Pore Pressure and Fracture Gradient

AbstractFew wells targeting high temperature, high pressure intervals in most tertiary sedimentary basins have achieved their objective in terms of technicalities and cost. Since most shallow targets have been drilled, exploration focus is drifting into deeper plays both onshore and in deep offshore areas. To ensure safe and economic drilling campaigns, pore pressure prediction methodologies used in the region needs to be improved. The research aims at generating and testing a modification of Eaton’s equation fit for high temperature, high pressure intervals on a field. The evolution of pore pressure in the field was established from offset well data by making several crossplots, and fracture gradient was computed using Mathew and Kelly’s equation. Eaton’s equation parameters were then calibrated using several wells until a desired field scale result was achieved when compared with information from already drilled intervals i.e., kicks and RFT data. Seismic velocity data resulting from high density, high resolution velocity analysis done to target deep overpressured intervals were then used to predict 1D pore pressure models at six selected prospect locations. Analyses reveal depths shallower than 3800 m TVD/MSL with geothermal gradient 3.0 °C/100 m and pressure gradient less than 1.50sg EMW are affected mainly by undercompaction; depths greater than 3800 m TVD/MSL with geothermal gradient of 4.1 °C/10 m and pressure gradients reaching 1.82–2.12sg EMW are affected by unloading with a narrow drilling margin for the deep highly pressured prospect intervals. Eaton’s n-exponent was modified to 6, and it proved accurate in predicting high overpressure in the first prospect wells drilled.

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Pore Pressure, Fracture Gradient, Shallow Hazards and Reservoir Integration for Well Location Selection and Well Execution

10.3997/2214-4609.202038006 ◽

2020 ◽

Author(s):

T. Harrold ◽

M. Tilita ◽

J. Reveron Becerra ◽

S. Martinez Martinez ◽

P. Rouillé ◽

...

Keyword(s):

Pore Pressure ◽

Location Selection ◽

Well Location ◽

Fracture Gradient

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Mitigating Well Construction Challenges of a Caspian Deepwater Exploratory Well: A Cementing Perspective

10.2118/207007-ms ◽

2021 ◽

Author(s):

Irfan Kurawle ◽

Ansgar Dieker ◽

Adriana Soltero ◽

Svetlana Nafikova

Keyword(s):

Pore Pressure ◽

Long Term Effects ◽

Lost Circulation ◽

Well Integrity ◽

Pore Pressure Prediction ◽

Wellbore Strengthening ◽

Selective Placement ◽

Fracture Gradient ◽

Comprehensive Modeling

Abstract BP returned to Caspian deepwater exploratory drilling in 2019. The exploration well was drilled on the Shafag-Asiman structure in water depths greater than 2,000 ft. Well challenges included high shallow water flow (SWF) risk with multiple re-spuds on the nearest offset, lost circulation due to complex wellbore geometry combined with a narrow pore and fracture gradient window, and uncertainty in pore pressure prediction in abnormally pressured formations with a new depositional model. In addition, a well total depth more than 23,000 ft, eight string casing design and bottom-hole pressures greater than 20,000 psi presented a truly modern-day challenge to well integrity. A six-month planning phase for the cementing basis of design concluded by delivering slurry designs capable of combating SWF, qualified by variable-speed rotational gel strength measurement. Engineered lost circulation with selective placement of wellbore strengthening materials in combination with cement and mechanical barriers to provide isolation and integrity for the life of the well. Exhaustive pilot testing to account for changes required a cement design based on pore pressure variation and comprehensive modeling for hydraulics, centralizer placement, and mud displacement. This was complemented by a custom centralizer testing process specifically designed to simulate forces exerted in wells with similar complexity. Long-term effects on cement were evaluated, not only for placement but also for future operations including pressure and temperature cycles during wellbore construction or abandonment.

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