The Southern Junggar Geomechanical Analysis Of Complex Structures And The Underground Complex Mechanism

Good hydrocarbon condition is possessed in the south edge of Zhunger Basin in Xingjiang. For many years the area has been thought to be enormous potentiality for exploration and is the advantageous successor of hydrocarbon resource . Now many hydrocarbon-bearing structure and petroleum accumulation zones have been discovered . In the drilling aspect, there is inevitable complicated downhole problems, the penetration is seriously restricted because there are great thick gravel payer , upgrowing big dip angle block , crustal stress , multiple pressure system , meanwhile tectonic movement leads to formation breakdown and formation caving and leak-off. In order to realize drilling safely and quickly at the south edge of Zhunger Basin, the complicated downhole problems must be resolved . It is very important to study the mechanical principle and mechanism of the complicated downhole problems which is much useful for improving the exploration of Zhunger Basin.For the drilling problem at the south edge of Zhunger Basin, the fundamental reason of its complication has been systematically analyzed from geological mechanics , based on the data of experiment of rock mechanics in door and on-site . Using the principles and methods of finite element analysis on solid mechanics, Models have been established to analyze the mechanism under this condition . By studying the mechanism thorough (including borehole stability , borehole caving , lost circulation ) , countermeasures and measures can be got to prevent downhole trouble.Because recent tectonic movement has been strong , many formation of the south area has formed fracture belt and has been big formation dip . Formation collapsing is dual nature , namely when the mud pressure is lower than caving pressure , borehole wall will collapse , but the mud pressure is higher than pore pressure , the mud will come into the microcrack . When such formation being drilled , borehole is prone to collapse and leak . In this paper nonliear principle and method of rock mechanics are used to analyse the geological mechanical problems of mountain front structure at the south edge of Zhunger Base in Xingjiang and adequate principles and methods are offered to research these rock mechanics mechanism.The crustal stress problem is major difficulty during drilling at the south area of the Base and is the fundamental reasons of the complicated downhole condition during drilling . Thesouth area has formed strong wrest-compressed stress field because of the effect of tectonic movement, so the crustal stress is abnormal, the crustal stress is strong in the area. Considering the actual geological characters of mountain front structure of Zhunger in Xinjiang, and the principle and method to study the magnitude and direction of crustal stress field of big dip block are proposed . By theoretic study , experimental study and practical application in the fields , the magnitude and direction stress field for the working block is determined decided.The drilling problems in the breakage block is caused by the reasons that the breakage block is new , the formation intensity is low, and is prone to hydrate, which brings bigger drilling problem. In this paper the theories of fracture mechanics and damaging mechanics are used to study the mechanism of borehole well instability for breakage formation at the south edge of the Basin , and the mechanism of rock mechanics and elastoplastic mechanics and analysis method of finite element are used to study the mechanism of the complicated downhole problems (including borehole instability , borehole collapsing , lost circulation) for the piedmont fractural formulation at the south edge of Zhunger . working mechanism of rock hydration affecting borehole wall stability and its factors have been studied .Besides theoretic study , in order to determine the magnitude and direction of crustal stress in the working block and the rock mechanics parameter , the experiments have been done including rock mechanics experiment, formation fracture experiment and so on, which provide the n...