responses in a Toe Thrust Environment

Tina Grace Fitts, Operations Geology Core Group, ExxonMobil Exploration Company, 233 Benmar, GP8 878, Houston, TX 77060-2501, phone: 281-654-5343, tina.g.fitts@exxonmobil.com, Richard J. Fink, Operations Geology Core Group, ExxonMobil Exploration Company, 233 Benmar, GP8 808B, Houston, TX, Joann Welton, Hydrocarbon Systems Analysis Division, ExxonMobil Upstream Research Company, Buffalo Speedway, Houston, TX, and Rachel H. Paez, Regional exploration, ExxonMobil Exploration Company, 233 Benmar, GP3-866, Houston, TX.

Observations (pore pressure and physical properties) from recent offshore drilling in a deltaic toe thrust belt show decoupling between under-thrust and thrusted sediments, suggesting that low angle detachments and thrusts are substantially weaker than the bulk section. Large variability in pore pressures was observed over the delta, but decoupling between sub-thrust and thrusted domains appears to occur in both normally pressured and severely overpressured regimes, so it appears that overpressure may not be the cause of low strength of the detachment. These data support previous models indicating that vertical changes in compaction state at individual well locations reflect vertical changes in mean and shear stress states as wells penetrate different structural domains. Results also show that changes in stress regime must be taken into account when using velocities for pressure prediction, as pressures may be over or under-predicted if stress regimes are not taken into account.

Petroleum Geomechanics and Pore Pressure Prediction
2006 AAPG International Conference and Exhibition, (November 5-8, 2006) Technical Program