Keywords: gas well drainage gas recovery technology
China Library Classification. : TE38 file identification code: a commodity code:1672-3791(2012) 05 (b)-0080-02 With the deepening of depletion mining, the gas field pressure drops, and the ability of lifting liquid in the wellbore is insufficient. The contradiction between low pressure and liquid carrying has become the main factor restricting gas well production.
1 Problems of the research object
(1) At the initial stage of a gas field development, some drainage measures were gradually implemented, such as optimizing pipe string, foam and plunger gas lift. In the middle and late stage of gas field development, weak drainage technology can no longer meet the production demand, so it is necessary to study strong drainage measures, and there is no mature experience reference in this regard; (2) At present, the wellhead pressure of the gas well with liquid accumulation under the jurisdiction of an oil production plant is still high, and there are still some safety hazards in the implementation of mechanical liquid pumping gas production; (3) Mechanical drainage gas production requires high gas-liquid separation underground, and must be matched with an efficient gas-liquid separator; (4) The pay zone of gas well is buried deeply, so it is difficult to lift.
2 Key technologies and innovations
2. 1? Data survey
Common drainage gas recovery technologies include string optimization, foam drainage, plunger gas lift, continuous gas lift, sucker rod pump, submersible pump, hydraulic piston pump and jet pump. [ 1 ~ 2].
The earliest application of foam drainage in oil field was 1965, and foam flooding test was carried out in an oil field. Subsequently, foam flooding tests were also carried out in other oilfields. It is suitable for different effusion gas reservoirs, but it is generally suitable for formations below 70℃. With the increase of environmental temperature, the foaming ability and stability of foaming agent will be greatly reduced, especially in the high temperature stratum above 100℃, the foams produced by many foaming agents will disappear within 1 min ~ 2 min, or even not produce foams.
Mechanical drainage gas production is suitable for gas wells with medium depth. With the increase of depth and equipment specifications, the cost of mechanical drainage gas production increases, which requires good experience in rod string design and operation, and high requirements for sucker rods and pumps. Avoid formation water pollution of sucker rod and pump.
At present, continuous gas lift is a widely used gas lift method in major oil fields in China. There are three main ways of continuous gas lift: open gas lift, semi-closed gas lift and closed gas lift. Gas lift drainage gas recovery technology is suitable for weak injection, intermittent spontaneous injection and flooded gas wells.
Since 1980s, foreign countries have used electric submersible pumps to drain gas reservoirs strongly, so as to improve the ultimate recovery of water-drive gas fields. 1984, a certain gas field began to use submersible pump for strong drainage of water drive gas field. The practice of electric submersible pump drainage and gas production shows that the process parameters are adjustable, and the design, installation and maintenance are convenient, which is suitable for the recovery of flooded wells and the strong drainage of gas reservoirs.
Jet pump was first used in oil well pumping at about 1970, and then it was gradually popularized. A gas field began to use jet pump to drain water and produce gas on 1992. It is suitable for wells with high sand ratio, high H2S and CO2 content, high chloride ion content and high gas-liquid ratio. The well depth is more than 6000m, the liquid production is less than 2385m3/d, and the well temperature is above 260℃.
Screw pump is a new type of oil recovery device, which was invented by Frenchman René Mohino in 1929. It was not widely used abroad until 1980s, and it was mainly used to produce crude oil with high viscosity, high sand content and high gas content. China has introduced and applied it to petroleum production since 1986. Screw pump can be used for gas well and coalbed methane well drainage and gas production, but it has not been applied on site in China at present.
See table 1 for the comparison of the advantages and disadvantages of various common liquid drainage gas recovery technologies.
2.2? Selection of drainage technology
With the deepening of mining degree, the pressure in each block has dropped seriously. In early 2009, it dropped to 12.92MPa (26.93MPa at the initial stage of production), down to 14.0 1MPa, down by 52%, and the average formation pressure coefficient was 0.5, so the flowing capacity was seriously insufficient. Using the weak drainage technology of this gas well (optimizing pipe string)
Air-lift drainage technology needs high-pressure air source, the ground flow is complex, the investment cost is high, and it is difficult to implement.
At present, screw pump drainage gas production has not been applied.
Hydraulic jet pump drainage technology requires high ground power and pipelines, and is rarely used in an oil field, so it is not selected.
Therefore, mechanical swabbing and electric submersible pump drainage gas production technology are selected to discharge the bottom-hole liquid of the gas field.
According to the theoretical displacement calculation, wells with daily production of more than 25m3 are drained by electric submersible pump, and wells with daily production of less than 25m3 are pumped and drained by machine.
2.3? technical characteristics
2.3. 1? Mechanical pumping
After 20 10 years of mechanical drainage gas production technology test, the drainage gas production technology is basically mature and has the following outstanding characteristics.
