Thanks Mr. Ashkan very much for this valuable answer , please can you suggest some researches or books to help me studying this area.

Dear Fahd,

I have done a large (80 well) regional study of pore pressures and present-day stresses in the Nile Delta. However, unfortunately, I have only so far only published the results on present-day stress orientations and some brief comments on stress regimes. However, I have done a bit of work on the overpressure origins, as well as compiled a number of papers and theses on overpressure in the Nile that will be useful.

On overpressure origins, it is correct that the primary overpressure generation mechanism is disequilibrium compaction (as expected – high deposition rates and fine grained sequences). However, porosity-vertical effective stress analysis also shows some evidence for additional components of overpressure generated by fluid expansion (likely gas generation, a clay diagenesis influence or vertical transfer).

I have too much information to really share here. I will put some references below, but it may be easier if you contact me by e-mail ([email protected]) – I can set up a dropbox link with these papers and some other information for you.

Might I also suggest that you join and ask this question on the Overpressure and Pore Pressure Prediction group on Linked In - you might get more information from the 2600+ people in that group!

Some Nile Delta pore pressure and stress references

Nashaat, M. (1992). "Geopressure and geothermal studies in the Nile Delta, Egypt." M.Sc thesis, faculty of science, Al Azhar University, Cairo: 133.

Nashaat, M. (1998). "Abnormally high formation pressure and seal impacts on hydrocarbon accumulations in the Nile Delta and North Sinai basins, Egypt." AAPG Memoir 70: 161-180.

Andreoletti, C., N. Bienati, et al. (2009). "Integrated approach to imaging and pore pressure prediction in the Nile Delta." International Petroleum Technology Conference held in Doha, Qatar: 1-6.

Badri, M. A., C. Sayers, et al. (2001). "Pore pressure prediction data using seismic velocities and log data in the offshore Nile delta, Egypt." 2001 SPE Middle East Oil Show held in Bahrain: 1-7.

Shaaban, F., R. Lutz, et al. (2006). "Source-rock evaluation and basin modelling in NE Egypt (NE Nile delts and northern Sinai)." Journal of petroleum geology 29(2): 105-124.

Heppard, P. D. and M. O. Traugott (1998). "Use of seal, structural, and centroid information in pore pressure prediction." Amoco Exploration and Production Technology Group, Houston, Texas.

Tingay, M., Bentham, P., De Feyter, A. & Kellner, A., 2012. Evidence for non-Andersonian faulting above evaporites in the Nile Delta. In: Healy, D., Butler, R.W.H., Shipton, Z.K. & Sibson, R.H. (eds.) Faulting, Fracturing and Igneous Intrusion in the Earth's Crust. Geological Society of London Special Publication, London, 367, 155-170.

Tingay, M., Bentham, P., De Feyter, A. & Kellner, A., 2011. Present-day stress field rotations associated with evaporites in the offshore Nile Delta. GSA Bulletin, 123, 1171-1180.

Dear Mr. Mark

Thanks very much for your valuable answer , your interest is highly appreciated. I will send you email regarding this topic.

Mann, D. M. and A. S. Mackenzie, 1990. Prediction of pore fluid pressures in sedimentary basins. Marine and Petroleum Geology, 7(1), 55–65. http://doi.org/10.1016/0264-8172(90)90056-M

Thanks Mr. Fernando

Nile Delta considered young charachterized by rapid sedimentation rate and then shale water confined in the pore space and hence led to over pressure. The result is increasing porosity by depth not decreasing . For example giant Temsah gas filed where porosities can reach over 20% at great depth

Thanks very much for your valuable answer.

Dear Fahd Badran: Anomalous pressure can be a consequence of some mechanical and chemical processes that could performance independently or in relationship with each other. The common of overpressure are in two groups, following the Xinong et al., 2003 ideas:

1- Autochthonous overpressure structures, where there is no fluid flow into the closed system during the deposition. Significance overpressures due to under compaction and fluid expansion are of this type and happen inside, or proximal to, the reservoir rocks in which they were generated (Lee and Deming, 2002; Swarbrick and Osborne, 1998; Tingay et al., 2009).

2- Allochthonous overpressure arrangement is somewhere an extra very overpressure fluid-flows into the system through lateral/vertical pressure transfer.

Also, you can be thinking about the origin of overpressure in the following mechanisms, in order of importance:

· Disequilibrium compactation

· Fluid expansion

· Clay diagenesis

· Kerogen maturation

· Pressure transfer vertical / laterally

· Aquathermal expansion

· Hydrostatic pressure

· Uplift

· Hydrodynamic buoyancy

· Gypsum to anhydrite transformation

· Coal dewatering

· Osmosis

Following the M. Nashaat 1998 AAPG paper "Abnormally high formation pressure and seal impacts on hydrocarbon accumulations in the Nile Delta and North Sinai basins, Egypt": "...The abrupt development of pore pressure in the southern part of the Nile Delta is believed to be due to changes in the volume of pore fluids or rock matrix as a consequence of either aqua thermal expansion, hydrocarbon generation, or thermal cracking of oil to gas in the lower Miocene-upper Oligocene compartment. Fluid flow in the Nile Delta and North Sinai Basins is mainly due to compaction and thermal-driven forces..."

I attached Nashaat´s paper, please, note that the Author is in RG: https://www.researchgate.net/profile/Mohamed-Nashaat-4, and there is more material to add to understand your question.

Please, let me know if my answer helps you or you need additional ideas,

Best regards, Mario E. Sigismondi