Research On The Process Plan Of Scattered Natural Gas Recovery In S Gas Field

Although there are numerous scattered natural gas wells in the S gas field, most of them can only adopt intermittent development. For the low single-well production, short stable period, meanwhile the pressure attenuation is fast, so it takes much longer to build up the pressure by making the gas well shut. In the process, it also produces large quantity of water, regular gathering and transferring procedure cannot be used. As a result, these scattered natural gas wells have not been effectively exploited and utilized. Once the natural gas produced by these scattered gas wells can be recycled effectively with low cost, great economic and social benefits will be brought undoubtedly. To address those issues, based on the requirement of the low-cost development strategy of S gas field, this article aims to conduct a exploration on the recovery process of scattered natural gas in S gas field, with the purpose of achieving low-cost and effective recycle of scattered natural gas and fully tap its potential. The major contents can be concluded as follows:(1) Based on the test data of scattered natural gas wells of S gas field,10 scattered natural gas wells which possibly bring recycling benefits were selected. According to the test gas production, water production, open flow potential and proration situation, the fluctuation range of key parameters of recovery process was determined. Meanwhile, a well with similar production in the same block were chose as the reference to predict the single-well production of the target scattered natural gas wells. The results showed that the cumulative predicted yield of 10 wells is 0.1987×108m3.(2) Based on the natural gas reservoir characteristics of the S gas field and the specific operating mode of the scattered natural gas wells, by conducting analysis on the technical feasibility and economic rationality of separation, dehydration and hydrate control, the feasible wellsite recycling and unloading gas decompression process scheme were proposed. Through analysis on the prevention of gas hydrate and technical and economic comparison the current study came up with two schemes:one is "use water jacket heater before throttling and adopt the molecular sieves for the deep dehydration in winter" wellsite recircling process; the other is "use water jacket heater before throttling" gas gathering station and gas unloading and decompression.(3) The study is based on the optimization of specific operating modes and technical schemes of S gas field, and recycling state of the supercharged recycling process and deflated recycling process of interval exploration wells and continuous wells. With fully considering technical feasibility and economic rationality of the separation, dehydration, supercharge, electricity using, wastewater treatment, equipment layout, hydrate prevention schemes, the wellsite recycling processes and the gas uploading and decompression process were designed. Meanwhile,selection of the main process equipments, device prizing design as well as vehicle were conducted, with device performance and investment being estimated.(4) By establishing truck tanks filling process, the gas tanker unloading model and analyzing dynamic process of truck tanks charging and discharging, the calculation formula of flow under the condition of critical flow and sub critical flow were derived. Also,the study proposed a truck tanks filling and unloading time calculation method, and develop a calculation program of that. with the pipe diameter, wellhead pressure,truck tanks pressure factors influence on the truck tanks filling time and variation being analyzed.The results show that:1) Truck tanks filling time less than 38mm diameter range change rapidly and evenly;2) The truck tanks loading time increases linearly with the wellhead pressure;3) At the end of filling, when the differential pressure of the wellhead and the truck tanks is in the range of 0?0.5MPa, the filling time of truck tanks changes rapidly.(5) By utilizing gas unloading time calculation program of truck tanks, the influence and changes of different process, truck tanks pressure, truck tanks surplus pressure and other factors to unloading time are calculated and analyzed. The results indicate that1) Gas unloading time of truck tanks changes rapidly within 38mm diameter range of pipe;2) Truck tanks unloading time performs linear growth with tanks pressure increasing; 3) When the surplus pressure of truck tanks less than 3MPa, unloading time changes rapidly by influence of surplus pressure. However, the unloading time keeps constant when the surplus pressure is higher than 3MPa.(6) Through the rule analysis of gas loading or unloading time and the calculation of tank aeration rate to various water capacity truck tanks,the research deliberately choose 22m3 water capacity tank type, with considering the loading or unloading time, aeration rate satisfied transport needs of scattered wells minimum distribution, and economic feasibility. According to different wellhead pressure situation of interval exploration wells and continuous wells, we adopt none-pressurization recovery and under pressurization recovery to calculate the number of truck tankers.(7) Based on the estimation of device investment and truck tankers number, we determined the exploration and recovery procedure of single well by calculating the main cost of none-pressurization recovery and under pressurization recovery, and analysising the single well's recovery economic benefits on internal sales and CNG sales. The recycling project is evaluated financially upon the cash flow method, breakeven analysis method, and sensitivity analysis method. It can be concluded that:1) By adopting internal sales way on the basis of 1.04 yuan/m3 current price, the project cannot gain any profit, cause recovery project financial net present value is-1056.9 thousand yuan, and net present value is negative; 2) By utilizing CNG sales way on the selling price of 3.2 yuan/m3, profitability of the project is good, cause financial internal rate of return is 39.67%, and the recovery period is short; 3) It can be pointed out by sensitivity analysis that selling price and annual gas production are both sensitive to the financial net present value of two sales ways; 4) Project breakeven analysis shows, the gas price by internal sales is 1.15 yuan/m3. Otherwise, annual gas production of project breakeven by the way of CNG sales should take 27.9% percent of the predicted average annual gas production.