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WELLBORE CHART
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Enlarged Well bore
Wellbore Collapse
Stable Wellbore
Rubble Zones
Fracturing and Ballooning
Tensile failure along the wellbore circumference caused when shale pore pressure exceeds hydrostatic pressure of drilling fluid column.
Shear failure, occurring when wellbore stresses receive insufficient support from the mud weight. Can be aggravated by changes in well bore azimuth and inclination.
Well bore pressure prevents formation fluid influx or well bore collapse, and does not exceed fracture pressure.
Stress-related failure of brittle rocks. Often natural earth stress fields, especially near salt bodies and active fau Its.
Fractures open due to increased pressure when circulating mud. Fractures close when circulation stops.
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UlOt(fOR PUJIoE STRIJCIIIRE ON CAV1IIG8
Splintered shale '--._,,,, cuttings exhibit
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/ong, concave shape.
WeI/bore covings exhibit non-paral/e1, angular edges; may appear gouged,
Happy dril/er, reduced risk and costs.
WeI/bore cavings are tabular with paral/el surfaces.
r ..... , "/"r-'~.~");'''''''''''' ''"'''''''''Jo" ",-,,,'''''~JJ_ ................. '''. / . 1 .~! . Drilling fluid
losses are indicative of a bal/ooning weI/bore.
"'-"'"'-""~.:';'-.. -.-'~ -.... --.-.. --.- ----.-~.-. ......, ..... _ .... --_.-. -'-"-' ------_. ----------._ .. _ . . _._. . ..
• Stop drilling and increase mud weight • If cavings cannot be controlled, set
casing to avoid influx and/or stuck pipe
• Decrease ROP • Increase flow rate • Increase mud weight gradually until cavings are sparse
• Maintain clean well bore • Avoid swab and surge pressures • Use real-time modeling to derive optimum mud weight for borehole stability
• Minimize changes in mud weight and swab/surge pressures
• Avoid reaming and mechanical agitation of rubble zone
• Monitor trips through destabilized zones • Watch for avalanches and stuck pipe
until zone is cased
• Manage fracture growth by reducing ECD and mud weight
• Locate fracture using time-lapse logging • Minimize surge pressures on fracture • Monitor and reduce the volume and t ime
trend of flow back • Apply polymer or LCM to damaged interval
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