Overview

The normal Horner and/or Miller, Dyes, and Hutchinson methods are applicable to drill-stem tests. At times, shortcut methods as used by service companies in field analysis are reliable. The drill-stem test often uses two bombs, and one or more flow and shut-in sequences are recorded, as illustrated in Figures C 1 and C 2. To illustrate how a typical DST is performed, we will examine a schematic chart (Figure C 1) of pressure versus time from a test with two flow periods and two shut-in periods.

Figure C 1: Schematic of drill-stem test pressure chart.

Figure C 2: Interpretation method for pressure buildup: Horner plot with minimum after flow obtainable with packer.

• Point A: Tool is lowered into the hole.

• Point B: Tool is on bottom.

• Point C: Packers are set, the mud column is compressed, and a still higher pressure is recorded.

• Point D: Tool is opened for an initial flow period and the pressure drop as shown.

• Point E to point F: Fluid accumulates in the drill stem above the pressure gauge, the well is shut in, and pressure rises to point F.

• Point G to point H: After a suitable shut-in period, the well is reopened for a second final flow period from point G to point H.

• Point H to point I: Final shut-in period.

• Point J to point K: Packers are then released; the testing device is then removed from the hole.

C.1 Normal Routine Drill-Stem Test

The first flow is very short and is designed to remove any...