The Purpose of a Well Test
The five main reasons for testing a well, and how the objective shapes every later decision.
12 min
Activities: 0 of 2
A well test is a planned period in which a well flows, or is shut in, while the crew measures what comes out and how the pressure behaves. It is one of the few times anyone can see a reservoir at work. Logs and core samples describe the rock near the well. Seismic data describes the shape of the structure. Only a test shows how fluid really moves through the rock and into the well.
A well test is expensive. On an offshore exploration well, every day of rig time costs a great deal, and the test may take a week or more. So every test must have a clear objective. The objective decides the test type, the equipment, the duration, the rates and the samples. A test with no clear objective often produces data that answers no question.
Five reasons to test a well
Two kinds of data
Every test collects two kinds of data. The first is flow data: the rates of oil, gas and water, and the properties of each fluid. The second is pressure transient data: how the bottom-hole pressure changes over time when the rate changes. Flow data answers "what and how much". Pressure transient data answers "why", because it reveals the rock and the near-well condition.
Most objectives need both. A productivity question needs stable rates and a reliable bottom-hole flowing pressure. A reservoir description question needs a clean, long build-up recorded by an accurate downhole gauge. Fluid characterisation needs representative samples taken under stable conditions.
Match each objective to its main question
Pair each test objective with the question it answers.
- Exploration
- Productivity
- Reservoir description
- Allocation
- Regulatory
Which source of data shows how fluid actually moves through the rock and into the well?