The pore pressure, bulk density and lithology prediction

Oloruntobi, Olalere Sunday (2019) The pore pressure, bulk density and lithology prediction. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

The pore and fracture pressures are the two most important parameters required for the effective well design. In general, the difference between the two parameters at any given depth dictates the drilling window with no consideration for wellbore stability. While pore pressure prediction from the drilling parameters started in the mid-nineties, very few improvements have been made in these areas when compared to other pore pressure prediction techniques such as seismic and well logs. Pore pressure prediction using the d-exponent method does not consider the effect of bit hydraulic energy on the rate of penetration (ROP). This limits the application of the d-exponent to mostly hard rock environments. Under downhole conditions where the bit hydraulic energy has a significant influence on the ROP (soft rock environments), the d-exponent method may produce inaccurate results. Hence, the primary goal of this research is to develop new pore pressure prediction models from the drilling parameters that incorporate the bit hydraulic energy, making them suitable for any subsurface drilling conditions. The new pore pressure prediction models use the concept of specific energy to predict the onset of overpressure. The concept of specific energy is then extended to the real-time identification of subsurface lithology. Furthermore, overburden pressure is an important input parameter in pore pressure prediction. Inaccurate prediction of overburden pressure may result in the erroneous prediction of pore pressure which can lead to well control and process safety incidents. In areas where density logs are not available, synthetically derived density logs are used for overburden pressure computations. In this research, an attempt is also made to improve the accuracy of pore pressure prediction by improving the accuracy of overburden pressure computation via improvement in density logs prediction. Finally, since pore and fracture pressures are closely related, an attempt is made to develop a new fracture pressure prediction model for the Niger Delta basin.

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