So as to analyze the influence Adapalene from the drilling fluid to the wellbore stability with the Nahr Umr Shale, experimental studies were carried to the influence of drilling fluid over the rock mechanical house. We tested the shale power of Nahr Umr Shale right after immersing it in different varieties of drilling fluids. Table six demonstrates the uniaxial compressive power (UCS, MPa) selleck inhibitor effects from the check. Figure four illustrates the comparison with the strength variation rule versus the time after immersing in numerous varieties of drilling fluid.Figure 4Comparison in the shale strength decrease right after immersing.Table 6Experimental effects of shale UCS after immersing in drilling fluid.Figure 4 shows that the shale UCS decreases enormously immediately after immersing it within the organic salt drilling fluid, the subsequent may be the KCL-polymer drilling fluid; the strength while in the Gel-polymer drilling fluid altered a little.
Consequently, the Gel-polymer drilling fluid advantages the wellbore stability from the Nahr Umr Shale.Below the drive force with the ionic concentration variation, the free water while in the drilling fluid which flows to the formation would lessen the rock strength, that is the primary reason to the collapse in Nahr Umr Shale; on top of that, since the formation is incredibly hard and brittle and the fractures are wealthy internally, if the drilling fluid sealing capacity just isn't excellent enough, the drilling fluid and filtrate would flow to the rock along the microfracture underneath the difference in the drilling fluid column strain and pore pressure, so as to weaken the formation power and lead to wellbore collapse.
So, the raising of the ionic concentration on the drilling fluid and enhancing the tilldrilling fluid sealing capacity is the crucial to the wellbore stability on the Nahr Umr Shale.5. Time-Dependent Collapse PressureAccording to mechanical concepts, the key cause for borehole collapse is induced by shear failure for the purpose that stresses loaded on rock all around the borehole exceed the rock power, due to lower mud column pressure. Now, brittle formation collapse will create plus the borehole will enlarge; for plastic formation, plastic deformation be will generated and borehole shrinkage will likely be encountered.
Generally, borehole collapse will take area from the minimum horizontal tension path, �� = ��/2 or 3��/2 ; the borehole tension on minimum horizontal stress direction [13�C20] is as follows:��r=P?��?(P?Pp),�Ҧ�=3��H?��h?P+��[��(1?2��)one?��??](P?Pp),��z=��v+2��(��H?��h)+��[��(1?2��)1?��??](P?Pp).
(1)Assume that secure coefficient FS  is as follows:FS=��ntg��+C��.(2)And letM=1+(FS?one)cos?2��.(3)Exchange usual anxiety ��n as principal tension ��1 and ��3:��n=��1+��32?��1?��32sin��?��Pp.(four)Rewrite Mohr-Coulomb criterion :M(��1?��3)?sin��(��1+��3?2��Pp)?2Ccos?��=0.(5)Based on distinct borehole pressure situations, borehole collapsing pressure expresses as a different type.