Ahmet Serkan Cenberlitas 's Thesis
by
Ahmet Serkan Cenberlitas
University of Texas at Austin, 2006
Supervisor: Kenneth E. Gray
One of the most critical aspects of a drilling and completion operations is wellbore
stability. Wellbore instability can jeopardize drilling goals and can cause costly wellbore
stability related problems. Along with wellbore stability, abnormal pore pressure is another
important aspect for well design in drilling and completions. Estimating the location and
magnitude of abnormal pore pressures, along with wellbore stability, are important aspect
for well design. Those two issues can be critical problems in underbalanced and/or
directional wells. A better understanding of wellbore stability mechanisms in rocks and
abnormal pore pressure prediction knowledge are imperative, to solve stability or pressure
related problems in drilling and/or completion operations. The objects of this study are
(1) to determine how different parameters affect borehole stability analysis and (2) to
quantify abnormal pore pressure and locations for common field situations.
Sensitivity analyses have been carried out for a large number of relevant, sensitivity
analyses illustrates how all the different parameters contribute to wellbore stability.
Moreover, this study presents the geophysical transformation method for abnormal pore
pressure prediction.
WELLSTAB-PLUS (wellbore stability analysis model) developed by Maurer Technology assumes
subsurface formations are linearly elastic, homogenous and isotropic. WELLSTAB-PLUS couples
a linear mechanical/chemical poro-elastic failure model to analyze stresses and stability
in deviated wellbores. The model was used to perform wellbore stability and sensitivity
analysis by considering Mohr-Coulomb and Drucker-Prager failure criteria. Based on
sensitivity analysis, variables used in the model were classified those having the greatest
effect, and those having little or no effect. Predictions of stability and the range of
stable borehole pressures or mud weights were proposed. The impact of changes in critical
parameters was analyzed.
PORE (Abnormal Formation Pressure Detection and Estimation Model) developed by Maurer
Technology, was used to determine abnormal pore pressure for two cases by analyzing
geophysical prospecting. In this study, Pennebaker plots from seismic velocity data were
used to determine formation pore pressure by comparing depth versus seismic velocity or
(its reciprocal travel time), with divergence from normal the trend line indication of
abnormal pore pressure. From case studies, the location and magnitude of abnormal pore
pressures and fracture gradients were proposed using PORE.
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