STUDY ON A SPACING OPTIMIZATION METHOD OF ADVANCED EXHAUST WELLS FOR SHALLOW GAS IN HANGZHOU BAY AREA

For engineering constructions encountering shallow gas geological disasters, laying advanced exhaust wells is an effective method to control hazards. To deeply understand the shallow gas and water transport law in a gas reservoir during the exhausting process is of great significance for designing wells to efficiently exhaust harmful gas. Based on the two-phase seepage principle of unsaturated soil and a typical geological model of shallow gas buried in Hangzhou Bay, the migration process of the gas-water interface in the gas reservoir under controlled exhaust conditions was studied using the numerical simulation method, and the factors affecting the layout of advanced exhaust wells were discussed. A spacing optimization method for the exhausting wells was proposed and applied in practical engineering. Results show that the gas-water distribution patterns and gas emission effects in a gas reservoir are significantly different at different gas emission rates. The spacing setting of engineering advanced exhaust well can be reasonably optimized according to the longest flooding time and the minimum remaining gas reservoir thickness. The original pressure in the gas reservoir is the most significant factor affecting the optimal layout of exhaust wells. However, the water permeability coefficient of the soil below the gas reservoir and the thickness of the original gas reservoir have no obvious influences on the optimal value. The effect of adjusting well spacing to improve the exhaust effect of vertical exhaust wells weakens as the pressure coefficient of the gas reservoir decreases. If the pressure coefficient is large, the well spacing should be appropriately reduced; otherwise, it should be moderately increased. For engineering constructions encountering shallow gas geology with small gas pressure, developing the technology of laying horizontal exhaust wells is conducive to improving the exhaust effect. In addition, a safe and reasonable distance from surrounding buildings(structures) should also be considered in the designing of advance exhaust wells, which is useful to achieve the purpose of high efficiency, safety, and avoiding investment waste.