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The third horizontal nicely N002H made use of saturated salt water drilling, but there have been lots of sticks between 3660m and 3895m in the Nahr Umr Formation, and there were cavings with the shaking display.The two wells from the three horizontal Trichostatin A TSA wells have sidetracking resulting from sticking, only one horizontal nicely was drilled efficiently, so Acarbose it illustrates the big effects of wellbore instability challenges inside the oilfield. The wellbore instability has critical effect for oilfield drilling, and it restricts the exploration and advancement from the oil area. As the improvement wells are frequently directional wells or horizontal wells, and also the wellbore instability danger is wonderful, wellbore stability evaluation is required inside the Halfaya Oilfield. four. Wellbore Instability Mechanism4.1.



Character of the Instable ShaleFigure one exhibits the logging information of your Nahr Umr Formation of N004 effectively. The GR logging displays the formations are mainly sandstone and shale. The caliper logging exhibits that you will discover each stable and instable intervals. In contrast to the GR logging data, the lithology of collapsing interval is shale along with the sandstone interval is stable. In accordance towards the interval transit time logging data, the interval transit time of your Nahr Umr Shale is certainly larger compared to the adjacent sandstone interval. The density logging information with the shale are clearly reduced than the adjacent sandstone interval. The reasons for this phenomenon will be the rich internal microfractures, drilling fluid, plus the filtrate seepage. This can be viewed from the photograph in the Nahr Umr Shale (Figure 2).



In addition, the form of cavings of the Nahr Umr Shale indicates that the shale is enriched in fractures (Figure 3). Figure 1The comparison with the logging information in Nahr Umr Formation. GR: purely natural gamma logging; CAL: caliper logging; AC: acoustic transit time logging.Figure 2The core of Nahr Umr Shale.Figure 3The shale cavings of your Nahr Umr Shale of N006H Well.The primary cause for wellbore instability in really hard brittle shale with plenty of fractures is as follows [5�C11]. In case the sealing capability of your drilling fluid is not really ample or even the ionic concentration isn't adequate to balance the formation water ionic concentration, the towarddrilling fluid and the filtrate would movement to the microfractures under the driving electrical power through the fluid column pressure difference of drilling fluid plus the ionic concentration variation.



This would lead the friction coefficients in the fracture plane to reduce, the effective stresses about the wellbore to reduce, the formation all-around the wellbore to turn out to be loose, as well as assistance with the drilling fluid column towards the wellbore wall lower. So the formation fluid will movement into the wellbore. Through the reaming and back reaming, the disturbance from the rigs to your loose formation will lead to wellbore instability.4.2.