Drill-stem testing (DST) in exploration wells is the last step of oil and gas exploration. It is the moment of truth in the quest for the elusive oil and gas.
Witnessing a drill-stem test can be daunting as the company has invested a lot of time and money to find a new oil or gas field. As DST results can move the company’s share prices, during the test, the test results can only be communicated to a few people back in the company headquarters.
I have witnessed both successful DST and unsuccessful DST.
Here are the five moments of truth of a DST in exploration wells.
The first moment of truth is after the DST valve is open, you begin to see air bubbles showing up in a bucket of water that is placed on the rig floor. As the air bubbles become stronger, you know something is coming out from the test interval.
The second moment of truth is when you see the fire at the burner. When you see the flare, it confirms you have found hydrocarbon.
The third moment of truth is when we know the flow rates of the hydrocarbon fluids that come out from the well.
The fourth moment of truth is after you have measured the initial bottomhole shut-in pressure and the final shut-in bottomhole pressure. Reservoir engineers will love these two pressures to be about the same. If the final BHSI pressure is much lower than the initial BHSI pressure, it may indicate the reservoir is quite small.
The fifth moment of truth is when you know the fluid composition when you receive the fluid analysis report from the laboratory. This last moment of truth may kill all the prior excitements during a DST.
Here is to illustrate the significance and implications of the composition of the reservoir fluid.
In 1973, AGIP discovered the huge East Natuna gas field off northern Natuna Island of Indonesia. However, as the gas contains a very large percentage of CO2 – 71% – the huge gas field is still undeveloped today.
Finally, perhaps the best moment of truth in a DST is when a difficult and high-risk test, such as testing a high pressure or high H2S well, is completed successfully and safely, and the people involved in the test can leave the rig with a sense of accomplishment.
This article is written by Jamin Djuang, the author of The Story of Oil and Gas: How Oil and Gas Are Explored, Drilled and Produced.
