The southern edge of the Junggar basin in China has great potential for oil and gas exploitation. However, during drilling in this area, many borehole problems occurred, which leads to low rate of penetration and long drilling cycle. The main reasons from the geological aspect was that this area was affected by tectonic process, which leaded to development of complete tectonic, formation nappe along fault, big dip angles and poor stability. The Formation E2-3a was dominated by mudstone which was sensitive to water and can easily cause shale hydration expansion and dispersal. The instability of the formation is one of the major causes of borehole collapse and tight hole shrinkage. In order to improve the drilling speed and accelerate the process of exploration of southern edge in Juggar basin, the drilling fluids used in this region are studied based on data of geology and drilling data in this paper, Based on the characteristics of the formation E2-3a, a new high density PRT-organic salt drilling fluid is selected by conducting a large number of laboratory tests. Test results of the inhibitory, sealing and stain resistance of this fluid indicates that it could satisfy the drilling requirement in southern edge of the Junggar basin. And field applications also turned out to be positive, the drilling speed was increased by 22% and drilling cycle was reduced by 4 days.

In this paper, the displacement discontinuity initiation conditions are deduced based on potential energy principle. The finite element discrete of weak form of governing equation is developed by combination of displacement discontinuity evolution conditions and discontinuity connection which material derivative describes.