Stressed-Shale Drilling Strategy—Water-Activity Design Improves Drilling Performance

Jian-guo, Zhang; Rojas, Juan Carlos; Clark, David E.

doi:10.2118/102498-pa

Cited by 21 publications

(5 citation statements)

References 24 publications

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“…The water vapor desorption method has been applied to shales to characterize their water activity-saturation relationships, mainly in the development of drilling mud (Chenevert, 1970;Mody and Hale, 1993;Oleas et al, 2010). The theory is that once the water activity of a shale formation at its in-situ saturation is known, the water activity of the drilling fluid can be matched to it in order to combat fluid loss and subsequent swelling (Chenevert, 1970;Mody and Hale, 1993;Zhang et al, 2008). However, none of these studies have noted that water activity can be converted to Pc for characterizing the capillary pressuresaturation relationship.…”

Section: Figurementioning

confidence: 99%

Capillary pressure – saturation relationships for gas shales measured using a water activity meter

Donnelly

Perfect

McKay

et al. 2016

Journal of Natural Gas Science and Engineering

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Hydraulic fracturing of gas shale formations involves pumping a large volume of fracking fluid into a hydrocarbon reservoir to fracture the rock and thus increase its permeability.The majority of the fracking fluid introduced is never recovered and the fate of this lost fluid, often called "leak off," has become the source of much debate. Information on the capillary pressuresaturation relationship for each wetting phase is needed to simulate leak off using numerical reservoir models. The petroleum industry commonly employs airwater capillary pressuresaturation curves to predict these relationships for mixed wet reservoirs. Traditional methods of measuring this curve are unsuitable for gas shale's due to high capillary pressures associated with the small pores present. A possible alternative method is the water activity meter which is used widely in the soil sciences for such measurements. However, its application to lithified material has been limited. This study utilized a water activity meter to measure airwater capillary pressures (ranging from 1.3 -219.6 MPa) at several water saturation levels in both the wetting and drying directions. Water contents were measured gravimetrically. Seven types of gas producing shale with different porosities (2.5 -13.6%) and total organic carbon contents (0.4 -13.5%) were investigated. Nonlinear regression was used to fit the resulting capillary pressurewater saturation data pairs for each shale type to the Brooks and Corey equation. Data for six of the seven shale types investigated were successfully fitted (median R 2 = 0.93), indicating this may be a viable method for parameterizing capillary pressuresaturation relationships for inclusion in numerical reservoir models. As expected, the different shale types had statistically different Brooks and Corey parameters. However, there were no significant differences between the Brooks and Corey parameters for the wetting and drying measurements, suggesting that hysteresis may not need to be taken into account in leak off simulations.

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Section: Figurementioning

confidence: 99%

Capillary pressure – saturation relationships for gas shales measured using a water activity meter

Donnelly

Perfect

McKay

et al. 2016

Journal of Natural Gas Science and Engineering

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“…Several researchers have made the case that increased drilling fluid density penetrates the fractured shale more easily, and this increase in pressure in the fractures (and the resulting lubrication of the bedding planes) serve to lower the effective stress that leads to shale failure (Last et al 1995;Labenski et al 2003;Zhang et al 2008). On the other hand, others have made the case that increases in drilling fluid density increased stability (Santarelli et al 1992;Gallant et al 2007;Ottesen 2010).…”

Section: Mud Weight and Hydraulic Effectsmentioning

confidence: 99%

Wellbore Pressure Management in Unstable Shales: It's Not Just About Rocks

Hemphill

2012

SPE Annual Technical Conference and Exhibition

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Much of the drilling in unconventional resource plays occurs in unstable shales, which are usually fractured and can be easily destabilized. Drilling through them successfully can be difficult at best, and many high-angled holes in these plays are often lost due to mechanical instability. This paper examines the problems of shale gas drilling from the theoretical perspective of Wellbore Pressure Management (WPM) and keys in on the effects of equivalent circulating density (ECD) while drilling and on the effects of equivalent static density (ESD) when there is no circulation.In this paper the following questions pertaining to drilling a typical fractured shale or highly-laminated weak zone are addressed from the WPM perspective: What mud density do I need to drill a fractured shale?  Why can a typical shale gas play well be drilled with no drilling problems, yet becomes very unstable on the last trip out of the hole before wireline logging or running casing?  Why are drilling problems especially acute in laminated shales or similar weak zones?  Why is the wellbore unstable while the drilling density is within the range demarcated by the Safe Drilling Window?  Why does shale instability often not improve significantly when drilling fluid density levels are increased?  Which tools in the driller's toolbox are often used that actually make the wellbore stability issue more problematic?By using a Wellbore Pressure Management approach to understanding instability in fractured shales, the reader can readily see how to best deal with the problem in the field and hopefully improve stability in future wells.

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“…It is important to note that determinating water activity of the shale is difficult to obtain in their in-situ conditions since these values depend on temperature, pressure and the components of pore fluid. To determine the shale formation activity, the modified method of effective mean stress proposed by Zhang, Rojas & Clark (2008) which uses geomechanical data to generate a record of activity with depth, was used.…”

Section: Water Activity Of Carbonera Formationmentioning

confidence: 99%

“…The membrane efficiency depends on both the rock properties and the drilling fluid. Rock properties like CEC, permeability, and pore throat; and fluid proper- ties like ratio of the hydrated ion (solute) define the membrane efficiency values in the rock-drilling fluid system as stated by Zhang et al (2008).…”

Section: Membrane Efficiencymentioning

confidence: 99%

Selection of OBM salinity through effective osmotic pressure evaluation in carbonera shale for colombian foothills

Fernández-Vera

Corzo

Saavedra

2010

CT&F Cienc. Tecnol. Futuro

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Wellbore instability in shales is attributed to many factors. Two of them are mechanical effects and physico-chemical effects. Drilling and drilling fluid cause physico-chemical interaction and the flux of water and ions that may alter the shale stress state through pore pressure and shale strength. This paper presents the analysis of the chemical osmosis phenomenon between drilling fluids and shale formations to evaluate the chemical parameters necessary for modeling the aqueous flux. These parameters are the drilling fluid activity (Adf), shale activity (Ash) and membrane efficiency (ME). This work also characterizes the shales for drilling purposes and describes an integrated methodology to obtain the magnitude of the chemical parameters. Furthermore, it is stated how the generation of effective osmotic pressure between the formation and drilling fluid define the water flux direction. Finally, the application of the results of the chemical analysis to Carbonera shale is presented. The design of laboratory tests for two mud formulations, Mud A and Mud B, and the field application is also showed. The Mud A is a balanced activity mud and the Mud B is a high salt concentration mud which may produce water flux out of the shale formation (dehydration) during drilling, in some sections of the wellbore, increasing the formation strength. The results presented in this paper will help to reduce the risks associated with wellbore instability during the drilling of shale formations and thereby lowering the overall non-productive time and reducing drilling costs.

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Stressed-Shale Drilling Strategy—Water-Activity Design Improves Drilling Performance

Cited by 21 publications

References 24 publications

Capillary pressure – saturation relationships for gas shales measured using a water activity meter

Capillary pressure – saturation relationships for gas shales measured using a water activity meter

Wellbore Pressure Management in Unstable Shales: It's Not Just About Rocks

Selection of OBM salinity through effective osmotic pressure evaluation in carbonera shale for colombian foothills

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