Empirical and numerical approaches for geomechanical characterization of coal seam reservoirs

A numerical study on optimization of multilateral horizontal wellbore patterns for coalbed methane production in Southern Shanxi Province, China

“…Horizontal multilateral wells are capital intensive and careful consideration of stability is imperative to protecting investments. Several researchers have examined wellbore stability based on characteristics of the wellbore (Gentzis, 2009), the mechanical properties of the reservoir (Deisman et al, 2010;Hawkes, 2007;Whittles et al, 2007), and drilling design (Gentzis et al, 2009a(Gentzis et al, , 2009b. However, there is little evidence of work examining probability of wellbore collapse based on the geometry of the drilling pattern alone, which can provide valuable guidance in reservoirs that are highly heterogeneous or poorly characterized.…”

Numerical investigation of the scale effect and anisotropy in the strength and deformability of coal

“…Furthermore, coal specimens usually deteriorate rapidly after they are removed from the mine due to the temperature and humidity changes (Bieniawski, 1968a). Laboratory and field tests on coal have shown the importance of scale effects with a significant decrease in strength and stiffness with increasing specimen size (Bieniawski, 1968a(Bieniawski, , 1968bDeisman et al, 2010;Medhurst and Brown, 1998;Vanheerden, 1975;Wagner, 1974), see Fig. 1.…”

“…Medhurst and Brown (1998) adopted the generalised Hoek-Brown criterion to scale parameters of intact coal to in situ peak strength parameters. Deisman et al (2010) also used the GSI to characterize the mechanical properties of a coal seam reservoir and suggested that the GSI is able to represent the influence of scale effects on coal strength. Esterhuizen (1998) stated that the GSI can be used to estimate the strength of large scaled coal.…”

Time delay effect due to pore pressure changes and existence of cleats on borehole stability in coal seam

“…(Gu and Chalaturnyk, 2005;Deisman et al, 2010). In fact, during drilling, pore pressure changes is also likely to happen because BHP can't keep the same as pore pressure all the time.…”