Research On Gas Production Theory In Low Permeability Gas Reservoir

Low pressure and low permability gas fields are abundant in China.Gas well productivity in these kind of gas fields is very low due to low porosity and low permability. It is difficult to develop the gas filed economically.In order to enhance gas well productivity ,some effective and low cost production techniques must be applied .The paper mainly researchs on some theoretical problems which may be encountered in low permeability gas well production,includes mutil-layer commingled production theory,liquid carrying critical flow rate theory ,plunger gas lift and downhole choke theoretical model and design program。There are much differences between oil well and gas well commingled production theory because gas physical properties change greatly with pressure and temperature. Based on integration of geology, gas reservoir engineering and gas production, physical and mathematical model of commingled production were given with consideration of water production. Software which can calculate maximum 5 layers commingled production was programmed. A new liquid carrying critical flow rate model was brought out under the condition of high GWR (Gas water Ratio) and low GWR. It was confirmed that liquid was existed in the form of flat drop in high GWR situation, and the concept of theoretical liquid holdup rate and practical liquid holdup were introduced to determine effectiveness of carrying water under low GWR.Various factors may be influence critical flow rate were also analyzed under high and low GWR.Field applications showed the new model had good coincidence with well performance. Plunger dynamic lift model was presented considering gas flow from formation to well bore and from well bore to pipelines; also factors which influence plunger lift were analyzed. It is concluded that high production and normal running can only be achieved in plunger lift well when tubing pressure and casing pressure, and also afterglow open well time were set rightly. Low pressure and low production well downhole choke theoretical model was given for optimizing choke size and depth of setting. Production data from several wells before and after setting choke shows the designs were appropriate and downhole choke can lower the incoming line pressure and prevent formation of hydrate effectively. It can precipitously decline development cost, and be of great generalized value.