Unocal Alaska Web-Based, Gas-Lift Surveillance
Unocal Alaska Web-Based Gas-Lift Surveillance
By:
Paul Burtis and Chris Ruff
Unocal Alaska
Scott Herman
Unocal
February 5, 2002
Houston, Texas
Copyright, Union Oil Company of California, 2002
Burtis, P. B., Ruff, C. A., Herman S. R. Page 4 01/15/02
Unocal Alaska Web-Based, Gas-Lift Surveillance
Abstract
A brief overview will be presented of Unocal Alaska's recently created and installed web-based software that captures well information (e.g., gas pressures, rates, flow rates & pressures), compares the current data to defined engineering boundaries, and then alarms the engineer / technician of sub-optimized producers. The paper also discusses how this new technique is integrated with standard surveillance technologies (e.g., flowing pressure traverses, nodal, echo-meters, pressure charting) to optimize production, minimize well downtime, and optimize surveillance staff-time.
Introduction / History
Oil production operations in Alaska's Cook Inlet are mature. Initially discovered in the 1950's, cumulative recovery from this region has surpassed 1 billion barrels. Unocal Alaska operates 130 wells from 10 offshore platforms in water depths up to 150 feet in the Cook Inlet (Figure 1 depicts Unocal’s operational area). Well production from this mature basin currently averages 24,000 bopd, 190,000 bwpd and 184 mmcfpd. The fields have 87 gas lift wells, 6 electric submersible pumped wells and 43 hydraulically pumped wells. Typical wellbores include 3-1/2” and 4-1/2” tubing set in 9-5/8” production casing. A sample wellbore sketch of a gas lifted completion is included as Figure 2 (Listing of particular configurations and devices in this Figure and other parts of the paper are not intended to convey Unocal approval, but only provide a description of a representative well configuration). Pressure in many of the fields is maintained from a waterflood through 44 wells injecting 140,000 bwpd. Production was initiated in this basin in 1966 and peaked in 1976 at 130,000 bopd.
Typically, Unocal’s worldwide staff has stewarded their gas lift design and optimization work either by a gas-lift vendor-driven process or by a Unocal staff-driven process. The vendor process, which dominates in many business units, typically involves the design being provided by the service company and is based on well and equipment data that is provided to them. This process is often used in areas where the staff must prioritize this work towards the bottom of their action list. Other work that is perceived to be higher-value work or more management-visible work often drives the work day. However, gas lift design and optimization work has historically proven to be some of the most profitable production optimization work based on the low cost of the work and substantial production increases realized. Table 1 depicts a sample analysis of the work performed in year 2000.
Table 1
Unocal Alaska Gas Lift Program - 2000
Total Rate Gain (boe/day) / EstimatedFunds Spent ($ US) / # of Jobs / Success Rate (%) / Estimated
Payout (months)
2,115 / $225,000 / 15 / 87% / 0.3
Often, gas lift service companies also heavily participate in the optimization process once the wells are placed on production. This may involve yearly platform visits by the service provider to troubleshoot wells. This work typically involves a screening process by reviewing key well test parameters such as gas production and injection rates, gas injection pressures and well fluid rates. Field operators typically review daily gas lift operations and try to optimize production by varying gas injection rates and monitoring resulting fluid test rates. Additionally, two-pen tubing and casing pressure charts would be reviewed for anomalous characteristics.
However, this process often yields sub-optimized production. Troubleshooting on a timetable often results in many wells producing at sub-optimized rates if well condition change sometime before the vendor platform visit. Optimum gas lift designs are based on specified producing conditions (e.g., rates, water cuts, bottom hole pressure, etc) that are constantly changing. Timed optimization allows wells to produce at below-par rates for extended periods of time.
Additionally, farming the design out to the service company leaves many important staff uninformed about key operating parameters that are required to optimize gas lift production. If the production engineers and field operators do not know injection pressures, volumes, and depths, then recognizing sub-optimum production is often impossible.
The Unocal Alaska-driven surveillance process utilizes three key elements to optimize production real-time. These include the following:
- Dedicated Staffing – Based on the perceived value of optimized gas lift production, a technician has the defined responsibility of stewarding all gas lift operations in Unocal’s Cook Inlet wells. This includes working with the field staff to quickly identify problem wells, keeping nodal models on all gas lifted producers that have been validated by flowing pressure traverses, and to make repair recommendations to Field Management. Engineers are then freed up to focus on higher capital-intensive drill well, workover and facility upgrade programs.
