Well testing provides useful data for reservoir characterization during various stages of field life, from exploration, development to production. The key information that are typically can be obtained are, information on reservoir properties, deliverability, and pressure data. However, if the data acquisition during the well testing is compromised it can also lead to incorrect data and could lead to a wrong understanding of the reservoir and could results in sub-optimal field development. Therefore, it is important to emphasize on the quality of the data being acquired.
This paper captures the experiences gained for a high-pressure-high-temperature (HPHT) exploration well DST where data acquisition was compromised in the 1st well drilled in the structure. A combination of temperature transient effect and tubing movement in the well during shut in resulted in data quality which can't be interpreted with confidence. The lessons learnt from the same was captured and addressed successfully in the subsequent well which enabled quality data acquisition.
The objective of this paper is to share the challenges and mitigation strategies for a HPHT DST with the help of two DST operation where the challenges resulted in less-than-optimum data quality and the one where they were mitigated. The range of challenges came from planning, to gauge placement, to identify potential problems early, and even having proper contingency plans to cater for unplanned events.
The paper also deals with some of the best practices which can help with any DST program. Key examples are pre-job modeling, accurate temperature measurement and modeling, real-time data acquisition, and a special focus on sampling as a part of a successful DST program.
Disclaimer
All parameters cited in this paper are purposely made in ambiguous manner to maintain confidentiality of the data.
In 1994, two exploration wells were drilled consecutively to explore for gas prospectivity in Lang Lebah, a Miocene carbonate buildup in the geologic province of Central Luconia located in the Sarawak Basin in Malaysia. High overpressure and operational problems prevented both wells from fully evaluating the target. Postdrill analysis concluded that Lang Lebah has limited potential due to poor reservoir quality, small gas column, and challenging drilling conditions. For these reasons, it was left dormant for 25 years. In 2016, new 3D broadband seismic acquisition and megamerge reprocessing of 3D seismic data sets followed by an integrated application of multidisciplinary workflows successfully derisked key petroleum system elements of the Lang Lebah structure, yielding a more optimistic view of its potential. A new well was justified at Lang Lebah and resulted in one of the major gas discoveries of 2019.
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