Mechanical And Chemical Shale Stability Research And Application Of Collaborative Action

Wellbore instability, in the broad sense includes not only the brittle shale wellbore collapse spalling, plastic shale borehole shrinkage and viscoplastic deformation, including water in drilling fluid under pressure of formation fracture and borehole wall during drilling and completion, often appear collapse, fracture, diameter shrinkage size conditions. Wellbore instability is the major oil gas field exploration and development process of the world over a long period of time, one of the downhole problems most often encountered, which seriously affects the oil and gas exploration and development process, and even cause personal injury to the construction site personnel. According to statistics, the world’s oil drilling company, year only for protecting borehole wall stability cost as much as$1000000000, and the processing of wellbore stability problems, an increase of5%to6%of total drilling time. Because in the drilled strata, nearly75%for shale, shale wellbore and caused by the instability of up to more than90%, therefore, the research on wellbore stability problem at home and abroad are focused on shale stability, the results obtained can not only accelerate drilling speed while achieving low cost drilling, also can enhance the core competitiveness of drilling technology in China in the world.This paper analyses the reason of borehole instability phenomenon fundamentally, including two aspects of mechanics and fluid physical-chemical action, these two areas are mutual influence, mutual restriction, inseparable. Confirmed by the previous practice, only from the problem of mechanical and fluid physical and chemical effects on the single borehole instability research is not feasible, we must consider the impact of the two factors, solve the problem of wellbore instability can be effective. Therefore, this is the future development direction of shale borehole stability study.Characteristics of the main components of clay minerals in shale is play a decisive role in shale properties, this paper has carried on deep research to the clay mineral characteristics, summarizes several characteristics and wellbore stability is closely linked to the influence of wellbore stability, including specific surface area, cation exchange capacity, hydration, pore the water activity. And the research according to the domestic and foreign, based on a summary of previous research progress and fully absorb the results of previous studies, research on combining shale itself component characteristics and physicochemical properties of in situ, derivation of stress state, the pore pressure, characteristics of geological structure and rock properties and parameters of the inherent determination and calculation method, the summary; properties and comprehensive research of drilling fluid, as well as the influence of the stress distribution on the wall, is the main effect on the P collapse of wellbore stability; rock mechanics and fluid physical and chemical mechanism of synergistic effect.In the clear the shale stability failure root cause and basic established foundation shale stability theory system, summarizes the existing research on wellbore stability experiment method and the advantages and disadvantages of these methods. Due to the complexity of the wellbore instability reasons, lead to the results of theoretical calculation and engineering practice has certain error, is still not a device can visually observe drilling fluid for dynamic process of borehole purposes, there is an urgent need to help researchers in real-time, dynamic understanding of wellbore instability process device, this has become the key node of the current study on the stability of the shale has made a major breakthrough.Combined with the theoretical research results, in order to evaluate the influence of instability of drilling fluid shale, the development of borehole stability evaluation device of high temperature and high pressure mud page making, using shale composition and physicochemical properties of artificial borehole data compression, dynamic state and simulation, temperature and pressure inside the well drilling liquid, to truly develop flushing damage of drilling fluid to borehole wall. According to the borehole stability evaluation device development in this way and domestic shale, ultrasonic imaging technology, hydraulic pressure transfer mechanism and effect of chemical penetration, development of the high temperature and high pressure the shale stability evaluation device, and established the corresponding evaluation method, which provides a new method for evaluation of the shale stability. The evaluation device including artificial borehole simulation device, high temperature and high pressure three axis pressure chamber, temperature, pressure and confining pressure control system, drilling fluid dynamic circulation system and data acquisition and processing system. Through the experiment, the design of instrument and experimental method was optimized, and presents experimental ideas opinions and in-depth development of device to improve the device of other functions, including reducing artificial borehole wall thickness, to achieve ultrasonic ranging automation, improve software operability etc.. The experiment of single factor increase device, through the analysis of experimental results well within the environment, core component, drilling fluid filtrate composition, the return velocity of drilling fluid and other factors on the influence of wellbore stability. Experiments show that through the pressure transfer, chemical between hydraulic pressure and drilling fluid and formation water potential difference is the driving force of fluid into the borehole walls, to control the shale pressure transmission and prevent drilling fluid filtrate into the amorphous layer, need to increase the drilling fluid inhibition, plugging, film and effect, so as to keep the mud borehole stability of the page. Improvement and expansion of experimental ideas of these devices, which makes the development of the high temperature and high pressure mud page Iwai wall stability evaluation device can perform a variety of experiments on the wellbore stability, to achieve maximum device utilization, but also for improving the performance of drilling fluid, the increase of shale Iwai wall stability provides more, more effective basis.We use the linear expansion method for the screening of novel mud shale hydration inhibitor, screening out code for efficient inhibitors of JHSZ and JHGX, through the further experiment, the optimum concentrations of these two inhibitors are added in drilling fluid system are respectively0.5%and3%. High temperature and high pressure the shale stability evaluation application developed device, artificial borehole simulation experiment, evaluation of inhibitory effect on inhibitor screened, confirm the stability of borehole wall effect is good. Use of mechanical and chemical stability of the shale synergy results, wellbore stability problems of Weizhou11-2oilfield was analyzed and calculated, the calculation error of the results and the measured data in the range of allowed, determine the drilling fluid "to maintain wellbore stability safety density window," confirmed the mechanical stability the shale chemical coupling mechanism of borehole stability plays a positive and effective role.The results of this study can not only the development and utilization of Weizhou11-2oilfield adjacent field to provide theoretical guidance, the selected model inhibitor plus small amount, low cost, excellent performance, the high temperature and high pressure the shale stability evaluation device in China to fill the blank in the research on simulation experiment method in dynamic wellbore stability, and realize the maximization of the functioning of the device, expected to be large-scale use and promotion, applied to a broader development of oil and gas field.