Study on the effect of abandoned oil casing on the roof of working face

In the overlapping area of coal and oil and gas resources, due to the deeper oil deposits, the oil wells penetrate the coal strata, and the abandoned oil well casing acts on the deformation and damage of the working face roof, changing the original mechanical state of the roof. At present, the phenomenon of toxic and harmful gases such as CH4 and H2S seriously exceeds the standard in the well, which is partly due to the diffusion of the oil formation into the coal-bearing strata especially through the old and broken casing. Therefore, it is important to study the structural characteristics of the overburden rock, movement damage law and support load under the influence of abandoned oil casing to provide a theoretical basis for roof control in the resource overlap area and an important basis for the diffusion of oil and gas in coal-bearing strata. In this paper, the influence of abandoned oil casing on the roof of working face is studied in the background of Shuangma coal mine. The study shows that: 1. Through mechanical analysis and calculation, the petroleum casing increases the shear resistance of the rock and soil body, slightly increases the internal friction angle of the surrounding rock, increases the cohesive force of the casing anchor solid by 91.5 MPa, the elastic modulus is 16884 MPa, and the Poisson’s ratio is 0.274. This changes the bearing capacity, force characteristics and mechanical parameters of the rock body, and improves the stability of the rock body. 2. The physical similarity simulation experiment with and without casing shows that due to the influence of casing, the initial incoming pressure step at the working face increases by 18m, the average period incoming pressure step increases by 6.93m, the working resistance of the support increases by 1698kN, and the incoming pressure strength increases, the pressure increase zone expands by 10-30m, the peak stress increases by about 1OMPa, the sinking of the overlying rock layer decreases in different degrees at different levels, especially at the place with casing. 3. Through UDEC numerical simulation experiments, it is concluded that the influence of casing increases the average cycle pressure step of working face by about 5m, decreases the basic top sinkage by 0.5cm, expands the pressure increase zone of surrounding rock by 10-30m, increases the stress peak by about 1OMPa, and reaches up to 60MPa, decreases the deformation and damage of overlying rock, and the stress concentration around casing is more obvious. The result is similar to the physical simulation experiment.4. Through the field measurement, it is concluded that due to the influence of Ma Tan 31 oil wells, the working resistance of the stent is larger near the oil well side than the other side when the top plate of the working face comes to pressure, the working resistance of the stent also decreases with the increase of the distance from the oil well, and the intermittent overhanging phenomenon exists behind the stent. According to the results of the mine pressure observation, the measured load of the bracket is estimated to be 8162.34KN~9287.34kN, and the hydraulic bracket ZY10000/22/45D selected for the working face can meet the requirements of the roof control of the working face.

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