- Informed decisions based on data - Flowing pressure traverses, nodal models, two-pen charting and acoustic surveys are regularly performed to ensure each well’s optimum producing ability is known. Figure 3 depicts a flowing pressure traverse representation that is performed. With the assistance of the nodal design and vendor valve characteristics all key operating parameters are known and stewarded. Table 2 list the number of surveys conducted in Unocal Alaska’s Cook Inlet
Table 2
Unocal Alaska Surveillance Program - 2000
PBU’s / Flowing Pressure Traverses / Nodal Models / Acoustic Fluid Levels & 3-Pen Charting7 / 14 / 25 / 15
Listed below are some metrics relating the level of Unocal Alaska optimization work performed in 1999 to the number of their active completions (based on offshore Cook inlet well counts dated 10/14/99)
· Gas lift optimization work performed on 19% of active gas lift completions.
· Flowing pressure traverses run on 34% of active gas lift completions.
· Gas lift diagnostics run on 30% of active gas lift completions.
- Web-assisted surveillance – A web-based tool that was created to monitor waterflood performance was adapted to steward the gas lifted production. Upper and lower control limits on fluid rate, oil rate, formation gas, tubing pressure, gas-oil ratio, gas injection pressure, and gas injection rates are defined and automatically flagged if they are exceeded. The web tool is described in more detail below.
Web-Assisted Surveillance
A web-based system was created initially to track waterflood injectors since upgrades were needed for Y2K compliance. Web technology changes led to these new possibilities including well test monitoring and then a “One-Stop Shop” for all well surveillance data. This included wellbore data, well histories, well service reports, logs, well status and tests and key surveillance data Figures 4, 5 and 6 depict sample pages from the web site.
The process included the following basic steps.
- Run computer surveillance report web page.
- Review exceptions.
- Go to the tabular and graphical data to determine the type of problem.
- Go to basic well data to obtain more information (e.g., histories, schematics, directional surveys, etc.).
- Review and adjust guidelines (control limits), contact the foreman or identify further analytical work.
The benefits of this system included the following:
- Identified problem wells earlier.
- Integration with the field for better gas lift optimization.
- Minimized time searching for and gathering data.
- Increased reliability of data due to single source.
Results / Impact
The program has resulted in a 390 bopd rate increase (3%) from an expense of $83,000 from 8 wells in the year 2001. Typical payouts range from 12 days to 30 days.
Before the surveillance program was initiated, a problem well could go unnoticed for over 60 days. This was mainly due to the time it took to review well tests for hundreds of wells. The well surveillance program is run on a daily basis and well work can be accomplished within 48 hours after the program flags the well. The average loss in production from a well that was having problems, such as a decaying gas lift design, was ~50 bopd. The resulting 2001 program revenues from this production were $480,000 US.
Future Plans
Based on the need to optimize production and staff time, future plans include expanding the use of web-based surveillance tools to the following.
- Equipment surveillance (Done Fall 2001 with email notification).
- Pipeline surveillance (Done but not yet implemented).
- Environment surveillance.
- Further automate surveillance notifications via email, cell phones, etc.
- Automate data capture.
Additionally, corporate programs are focusing on taking this real-time surveillance data (including drilling and workovers) and feeding it directly into reservoir surveillance and other PC applications. The program objective is to only handle data once so that it will optimize performance, staff-time and data quality.
CONCLUSIONS
- Gas lift completions require more continuous surveillance to provide optimum returns to the operator and the use of web-based tools enables this.
- Web-based technology is available (either developed internally or off-the-shelf) to push notification of sub-optimum performers to the operator.
- This technology requires the operating staff to understand the key gas-lift metrics and to input them into a database. Once done, the staff time is optimized by letting them focus on other capital intensive projects.
ACKNOWLEDGEMENTS
The authors wish to thank the management of UNOCAL ALASKA for permission to publish this paper.
REFERENCES
1. Harris, J. L. , Shipp, D. D.,: “Application
of ESP Technology in Alaska’s Cook Inlet
Reservoir and Electrical Challenges”, Paper presented at the 19thth annual SPE Electrical Submersible Pump Workshop, Houston, TX. April 2001.
Burtis, P. B., Ruff, C. A., Herman S. R. Page 4 01/15/02
Unocal Alaska Web-Based, Gas-Lift Surveillance
FIGURE 1
Unocal Alaska Operations Map
FIGURE 2
Typical Unocal Alaska Gas-Lift Completion
FIGURE 3
G-15RD Gas lift Flowing Pressure Survey Results
FIGURE 4
Web-Based Gas-Lift Design / Operation Control Limits –Input Page
FIGURE 5
Web-Based Gas-Lift Design / Operation Control Limits – Surveillance Page
FIGURE 6
Web-Based Gas-Lift Design / Operation Control Limits – Surveillance Page 2
Burtis, P. B., Ruff, C. A., Herman S. R. Page 10 4/25/01