Study On Mechanics Of Shaft Wall Instability In Honghe Oilfield

Honghe oil field as main blocks of North China Petroleum Engineering Co., LTD., Sinopec, which proven reserves reach to4.53×108t. However, borehole instability of coal seam caused a series of downhole complicated conditions, as drilling pipe sticking, logging blocked, etc., in the horizontal wells drilling processes, which lead to a very low average penetration rate and long drilling cycle, and efficiency development of Honghe oil field.In order to effectively solve coal seam collapse problem of Honghe oil field, this Paper studied the coal rock micro structure, mechanical properties, and permeability and porosity characteristics with combining the Honghe oil field drilling conditions. Secondly, Honghe oil field coal seam collapse pressure calculation model is established from the mechanics perspective with the combining of the intensity of coal and rock failure criteria, coal rock mechanics properties and permeability and porosity characteristics. Then, affecting factors of Honghe oil field coal seam collapse pressure were researched in this Paper based on the established collapse pressure calculation model, such as in-situ stress, wellbore trajectory, cleat development degree of coal rock, coal rock permeability and coal rock porosity characteristics, drilling fluid percolation time with the using of Mathcad software. Finally, coal seam wellbore collapse control measures were proposed through the computing and analyzing of test well, which also evaluated by the field application.These research show that:(1) borehole instability of coal seam in Honghe oil field is main caused by its mechanical instability, the lower the coefficient of coal rock, the lower intensity of coal rock, and the higher coal rock collapse pressure; the smaller the "comprehensive permeability coefficient" of coal seam, the lower coal rock collapse pressure, and vice versa.(2) Honghe oil field coal borehole wall stability control measures including: control the reasonable density of drilling fluid and drilling fluid performance, improve the drilling fluid inhibition appropriately, control the tripping speed strictly, reduce the drill string collision, and drilling through the multiple coal seam quickly with a low borehole declination angle.(3) Honghe oil field coal rock collapse pressure calculation model and coal rock collapse prevention measures are worth popularizing in the Honghe oil field application as its high applicability.In short, the systematic research of Honghe oil field coal seam wellbore instability mechanism and its influencing factors of coal seam collapse pressure, Honghe oil field coal seam collapse prevention measures, have shows its positive significance to shorten the Honghe oil field drilling cycle, reduce drilling cost, and improve the efficiency of Honghe oilfield efficiency development.