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Elemental Analysis as a Tool in Determining Wellbore Stability Issues

Abstract

Solutions to deviated and horizontal wellbore stability issues can be complex. Problems such as lost circulation, stuck pipe, pack off, tight hole and enlarged cuttings can occur while drilling. Drilling techniques, mud pump pressure surges, mud type, weights and additives, cleanup cycle design, borehole azimuth, structure, anisotropic stresses and formation characteristics may be contributing factors in any combination. Determining a wellbore's failure point is a critical first step toward finding a solution to a stability issue. Borehole imaging-while-drilling tools help but can be costly since an operator would need to routinely run the tools in wellbores in order to “catch” a wellbore failure. Analysis of breakdown/breakout mud weight failure envelopes help as predictive tools but may not be definitive in an actual wellbore failure situation. Wellbore “rubble” (enlarged rocks exiting the well that were not caused by cutting action from the drill bit) can be elementally/compositionally analyzed more precisely to determine where in the rock column the failure occurs. X-Ray Diffraction (XRD) works well to determine bulk mineralogy; however this technique can fall short when trying to differentiate various organic shale sequences and para-sequences. Elemental analysis and chemostratigraphy offer a more in-depth analysis to determine sequence stratigraphic units in mud rocks where type sections are available. This paper details a case study where the utilization of elemental analysis and chemostratigraphy to successfully pinpoint a series of wellbore failure events in the Marcellus Shale Play in southwestern Pennsylvania.