The issues and challenges encountered in exploiting cased hole reserves in mature oilfields on land in Trinidad, operated by Petrotrin, are presented, with mechanisms for overcoming these challenges.

Idle and uneconomic, low producing wells are identified as potential candidates and a documented workflow is followed. This opportunity is pursued on an annual basis via an NRT (New Reserve Type) project by the Petroleum Engineering Department. Conformance with the workflow provides a mechanism for risk mitigation. The petrophysical data set available for evaluating a prospective NRT is inadequate, electric logs are very old or not available. Production from the reservoir has changed the profile of the fluid content over the years and an electric log run in the past does not give a true reflection of the current fluid saturations. This leads to failed NRT’s. Net Oil sand maps in the past also do not reflect the current situation. It was also observed that poor cementation practices have given rise to situations where oil and water sands are poorly isolated.

Conforming to the documented procedures has minimized the risks and has resulted in successful NRT programs. The financial year 2014 – 2015 proved to be one of success for this project with an increase in oil production by 463 barrels of oil per day. Forty (40) recompletions were planned, to give an increase in production of 397 barrels of oil per day. Thirty eight (38) wells were attempted, of which thirty (30) wells were successfully recompleted and put on production.

The recent 3D seismic on land has provided a re-evaluation of reservoirs and structures and this is now being used as an input in improving the success rate. The learnings from this project play a significant role in informing the Company’s future business plans both in terms of upstream and downstream side of the business.

Since there are also a number of small operators, it is the intention to share our learnings so that these operators can cost effectively address the issues when encountered.

Keywords:
production monitoring, Drillstem Testing, Reservoir Characterization, well logging, drillstem/well testing, oil field, log analysis, Upstream Oil & Gas, net oil sand map, production data
Subjects:
Well & Reservoir Surveillance and Monitoring, Reservoir Characterization, Formation Evaluation & Management, Open hole/cased hole log analysis, Drillstem/well testing
Copyright 2016, Society of Petroleum Engineers
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