Gas Lift Allocation Program (GLAP)

Integrated engineering tool in automation Real time optimization MS access database Total system analysis Gas lift performance Multiphase flow correlation Wellbore heat transfer Optimization of allocation with Gas availability and economic constrains  Network configurations

Equipped with the same technological features as GLOP, GLAP optimizes the allocation of gas to a gas lifted field. It can be used as a stand-alone PC software and it has been successfully integrated into automation systems to provide set points for injection rates to wells in the system. Optimization can be based on:
 

• Maximization of oil production from the field, or
• Maximization of profit from the oil production. This option takes into account the cost of injection and revenues from oil production
• Limited or unlimited gas availability
• No injection gas option for poor performing wells. If selected this option allows more gas injection to other wells when necessary by penalizing poor performing wells
• Ability to handle a field with:
 
• constant separator pressure (Wells flow to a manifold and then to a separator), or
• constant discharge pressure (Well flows to a separator or terminal pressure is constant)

GLAP accurately predicts the individual and the total gas-lift performance for oil wells and then optimizes the distribution of the lift gas available for the field.  The optimization maximizes either the production or the profit from gas lift.

GLAP is capable of predicting the behavior of most common surface gathering arrangements.  These surface configurations can be classified as Constant Discharge Pressure or Constant Separator Pressure operations.

GLAP's MS Windows based user interface improves the user's productivity.  Point-and-click access to data and program operations enhances the usability. The program displays the user input and calculated results in both tabular and graphical formats.  GLAP uses MS Access database for storing well and field data.

Gas Lift Performance Module

Gas lift performance calculation in GLAP is based on advanced multiphase flow modeling techniques, flexible well description capabilities and various fluid property correlation.

In addition to industry standard correlations, GLAP offers the latest mechanistic models for more accurate prediction of flow conditions in wellbore and surface flow lines.

Well description capabilities include
 

• Reservoir IRS
• Gravel pack or perforated completion
• Tubing or Casing-annulus as production flow conduit or combination thereof.
• Tapered tubing or casing configuration.
• Well deviation profile.
• Gas lift mandrels in place.
• Multiphase flow modeling
• Chokshi, Schmidt, Doty Mechanistic Model
• Ansari Mechanistic Model
• Hagedorn & Brown
• Duns & Ros
• Orkiszewski
• Aziz, Govier & Fogarasi
• Beggs & Brill
• Sub-Surface Safety Valve
• Well Head Choke
• Surface Flow lines

Depending on the field configurations, the user may select either of the following two options:

• Constant Discharge Pressure (CDP) - In this case the well may have a flow line, and its flow is not affected by the other wells.  The discharge pressure refers to either the wellhead pressure (if the well has no flow line), or the pressure at the flow line outlet (if the well has a flow line).
• Constant Separator Pressure (CSP) - In this case each well must have a flow line, and all wells discharge to a common manifold where complete mixing of the fluids is assumed to take place.  From the manifold, the fluids are carried through trunkline(s) to a constant pressure separator.

Allocation Optimization Module

The total gas injection rate (specified or calculated) is distributed among the wells in order to obtain the maximum production from the wells. The optimization is based on the equal slope algorithm.  The target of the optimization is to maximize either the production or the profit from gas lift.  Several operational constraints can be imposed on the optimization to properly model the field conditions. These constraints include

• The limited or unlimited availability of lift gas
• System capacity to handle the production
• Economic parameters such as cost of injection, water disposal and price of oil
• Lower limit of injection gas to some wells
• Poorly performing wells can be penalized.

As an Integrated Engineering Tool

Gas Lift Allocation Program (GLAP) can be easily integrated into any gas lift automation system.  Optimization and the engineering core of the GLAP program has been utilized as an integrated engineering tool for gas lift automation system.  When integrated into the DCS system, GLAP performs the following functions:
 

• Acquisition of data from the DCS system either automatically or on demand.
• Validation of the data for predefined ranges.  Alarms are issued if any inconsistencies are encountered.
• Calculation of optimum injection rates based on static and dynamic data.
• Calculated set point values are downloaded to the DCS system.
• Comparison of actual and predicted production and injection rates. Alarms are issued if any violations of predefined tolerances are encountered.

The benefits of an automation system include:

• optimum production
• accurate control
• closer monitoring
• stability

While accurate control and close monitoring can be expected from any automation system, the optimum production and stable operation can not be achieved without integrating reliable and accurate gas lift software into the automation system.