Field Application of a Plugging Borehole Wall Anti-Collapse Agent XZ-OSD in the Piedmont Structural Belt on the South Margin of Junggar Basin

Borehole wall collapse and mud losses have been occurring during drilling operation in the piedmont structural belt on the south margin of Junggar Basin. By experimentally analyzing the rock samples and drilled cuttings taken from the target drilling area, the borehole wall collapse mechanisms were understood. The experimental results show that borehole wall collapse results from the broken formations, oil phase damaging and strong water sensitivity of the formation rocks. Based on this knowledge, an oil based drilling fluid was chosen to drill the water sensitive formations, and XZ-OSD, a borehole wall anti-collapse preventing agent with strong plugging capacity, was selected for use in the oil based drilling fluid. XZ-OSD can plug pores of different sizes in the formations, bond the broken formations together, and form oleophobic adsorption layer on the surfaces of the rock, thereby preventing the borehole wall collapse caused by broken formations and oil phase damaging. Field application showed that, compared with the offset wells, the percent rate of hole enlargement of the 3^rd and the 4^th intervals of the well GHW001 was reduced by 46%-49%. In another well Hutan-1, an exploratory well, the percent rate of hole enlargement in the 5^th interval, in which the mud was treated with XZ-OSD, was reduced by 83.3% compared with the 4^th interval of the well. The use of XZ-OSD effectively solved the problem of borehole instability in the southern margin of the Junggar Basin, and provided drilling fluid technical support for high quality drilling in this area.