In Malaysia, most of the production wells depend on an artificial lift to achieve an excellent flow. Among many artificial lift methods, operators find gas lift as the most reliable and commercially effective to optimize production. The challenges to always make the Inflow Performance Relationship (IPR) curve and Vertical Lift Performance (VLP) curves intersect with each other being the bread and butter of every Surveillance Engineer’s task to ensure continuous production flow of their assets.
So, why do we need production optimization?
As the reservoir and well age, properties of production flow change such as increasing water cut, lowering Gas-Liquid Ratio (GLR), reservoir pressure drops, flowing bottom hole pressure increases, more sand production, flow assurance issues, etc. These changes mainly affect the gas lift design system, which is used since the unloading process of the well took place. Remember! A gas lift system is connected to all the other wells in the asset. Thus, if one well is being imparted due to poor gas lift surveillance, it will affect the entire production system. Usually, they blame the Gas Lift System if a well is experiencing production hampering.
So, what are the things that need to be surveilled for an optimized Gas Lift System?
- Are your wells being lifted from the optimum injection point or depth?
- Are your wells experiencing multi-pointing?
- Is the gas lift injection rate used over/under injected?
- Is the gas lift injection pressure over/under pressure?
- Are you using the optimum port size for your gas lift valves?
- Is the gas injected being robbed for dual string applications?
- How much back pressure from the wellhead and flowline affecting your fluid flow?
- Is the production tubing sized correctly?
- Most importantly, are your production flow properties (well test) being tested regularly and how accurate is the data obtained?
Figure 1 Adopted from ©AppSmiths Technology 2017, AppSmiths® Basic Gas Lift Class – Session 3
So, what are the tools/method available to aid Gas Lift Optimization?
- Real-time Monitoring & Analytics System (Mini well test)
- Static and Flowing Gradient Survey
- Permanent Downhole Gauge (PDHG) Data
- Tubing Integrity Test (TIT)
- Installation of Distributed Temperature Sensor (DTS)
- Installation of Digital Intelligence Artificial Lift, DIAL® valves
- WellTracer® Survey
Among the methods stated above, WellTracer® can cover every important parameter to optimize a gas lifted well. WellTracer® has the advantage to analyze dual string wells without needing to do an intervention. Hence production can continue even during the survey period.
So, what is WellTracer®?
- Around 40-50 lbs. of CO2 gas is injected into the A-annulus of the well via a gas lift injection line.
- The concentration of the injected CO2 gas is recorded at the wellhead.
- The injected CO2 gas traveled along with the gas lift injection gas in the annulus and u-tubing back to the production tubing via any communication port between the production tubing and A-annulus such as, via Gas Lift Valves, SSD, or any holes on the tubing.
- The velocity of the traveled CO2 gas from the A-annulus to the production tubing to reach the surface is calculated and correlated with the depth of entry point/u-tubing point in the well. Hence, every depth of communication between annulus and production tubing is determined.
What are the outputs of the WellTracer® Survey?
- Identification of primary point of lifting/gas lift injection depth.
- Identification of multi-pointing resulted from holes on the tubing or leakage of unloading or dummy valves.
- Multi-pointing determination that gives an estimation of the percentage of gas entry/concentration on various entry points.
- For dual string wells, the percentage of gas lift robbing can be quantified.
- Analysis of the results indicates various gas lift optimization opportunities such as optimum injection depth, optimum injection pressure (over/under pressure), the optimum injection rate (over/underrate), the possibility to bean up the well with sand control advice, the possibility to deepen the gas lift injection point for greater outflow, the needs for a gas lift valve changeout and the needs for installation of tubing patch to remediate tubing holes.
Advantages of WellTracer® Survey?
- No well intervention required. That means production continues even during the survey period.
- Minimal equipment needed and lesser hook up and commissioning period.
- Very suitable for wells that are flowing unstable such as pressure survey showing inconclusive results.
- Lesser HSE complications as minimal crew needed to conduct the survey.
- Results can be used to verify gas lift and production models built-in software such as Prosper and Winglue.
- Able to troubleshoot unstable wells, giving a picture of what happens when the well is surging or slugging.
- Able to understand production behavior more precisely in dual string wells covering gas robbing issues, gas lift split ratio, and gas lift valves performance dynamically during injection through common/annulus sharing.
- Gives an overall indication of whether a well is gas lifted, overbalance/underbalanced versus the productivity index of the well. This reflects greatly in reducing the lifting cost of the well.
If you would like to know more about WellTracer® do feel free to send us an email here at email@example.com and we will be more than happy to share some insights with you.