An industry consortium works to advance the difficult task of artificial lift in difficult-to-produce wells.
by By Cleon Dunham, Oilfield Automation Consulting Upstream Pumping Solutions Editorial Advisory Board
August 1, 2012

The majority of new wells drilled for both oil and gas production are horizontal. At some point, most will require artificial lift to produce the liquid hydrocarbons and/or dewater the gas wells. However, artificial lift of horizontal wells presents many challenges. It can be particularly challenging in the shale assets, where wells are often deep with long lateral sections.

To address these challenges, the Artificial Lift R&D Council (ALRDC) invited several companies to form a consortium to develop new methods and understanding for advancing the artificial lift of these wells with more than 20 companies attending the kickoff meeting. The R&D work for this consortium is being led by the University of Tulsa. This article discusses the status of this effort and presents some of the challenges that consortium members face.

Industry Trends

The face of the hydrocarbon production industry has changed dramatically during the last few years. The largest change is the production of natural gas, condensates and oil from shale formations. Figure 1 shows the major shale basins in the world—not including unassessed areas in Russia; China; and parts of South America, Africa, the Middle East and Southeast Asia. The potential is enormous.

Figure 1. Major shale basins of the world

Production of gas and oil from shale formations requires drilling, completing and operating horizontal wells. These are needed to contact large portions of the reservoirs and the natural micro fractures they contain. The wells must be treated with multistage hydraulic fractures to allow oil and gas to flow from the reservoirs to the wellbores. Figures 2 and 3 show the horizontal wells that have been drilled in the Marcellus Shale in Pennsylvania and the Barnett Shale in Texas. These are only two examples of the development activity, but they show the significant rate of increase during the last few years.

Figure 2. Marcellus Shale wells drilled

 

Figure 3. Producing Barnett Shale wells

 

Producing horizontal wells presents many challenges:

  • Much of the water used to fracture the wells must be produced back from the formations to reduce back-pressure and clear flow paths for gas and oil production.
  • Often some of the sand used to prop fractures open will be produced with this water. Both the water and sand must be artificially lifted.
  • Most artificial lift systems are designed to work in vertical sections of wells. Methods must be developed to help sweep and lift fluids from the deviated and/or horizontal portions.
  • Most horizontal wells are not actually horizontal. Figures 4 and 5 show typical basic and complex horizontal well profiles. These vary from “toe up,” to essentially horizontal, to “toe down.” Each profile presents special production challenges.
  • Often the horizontal portions of the wells have up and down undulations (see Figure 6). Water can accumulate in the low spots and be produced to the vertical part of the well in slugs. This can make artificial lift challenging, especially when using pumping systems. There is a need for improved understanding and models to determine the critical gas flow velocity in horizontal wells. Reasonable methods exist to determine the critical velocity needed to lift liquid from vertical gas wells.

Figure 4. Basic horizontal well profiles

 

Figure 5. Complex horizontal well profiles

 

Figure 6. Typical undulations in horizontal wells

 

Horizontal Well Consortium

The goal of the Horizontal Well Consortium is to work cooperatively in the petroleum industry to:

  • Develop recommended practices for the artificial lift of horizontal wells
  • - Make recommendations for the design and operability of horizontal wells with regard to artificial lift
  • - Improve the selection, deployment, operation, maintenance, monitoring and control of production and artificial lift solutions, equipment and practices to optimize the recovery of natural gas and associated liquids from horizontal oil and gas wells
  • Advance the knowledge and effectiveness of people who design and operate horizontal wells

Survey of Operating and Service Companies

A survey (see Figure 7) was conducted of interested companies to understand their challenges and priorities for dealing with horizontal wells.

Figure 7. Survey results

The highest priority items that the companies feel should be pursued are:

  • Investigate flow pattern behavior and development of new/improved models for understanding flow and critical rate in horizontal wells.
  • Make recommendations for well geometry and wellbore trajectory. Is the best wellbore trajectory toe up, horizontal or toe down? Reasons may exist to avoid undulations in horizontal wells. The pros and cons of drilling sumps before the heel of the wellbore need to be understood.
  • Understand well design issues—such as placement of end of tubing, location for gas injection and size of casing needed. A need exists for evidence to support recommendations for using casing sizes large enough to accommodate optimal types of artificial lift systems.
  • Choose the optimum method of artificial lift for horizontal wells. The ALRDC has historically sponsored industry efforts to develop information and methods to assist in selecting the best or optimum method of artificial lift for wells. Recommendations and guidelines are needed for which method(s) of artificial lift are most suitable for different horizontal well operating conditions.
  • Conduct a comprehensive review of all available literature to determine current best practices for artificial lift of horizontal gas and oil wells.

This list is not exhaustive. New ideas will be generated as this project unfolds..

Consortium R&D Plan

The priorities will be addressed with four projects. Other projects will likely follow as the work of the consortium continues.

• Project 1—Understand flow regimes and critical flow rates and investigate multiphase flow behavior in horizontal gas wells

- Deliverables

  • Understanding of liquid loading in horizontal wells
  • Liquid loading criteria
  • Experimental data
  • Efficiency of self-unloading while wells still flow on their own
  • Guidance to determine optimum horizontal well geometry from the unloading perspective

• Project 2—Investigate artificial lift techniques in horizontal gas wells, which will help with:

- Selection of optimum method(s) of artificial lift in horizontal wells

- Placement of end of tubing; location for artificial lift equipment (pump, gas lift); and casing size

- Design of well construction and applicability for different artificial lift techniques

- Deliverables:

  • Unloading performance of various artificial lift methods and their comparative analysis
  • o Tubing inserts
  • o Gas lift
  • o Surfactants
  • o Pumping systems
  • Impact of slugging on the performance of artificial lift
  • Experimental data
  • Analysis of setting the location of artificial lift equipment

• Project 3—Develop guidelines and recommended practices for horizontal gas wells

- Summarize industry education and literature information

- Develop guidelines for when to start artificial lift operations in horizontal wells

- Deliverables:

  • Database consisting of both field and experimental data
  • Analysis of the data
  • Guidelines and recommended practices based on field and experimental data

• Project 4: Investigate multiphase flow behavior in horizontal oil wells

- Deliverables:

  • Understanding of the oil dominant flow behavior of horizontal wells
  • Experimental data
  • Model describing the flow behavior

Consortium Status

Currently, seven member companies make up the consortium. More are expected to join. The consortium will officially begin its work in summer 2012. The next meeting will be in August 2012 at the University of Tulsa. A tentative R&D timeline has been developed (see Figure 8) for the organization.

Figure 8. Tentative Consortium R&D Timeline

Horizontal Well Artificial Lift Consortium Membership

Membership in the consortium is open to any operating company, service/supply company, consulting company or university. The membership terms are detailed in a letter of agreement that has been supplied to interested organizations and can be made available to any other interested organization. No member company may sell, give or otherwise make results available to any non-member of the consortium without the expressed permission of the consortium advisory board. For more information, visit www.alrdc.com.