The campaign will comprise of two wells, an exploration well designed to test the Tambak prospect beneath the central area of the Mako gas field, and an appraisal well designed to primarily appraise the intra-Muda sandstone reservoir in the southern area of the Mako field, as well as gather stratigraphic information from the Lower Gabus interval. The Indonesian authorities have requested the naming convention Tambak-1 for the exploration & appraisal well and Tambak-2 for the appraisal well. The Asian Endeavour-1 jack up rig, owned by China Oilfield Services Limited (COSL), has been contracted for the drilling campaign.
The Tambak-1 well will appraise the central area of the Mako field and will evaluate the intra-Muda sandstone reservoir of the Mako field, which is prognosed at a depth of approximately 385 m below sea level. A full suite of wireline logs will be run before the well is deepened to test the Lower Gabus Tambak prospect beneath the base Muda unconformity. The well is expected to be drilled to a total depth (TD) of approximately 1370 m subsea.
The Tambak prospect is a three-way dip closed inverted anticlinal structure, of approximately 15 km2 in areal size. The reservoir is prognosed to be early Oligocene-age fluvial & lacustrine sandstones of the Lower Gabus formation, and to be charged by the underlying syn-rift lacustrine source rocks of the Benua shale. Numerous nearby analogue fields found in similar inversion structures are seen in the West Natuna basin, including Kerisi, Anoa Forel and KF.
Amplitude versus Offset (AVO) modelling work across the Tambak prospect supports the potential for gas-charged reservoir sandstones being present in the structure, with a strong correlation between the modelled seismic response and the actual seismic data being seen. This helps de-risk the prospect, which the partners believe has a 45% chance of technical success and a mid-case resource potential of circa 250 Bcf.
Including an extensive testing programme in the event of success, the drilling time from spud to completion is expected to be around 33 days. The well will be plugged & abandoned at the end of the drilling programme.
Tambak-2 is designed to evaluate the reservoir properties and deliverability of the intra-Muda sandstones in the southern area of the Mako field. The intra-Muda sandstone reservoir is prognosed to be encountered at a depth of c. 380 m below sea level. A full suite of logging and coring is planned across the Mako reservoir and the well is expected to TD at approximately 595 m below sea level. The expected total time to drill, log, core & evaluate the well is approximately 33 days.
The well will be the most southerly test of the Mako field and represents a significant step out from the Mako South-1 well (over 13.5 km to the northeast). An independent review by Gaffney Cline & Associates ascribed gross 2C resources of 276 billion ft3 (48.78 million boe) of recoverable dry gas in the Mako field with gross 3C resources of 392 billion ft3 (69.3 million boe) representing additional field upside. The well has the potential to move 3C resources to the 2C category and likewise 2C resources to the 1C category, which will further improve the commercial attractions of the field itself, as well as help the gas marketing effort.
Costs and timing
The gross cost of the programme is expected to be approximately US$17 million - US$19 million to the PSC partners on a fully tested basis, including rig mobilisation and de-mobilisation, for which London listed Coro Energy Plc (Coro) is funding US$10.5 million. Empyrean will fund 8.5% of the drilling campaign costs over and above the Coro funding. The upside range of costs reflects the additional costs involved in testing the Tambak prospect should logging provide encouragement for testing. The Asian Endeavour-1 jack up rig will shortly mobilise for Singapore from the COSL yard in Shanghai. On the current schedule, the rig is expected to mobilise from Singapore to the first location in late September 2019.
Empyrean CEO, Tom Kelly, commented: “The upcoming drilling campaign at the Duyung PSC in Indonesia promises to be very exciting and somewhat unique in that we are combining a lower risk appraisal component with a high impact exploration prospect. In our view, the main aim of the drilling is to appraise the Mako gas discovery and convert the current 3C resources into 2C resources. This alone would increase the value significantly at Mako. Any new discovery at Tambak would be an absolute bonus. We look forward to providing updates as this exciting drilling campaign swings into action shortly.”
Read the article online at: https://www.oilfieldtechnology.com/offshore-and-subsea/19082019/empyrean-energy-drilling-programme-offshore-indonesia-approved/