Badarinadh Vissapragada

Radial profiling of the three formation shear moduli and its application to well completions

Near-wellbore alteration in shear stiffnesses in the three orthogonal planes can be described in terms of radial variations of the three shear moduli or slownesses. The three shear moduli are different in formations exhibiting orthorhombic or lower degree of symmetry, as is the case in deviated wellbores in triaxially stressed formations. These shear moduli are affected by factors such as overbalanced drilling, borehole stress concentrations, shale swelling, near-wellbore mechanical damage, and supercharging of permeable formations. The two vertical shear moduli C44 and C55 in an anisotropic formation with a vertical x3 -axis are obtained from crossed-dipole sonic data, whereas the horizontal shear modulus C66 is estimated from borehole Stoneley data. The effective shear modulus C66 is smaller than the vertical shear moduli C44 or C55 in a poroelastic formation exhibiting high horizontal fluid mobility. Consequently, analyses of radial profiling of the three shear moduli in a reasonably uniform lithology ...

Borehole Acoustic Reflection Survey for High Resolution Imaging

Summary Borehole Acoustic Reflection Survey (BARS) data were acquired in the Brent formation in the Norwegian North Sea in an exploration well for Hydro. In total, an interval of approximately 300 m was logged. Initial near-wellbore formation images were obtained within 24 hours. The quality of the sonic waveform data was very good. However, significant uncertainties in the actual tool depth caused by rough weather conditions during the time of logging, affected to some extent the coherence and the range of the formation images. The high-resolution image shows an interface dipping at 5° and clearly visible for at least 45 ft away from the well bore. The dip of the interface is in agreement with the expected local geology at the well location. The highresolution event can be correlated to a 1 m thin coal bed intersecting the borehole and indicated by the petrophysical logs. The coal bed is interpreted as the Top Etive Formation. The BARS images helped characterizing the l o cal g eol og y an d th e res erv oi r. In ad di ti on , t h e hi gh resolution sonic images augment the understanding of the seismic responses in the reservoir section.

Radial Profilings Integration For Optimal Well Completion Design

Most of the existing analyses of borehole propagation assume the surrounding formation to be radially homogeneous. However, formations subject to large tectonic stresses often exhibit radially varying acoustic properties owing to the near-wellbore plastic yielding caused by stress concentrations surrounding the borehole (Blakeman, 1982; Gnirk, 1972). Therefore there is a need to provide both the detection and estimation of the radial extent of near-wellbore alteration in reservoir intervals. In order to provide this information, we propose an integration of the three recently developed profiling algorithms, monopole, dipole, and Stoneley. The Dipole Radial Profiling (DRP) of vertical shear slownesses and the Stoneley Radial Profiling (SRP) of the horizontal shear slowness algorithms provide estimates of near-wellbore alteration in shear stiffnesses in the three orthogonal planes in a vertical wellbore parallel to the well axis. The near wellbore alteration can be described in terms of radial variations of the three shear moduli or slownesses. The three shear moduli are affected by several factors, such as overbalanced drilling, borehole stress concentrations, shale swelling, near-wellbore mechanical damage, and supercharging of permeable formations. The Monopole Radial Profiling (MRP) of compressional slowness algorithm provides a preliminary estimate of near-wellbore alteration at the well-site. The MRP algorithm identifies depth intervals that exhibit decreasing compressional slowness away from the borehole surface that may be caused either by near-wellbore stress distributions or plastic yielding of the rock. Application to real data will be presented to illustrate the motivation of such integration for optimal completion design.