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Abstract 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.
- South America (0.94)
- Europe (0.70)
- North America > United States > Texas (0.69)
- South America > Colombia > Casanare Department > Llanos Basin > Cusiana Field > Mirador Formation (0.99)
- North America > United States > Texas > Permian Basin > Yeso Formation (0.99)
- North America > United States > Texas > Permian Basin > Yates Formation (0.99)
- (24 more...)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Pressure Management (1.00)
- Well Drilling > Drilling Operations (1.00)
- (5 more...)
ABSTRACT: Much of the drilling in unconventional resource plays occurs in unstable shales, which are usually fractured and can be easily destabilized. Successful drilling through them can be difficult at best, and many high-angled holes in these plays are often lost due to mechanical instability. This paper looks at the drilling 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. INTRODUCTION Drilling problems in unconventional resources wells typically involve fractured or laminated shale zones. These formations are by their nature weak, and susceptible to pressure fluctuations that occur during the normal course of drilling. Turning on the mud pumps and later turning them off when a connection is made happens regularly while drilling. Other fluctuations can occur when wellbore instability becomes a problem, and poor hole cleaning, pack-offs, etc. often result. To deal with the instability issues, drillers will often rely on backreaming, which often produces pack-offs and creates additional pressure spikes. In short, the pressure fluctuations become worse instead of improving. These pressure fluctuations have previously been called ‘wellbore flexing’ or ‘pressure cycling [1] in the literature. It is only with a better understanding of the causes and outcomes of these pressure fluctuations in unstable shales that the drilling industry can more efficiently drill these wells - hence the term ‘Wellbore Pressure Management’, or WPM for short. In Fig. 1, an outcrop of an unstable shale of the type discussed in this paper is shown. WELLBORE STABILITY MODELING Typically, before a well is drilled, the Operator engages in a wellbore stability study in order to identify the ranges of the Safe Drilling Window.
- North America > United States (1.00)
- Europe > Norway > Norwegian Sea (0.24)
- South America > Colombia > Casanare Department > Llanos Basin > Cusiana Field > Mirador Formation (0.99)
- North America > United States > Alaska > North Slope Basin > Greater Point McIntyre Area > Niakuk Field > Kuparuk Formation (0.99)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Well Drilling > Pressure Management (1.00)
- Well Drilling > Drilling Operations (1.00)
- (5 more...)