Interaction mechanism and development suggestions for the full cycle construction effect of surface horizontal wells in unmined coal mines

To explore the differences in fracturing effects of different levels of ground level wells in unmined coal mines, and to reveal the interaction mechanism of construction effects in various stages of gas control throughout the entire cycle, combined with the construction status of ZJ2−1 and ZJ2−2 wells in Zhujidong Mine, the differences in fracturing effects of each section and level were analyzed from the perspectives of fracturing construction scale, fracturing construction curve, and pressure drop data, and compared and verified with microseismic monitoring results; Analyze the impact of drilling and fracturing effects on gas and water production efficiency, as well as the reasons for production shutdown, reveal the interaction mechanism between the entire cycle of surface horizontal well drilling, fracturing, and drainage engineering, and propose key issues and suggestions for gas control in surface horizontal wells in unmined coal mines. The results showed that the fracture opening effect of the coal seam in ZJ2−2 well was better than that of the top and bottom plate fracturing in ZJ2−1 well and ZJ2−1 well, while the microseismic results showed that the top and bottom plate fracturing had better fracture opening effect than the coal seam fracturing. This is because the fracturing effect is not only good, but also requires uniform crack opening and high crack persistence. The drilling effect is reflected in two aspects: drilling trajectory and wellbore stability. Drilling trajectory not only directly affects wellbore stability, but also affects fracturing effect. Fracturing construction will reduce wellbore stability, and wellbore stability is the foundation for ensuring the smooth progress of drainage projects. The stability of the wellbore cannot be ignored due to factors such as drilling layer, fracturing construction, reservoir rock layers, and long-term immersion. Good fracturing effect is only a necessary condition for good drainage effect, and the quality of drainage effect is largely influenced by the stability of the wellbore and the refinement of drainage system. The production stages of both wells can be divided into five stages: backflow, upward production, stable production, shutdown, and re production of gas. The backflow rate of ZJ2−1 well is relatively high and greater than 1, indicating the invasion of adjacent water sources, resulting in poor gas production of ZJ2−1 well with better fracturing effect. Finally, the key issues in the gas control process of surface horizontal wells in unmined areas of coal mines were summarized from the perspectives of optimal selection of surface horizontal well gas control technology, precise control of drilling trajectory, stability control of wellbore, optimization of drainage system, and detection of water storage environment. Corresponding development suggestions were provided in order to provide ideas for gas control of surface horizontal wells in unmined areas of coal mines.