production optimization

Production Optimization

January 21, 2016

Win Nyunt Aung Production Engineer

Operation and Maintenance Team 1 Petroleum Operations Division

Categories:

What is Optimization?

Well Performance and System Analysis Production System Reservoir Fluid How do we get hydrocarbons to surface? Tubing Performance (Vertical Lift) Tubing Size Selection

System Analysis (Using Nodal Analysis)

Understand the components of Inflow Performance

Understand the components of vertical lift Performance

Understand combination of Inflow & vertical lift

performance

Objectives


Production Optimization means… Balance between Production rate / Deliverability and demand Production Optimization includes a good understanding about Production

Systems and Reservoir Fluid

Well Performance & Production System

Production System

Reservoir Fluid

Phase Behavior Dry gas / Wet Gas, Condensate, Oil, Water

Fluid Properties Gas Properties Liquid Properties

Laboratory Measurements Composition Constant Volume Depletion

Reservoir Fluid Properties

Phase Behavior

The reservoir fluid can be classified into basically three types

i.e., single phase, two phases, or a combination.

Such information is used to determine the type of IPR equation

to be used.

From a technical point of view, the various types of reservoirs can be defined by the location of the initial reservoir temperature and pressure as commonly shown on pressure-temperature … (PT) phase diagrams.

Segments

Rock Properties & Reservoir character Reservoir Fluid qualities Reservoir flow paths The effect of pressure drop and back pressure on fluid flow in the Reservoir Fluid behavior in approach / entry to the wellbore Lift type and Optimization of flow from bottom hole through the tubing Operations effect on the flow rate… Choke setting Restrictions Separator operations Pipeline Start up/ shut down operations, stabilizing

System Analysis System Analysis

Well deliverability is determined by a well’s inflow performance.

The Inflow Performance Relationship (IPR) is defined as the functional relationship between the production rate and the bottom hole flowing pressure.

Productivity Index (PI or J) expresses the ability of a reservoir to deliver fluids to the wellbore.

Productivity Ratio (PR) is the ratio of actual productivity index to the ideal productivity index where skin, s=0.

Reservoir Deliverability System

Inflow Performance & Productivity Index

A commonly used measure of the ability of the well to produce …is Productivity Index

Defined by the symbol “J”, it is ratio of the total fluid flow rate to the pressure drawdown….

Drawdown (∆P) = (Pr- Pwf)

In generally,

PI = J = Q/ ∆P PI = Productivity Index Q = Flow rate, ∆P = Pressure drawdown, Pr = Average drainage pressure (static), Pwf = bottom hole flowing pressure,

System Analysis

In Flow Performance Relationship - IPR Curves The Inflow Performance Relationship (IPR) for a well is the relationship between the flow rate of the well q and the flowing pressure of the well Pwf. In single phase flow this is a straight line but when gas is moving in the reservoir, at a pressure below the bubble point, this in not a linear relationship.

Tubing Performance (Outflow Performance)


Picture yourself at the bottom of the flowing well …… Now this time …… Look up into the tubing …… What would prevent flow from the well? What would make this well produce more?


The outflow system takes energy from the inflow system and use that energy to get the total fluid rate to surface

For the outflow system, the higher the pressure at the bottom of the well, the more fluid can be pushed from the well

( In order to overcome friction)


Another convenient view of the Outflow is on a Depth Vs. Pressure graph (These are pressure in the tubing)

Factor Affecting Vertical Lift

Flowing Tubing Pressure Length of Tubing (Depth)

Friction factors

Tubing Diameter (ID)

Fluid Composition (Liquid / Gas)

Line Size Criteria

Erosional Velocity

Inflow Performance Relationship (IPR) & Tubing Performance Curves

System Analysis (Combination of Inflow Vs. Outflow)

IPR & TPR curves can be combined to find the Stabilized Flow Rate (Point of Natural Flow)

Tubing shoe reaches the perforation depth****

Wellbore flowing pressure and tubing intake pressure

are considered at the same depth

At a specific rate when these two pressures are equal, the flow system is in equilibrium and flow is Stable



Flowing bottom hole pressure (Pwf) = Tubing intake pressure(Pwf e) … the stable flow rate***

Production Rate & Tubing Sizing

Production Rate & Wellhead Pressures

Production Optimization using Nodal Analysis

Production Optimization Using Nodal Analysis

Well deliverability is determined by the combination of well inflow performance and wellbore flow performance. This work focuses on prediction of achievable fluid production rates from reservoirs with specified production string characteristics. The technique of analysis is called ‘‘Nodal analysis’’.

Its application to well producing systems was first proposed by Gilbert (1954).

Applications

Typical Applications include: Estimation of flow rates Selection of Tubing size Selection of Flowline size Selection of Wellhead pressure & surface choke Artificial Lift Design Estimation of the effects of reservoir pressure depletion Identification of flow restrictions

Optimization Procedure

Identify the components in the system

Select one component to be optimized

Select the node location that will best emphasize the effect of change

Develop expression for inflow and outflow

Calculate pressure drop versus rate for all components

Determine the effect of changing the characteristics of the selecting component Repeat the procedure for each component

Optimize the production system

Start Select Model Options

Set up and Match PVT Model

Input System Equipment & IPR

Yes

Match IPR & VLP

Calculate System Sensitivities

Performance Acceptable?

Review Design

Finish

Production

Optimization

Production

Optimization

Nodal Analysis

To simulate the fluid flow in the system, it is necessary to ‘‘break’’ the system into discrete nodes that separate system elements (equipment sections). Fluid properties at the elements are evaluated locally.

Nodal analysis is performed on the principle of pressure continuity, that is, there is only one unique pressure value at a given node regardless of whether the pressure is evaluated from the performance of upstream equipment or downstream equipment.

The performance curve (pressure–rate relation) of upstream equipment is called ‘‘inflow performance curve’’; the performance curve of downstream equipment is called ‘‘outflow performance curve.’’

The intersection of the two performance curves defines the operating point, that is, operating flow rate and pressure, at the specified node.

Production

Optimization

IPR & VLP Plot

Before Optimization

97 MMscf/day


Effect of tubing size

79 MMscf/day

91 MMscf/day

104 MMscf/day


Effect of Wellhead pressure

76

MMscf/day

94

MMscf/day

101

MMscf/day


Effect of water cut

97 MMscf/day

80 MMscf/day


Skin Effect

114 MMscf/day

84 MMscf/day


After optimization

Specifications:

Tubing size: 6.18 inch

Wellhead pressure: 2000 psi

Assumptions:

Water Cut: 5%

Skin Factor: +1

Results

During the production, chosen well with tubing Size of 3.95" and 4.78" causes restriction because of tubing. But the production rate increases at the production with tubing Size of 6.18".

According to production potential of the well and reservoir and Capacity of surface equipment Wellhead Pressure 2000 psi for the well is appropriate.

If the creation restriction in bottom hole completion or Formation damage, inflow performance can be Improve using the Work Over Such as Hydraulic Fracturing or Acidizing.

According to formation stability (type and structure of reservoir rock), completion by the method of open hole is appropriate and there’s no need to mechanical integrity in the junction.

Commonly Accepted Correlations

Correlation Recommendations

Computer Programs for System Analysis

Thanks for your attention !

production optimization

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