Estimating mechanical properties of shale from empirical correlations

Borehole-stability prediction requires knowledge of the mechanical properti es of the formations which. is rarely available in shale sections. This pap er presents empirical correlations to assist in predicting shale mechanical properties. The correlations are based on extensive laboratory testing of shale cores primarily from the North Sea. The acoustic P-wave velocity is a primary input parameter in several of the correlations; thus, various sour ces of the P-wave velocity such as sonic wireline, sonic measurement while drilling (MWD), and acoustic measurements on cuttings may be used to obtain somewhat continuous estimates of shale mechanical properties. Borehole-sta bility evaluations can be made at different stages in the drilling process (planning, while drilling, and post-analysis). Other applications of the co rrelations where shale mechanical properties are required are evaluation of overburden compaction during depletion and optimization of the drilling pr ocess (selection of bit type, bit parameters, etc.).