Pressure Transient Analysis
in Drawdown and Buildup
Dual flow Dual shat shat in test
Exploration Well Test Objectives
1. Determine the nature of the formation fluids
2. Measure the well productivity
3. Measure temperature and pressure
4. Obtain samples for lab analysis
Exploration Well Test Objectives
5. Obtain information for reservoir description
(permeability , heterogeneity)
6. Estimate completion efficiency
Dual Flow - Dual Shut in Test
Initial flow and shutin designed to establish
communication with the reservoir
Initial flow as short as possible
Major flow period long enough to give
sufficient depth of investigation
Dual Flow - Dual Shutin Test
Often 6 - 12 hours is adequate
At least six hours of stable operation to
ensure reasonable estimate of productivity
and good samples
Multirate necessary in gas wells
Major shutin 1 - 2 times the duration of
the flow period
Methods of Gaining Information on Reservoir Characteristics
A. Seismic and associated geological studies
B. Information obtained during the well drilling program
C. Wireline formation testing
1. Virgin Reservoir (Exploration and Appraisal Wells)
Methods of Gaining Information on Reservoir Characteristics
2. Produced Reservoir (New development wells)
D. Pressure - Flow testing of wells
1. Exploration and appraisal wells (DST)
2. Production or injection wells
E. Analysis of reservoir performance
- simulator history matching
Principal Objectives of Well Testing
Determine the average permeability of the reservoir
Determine the near wellbore alteration i.e. the skin factor
Measure the reservoir pressure
Attempt to locate the position of boundaries / discontinuities
Types of Pressure Transient Test
Principal Objectives of Well Testing
Pressure Drawdown (Reservoir Limit) Test
Pressure Bu ildup or Fa lloff Test
- Drill Stem Te st (Downhole valve)
- Production or Injectio n Well Test
In terference Test
Pulse Test - horizontal or vertical
Transient Well Testing
Buildup Analysis - Horner (Theis) Plot
From Steady-State Radial Flow TheoryNear Wellbore Altered Zone
Hawkins Equation - Open-Hole
From Steady-State Radial Flow Theory
Well Productivity
The well P.I. depends mainly on:
Permeability - Thickness Product
Oil Viscosity
Overall Skin Factor
Drainage radius
Wellbore radius
Formation volume factor
are of secondary importance
Well Productivity Index, Jsss
Determination of Average Pressure
Flow Regimes
Detection of Depletion
Some Well Test Models
Homogeneous Finite
Composite Infinite
Reservoir
No Flow
Boundary
Composite Infinite
Reservoir
No flow boundary
Single Linear Fault
Model Reservoir
Assumptions
Well completed over entire thickness of formation
Homogeneous and isotropic porous medium
Uniform formation thickness
Bounded above and below by impermeable barrier
s
Porosity and permeability constant
Assumptions
Lead to Radial 1-D Flow
Formation contains a single phase liquid with constant viscosity
and small and constant compressibility
Leads to Diffusivity Equation
Nomenclature
k Permeability of porous medium
Porosity of porous medium
Fluid viscosity Fluid density
c Fluid compressibility h Formation thickness
φ
µ
ρ
p Pressure t Time
Nomenclature
r Wellbore radius
q Oil flow-rate (stock tank conditions)
B Formation volume factor r External radius
r Radial coordinate p Initial pressure
Hydraulic diffusivity
To be continued