Gas Lift
This page shows detailed performance, gas traverse, production, IPR/VLP performance of gas lift specifically.
The following are the numbered sections of this page which are explained further below:
On expanding well panel, we can select wells from a list of the wells as per asset selection. The following is the key information in the Well selection panel:
- Arrange by - Grouping wells as per group.
- Well Name – Single well selection is available.
- Lift Type (in front of well names – such as GL). For example:
- W-GL Well 59
- Error or warning (in front of Lift type) - for example “W-GL Well 90” has a warning with respect to Gas Lift Valve depth > End of Tubing
Please note that it is possible to select only single wells on this page. The data gets refreshed based on the selected well from the well panel.
For analysis of a particular date, the user can select the date from the top right corner. In addition to the date, a user can update the settings that affect the way gas lift performance curve.
- Oil Price – It defines the revenue function for the produced oil.
- Gas Price – It defines the revenue function for the produced gas.
- Water handling cost – It defines the cost function for the produced water.
- Gas buyback cost – It defines the cost function for the injection gas.
- Min Gas Lift Rate – This is the minimum boundary condition to ensure that we can inject the gas into the well in a stable manner.
- Max Gas Lift Rate – This the maximum boundary condition to ensure that we can inject without causing any integrity or capacity issues.
- Performance curve Step size – This is the step size by which the algorithm increments the gas injection rate to see the impact on the overall revenue and cost function. (Note: Additional steps will be added near to the critical rate)
- Oil Rate Increase Threshold – This is the minimum oil rate increase required for the next iteration of increasing gas injection rate to see the impact on the overall revenue and cost function.
- Consider Liquid loading for Oil – The liquid loading check is applicable for a gas producing well, this flag can be used additionally if the overall gas production is at a higher level, and we might encounter liquid loading.
- Use 7-day median inputs – This is a setting to input a stable injection rate rather than a fluctuating gas injection rate for the optimization process.
Clicking on the wellbore diagram option gives a pictorial view of the wellbore diagram with the details such as casing, tubing, packer, gas lift valve, ESP, formation, etc. Also, a deviation survey is available.
Users can select a date from the dropdown menu to see the applicable downhole equipment.
- Moving the cursor to the tubing displays a summary of tubing information.
- Moving the cursor to the casing displays a summary of casing information.
- Moving the cursor to the formation displays a summary of formation.
In addition to wellbore diagram, wellhead diagram provides a pictorial view of the latest reading of the surface parameters and subsurface parameters:
- Surface Parameters (Pressures)
- Tubing pressure
- Flowline pressure
- Casing pressure
- Choke settings
- Surface Parameters (Rates)
- Oil Rate
- Water Rate
- Gas Rate
- AL Parameters - GL Injection Rate or ESP Frequency
- Subsurface Parameters - Downhole gauge pressure
Gas lift performance curve is calculated using a sensitivity on Gas Lift injection rate and corresponding effect on production parameters.
To generate this gas lift performance curve for a particular day, reported CHP, THP and Gas Injection rates are used along with valve data (such as R value and PTRO).
First, a production and injection traverse are computed simultaneously from the surface node down to the first gas lift valve. The production traverse assumes a total gas rate of produced gas + injected gas from the surface to the first valve. At the first valve, downhole opening and closing pressures are computed by calculating the dome pressure (closing, PVC), and then using the R-value and production pressure to determine opening pressure (PVO). See the section below for more details on opening and closing pressure calculations. Then, using the injection pressure at depth, a comparison is made to PVO/PVC to determine if that valve is open flowing, open not flowing, closed, or "likely closed" (indeterminant state with injection pressure between PVC and PVO).
If the valve is open, the modified Thornhill-Craver (TC) equation (default) or API RP 11 V2 is used to compute the gas flow rate through the valve, depending on configuration and available data. See below sections for more information.
Any remaining injection gas that cannot pass through the first open valve will be assumed to travel downward. The traverses continue downward, with gas rates modified accordingly to the next valve, where the previous step is repeated to check valve status and flow rate through the valve, if applicable. Any valves deeper than the intersection of the production and injection traverses are considered submerged.
The following diagram illustrates the methodology.
Finally, a BHP is calculated and using the IPR (Inflow performance relationship) for this day, all phase rates (Oil rate, Water rate, and Gas rates) are estimated. Using these rates, a cashflow value is estimated using the following formula and Performance Curve Settings:
The same process is used for multiple gas lift points as per settings discussed in Date Selection and Settings.
As per the Date Selection and Settings Performance Curve Settings, the curve is generated between the “Min Gas Lift Injection Rate” and “Max Gas Lift Injection Rate” using a step change as per “Performance Curve Step Size”.
There are two types of opportunities:
- Decrease in the Gas lift injection rate and hence reduce the operation cost.
- Increase in the gas lift injection rate and corresponding increase in oil production in a way that the revenue increase due to additional oil supersedes the cost increment due to additional gas lift injection rate.
