Gas Lift Optimization and Design Program (GLOP)

Program Overview

Developed on the concept of system analysis, the program includes the complete flow path of a gas lifted well.

• Mechanistic Models for Vertical Multiphase Flow: GLOP utilizes two mechanistic models for proper handling of multiphase flow in vertical and deviated well. These models include Chokshi, Schmidt and Doty model (which has been developed by GLOP developers based on extensive research at TUALP) and Ansari model. The mechanistic models can be utilized to predict tubing performance for a wide range of flow conditions since they are derived from fundamental mass, momentum equations.
• Valve Dynamics: GLOP is the only software that contains dynamic flow performance of the gas lift valves. The developers of GLOP conducted research in this area for over ten years.
• Casing Flow Stability: GLOP is the only software that checks for stability of the designed installation based on Alahanati et al. criteria. This feature alerts the designer about possibility of casing heading, and offers helpful solutions to eliminate the instability.
• Unloading Valve Design: Interaction between casing-tubing annulus and reservoir is taken into account while designing unloading valves. This results in less of unloading valves than the conventional approach. This is very important for fields with low bottom hole pressure but very high productivity.
• Choice of three design methods: (Injection) Pressure Operated Design; Proportional Response Design; and Fluid Operated Design.
• Troubleshooting: GLOP can determine wether your current installation is operating properly. Valve settings and production conditions are taken into account for predicting the operating status of the valves. Troubleshooting for all three types of valves is supported.
• Dynamic Unloading Simulation: GLOP captures the transient nature of the gas-lift unloading process by simultaneously solving time dependent mass, momentum and energy balance equations for multiphase flow.
• Hydraulic Tables: Some reservoir simulators use hydraulic tables to couple wells and reservoir. GLOP can generate these tables for ECLIPSE reservoir simulator.
• Field Tested: GLOP is used by over 80 gas lift specialists all over the world. The feedback from these specialists has helped us in keeping our product on the forefront of technology.
• Easy-to-use Windows interface: This powerful program has user-friendly Windows interface to boost your productivity. Point-and-click editing charts, data access tool bars are a few of user interface features.

GLOP Gas Lift System Analysis

• Comparison of multi- phase flow correlations with well data.
• Gas lift performance.
• Installation design.

Multi-Phase Flow Correlation Selection
If actual field production and pressure data are entered, the program will compare them graphically with the multi-phase correlation flowing pressure traverses, so the "BEST FIT" can be selected.

Gas Lift Perfomance

The system is analyzed to determine the potential production rate of the well and the injection gas requirement. The results are used to calculate the installation designs; - valve depths, sizes and adjustments - for unloading and producing the well at the desired rate.

Installation Design

After a design rate is selected, design runs can be made to properly space unloading valves and the operating valve. Appropriate valve settings are also calculated during an installation design nun. GLOP supports the following design methods:
 

• Injection pressure operated
• Production pressure operated
• Proportional response

Each of these methods can be used for a new design or a re-design with side pocket mandrels in place. Actual gas lift valve flow performance for several valve manufacturers is available, or a modified Thornhill - Craver equation can be selected.

Design Options

A multitude of design options offered in GLOP provides you with great flexibility to analyze or design a system that best matches yours. The options include:
 

• Minimum unloading rate
• Minimum gas injection pressure drop to start injection can be selected
• First unloading valve location can be adjusted by using the following:
• Higher "kick-off" gas injection pressure
• Lower well head pressure (pit)
• Spacing gradient less than the "kill fluid"
• Static liquid level and flow back into the reservoir
• Spacing of the unloading valves can be adjusted by using the following criteria:
• Selecting valve size and number during calculation process.
• Spacing gradient less than the "kill fluid"
• Increased transfer pressure
• Design flowing temperature can be selected between the limits of the flowing model profile and the Geothermal gradient
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• Operating valve - either a valve or an orifice can be used.

Hydraulic Table Calculations for Reservoir Simulator
Reservoir simulators use hydraulic tables to couple wells to the reservoir.  GLOP can generate hydraulic tables for Eclipse reservoir simulator.

Transient Unloading Simulation
GLOP's unloading simulator captures the transient characteristics of an unloading process by simultaneously solving the time dependent mass, momentum and energy balance equations using a finite difference scheme.  The simulator takes into account the valve performance and interaction between the wellbore and reservoir.

Systems Analysis
Tubing performance curves for outflow sensitivity parameter and user defined gas injection rates versus Inflow performance curves for inflow sensitivity parameter, are plotted.
 

Reservoir and Perforations or Gravel Pack
Four methods of calculating inflow performance are available:

• Straight Line (Constant Productivity Index) - this method assumes a linear relationship between the flow rate (through sections 1 and 2) and the flowing bottom hole pressure.
• Vogel - this method uses a linear equation for pressures above the reservoir bubble point and a  non-linear equation below the bubble point
• Darcy - this method calculates the productivity index from the reservoir and fluid data.
• Fetkovich - this method uses non-linear equations and requires measured data sets (flow rates with corresponding flowing bottom hole pressures - min. 2 sets).

Tubing / Casing

The calculations performed for this section consider the following:
 

• Tubing or Casing-annulus as production flow conduit or combination thereof.
• Tapered tubing or casing configuration.
• Well deviation profile.
• Gas lift mandrels in place
• Multi-phase flow using currently accepted correlations and mechanistic models:
• Chokshi, Schmidt, Doty Mechanistic Model --  Hagedorn & Brown
• Ansari Mechanistic Model  --  Duns & Ros
• Aziz, Govier & Fogarasi -- Orkiszewski
• Beggs & Brill
• Flowing temperature profile:
• Mathematical flowing temperature model.
• Linear gradient
• Fluid PVT Correlations:
• Standing -- Lasater
• Vazquez &Beggs -- Glaso
• Kartoatmodjo & Schmidt

The calculations performed for this section consider the flow restriction caused by the reduced diameter of a sub-surface safety valve.

Well Head Choke

The flow restriction caused by the well head choke is calculated for this section.

Surface Flowline

The flow line calculations performed for this section consider the following:
 

• Flow line profile, length, and size.
• Horizontal multi-phase flow using current correlations.

The separator operating pressure and temperature define the end conditions of the flow path.

Lift Gas Supply Source

The lift gas supply operating pressure, temperature and allocated injection rate are important factors in the analysis.
 

Sensitivity Analysis

• Productivity index
• Reservoir pressure
• Combination of the average reservoir pressure and productivity index
• Perforation shot density

Outflow
The effect of changes in the following outflow parameters can be studied:
 

• Production flow conduit -Tubing or Casing-tubing annulus
• Tubing size
• Casing size - for annulus flow configuration Water cut
• Flow line size
• Well head or separator pressure
• Flow line choke size
• Lift gas system pressure
• Pressure drop at gas injection point

Results

The results of the calculations are output in both graphical and tabular form. Either a complete listing or a summary of the tabular output can be selected. The results can be viewed on the computer screen or the printed hard copy

Hardware Requirements

The program is written to run on an IBM compatible 386 or higher PC, with the following configuration and software:

MICROSOFT WINDOWS (version 3.1 or higher)
RAM - 8 MB
DISPLAY - VGA or higher
MOUSE
HARD DISK REQUIREMENTS: - 6 MB.
PRINTER: supported by WINDOWS version 3.1