ESTIMATION OF TIME EFFECT ON SIZE OF WASHOUT OF LITHIFIED SHALE
FSBEI HPE “Ukhta State Technical University”, Ukhta, the Russian Federation
Stability of wellbore is one of the main factors affecting the well construction process on every stage – staring from drilling and end run and cement casing. Instability of open hole lead to such problems as significant washouts, increase in torque and drag, stuck pipe, low quality of logging and cement job.
Lithified shale deposits create about 70% of all problems related to instability of open hole. Currently the description of the root causes of the instability of shale as well as different methods and methodic to solve this problem could be found in different open sources. Most of them reference to the time dependent wellbore instability in shale formations, meaning that longer hope keeps open – higher probability that shale will lose the stability.
As it was proven in several studies the shale stability problem is related mainly to penetration of drilling fluid into laminations / fractures (between bedding planes and through the microfractures of shale) causing the mechanical failure and thus the loading of the well with cavings. It was noticed that amount of cavings increase over the time and has been suggested that filtrate of a drilling fluid continue penetrating into the formation and bigger volume of a rock is affected.
The objective of this paper is to review the effect of time on the size of washouts in shale deposits and estimate the boundary values when shale loses the stability.
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exposure time; lithified deposits; shale; stability; washout; временной фактор; коэффициент кавернозности; литифицированные отложения; сланцы; стабильность DOI 10.17122/ogbus-2014-4-36-49 References to this article (GOST) Ruzhnikov A.G. ESTIMATION OF TIME EFFECT ON SIZE OF WASHOUT OF LITHIFIED SHALE // Electronic scientific journal "Oil and Gas Business". 2014. №4. P.36-49. URL: http://ogbus.ru/issues/4_2014/ogbus_4_2014_p36-49_RuzhnikovAG_ru_en.pdf