The wellbore instability of a fracture shale formation is an issue often encountered in drilling. A fracture formation of the hydration property is often associated with severe borehole collapse. The shale beddings are actually micro-fractures according to the microstructure observations by SEM. The content of the clay minerals of the shale is 30%-40% determined by XRD equipments, and shows a strong hydration property. The shearing strength of the shale is tested by shear experiments, the cohesion and the internal friction angle are determined under different water contents, and the results are regressed. Based on the Darcy linear percolation law, the seepage equation for the drilling fluid is obtained. Through the well circumferential stress analysis and combined with the above results, the collapse equation is obtained. Collapse pressures are calculated under different mud densities and soak times. The calculation results show that the high density drilling fluid accelerates the seepage with increased water amount and reduces the strength against fracture, which leads to more easy formation collapse. Improving the drilling fluid density is unfavorable for the wellbore stability of the fractured shale formation. Measures should be taken to improve the drilling fluid plugging ability and the inhibitory ability, reducing the amount of mud filtrate invasion.
CAO Yuan
,
DENG Jingen
,
YU Baohua
,
FAN Baitao
,
ZHAO Kai
,
XU Yongmeng
. Impact of Drilling Fluid Density on Fractured Shale Collapse Pressure by Chemical-mechanical Method[J]. Science & Technology Review, 2014
, 32(25)
: 40
-45
.
DOI: 10.3981/j.issn.1000-7857.2014.25.006
[1] Edwards S, Matsutsuyu B, Willson S. Imaging unstable wellbores while drilling[J]. SPE Drilling & Completion, 2004, 19(4): 236-243.
[2] Okland D, Cook J M. Bedding-related borehole instability in high-angle wells[C]//Proceedings of SPE/ISRM Rock Mechanics in Petroleum Engineering. Texas: Society of Petroleum Engineers, 1998: 413-422.
[3] Ottesen S. Wellbore stability in fractured Rock[C]//Proceedings of IADC/ SPE Drilling Conference and Exhibition. Texas: Society of Petroleum Engineers, 2010: 1-8.
[4] Santarelli F J, Dardeau C, Zurdo C. Drilling through highly fractured formations: A problem a model and a cure[C]//Proceedings of SPE Annual Technical Conference and Exhibition. Texas: Society of Petroleum Engineers, 1992: 481-490.
[5] McLellan P J, Cormier K. Borehole instability in fissile, dipping shales, Northeastern British Columbia[C]//Proceedings of GTS: Gas Technology Symposium. Texas: SPE, ETATS-UNIS, 1996: 535-547.
[6] Fontana H, Paris J M, Ong S. Borehole stability (geomechanics) modeling and drilling optimization practices improve drilling curves in naturally fractured shale—a south Argentina experience[C]//Proceedings of SPE/ IADC Middle East Drilling and Technology Conference. Texas: Society of Petroleum Engineers, 2007: 1-9.
[7] Tan C P, Chen X. Factors governing mud infiltration and impact on wellbore stability in fractured rock mass[C]//Proceedings of Alaska Rocks 2005 The 40th US Symposium on Rock Mechanics (USRMS). Alaska: American Rock Mechanics Association, 2005: 1-13.
[8] Last N, Plumb R, Harkness R, et al. An integrated approach to evaluating and managing wellbore instability in the Cusiana Field Colombia South America[C]//Proceedings of SPE Annual Technical Conference and Exhibition. Texas: Society of Petroleum Engineers, 1995: 147-160.
[9] Labenski F, Reid P, Santos H. Drilling fluids approaches for control of wellbore instability in fractured formations[C]//Proceedings of SPE/ IADC Middle East Drilling Technology Conference and Exhibition. Texas: Society of Petroleum Engineers, 2003: 1-8.
[10] Gallant C, Zhang J, Wolfe C A, et al. Wellbore stability considerations for drilling high-angle wells through finely laminated shale: A case study from terra nova[C]//Proceedings of SPE Annual Technical Conference and Exhibition. Texas: Society of Petroleum Engineers, 2007: 1-11.
