Browsing by Author "Nwanro, Chidindu Peace"

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    Development of suitable failure criteria for designing sufficient mud weights for Niger Delta well
    (Federal University of Technology, Owerri, 2022-02) Nwanro, Chidindu Peace
    Drilling the well to the target depth comes with it a lot of challenges; part of the issues related to drilling both vertical and deviated wellbores is related to the type of formation failures and well problems observed during drilling. Wellbore direction and deviation changes during drilling while the formation is the same, the effect of transformed stresses around the wellbore wall will be different. This is obvious that neither rock properties nor in-situ stresses can be changed to mitigate the failures of the wellbore. However, the density of the drilling mud can significantly control the situation. Large wellbore pressure due to using high mud density could enforce the formation to open in tensile mode, which in due course may result in mud loss or ultimately fracturing the formation. Also, using a low density mud, corresponding to low wellbore pressure may result in rock failure in shear mode and consequently breakouts. Most drilling engineers do not incorporate thorough wellbore stability analysis as part of well planning due to the complexity of wellbore stability models and thus employs the traditional practice which is identifying the pore pressure and adding extra pressure typically 100-200psi in mud equivalent as safety margin. Predicted mud weights in this manner end up in failed states resulting in several types of problems such as stuck pipe, lost circulation, formation damage and well control problems simply because either the mud weights designed are not sufficiently screened or those operating them lack the basic understanding of such mud systems. Five case studies were considered in this work to analyze the well and mud data from previously drilled wells with typical wellbore stability issues in the Niger Delta Region. A problem diagnostic was conducted to determine the main cause of the instability issues in these wells. Based on our findings, an excel based spreadsheet was developed for all the data and to perform all calculations. A coupled Mogi-Coulomb criterion further developed predicts the safe mud weight window in an iterative manner and describes the rock failure more accurately than does the traditional Mohr-Coulomb criterion which is independent of the intermediate principal stress, and presents a very slim mud weight window. Results of this study can help well trajectory optimization, proper mud weight determination, hydraulic fracturing job, sanding analysis and reduce non-productive time (NPT) while drilling.