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The third horizontal properly N002H employed saturated salt water drilling, but there were many sticks concerning 3660m and 3895m inside the Nahr Umr Formation, and there have been cavings at the shaking screen.The 2 wells from the three horizontal Acarbose wells have sidetracking due to sticking, just one horizontal effectively was drilled effectively, so CP-690550 akt it illustrates the large results of wellbore instability troubles during the oilfield. The wellbore instability has significant affect for oilfield drilling, and it restricts the exploration and growth during the oil field. As the improvement wells are frequently directional wells or horizontal wells, as well as wellbore instability risk is fantastic, wellbore stability analysis is required in the Halfaya Oilfield. 4. Wellbore Instability Mechanism4.one.



Character from the Instable ShaleFigure 1 demonstrates the logging data on the Nahr Umr Formation of N004 properly. The GR logging displays the formations are primarily sandstone and shale. The caliper logging exhibits that you'll find both stable and instable intervals. Compared for the GR logging information, the lithology of collapsing interval is shale plus the sandstone interval is steady. According towards the interval transit time logging data, the interval transit time of your Nahr Umr Shale is naturally larger compared to the adjacent sandstone interval. The density logging data on the shale are of course lower than the adjacent sandstone interval. The motives for this phenomenon would be the rich inner microfractures, drilling fluid, and the filtrate seepage. This can be witnessed in the photograph in the Nahr Umr Shale (Figure 2).



On top of that, the shape of cavings with the Nahr Umr Shale signifies the shale is enriched in fractures (Figure three). Figure 1The comparison from the logging information in Nahr Umr Formation. GR: all-natural gamma logging; CAL: caliper logging; AC: acoustic transit time logging.Figure 2The core of Nahr Umr Shale.Figure 3The shale cavings of the Nahr Umr Shale of N006H Very well.The main cause for wellbore instability in really hard brittle shale with plenty of fractures is as follows [5�C11]. Should the sealing capacity on the drilling fluid is just not enough or the ionic concentration will not be enough to balance the formation water ionic concentration, the meandrilling fluid as well as the filtrate would flow to the microfractures underneath the driving electrical power through the fluid column pressure distinction of drilling fluid along with the ionic concentration variation.



This would lead the friction coefficients in the fracture plane to lower, the powerful stresses all-around the wellbore to lessen, the formation around the wellbore to come to be loose, and also the assistance in the drilling fluid column to the wellbore wall lessen. So the formation fluid will flow to the wellbore. Through the reaming and back reaming, the disturbance of the rigs to the loose formation will cause wellbore instability.4.two.