(1) wellhead blowout prevention. The sucker rod blowout preventer with pressure resistance of 2 1MPa is used to prevent sucker rod blowout in production; Adopt a new wellhead sealer. Two-stage sealing device can be completed by one person by replacing the filler wellhead without sticking or leaking. The inner filler is made of the best chlorinated nitrile material at present, which is spiral. (2) Constant pressure safety valve. The pressure difference can reach 10MPa, which can prevent the liquid from flowing back to the wellbore; Constant pressure is used to ensure the immersion of the pump during production. (3) Deep pumping technology of FRP sucker rod. Φ φ25mm FRP sucker rod is combined with Φ 22 and Φ19mm common sucker rod string, and the combination ratio is 5∶6∶5. Effectively reduce the load, and the pump suspension reaches 3180m m (4) On-site non-stop sampling test. Adopt new power diagram and liquid level tester. Only a fixture is needed to measure the lateral deformation of the polished rod, which changes the traditional vertical tension variable of the polished rod and reduces the testing difficulty. (5) The bent beam pumping unit series is selected as the pumping unit for pumping and discharging liquid and gas. ⅱcyjq 14-6-73HP .
According to the daily drainage volume is less than 25m3, φ 28 mm, 32mm and 38mm sand control rod pumps can meet the drainage requirements.
An improved 35/65 wellhead (excluding the small four-way) was adopted, and sucker rod blowout preventer, high pressure packing box and constant pressure relief valve were installed at the wellhead to ensure safety.
2.3.2? electric pump
(1) Wellhead seal. Kyd 35/80-65 Ⅱ is a special kind of electric pump, which is used for drainage and gas production wellhead. The test pressure of wellhead hydraulic seal is 35MPa, which ensures the wellhead safety during gas well production. Considering the particularity of gas well, the international standard BIW wellhead crossing is adopted for wellhead cable crossing. The wellhead crossing of submersible motor cable not only has good electrical conductivity and insulation under high pressure, but also has good air tightness. (2) underground airlock. After filtration, the gas well discharges liquid, and the gas-liquid ratio is higher than that of the oil well. Therefore, the combination of high-efficiency separator and gas processor with the strongest gas treatment ability is adopted for gas-liquid separation. (3) Power transmission. Using three lead-clad cables at 120℃ is beneficial to prevent natural gas corrosion. (4) The casing is 5 1/2 ",the motor in the electric pump unit is 1 14P series, and the rest are 10 1 series. A gas well is basically reformed by fracturing, and the electric pump unit needs sand control, so the electric pump unit chooses sand control pump. The designed displacement of electric pump unit is 30m3/d, the lift is 3000m, and the actual pump suspension is 2800m.
2.4? Technical improvement
On the basis of the implementation of liquid drainage and gas production technology in 20 10 test, the liquid drainage and gas production technology of electric submersible pump will no longer be applied in 201,mainly because the displacement of electric pump is large, which is not suitable for the actual liquid production of a gas well in a factory. Intermittent method will greatly shorten the service life of electric pump, so 20 1 1 will all use drainage gas collector.
The technical improvement is as follows.
(1) In the aspect of downhole gas lock, high-efficiency gas separator with sieve tube is selected to replace high-efficiency gas anchor. The gas separation process is mainly completed in the annulus of oil casing, which has high gas separation efficiency and is suitable for wells with high gas-liquid ratio. (2) The tubing anticorrosion protector is installed on the pipe string above the pump base to prolong the service life of tubing. (3) According to the test conclusion of 20 10, φ38mm rod sand control pump was selected for trial use. (4) According to the well depth, 14 beam pumping unit is selected for a certain block, and 16 beam pumping unit is selected for some wells in a certain block.
3 implementation and effect
By the end of February, 20 1 1 year, 2 1 well had achieved mechanical pumping, and 1 well had achieved electric pumping, with good production, and 5 wells had achieved high oil pressure (up to 3.0MPa) by mechanical pumping.
The pumping units are 14 and 16 curved beam pumping units. The stroke is 3.6m~4.8m, and the number of strokes is 4.0 ~ 5.0 times /min. The daily liquid output is 225.8m3, the daily gas output is 254,000 m3, and the daily oil output is 46.7 tons. The pump efficiency is improved by 34.7%.
4 conclusion
The large-scale popularization and application of mechanical drainage gas production project has improved the comprehensive utilization rate of gas wells, effectively reduced the gas layer pollution, and is of great significance to the economic and rapid recovery of production of wellbore effusion wells, preventing edge and bottom water from rushing into gas reservoirs, improving the production level and efficiency of water-bearing gas fields, and enriching gas production technology.
refer to
[1] Study on gas-lift drainage technology of Yang gas-lift valve [J]. Petroleum mining machinery, 20 1 1, 40 (7): 18 ~ 2 1.
Li Wenbin, Liu Yanlong, Ye Sai, et al. Optimization of parameters of coiled tubing sand washing operation [J]. Oilfield Machinery, 20 1 1, 40 (1): 58 ~ 61.