测试压裂分析

Real-data.ppt 10/29/99 slide 4
Fracture Pressure Analysis - Limitations
• Fracture Entry Friction Evaluation
– Using surface pressure increases results uncertainty – Problematic near-wellbore friction level variable
– Deep penetration in specific layer – Avoid production of unfavorable components in neighboring layers
Real-data.ppt 10/29/99 slide 3
Fracture Pressure Analysis - Advantages
– Perforation friction + near-wellbore friction – A common cause of fracture execution problems
• Net pressure history matching
– “Calibration” of model solution to observed frac pressure data – Links fracture design and estimated frac geometry to observed fracture behavior
Real-data.ppt 10/29/99 slide 7
BALLOON ANALOGY FOR OPENING FRACTURE WITH CONSTANT RADIUS
Real-data.ppt 10/29/99 slide 8
FRACTURE GEOMETRY CHANGES WITH NET PRESSURE
Predicted net pressure Predicted fracture dimensions
Pnet =
50 psi
R w
= 650 feet = 0.25 in
Pnet =
Real-data.ppt 10/29/99 slide 11
800 psi
R w
= 260 feet = 1.6 in
LIMITATIONS OF SIMPLIFIED RADIAL FRAC CALCULATION TO ESTIMATE FRAC DIMENSIONS
• • • • No stress variations Lithology is assumed constant Permeability variations are ignored Mechanical rock properties do not vary with height • Simplified radial fluid flow • Not a predictive tool
• Basic analysis data collected (in some sense) during every frac treatment • Relatively inexpensive and quick diagnostic technique to apply • Provides a powerful tool for on-site diagnosis of fracture entry problems • Allows on-site design refinement based on observed fracture behavior
REAL-DATA NET PRESSURE ANALYSIS - OUTLINE
• • • • Introduction Applications and brief examples Steps in the engineering process Purpose, design and analysis of diagnostic injections
σ
V e E
= = = =
4,800 bbl (~ 27,000 ft3) (~ 760 m3) 0.5 2x106 psi 500 psi
R ~ w ~
416 ft 0.8 in
INFLUENCE OF NET PRESSURE
• Two radial fracture model solutions for the same treatment (no barriers):
W ellbore
Use predicted net pressure
Measured net pressure Net pressure Pump rate Predicted net pressure
Pay
Pay
Pump time W ellbore
Use measured net pressure
3
Post-frac m odeling review and incorporate other fracture diagnostics
4
M atch m odel net pressure to observed net pressure
Perform treatm ent
Explore / bound alternative explanations for observed net pressure
• Net Pressure History Matching
– Indirect Diagnostic Technique - frac geometry inferred from net pressure and leakoff behavior – Solution non-unique – careful & consistent application required for useful results – Technique most useful when results are integrated or calibrated with results of other diagnostics
– Focus: Young’s modulus and permeability
• Well completion and perforations • Treatment schedule, proppant and fluid characteristics • Treatment data
– With “anchor points” – At least 3-second sampling rate with surface pressure, slurry rate and proppant concentration
Pay Matching measured net pressure with model net pressure Net pressure
Pump time
Real-data.ppt 10/29/99 slide 2
MOTIVATION FOR REAL-DATA FRACTURE TREATMENT ANALYSIS
• Bottom line: increase well production and reduce treatment cost by optimization • Reduce screen-out problems • Achieve “appropriate” fracture conductivity and length • Control where fracture is growing
• Two modeling solutions for the same treatment; if 500 psi stress contrast exists around payzone
Predicted net pressure Predicted frac dimensions
Pnet = 100 psi
Interpret m odel results, m ake engineering decisions
Real-data.ppt 10/29/99 slide 15
Minimum Model Input Requirements
• Mechanical rock properties –wenku.baidu.comlog data
Real-data.ppt 10/29/99 slide 1
REAL-DATA FRACTURE TREATMENT ANALYSIS
Matching net pressure is a NECESSARY but not SUFFICIENT condition for estimating frac geometry
» Production data & welltest analysis » Direct fracture diagnostics
Real-data.ppt 10/29/99 slide 5
Primary Fracture Pressure Analysis Activities
• Evaluation of fracture entry friction
Real-data.ppt 10/29/99 slide 12
NET PRESSURE VS. FRICTION PRESSURE
Real-data.ppt 10/29/99 slide 13
NET PRESSURE MATCHING
Real-data.ppt 10/29/99 slide 14
– Fracture closure stress determination, fracture efficiency and required pad size – Rate stepdown analysis
• Guidelines for net pressure history matching • Estimating fracture dimensions
Basic Fracture P ressure A nalysis Steps
1 2
Pre-frac com pletion and fracture design Repeat process in succeeding stages or w ells
Determ ine fracture closure stress and m atch perm eability Characterize friction param eters using rate stepdow n tests Determ ine observed net pressure
e V =
•
2 πR 2w 3
4 eVE R= 3 σ
1 3
2 σ ⋅R w≈ π E
32 eVσ w = 3 2 3π E
2 3
1
For: Volume Efficiency Young’s modulus Net pressure Yields:
Real-data.ppt 10/29/99 slide 10
L = 1200 feet
Pnet = 800 psi
Real-data.ppt 10/29/99 slide 9
R = 240 feet
ESTIMATING FRAC DIMENSIONS USING REAL DATA AND RADIAL FRAC ASSUMPTION
Mass balance Elastic opening
Real-data.ppt 10/29/99 slide 6
DEFINITION OF NET PRESSURE
Net Pressure is the Pressure Inside the Fracture Minus the Closure Pressure Net Pressure = 2,500 - 2,000 = 500 psi