Key technologies for casing running in extended-reach wells:An example from J63-5H well
China boasts considerable tight gas resources with a broad development prospect.Many of these reservoirs with various targets have been exploited one after another in Bajiaochang gasfield,central Sichuan Basin.Among them,the reservoirs of the Jurassic Shaximiao Formation are the major contributor to field output.They are characterized by thin thickness and mini sandbody,and can be preferentially by extended-reach drilling.However,some features in such extended-reach wells,for instance complicated wellbore trajectory,small vertical depth and presence of cutting bed,often result in inadequate casing setting or forced in-situ cementing,thereby making horizontal section ineffective and restricting the recovery.It is necessary to investigate the key technologies for casing running and evaluate them by tests.Targeted Shaximiao reservoirs,J63-5H as an extended-reach well in this field is also a directional well with the largest ratio of horizontal displacement to vertical depth in Bajiaochang structure.In addition,after analyzing challenges for the running in this well,the key running technologies and the methods to calculate relevant parameters were discussed.These technologies include drifting,wellbore cleaning,inver-sion prediction on casing friction coefficients,and floating casing running.For drifting technology,both weighted and equivalent stiffness coefficients are evaluated to judge whether drifting assembly is compatible,so as to ensure both required stiffness and smooth drifting.For cleaning technology,the drilling-fluid flow velocity needed for keeping cuttings suspended is determined,the sand-carrying measures such as heavy drilling fluid,light+heavy drilling fluid,and extremely heavy drilling fluid are adopted,and the presence of cutting bed in wellbore is diagnosed on the basis of variations on equivalent circulating density(ECD)in annulus and the volume and size of cuttings returned,in order to eliminate blocking risks by this bed.For inversion prediction,based on the hook load in short trip,the inversion is conducted using the three-dimensional soft-string model to determine the friction coefficient in the vertical,kick-offand horizontal sections,which are believed to be relatively accurate.For floating casing running,the optimal setting depth of floating collar is defined.Finally,a simulation software is developed for casing running independently.Guided by this software,casing is set successfully in J63-5H well to the depth of 5,447 m with-in 30.83 h.With a small error between predicted and measured parameters,the software assists to complete the critical step in cementing.It provides a valuable tool for casing running in unconventional gas reservoirs during directional-well cementing,thereby facilitating such res-ervoirs in the efficient development.
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