Date post: | 14-Jun-2015 |
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M.Eng. Project DefenceBy: Aadrish Mir
Supervisor: Dr K.C. WattsReader: Dr D. Garagash
A STUDY OF PRODUCTION OPTIMIZATION OF AN OIL WELL USING PROSPER
The objective of the project is first given. Well deliverability and phase behavior concepts
are defined. Nodal Analysis & its applications are discussed. An introduction to PROSPER software is
mentioned. A case study emphasizing on the use of
production optimization of an oil well with PROSPER software is presented.
Presentation Outline
The objective of the project is to optimize well performance in order to maximize the production rate.
Oil reserves are depleting every day and oil prices are peaking, thus the role of production optimization cannot be neglected.
Objective
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
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.
Phase Behaviour
Fig 2.3 A typical p-T diagram for ordinary black oil (Ahmad, 2001).
A systems analysis approach, often called NODAL Analysis, has been applied to “analyze the performance of systems composed of interacting components.”
Its application to well producing systems was first proposed by Gilbert (1954).
Nodal Analysis
A partial list of possible applications of nodal analysis include: Selection of tubing size. Selection of flow line size. Analysis of an existing flow system for
abnormal flow restrictions. Artificial lift design. Prediction of the effect of depletion on
production capacity.
Applications
1) Determine which components in the system can be changed.
2) Select one component to be optimized.3) Select the node location that will best emphasize the
effect of the change in the selected component. 4) Develop expressions for the inflow and outflow.5) Obtain required data to calculate pressure drop versus
rate for all the components. 6) Determine the effect of changing the characteristics of
the selected component by plotting inflow versus outflow and reading the intersections.
7) Repeat the procedure for each component that is to be optimized.
Procedure
PROSPER is a well performance, design and optimization software.
PROSPER is designed to allow the building of reliable and consistent well models, with the ability to address each aspect of well bore modeling viz:
Pressure Volume Temperature (PVT) fluid characterization
Vertical Lift Performance (VLP) correlations for calculation of flow-line, tubing pressure loss and
Inflow Performance Relationship (IPR) for the reservoir inflow.
PROSPER
SYSTEMS ANALYSIS USING PROSPER
The well used in this case study will be designated as X-3
The field was developed using 5 wells and reached peak production in 1996. Since then, oil production has decreased rapidly due to an increase in water content
An economic limit of 1500 STB Oil/d/well was premised; i.e. producing at rates lower than that is not economical.
Case Study of Optimization of an Oil Well Using PROSPER
Water depth 300 (feet)
Average porosity 22 (%)
Permeability 200 (mD)
Kv/Kh 0.1
Top of sand 6400 (ft) TVDSS
Oil-water contact 6500 (ft) TVDSS
Initial reservoir pressure 3300 (psia)
Present reservoir pressure 2800 (psia)
Table 1 Reservoir Data
Table-5.1 PVT Data
Reservoir Temperature 150 (°F)
Oil API Gravity 40 (°API)
Gas Relative Density 0.80
GOR 550 (scf/STB)
Pb 2030 (psia)
Bo 1.27
Oil Viscosity 0.66 (cp)
Bg 0.0046
Gas Viscosity 0.022 (cp)
Bw 1.023
Gas Z Factor 0.73
Water Salinity 200000 (ppm)
Water Viscosity 0.67 (cp)
Depth,
(ft)
TVD
650 1605 2590 3600 4590 5587 6490
Pressu
re,
(psia)
525 735 990 1292 1629 1920 2266
Table-5.2 Pressure Survey
Table-5.3 Well Data Table-5 .4Well Equipment Data
Node NoComponent
Name
Measured
Depth (ft)
1Outlet node/
Christmas tree0
2 Riser 350
3 Wellhead 350
4 5.5” Tubing 850
5 S.C.S.S.S.V 850
6 5.5” Tubing 4000
7 5” Tubing 5600
8 7” Liner 6530.5
Oil Production rate,
(STB/d)4730
Water Cut, (%) 30
WH Flowing Temperature,
(°F)65
Pressure at Christmas tree,
(psia)445
Skin (Well Test) 2.92
PI or J (Well Test),
(STB/d/psi)12.36
Damaged Zone Relative
Permeability, (%)50
Damage Zone Thickness,
(In)12
Crushed Zone Skin 0.100
Damage radius, (ft) 4000
