Well Testing

2013

Well Testing Buildup pressure

Contents 1- Introduction 2- Objectives of buildup test 3- Test procedures 4- Advantages and disadvantages of buildup test 5- The pressure behavior 6- Pressure Buildup Testing Methods for Finite Reservoir

Introduction Well testing is the technique and method for the evaluation of well conditions and reservoir characteristics. It involves producing a well at a constant rate or series of rates, some of which may be zero (well closed in), while simultaneously taking a continuous recording of the changing pressure in the well bore using some form of pressure recording device.

Pressure buildup testing is the most familiar transient well-testing tech-unique. This has been used extensively in the petroleum industry. Basically the test is conducted by producing a well at constant rate for some time, shutting the well in (usually at the surface), allowing the pressure to buildup as a function of time. From these data, it is possible to estimate the formation permeability and current drainage area pressure, and to characterized damage or stimulation and reservoir heterogeneity or boundaries frequently.

The main objectives of buildup test 1- To estimate the reservoir pressure. 2- To estimate the formation permeability. 3- To estimate skin factor.

Test Procedure 1234-

Producing a well at constant rate for some time. Shutting-in the well allowing the pressure to build up in the wellbore. Recording the down-hole pressure in the wellbore as a function of time. Plotting versus Horner plot.

-Advantages of buildup pressure 1- Precise control of rate 2- P* can be determined -Disadvantage of buildup pressure Loss of production due to shut-in.

The pressure behavior •The pressure behavior of a well in an infinite-acting reservoir (i.e., during the unsteady-state flow period) is given by:

1- The skin effect

2- The pressure drop due to the skin

3- Flow Capacity

4- Damage factor

5- Flow Efficiency

Pressure Buildup Testing Methods for Finite Reservoir There are two methods to buildup test for finite reservoir 1- Hornor plot Horner plot is commonly used for new wells or when the production time is relatively small.

For an infinite-acting reservoir, an estimate of initial pressure is obtained by extrapolating the straight- line section of the Horner plot to infinite shut-in time. For finite and developed reservoir, the extrapolated pressure is not a good estimate of initial pressure and it called the false pressure.

2- Miller-Dyes-Hutchinson (MDH) Method -The MDH buildup requires a plot of buildup pressures versus the logarithm of buildup time. -The MDH method is best for older wells in bounded depleting reservoirs. -when the producing time is not known or can be estimated only roughly, MDH plotting can be used.