| Hydraulic fracturing is the key technology in the west area of Sichuan, whichapplied to the evaluation of explorations and developments in the low-permeabilitytight gas sandstones. Whether the flow-back efficiency is ideal or not after fractured,will influence the reservoir stimulation results directly. Currently, the flow-backmeasures, which are taken as randomly, will result in the occurrence of proppantsflowing back to large extent. There are some problems, such as the flowing backscheme is not rational, the formation is damaged severely, and the flow-back systemis not perfect. So it is necessary to form a system of proper flow-back technology,which deals with different reservoir properties and parameters of hydraulic fracturing.In the thesis, the theoretical research includes: the leak-off calculation by use ofthe2D model about fracturing fluid during the gas wells’ stimulation in the west areaof Sichuan, the leak-off volume of fracturing fluid near the fracture and thepenetration depth in the reservoir, the numerical calculation method of energy domainin the reservoir. The pressure and water saturation, which are around the fracture inthe reservoir after the well is opened and fluid is expelled, is calculated by use ofnumerical simulation method, and the start-off pressure drop is determined. Accordingto the residue water saturation relationship, the final flow-back ratio of the fracturedgas well is computed.The nozzle size for expelling fluid out of wellhead is optimized, consideringthese factors such as preventing proppants from flowing back and overcoming thestart-off pressure in the influence of water-block for tight gas reservoirs. Besides, inorder to testify the accuracy and reliability of the results, it is simulated by use ofEclipse software. The flow-back scheme about well Chuanxiao611-1is designed, andis compared with the on-site results. All of the testifications and practices on site showthat, the design method proposed in this thesis is reliable and feasible. |
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