Develop a well performance model using PROSPER
Simulate base case forecast under various operating conditions
Evaluate various development options to optimize oil production
Results
Case Study Objectives
Developing a well performance model using PROSPER
Table-5.5 Data entry in PROSPERFluid Oil & Water
PVT method Black Oil
Separator Single-Stage Separator
Flow Type Tubing Flow
Emulsions No
Well type Producer
Lift method None
Predicting Pressure only
Completion Cased hole
Gravel Pack No
Fig-5.2 IPR plot
Fig-5.3 Downhole equipment
Matching the Model
Table-5.7 Match dataOil Rate (STB/d)
Measured Calculated % Difference
4730 4704.4 -0.54061
Fig-5.7 VLP-IPR matching
Flow diagram for data entry and results in PROSPER
Since the PVT, VLP and IPR were matched to measured data, it was possible to move on and use the model to perform a system analysis
Simulate Base Case Forecast under Various Operating Conditions
Table-5.8 Reservoir pressure & water cut rangesTable-5.9 Oil rates at given parameter ranges
Table-5.10 Economic base case conditionsScenario Maximum Economic
Water Cut
Production Rate @ 30 (%)
Water Cut
Base Case 45 (%) 4703.(STB/day)
Reservoir
Pressure (psig)
Water Cut (%)
30 35 40 45
Oil Rate (STB/d)
2800 4703 3818 2993 2232
2700 3922 3073 2288 1564
2600 3120 2307 1436 0
2500 2292 0 0 0
Parameter Range
Water cut 30,35,40,45 (%)
Reservoir Pressure 2500,2600,2700,2800 (psig)
A sensitivity run on the current reservoir conditions for decreasing well head pressure (WHP) was performed.
WHP can be adjusted using choke in an oil well.
Reduction in WHP causes the drawdown to increase which in turn increases the oil production.
Evaluate Various Development Options to Optimize Oil Production
Changing WHPTable-5.11 Oil rate at various WHP & WC
Table5.12 Oil rate at economic water cut
Scenario Maximum Economic Water
Cut
Production Rate @ 45 (%)
Water Cut
Lowering christmas tree
pressure
70 (%) 6153 (STB/d)
WHP (psig) WC @ 45
(%)
WC @ 50
(%)
WC @ 60
(%)
WC @ 70
(%)
WC @ 80
(%)
Oil Rate (STB/d)
445 0 0 0 0 0
400 1538 0 0 0 0
300 3125 2294 0 0 0
200 4788 3873 2140 465 0
100 6153 5238 3463 1833 364
For further production of the remaining oil in the reservoir, adjusting the tubing size was required and sensitivity analysis of various tubing sizes (internal diameter) was performed.
The effect of increasing the tubing size is to give a higher node pressure for a given flow rate because the pressure drop in the tubing is decreased.
If the tubing is too small even though the reservoir may be capable of producing a large amount of fluid too much pressure drop occurs in the tubing.
Changing Tubing Size
Changing Tubing Size, continuedTable-5.13 Oil rate at various tubing internal diameter sizes
Tubing Size ID (in) Oil Rate (STB/d)
2.441 257
2.992 315
4.09 346
4.892 0
A gas lift for X-3 was undertaken based on current conditions and engineering assumptions.
The purpose of injecting gas into the tubing is to decrease the density of the flowing gas-liquid mixture and therefore decrease the required flowing bottom hole pressure.
As the gas rate is increased the fluid velocity and therefore the friction losses also increase.
Gas Lifting (Artificial-Lift Method)
Gas Lifting, continued
Table-5.15 Oil rate with various gas injection rates
Table-5.16 Economic oil rate with optimized gas liftScenario Maximum Economic Water
Cut
Production Rate @ 45 (%)
Water Cut
Optimised gas lift 80 (%) 6900 (STB/d)
Gas Inj. (MM scf/d)WC @ 45
(%)
WC @ 50
(%)
WC @ 60
(%)
WC @ 80
(%)
WC @ 90
(%)
Oil Rate @ Different Water Cut (STB/d)
2 6908 6091 4534 1870 824
3 7039 6233 4697 2003 900
4 7111 6313 4782 2075 938
Lowering the Christmas tree pressure to 100 psi is recommended because the well’s life can be extended to 70% water cut
The next possible option is to change the tubing size. However changing the tubing size is not recommended, since it does not produce a fruitful increment in oil production rate.
The gas lift method is more economically beneficial as it produces up to a maximum economic water cut of 80% with gas injection rate of 2-4 MM scf/d producing oil rates of 1800-2000 STB/d.
Case Study Results
Thank You