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