Tambak is a three-way dip closed inverted anticlinal structure, around 15 sq km (5.8 sq mi) in size. The reservoir is prognosed to be early Oligocene-age fluvial and lacustrine sandstones of the Lower Gabus formation, and to be charged by the underlying syn-rift lacustrine source rocks of the Benua shale. Potentially, the prospect could hold 250 bcf of gas. Tambak-2 will be the most southerly test of the Mako field to date and will, Coro said, represent a significant step out from the Mako South-1 well, which is more than 13.5 km (8.4 mi) to the northeast. Gaffney Cline & Associates has assessed 2C resources at 276 bcf of recoverable dry gas in the Mako field with gross 3C resources of 392 bcf through additional field upside.
Tambak-1 Well Appraisal and Flow test
Coro Energy has issued an update on drilling plans for the Duyung production-sharing contract in the West Natuna basin offshore Indonesia, in which the company has a 15% interest. The campaign will comprise one exploration well (Tambak-1), designed to test the Tambak prospect beneath the central area of the Mako gas field, and one appraisal well (Tambak-2), primarily investigating the intra-Muda sandstone reservoir in the southern area of the Mako field, also gathering stratigraphic data from the Lower Gabus interval.
China Oilfield Services Ltd.’s jackup Asian Endeavour 1 will drill the wells. The Tambak-1 well is located approx. 4.5 km north of the Mako South-1 location and is designed to both appraise the extent of the Mako gas field as well as to test the underlying Tambak prospect. The well will be drilled as a vertical well and is prognosed to intersect the top of the intra-Muda reservoir at a depth of approx. 389 metres below sea level. The well will be deepened below the base Muda unconformity (at a depth of approx. 517 m) to test the underlying Lower Gabus section.
The well is planned to total depth at approx. 1,370 metres below sea level. Total time to drill, log and test in the event of success is estimated to be approx. 33 days, after which the well will be plugged and abandoned and the rig de-mobilised. Coro remains fully funded for its share of costs associated with the current drilling campaign.
Conrad’s first well in the Duyung PSC, the Tambak-2, was spud in early October. The Tambak-2 well was primarily designed as an appraisal of the southern area of the Mako gas field. By mid-October, the Tambak-2 well was drilled to a total depth of 503 meters true vertical depth subsea and the well was confirmed as a successful appraisal of the Mako gas field. The next step in the campaign was an extensive drill stem test (DST) program. However, as reported in late October, Conrad hit a snag with the Drill Stem Testing at the Tambak-2 offshore well. Following the successful appraisal at Tambak-2, the Asian Endeavour-1 jack-up rig has been on location since Friday, November 1 and drilling of the Tambak-1 well has started, according to Empyrean Energy, one of Conrad’s partners in the project.