The Workflow
A major consideration for gas producers is liquid loading. At OVS, we have worked with several of our clients to add surveillance capability for liquid loading to their suite of automated workflows. With these surveillance tools early detection of liquid loading has been enabled, giving these clients advanced notice to plan for strategies to optimize production.
OVS uses critical gas rate predictions or historic trends to alert the production team to a potential problem and makes them available in the normal review systems. In addition to surveillance, these clients have also implemented sensitivity analysis to allow evaluation of potential changes to well equipment or operating conditions and measure their effect on the critical gas rate.
The Challenge
The Critical Gas Rate is the flow rate that has enough velocity to carry liquids such as condensate, oil or water. Wells that decline below this gas rate allow liquids to slip into the gas column and begin to accumulate in the well or “load up”. As the accumulation of liquids continues, gas rates will become erratic and eventually slow or stop production.
Identifying liquid loading early helps to avoid production delays or production losses. Empirical correlations are a common method for predicting the onset of liquid loading. A second method for detecting liquid loading is to look for changes in production profiles, such as a drop in water production or the ratio of water to gas. Changes in tubing and casing pressures could also be used to indicate potential liquid loading.
Production teams have thousands of wells to monitor for all sorts of issues. Applying correlations to all the wells or screening wells for subtle inflections in production or pressure profiles becomes a time-consuming task. As a result, the discovery of liquid loading is frequently made well after it has begun resulting in lost production.
The Solution
To satisfy the need for early detection of liquid loading, OVS has worked with its clients to implement surveillance by exception. Surveillance by exception (SBE) automatically directs the attention of engineers and operators to operational conditions that need attention.
For predictive liquid loading SBE, OVS automatically applies correlations such as Turner or Coleman to establish the critical gas rate. When a well’s production is within a certain range of the critical gas rate, say 10%, the engineer or operator will have that well added to their alert list. In addition to being useful in SBE, the results of the calculations are included in other tools such as the Well Review or Production Data Analysis.
Another surveillance option is to use OVS to evaluate trends indicating that liquid loading may have begun. The workflow will compare gas rates to target, water rates (or WGR) to previous values, tubing/casing differential pressures, or an increase in variability (gas spikes). If an alert condition is detected the team will be notified.
OVS also provides a sensitivity analysis allowing the engineer to use the correlations to evaluate how changes in the well could affect the wells ability to unload the well.
Final Thoughts
The SBE workflows have been applied in many areas using OVS. For clients operating gas wells, it has proved valuable in providing actionable alerts for wells showing signs of liquid loading or predicting possible onset. With this information the team can plan for future artificial lift or other intervention before production rates are significantly affected.
