4.1 Introduction

A pressure drawdown test is simply a series of bottom-hole pressure measurements made during a period of flow at constant production rate. Usually the well is closed prior to the flow test for a period of time sufficient to allow the pressure to stabilize throughout the formation, i.e., to reach static pressure. As discussed by Odeh and Nabor, ^[1] transient flow condition prevails to a value of real time approximately equal to

Semi-steady-state conditions are established at a time value of

In this section, we will discuss drawdown tests in infinite-acting reservoirs and developed reservoirs including two-rate, variable, multiphase, multi-rate drawdown tests. An analysis technique applicable to pressure drawdown tests during each of these periods including other types of tests is presented in the following sections.

4.2 Pressure-Time History for Constant-Rate Drawdown Test

Figure 4-1 shows the flow history of an oil well and can be classified into three periods for analysis:

• Transient or early flow period is usually used to analyze flow characteristics;

• Late transient period is more completed; and

• Semi-steady-state flow period is used in reservoir limit tests.

Figure 4-1: Schematic pressure-time histories for a constant-rate drawdown test (after Odeh and Nabor, J. Pet. Tech., Oct. 1966)

4.3 Transient Analysis Infinite-Acting Reservoirs

An ideal constant-rate drawdown test in an infinite-acting reservoir is modeled by the logarithmic...