2016_EJRNL_PP_XIANGJUN_LIU_1.pdf
Terbatas  Suharsiyah
» Gedung UPT Perpustakaan
Terbatas  Suharsiyah
» Gedung UPT Perpustakaan
As a serious problem in drilling operation, wellbore instability restricts efficient development of
shale gas. The interaction between the drilling fluid and shale with hydration swelling property
would have impact on the generation and propagation mechanism of cracks in shale formation,
leading to wellbore instability. In order to investigate the influence of the hydration swelling on the
crack propagation, mineral components and physicochemical properties of shale from the Lower
Silurian Longmaxi Formation (LF) were investigated by using the XRD analysis, cation exchange
capabilities (CEC) analysis, and SEM observation, and we researched the hydration mechanism of LF
shale. Results show that quartz and clay mineral are dominated in mineral composition, and illite
content averaged 67% in clay mineral. Meanwhile, CEC of the LF shale are 94.4 mmol/kg. The
process of water intruding inside shale along microcracks was able to be observed through high
power microscope, meanwhile, the hydration swelling stress would concentrate at the crack tip.
The microcracks would propagate, bifurcate and connect with each other, with increase of water
immersing time, and it would ultimately develop into macro-fracture. Moreover, the macrocracks
extend and coalesce along the bedding, resulting in the rock failure into blocks. Hydration swelling
is one of the major causes that lead to wellbore instability of the LF shale, and therefore improving
sealing capacity and inhibition of drilling fluid system is an effective measure to stabilize a
borehole