An Integrative Software Platform to Support Drilling Operations in Troublesome Formations

Abstract

AbstractA software product, called SAGE-WSA, has been developed to provide an integrative platform for experimenting impacts of various affecting factors and mechanisms on the drilling mud design and wellbore stability. The software packages analytical solutions of stresses, pore pressure, temperature, and chemical potentials around wellbore in both intact and fractured poroelastic media, and many failure criteria, including all often-used ones and some developed in-house. The software provides a friendly user interface for accepting inputs required for the well stability analysis and presenting computed results, such as mud weight window, failure region, stress distribution, etc., in form of charts, contour and spreadsheet. The application and performance of SAGE-WSA is demonstrated through calculating safe mud weight windows for drilling a few troublesome formations. In the low-permeability formations, the timescale of fluid diffusion around borehole is in the same order as drilling operation so the safe mud weight window is time-dependent. Computation shows that the critical mud weight calculated by SAGE-WSA converges to well-known Hubbert-Willis (H-W) solution for impermeable borehole at short time and Haimson-Fairhurst (H-F) solution for permeable borehole at large time. In high-pressure high-temperature formation, the time-dependent pressure diffusion and thermal diffusion are coupled. It is observed that the critical mud weight window is overestimated without considering cooling effect, which may cause formation permeability damage. In chemically active shales, the trouble comes from the chemical activity difference between drilling mud and the formation. In the analysis the poroelastic and chemical effects are coupled. For mud with lower activity, the water will be driven out of the formation and the pore pressure can be dropped significantly. In naturally fractured formations, the natural fractures speed up the diffusion process and degrade the mechanical strength, causing the safe mud weight window much narrower.