Study On The Borehole Stability In Deep Layers

In recent years, all kinds of advanced well drilling technology appeared unceasingly along with celebrated the deep natural gas field exploration and development in Qingshen gas field of Daqing. Considering the high temperature and easy collapsed in deep layer, it is being paid more and more attention to borehole stability and drilling fluid technology for preventing borehole from losing steady. The accurate analysis of borehole stability and suitable prevention technology can ensure drilling safely, quickly, and as possible as to reduce drilling pollution to reservoir. All that is a focal point for drilling technology in deep gas exploration and development in Daqing。For the problem of borehole stability, began from the causes of well unstable hydraulic reason and physical chemistry reason, the cause of borehole losing stability was analyzed. First using the convention log information and the laboratory experiment data of Xushen 10 well, in means of constructing the model, the parameters of rock elasticity and intensity were computed, such as three formation pressures (pore pressure, caving pressure, bursting pressure). So the possibility of the wall of a well losing stability can be analyzed in hydraulic aspect. Second, based on the shale mineralogical constituents of the collapsed layer of Xushen 12 well, combined with the analysis of physical and chemical properties, the physicochemical characteristics of inflation, dispersion, cation exchange capacity and zeta potential etc. are measured. The results indicate that those physicochemical characteristics have little influence on borehole stability. At last, the drilling system of anti-high temperature organosilicon instability prevention is investigated. The suitable drilling system has been attained by lab experiments, such as optimization of drilling fluid additives, evaluation of the rheological property for high temperature resistance, etc. This drilling system applying in Xushen 22 well has a good effect. Through research described above, the following conclusions are conducted:1. Some of deep layers in Daqing, the safe well drilling liquid density range is diminished with the increase of the depth. It makes the safe drilling more and more difficult.2. Through research and analysis, the causes for borehole wall collapsed are gotten: the first is hydraulic equilibrium problem.Second is the existence of deep fracture. Micro-fracture has certain destruction function on borehole stability. In addition the invasion of drilling liquid invades the expansion of the fracture and makes support to borehole wall lost that causes borehole wall unstable. 3. The physical and chemical characteristic of the deep rock reveals that the rock is difficult to inflate and disperse. It is a kind of hard fragility rock with micro-fracture. It is surmised that a well stability has a very big relations to flaking caused by water seepage along the micro-fracture.4. The drilling fluid system of anti-high temperature organosilicon instability prevention has a good anti-high temperature rheological property and against collapses ability. It can meet well drilling construction requirement of deep well.5. Using the drilling fluid with plugging agent to plug formation and reduce the filtration loss of drilling fluid can prevent formation borehole from loosing stability that caused by swelling (flooding) pressure of invasion of drilling-fluid.