Research on hazard classification and prevention technology of abandoned oil well in the overlapping area of coal and oil resources

Aiming at the problem of disaster prevention and control of abandoned oil wells in coal mining areas where coal and oil resources overlap, this paper takes the overlapping area of coal and oil resources of Ningdong coal field in the western edge of Ordos Basin as the research object. The hazard classification and prevention and control techniques of abandoned oil wells were systematically studied. By analyzing the structure, disaster types and multi-source disaster characteristics of abandoned oil wells, the hazards of abandoned oil wells can be divided into four categories: Class Ⅰ are mixed wells with water, oil and gas disaster; Class Ⅱ are mixed wells with water and roof disaster; Class Ⅲ are mixed wells with water, oil, gas and roof disaster; Class Ⅳ are roof disaster wells.On the basis of this, the comprehensive prevention and control ideas and schemes were put forward to block the disaster-causing channels of hazard sources and control the disasters that have already formed. Then a plugging depth model considering oil and gas penetration and floor damage was established. Surface plugging process of "through hole-well washing - inclination surveying-bottom making-plugging" and the downhole exposure treatment process of "monitoring-exploration-revealing-cutting-plugging" were formed. Furthermore, a comprehensive prevention and control system for oil and gas disasters has been put in place, which includes plugging, injection, spraying, increase, decrease, monitoring, protection and evacuation. Further field application was carried out in Shuangma No.1 coal mine. It has safely passed six abandoned oil wells including Matan No.31. Therefore, the expansion and upgrading of abandoned oil wells were effectively restrained, which can provide reference and demonstration for prevention and control of oil well disaster in similar coal mining areas in China.