The past few years have been challenging for the oil and gas industry. Many processes and operations have needed to adapt to lower oil and gas prices, caused in part by the COVID-19 pandemic. Understanding reservoir producibility and proving reserves are keys to generating a reservoir field development plan (FDP). However, the different processes to obtain such answers are strongly dependent on cost. The value of information is an extremely important criterion for operators to decide whether to proceed with their discoveries.

In an interval pressure transient test (IPTT), a formation tester is used to pump a fluid from a single point or small interval of the formation into the wellbore. Zones of interest can be isolated and tested separately zone by zone. Mud filtrate and reservoir fluids are pumped continuously using the downhole pump, and a downhole fluid analyzer (DFA) is used to monitor the fluid cleanup process. The post-pumping p pressure buildup can be analyzed in a similar manner to traditional well test analysis. Such IPTT have been available since 1980s; however, comparisons of IPTT to actual well tests and other permeability measurements were rarely published until the early 2000s. IPTT have been widely used in the past 20 years, especially in combination with dual packers, and more recently with single packers. Operation efficiency and safety have improved significantly. However, interpretation of the pressure transient obtained from an IPTT is not always well understood.

Frequently asked questions (FAQs) include the following:

  1. What is an IPTT or a vertical interference test (VIT)?

  2. How does an IPTT compare with other permeability measurements?

  3. What are the different scales of pressure transient data?

  4. How do we upscale zone permeability to an entire reservoir interval?

  5. What is next?

This paper will address these questions using both reservoir simulation and field data. The field examples are from different environments, ranging from shallow marine to turbidite to deepwater environments, with different fluid systems, such as black oil, heavy oil, waxy oil, gas, and gas condensate. Geographically, the field data include examples from South East Asia and the Middle East. Permeability obtained from pretests, IPTT, nuclear magnetic resonance (NMR), core analyses, and well testing will be compared.

Recently deep transient testing (DTT) has been introduced in the industry. With DTT, we can flow faster and longer than previously possible with formation testers, enabling pressure transient analysis in higher permeability and thicker formation. Further data quality improvements come from new, high-resolution gauges deployed with an intelligent wireline formation testing platform. This paper includes a review of the DTT method with several field examples.

Finally, the advantages and disadvantages of the different testing methods are discussed relative to the test objectives, with the intent to provide a cost-effective data selection method to ensure sufficient FDP input and to justify the value of investment to the relevant stakeholder.

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