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Chemical effect on wellbore instability of Nahr Umr Shale.

Yu B, Yan C, Nie Z - ScientificWorldJournal (2013)

Bottom Line: Wellbore instability is one of the major problems that hamper the drilling speed in Halfaya Oilfield.Complex accidents such as wellbore collapse and sticking emerged frequently in this formation.Finally, we put forward engineering countermeasures for safety drilling in Halfaya Oilfield and point out that increasing the ionic concentration and improving the sealing capacity of the drilling fluid are the way to keep the wellbore stable.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China.

ABSTRACT
Wellbore instability is one of the major problems that hamper the drilling speed in Halfaya Oilfield. Comprehensive analysis of geological and engineering data indicates that Halfaya Oilfield features fractured shale in the Nahr Umr Formation. Complex accidents such as wellbore collapse and sticking emerged frequently in this formation. Tests and theoretical analysis revealed that wellbore instability in the Halfaya Oilfield was influenced by chemical effect of fractured shale and the formation water with high ionic concentration. The influence of three types of drilling fluids on the rock mechanical properties of Nahr Umr Shale is tested, and time-dependent collapse pressure is calculated. Finally, we put forward engineering countermeasures for safety drilling in Halfaya Oilfield and point out that increasing the ionic concentration and improving the sealing capacity of the drilling fluid are the way to keep the wellbore stable.

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Related in: MedlinePlus

The shale cavings of the Nahr Umr Shale of N006H Well.
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Related In: Results  -  Collection


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fig3: The shale cavings of the Nahr Umr Shale of N006H Well.

Mentions: Figure 1 shows the logging data of the Nahr Umr Formation of N004 well. The GR logging shows that the formations are mainly sandstone and shale. The caliper logging shows that there are both stable and instable intervals. Compared to the GR logging data, the lithology of collapsing interval is shale and the sandstone interval is stable. According to the interval transit time logging data, the interval transit time of the Nahr Umr Shale is obviously higher than the adjacent sandstone interval. The density logging data of the shale are obviously lower than the adjacent sandstone interval. The reasons for this phenomenon are the rich internal microfractures, drilling fluid, and the filtrate seepage. This can be seen from the photo of the Nahr Umr Shale (Figure 2). In addition, the shape of cavings of the Nahr Umr Shale indicates that the shale is enriched in fractures (Figure 3).


Chemical effect on wellbore instability of Nahr Umr Shale.

Yu B, Yan C, Nie Z - ScientificWorldJournal (2013)

The shale cavings of the Nahr Umr Shale of N006H Well.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3824561&req=5

fig3: The shale cavings of the Nahr Umr Shale of N006H Well.
Mentions: Figure 1 shows the logging data of the Nahr Umr Formation of N004 well. The GR logging shows that the formations are mainly sandstone and shale. The caliper logging shows that there are both stable and instable intervals. Compared to the GR logging data, the lithology of collapsing interval is shale and the sandstone interval is stable. According to the interval transit time logging data, the interval transit time of the Nahr Umr Shale is obviously higher than the adjacent sandstone interval. The density logging data of the shale are obviously lower than the adjacent sandstone interval. The reasons for this phenomenon are the rich internal microfractures, drilling fluid, and the filtrate seepage. This can be seen from the photo of the Nahr Umr Shale (Figure 2). In addition, the shape of cavings of the Nahr Umr Shale indicates that the shale is enriched in fractures (Figure 3).

Bottom Line: Wellbore instability is one of the major problems that hamper the drilling speed in Halfaya Oilfield.Complex accidents such as wellbore collapse and sticking emerged frequently in this formation.Finally, we put forward engineering countermeasures for safety drilling in Halfaya Oilfield and point out that increasing the ionic concentration and improving the sealing capacity of the drilling fluid are the way to keep the wellbore stable.

View Article: PubMed Central - PubMed

Affiliation: State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing 102249, China.

ABSTRACT
Wellbore instability is one of the major problems that hamper the drilling speed in Halfaya Oilfield. Comprehensive analysis of geological and engineering data indicates that Halfaya Oilfield features fractured shale in the Nahr Umr Formation. Complex accidents such as wellbore collapse and sticking emerged frequently in this formation. Tests and theoretical analysis revealed that wellbore instability in the Halfaya Oilfield was influenced by chemical effect of fractured shale and the formation water with high ionic concentration. The influence of three types of drilling fluids on the rock mechanical properties of Nahr Umr Shale is tested, and time-dependent collapse pressure is calculated. Finally, we put forward engineering countermeasures for safety drilling in Halfaya Oilfield and point out that increasing the ionic concentration and improving the sealing capacity of the drilling fluid are the way to keep the wellbore stable.

Show MeSH
Related in: MedlinePlus