RESEARCH AND PRACTICE OF DIRECTIONAL DRILLING TECHNOLOGY IN DEEP COAL FORMATION OF DIBEI AREA

According to the requirements of well completion and fracturing operations, the deep tight gas wells are generally being limited by the complex li-thology and dip angle of the reservoir. The deep tight gas well in Dibei area of Tarim Oilfield needs to be deflected in the coal bed, but there arc some serious problems, such as the well collapse, drilling fluid loss, pipe stuck, low deflection rate and the difficulty of controlling the well trajectory. Based on the technical difficulties and the characteristic in unstable coal rocks, in this paper, the effective technical methods were proposed to solve these difficulties. Under the circumstance of ensuring the stability of the shaft wall, the Yangxia Formation coal seam can obtain an ideal slope building rate. The coal seams of Yangxia Formation should use bitumen instead of special shaft wall intensifies. The stability of the coal seam is poor. When drilling a single layer of coal with a thickness of more than 2 m, it is recommended to raise the hole every 1-2 m to verify the upper well-bore condition. Whenever it was found that there was an obstruction or card display when lifting or lowering, the borehole must be cleared before the next operation can be carried out, and no forced drilling is allowed. Drilling in the well section of coal-measure strata can appropriately simplify the drilling tool assembly. In the case of complex downhole conditions, the centralizer and other special tools should be thrown away to reduce the rigidity of the drilling tool. During the operation of the entire coal seam section, close attention should be paid to the pump pressure to prevent the collapse of the coal seam at the bottom of the well caused by the holding of the pump.