The Influence of Chemical Potential on Wellbore Stability

Abstract

An experimental investigation was begun to understand fundamental borehole stability mechanisms. This laboratory study was directed toward understanding why and how drilling-fluid chemistry affects borehole stability. The ability of drilling-fluid chemistry to alter shale mechanical behavior and the borehole stress state as a result of shale water content alteration was investigated. Experimental results demonstrate the influence of various drilling-fluid parameters (e.g., salt concentration, salt type, and diesel/water ratio) in @il-based drilling fluids on the water content, compressive strength, and mechanical properties of five shales. The influences of temperature and drilling-fluid exposure time on shale strength alteration also are addressed. The results are explained on the basis of chemical potential differences between oil-based drilling fluid and shale. The change in the shale water content caused by these differences is identified as the predominant factor leading to alteration of shale mechanical behavior and hence borehole stability.

A review of the shale wellbore stability mechanism based on mechanical–chemical coupling theories

“…Specifically, the water mechanical effort related to shale is considered the main factor in this instability (Yew et al, 1990;Hale et al, 1992;Deng et al, 2003). Chee and Mody (Mody and Hale, 1993) stated that analyzing the problems of shale wellbore stability based on mechanical mechanisms alone is inadequate; rather, the coupling mechanisms of mechanics and water chemistry in shale is more important.…”

Chemoporoelastic characterization of Ghom shale

“…This is the main reason that the triaxial loading tests on shales are commonly performed in undrained mode (Steiger and Leung, 1992;Aoki et al, 1995;Wu et al, 1997;Horsrud et al, 1998;Muniz et al, 2005). However, in a number of investigations drained triaxial tests are performed (Hale et al, 1992;Zhang et al, 2001). In this study both modes of loading are implemented to obtain the required mechanical parameters of the shale.…”

Drilling Fluid Technology: Performances and Environmental Considerations

“…Several studies on shale-fluid interactions confirm that various causes are at the origin of borehole instability: water adsorption, osmotic swelling and cation exchange. Different approaches to WBM design have been suggested depending on given shale formations (Darley, 1969;Chenevert, 1970;Roehl and Hackett, 1982;Beihoffer et al, 1988;Zamora et al, 1990;Hale and Mody, 1992;Bol et al, 1992;Cook et al 1993;Mody and Hale, 1993;Bailey et al, 1994;Simpson et al 1994;Durand et al 1995;Horsud et al, 1998;Pernot, 1999). Other recent studies focused on shale-fluid interactions Schlemmer et al, 2002;Van Oort, 2003).…”