Lift Gas Optimization

Lift Gas Optimization

Introduction

Lift gas optimization maximizes oil production and the financial performance of gas lifted wells, non-naturally flowing wells. It involves optimizing gas lift injection flow rates and prioritizing lift gas supply to more profitable wells. It is used for allocating lift gas to wells with desired compositions, assigning priority to wells for financial and ownership considerations, and continuously monitoring lift gas compressors to constrain lift gas injection to protect against compressor failures and unplanned shutdowns.

What is gas lift injection?

Gas lift injection is the process of injecting compressed natural gas into oil wells through downhole gas lift valves to lift the hydrocarbon fluids in the well. The lift gas reduces the oil density in the production tubing, and the drag of rising gas bubbles results in increased volumes of liquid rising to the surface. If one over-injects lift gas, decreased production may result due to higher production pressures and “foaming” of the lift gas within the production liquid.

What is a “Lift Curve”?

A well’s production rate as a function of the lift gas injected is called the “Lift Curve”. It is highly non-linear, climbing asymptotically to peak production, then declining again as over-injection increases. This lift curve is not simple, however. It is actually a “Lift Surface”, as the lift curve is also influenced by operating temperatures, wellhead pressure, reservoir pressure, and possibly other factors. Peak production is an ever-changing optimal point on an N-dimensional undulating surface.

Every well has its lift curve, and each well has different production characteristics because of well geometries, such as tubing diameter and casing length, and differing rheology, which can range from low-density amber crude to black “gloppy” emulsions. Additionally, well temperatures vary and operate in ever-changing pressures, production decline, and more.

What is a Gas Lift Optimization?

Lift gas optimization allocates available lift gas to maximize overall production, minimize costs and achieve other business objectives while operating within constraints such as compressor limitations, water production, and total liquid production rate capacity and downstream interactions of wells.

The Benefits of Optimizing Lift Gas

Lift gas optimization results in a variety of benefits:

  1. Higher Production, especially from aging fields. 15% gains are typical in our experience.
  2. Reduced Length of Operation of Fields. This reduces overall expenditures and HSE risks.
  3. The Best Economic Return.
  4. The Best Lift Gas Allocation.
  5. Inherent Compressor Monitoring.
  6. Inherent Multi-Phase Virtual Metering of Each Well, Pads, Platforms, and Central Processing.
  7. Justifies Advanced Analytics of All Aspects of Your Production Operations.

The Process of Lift Gas Optimization

  1. The first step is to digitalize your wells, test and production separators, pressures, and temperatures at the wellhead and production network. This is necessary to characterize the state of your wells, both during tests and in real time.
  2. Have a history of process conditions and test rates for each well. If you don’t have this, we can supply it.
  3. Execute multi-rate tests, varying injected gas rate while on test, capturing well test rates for gas, oil, or liquid.
  4. We model the operating conditions and lift gas rates vs. production for each well. Inherent in these models is each well’s gas lift performance curve (multi-dimensional lift surfaces).
  5. We gather your constraints, including available lift gas and other compressor constraints, and downstream production handling capacity, so we don’t overrun separators and hard limits on maximum and minimum lift gas for each well.
  6. For single well optimization, we “invert” the models to create Model Predictive Control (MPC). This allows you to put setpoints on each wells’ production if you like.
  7. For multi-well optimization, we generate live lift curves considering current well conditions, then walk back lift gas from individual wells’ peak production until one or more constraints are met. Essentially we dial back the well with the least change in production for lift gas employed, that is, the least slope at that step in the process. This results in the best allocation of lift gas within and bumping up against constraints. This is repeated on a frequency that makes sense for your asset.

This optimization can also include free-flowing wells by including the forward walk of production vs. FTHP (flow tubing header pressure) or other downstream pressure as wells interact in crude oil production networks. Electric submersible pump and other artificial lift method wells can also be included.

Conclusion

Lift gas optimization is a valuable tool to determine optimal gas injection rates and liquid production from your wells while respecting all constraints necessary for successful and safe operations while achieving your production target. It can also set lift gas rates on individual wells if single-well production optimization is desired. We would welcome the opportunity to discuss lift gas optimization to maximize production for your production wells and your entire assets with you in more detail.