Influence of formation anisotropy and axial compliances on drilling performance

Abugharara, Abdelsalam N. A. (2019) Influence of formation anisotropy and axial compliances on drilling performance. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Drilling provides the path to reach and exploit underground oil and gas reserves. Drilling oil and gas wells can be vertical, inclined, or horizontal. However, as non-vertical drilling has become dominant, success in increasing oil and gas production has been led by horizontal drilling. Trajectories of horizontal wells have three main curvature segments: vertical, inclined (diagonal or oblique), and horizontal, where the properties of the encountered formation during drilling may vary with inclination. Rocks, classified as anisotropic (i.e. shale), whose properties are directional dependent or classified as isotropic (i.e. fine-grained and sandstone), whose properties are not directional dependent, have high influence on drilling performance, especially in nonvertical drilling. The significant shift towards horizontal drilling has increased the interest in laboratory studies and research on directional drilling, particularly in shale, to evaluate the influence of anisotropy orientation on drilling performance (i.e. ROP), and therefore, choose optimal trajectory, enhance performance, and reduce costs. This dissertation focuses on: (i) developing an experimental procedure for classifying rock anisotropy through oriented physical, mechanical, and drilling measurements, (ii) evaluating the influence of shale (as VTI rocks) anisotropy orientation on drilling parameters, and (iii) investigating the enhancement of the drilling rate of penetration (ROP) by implementing the novel drilling technique of passive Vibration Assisted Rotary Drilling (pVARD). First, a laboratory baseline procedure was developed for a rock anisotropy characterization involving oriented physical, mechanical, and drilling tests on rock like materials (RLM). This research objective was to develop the procedure on synthetic rocks (RLM) as well as natural rocks, including shale, granite, and sandstone. Second, detailed oriented physical, mechanical, and drilling measurements were taken for the determined isotropic and non-isotropic rocks in stage I, then aimed to interlink all results of all measurements, through which isotropic rock classifications can be enriched, and confirmed. Third, compliant (i.e. pVARD) versus non-compliant (without pVARD) drilling was performed in various rocks for the purpose of evaluating the influence of axial oscillations on drilling performance. Also, the parameters behind enhancing ROP with compliant versus non-compliant were investigated in this research. Last, a relationship between oriented strength and oriented drilling parameters for isotropic and anisotropic rocks was developed. This research aims to establish relationships between strength variation, drilling performance, and the main drilling parameters that influence ROP in different rock types for the purpose of rock isotropy / anisotropy evaluation.

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