The Research Of Well Structure Design Of Ultra-deep Wells In Bokhtar Block,Tajikistan

Drilling engineering faced a lot of huge challenges of the petrophysical differences and blowout and leak in same layer,which in complex geological structure blocks to drill through a number of complex pressure systems and different physical properties of rock formations.Conventional well structures are difficult to meet the drilling characteristics of these complex exploration blocks.Therefore,in the complex geological structure block,it is necessary to expand the well structure of the ultra-deep wells.The shallow structure of the block is strongly deformed;the thick salt layer is developed;the old well is not drilled to the Jurassic carbonate reservoir under the salt,the old well depth of 6450m is the deepest;the buried depth of the Jurassic carbonate reservoir is expected depth of 6⁸km,The bottomhole temperature is close to 180°C and the pressure is close to150MPa,The reservoir contains H₂S and CO₂.In order to prove the Jurassic carbonate reservoirs under salt,it is necessary to drill a complex ultra-deep well.Reasonable well structure design can effectively ensure to drill the depth.In this paper,the well site is located in the Obigarm anticline,which is the most complex structure of Bokhtar block,in Tajikistan.The structural optimization and design of a well is completed with the existing pressure profile,temperature profile,stratigraphic sequence and old well data.Sametime,it's completed to select casings and check strength of casing based on dynamic thermodynamics,Which takes into account the case of salt casing proned to collapse,we introduced the formula about triaxial stress of the salt casing under the action of uniform and non-uniform external load.On the basis,the burst strength of the casing under different non-uniform external loading coefficients is obtained,and the design plate,which is about the strength of the casing under different diameter-to-thickness ratio and non-uniform external load factor,is obtained by experimental analysis.By contrast,the design results of specialized software and the design plate is basically consistent.The well structure program can provide some technical guidance for the construction site.