Pressure transient testing
Three Distinct Production Periods
Transient Region. Flow regimes that occur at different flow times for a well
flowing at a constant rate. The flowing bottomhole pressure is shown as a
function of time on both linear and semilog plots. In the transient region, the
reservoir is infinite-acting, and the flowing bottomhole pressure is a linear
function of log t. This region is amenable to analysis by transient methods. and
occurs for radial flow at flow times up to approximately:
where field units are used: t is time in hours, is porosity as a fraction, is
viscosity in cp, C is compressibility in psi-1, re is the external radius in ft, and k is
permeability in md.
Late-Transient Region. At the end of the transient region and prior to the
semisteady-state period, there is a transitional period called the late-transient
region. There are no simple equations that define this region, but the late-
transient period may be very small or practically nonexistent.
Semisteady-State Region. If there is no flow across the drainage boundary and
compressibility is small and constant, a semisteady- or pseudosteadystate
region is observed in which the pressure declines linearly with time. Pressures in
the drainage area decrease by the same amount in a given time, and the
difference between reservoir pressure and wellbore pressure remains constant
during this period. For radial flow, semisteady-state flow conditions
Definitions
Curve Shape During a Draw Down Test
Semi-logarithmic Plot of Pressure Drawdown Test Data
Curve Shape During a Pressure-Buildup Test
Horner Plot, Wellbore Pressure Data Plotted for MBH - Analysis
MDH (Miller-Dyes-Hutchinson) Plot
Downtrending Horner Plots
Uptrending Horner Plots
Extrapolation of MTR Straight Line
Extrapolation of MTR Straight Line
Radius of Investigation as a Function of Flow Time During a Pressure-drawdown Test
Radius of Investigation as a Function of Flow Time During a Pressure-buildup Test
Skin Region
Two Region Reservoir Model of Altered Zone Near the Wellbore
The rule of thumb is to use
Range of applicability of pressure methods at 100 oF
Figure 5-10 variation of and z
Empirical Deliverability equations (rawlins & schellhardt)
In terms of pressure squared (applicable only at low pressures).
In terms of psudopressure (applicable over all pressure ranges):
Fundamental of Pressure Transient Testing in Gas Wells
Pressure Transient Test Analysis In Gas Wells
Pressure Transient Test Analysis In Gas Wells
Pressure Transient Test Analysis In Gas Wells
Flow Efficiency (FE), Pressure Drop due to Skin (P)s, Radius of Investigation (ri)
The Unit of Calculations
Skin Calculation Procedure
In the equation for skin factor during the pressure buildup, Pws is measured just before
shutting in the well, and P1hr is obtained from
the straight-line portion (extrapolated if
necessary) of the buildup curve one hour after
shut-in.
Similarly, the straight-line portion of the drawdown data must be extrapolated to one
hour if the data do not fall on the semilog
straight-line.
Constant-Rate Gas Flow Test
Discrete-Rate Changes Gas Flow Test (Four Point Deliverability or Backpressure Test)
Discrete-Rate Changes Gas Flow Test (Four Point Deliverability or Backpressure Test)
Plot:
Where:
Non-Darcy Effects in a Gas Well Test (Four Point Deliverability or Backpressure Test)
Example-6.1
Example-6.1
Solution 6.1
Solution 6.1
Solution 6.1
Cartesian Plot of Multi-Rate Test Data
Solution 6.1
A strictly constant producing rate is impractical or impossible to maintain.
A more probable mode of operation is production at a constant surface pressure, and if tubing friction effects are negligible, the BHP also is constant.
At early times, however, both BHP & bottom hole rate may be changing rapidly.
Data obtained under these nonideal test conditions can be analyzed accurately with a simple modification of the transient flow equation for constant-rate production.
Variable-Rate Gas Flow Test with Smoothly Changing Rates
Surface Production Rate Schedule During Wellbore Storage Period
Bottom Hole Flow Rate or Afterflow Following Well Shut-in at the Surface
Variable-Rate Gas Flow Test with Smoothly Changing Rates
Example-6.2
Example-6.2
Solution 6.2
Solution 6.2
Solution 6.2
Solution 6.2
Solution 6.2
Gas Flow Test in Bounded Reservoir
Comparison of Dimensionless Pressure Responses for Liquid & Gas Solutions (after Hussainy)
Analysis of Gas-Well Buildup Test
Buildup Tests with Constant-Rate Production before Shut-In
Horners Approximation
Used to avoid the use of superposition in modeling the production history of a variable-
rate well.
Horners Approximation
Buildup Tests with Constant-Pressure Production Before Shut-In
Buildup Tests with Constant-Pressure Production Before Shut-In
Determining Average Drainage Area Pressure for Gas Wells
Determining Average Drainage Area Pressure for Gas Wells
MBH Dimensionless Pressure for Various Well Locations in a Square Drainage Area Locations
MBH Dimensionless Pressure for Various Well Locations in a 2:1 Rectangular Drainage Area
Example-6.4
Solution-6.4(Analysis Using Pressure Variables)
Solution-6.4(Analysis Using Pressure Variables)
Horner Plot Using Pressure
Solution-6.4(Analysis Using Pressure Squared Variables)
Solution-6.4(Analysis Using Pressure Squared Variables)
Horner Plot Using Pressure Squared
Solution-6.4(Analysis Using Adjusted Pressure Variables)
Solution-6.4(Analysis Using Adjusted Pressure Variables)
Horner Plot Using Adjusted & Adjusted Horner Time Ratio
Thank You