The vast majority of oil wells require some type of artificial lift method to bring the wellbore fluids to the surface. Four major lift methods include:
- Electric submersible pump (ESP)
- Gas lift
- Hydraulic pump (piston and jet pump)
- Beam pump
Gas lift works by injecting gas into the well tubing through gas lift valves in order to reduce the hydrostatic pressure on the fluid column below the pressure of the fluid in the reservoir formation.Optimizing the level of injected gas is important in maximizing the financial performance of the well pad or offshore platform. The challenge for most oil and gas producers is that they do not effectively maximize production with the most efficient use of gas lift resources. Emerson’s Darren Doige shared with me some of the reasons why this is.
The first challenge is that there is a lack of accurate and timely production data from the well tests. The optimal inject rate for a well is based on a ratio of injected gas rate to the liquid production rate. Under injecting the gas decreases the well production rate.
Over injection can cause a production decline because of backpressure effects of the gas in the production string or abnormal situations such as hydrate formation in the well or freezing of the injection choke. And, energy costs required to compress the gas are higher than what is required.
Another issue with over injection is that it can create higher separator operating pressures that increase backpressure on the well, which also reduces production rates.
For wells that require intermittent gas lift, the challenge is to establish the optimal injection frequency that removes the highest liquid volume from the well with the least number of injection cycles.
Now when considering a well pad or offshore platform with many wells that require gas lift stimulation, the challenge of maximizing hydrocarbon production becomes even more difficult. In many cases, there is a limited supply of natural gas available. The gas from the production separator must be treated, compressed and redistributed to the appropriate production wells.
Since each well has different production characteristics, it’s a matter of setting optimal injection rates for each well to ensure that over injection at one well is not limiting profitable production in another well. Variations in the supply of gas due to changes in compression efficiency or the production of natural gas means volume flow adjustments must made to all the wells on the system.
Also, the changes in well production characteristics, such inflow or water content, require them to be operated at a different optimal gas injection rates. Flow monitoring and control equipment must have the flexibility to maintain performance under a wide range of flows. This is true particularly in intermittent injection applications where there can be wide fluctuations in gas lift volumes.
To address these challenges, maximizing production requires optimizing gas lift injection flow rates automatically, prioritizing the gas lift supply to the most profitable wells and continuously monitoring the gas compressors to protect against common failures and unplanned shutdowns. Optimization may also be a function of the water handling capacities in the separator and water disposal systems and the gas or pipeline capacity.
An optimized gas life architecture includes compressor health monitoring, continuous well monitoring, separator control and management, and a gas lift optimizer to efficiently allocate the injected gas. Emerson’s Lou Heaver explains gas lift optimization in this quick 2-minute video.
You can also connect and interact with other oil & gas experts in the Oil & Gas group in the Emerson Exchange 365 community.