A few considerations while reviewing “Copilot opportunities”:
- Even if the “Critical Rate” is non optimal (not a max point on cashflow curve), it is the recommended opportunity if the max point on the cashflow curve is towards the left-hand side of “Critical Rate” – an unstable point on the performance curve.
- “Oil Rate Increase Threshold” setting is honored if the current operating point is more than “Critical Rate”.
- “Oil Rate Increase Threshold” setting is ignored in case well’s current operating point is below “Critical Rate”. In these cases, you might see a very minimal Oil rate increase opportunity.
In this section, inflow performance relationship and vertical lift performance (IPR and VLP) are plotted for two cases:
- Current operating point
- Well Test operating point.
Using this section, a user can quickly compare the well performance and operating points with respect to the well test data. A proximity of these points suggests greater confidence in the daily reading before a user can make an optimization decision.
Solid line below represents the daily value, and dotted line represents the well test information.
The following parameters are displayed:
- Oil – Measured value of daily/allocated readings.
- Gas – Measured value of daily/allocated readings.
- Gas injection rate – Measured value of daily readings.
- Water – Measured value of daily/allocated readings.
- Well test rates (As triangular icons)
- Test oil rate.
- Test gas rate.
- Test water rate.
- Set Point Change – If there is any recommendation for setpoint change, it would be available here.
- Optimal** – This trend shows the daily recommended optimal gas lift injection rate.
- Gauge Pressure - Measured value of Gauges available from daily readings.
- Calc BHP (Gauge) – Calculated BHP value using correlation at gauge.
- THP – Measured value of daily readings.
- CHP – Measured value of daily readings.
- Well test rates (As triangular icons)
- Test THP
- Test CHP
- Depth of Injection – This trend shows the daily recommended optimal gas lift depth.
Note – A consistent optimal gas lift injection rate is a good indicator of the required adjustments in the well operating point. As daily readings are sometimes prone to sudden spikes and outlier readings, users need to check whether the recommended optimal gas lift injection rate is consistently reported before making a final decision.
This table shows detailed information about downhole valve calculations. Clicking on a row will expand the full performance curve for that valve.
This is applicable for shallow injection, lift integrity, end of tubing injection and multivalve injection anomaly.
This anomaly is generated when:
- We have enough CHP to inject into a deeper valve.
- Due to the calculated status of PVO, PVC, a shallower valve is intaking complete injected gas.
This is a suboptimal production situation in which we can adjust valve parameters in a way that the injection occurs through deepest valve.
This anomaly is generated when:
- All the valves are closed as per PVO and PVC calculations using PTRO and d values.
- There is no packer in the well.
- At the end of the tubing, calculated CHP is greater than THP with a difference of greater than 50 psi.
This anomaly is generated when:
- As per the calculated pressure traverse in the annulus section and tubing section, all valves are closed as per the calculated PVO and PVC values.
- There is an actual gas lift injection (due to tubing in hole)
This is an integrity issue for further validation and improving optimization opportunity by injecting to deepest valve.
This anomaly is generated when:
- We have multiple valves open as per the calculated pressure traverse in tubing and casing, and calculated PVO and PVC values.
- Out of the open valves, the topmost valve is unable to ingest all gas. So, the remaining gas is passed through the next valves. For the calculation reference please refer to Gas Lift Performance and Traverse Curve
Below is the main dashboard for model settings of gas lift optimization.
- Oil Price – It defines the revenue function for the produced oil.
- Gas Price – It defines the revenue function for the produced gas.
- Water handling cost – It defines the cost function for the produced water.
- Gas buyback cost – It defines the cost function for the injection gas.
- Min Gas Lift Rate – This is the minimum boundary condition to ensure that we can inject the gas into the well in a stable manner.
- Max Gas Lift Rate – This the maximum boundary condition to ensure that we can inject without causing any integrity or capacity issues.
- Performance curve Step size – This is the step size by which the algorithm increments the gas injection rate to see the impact on the overall revenue and cost function. (Note: Additional steps will be added near to the critical rate)
- Oil Rate Increase Threshold – This is the minimum oil rate increase required for the next iteration of increasing gas injection rate to see the impact on the overall revenue and cost function.
- Consider Liquid loading for Oil - The liquid loading check is applicable for a gas producing well, this flag can be used additionally if the overall gas production is at a higher level, and we might encounter liquid loading.
- Use 7-day median inputs – This is a setting to input a stable injection rate rather than a fluctuating gas injection rate for the optimization process.
- Well Test Gas Lift Performance Override Toggle - When enabled, the platform will utilize well test rates and pressures as inputs to calculate the Gas Lift performance curve exclusively on well test days. For non-well test days, calculations will revert to using allocated production data.
- Well Test Opportunity Toggle - When enabled, opportunities will be generated and displayed on the well performance dashboard for well test days only. On days without well tests, no opportunities will appear on the dashboard.
