Duyung Production Sharing Contract (PSC) partners will commission an independent assessment of Mako field resources offshore Indonesia—expected to be completed in first-quarter 2020—using information collected from operations at the Tambak-1 well, partner Coro Energy plc reported. Following this work, the marketing of Mako gas will continue.
The Tambak-1 well, on the north-east flank of the Mako structure, was designed to appraise Mako gas field and test the underlying Tambak exploration prospect. Operations have concluded following the cased hole drill stem test (DST), which flowed dry gas at a maximum flow rate of 11.4 MMscf/d on a 2.8 in. choke with well head tubing pressure being maintained at 225 psi. Onsite gas composition analysis confirmed this to be high quality, dry, sweet natural gas.
The well encountered 24 m of intra-Muda reservoir sandstones at 389 m true vertical depth subsea, confirmed a common gas-water contact across the field, and culminated in a DST reflecting the potential deliverability of the Mako reservoir. Reservoir pressure data confirms Mako field to be a simple, single gas tank system.
The well was deepened beneath the field to 1,543 m TVD subsea to test the Tambak exploration prospect. The well encountered multiple sandstone intervals in the Lower Gabus section as predicted, with corresponding hydrocarbon shows seen while drilling. However, petrophysical interpretation of wireline log data concluded that these sandstones have low gas saturations and attempts to collect fluid samples and pressure data demonstrate low permeabilities. The well is being plugged as planned, prior to the Asian Endeavour 1 rig being demobilized.
The results overall confirm Mako field as “a very valuable gas resource,” said James Menzies, Coro Energy chief executive officer. “The data demonstrates the excellent reservoir characteristics across a huge areal extent, with good porosity, high permeability and the DST has again demonstrated the deliverability of the Mako reservoir. The DST is particularly significant as the test was conducted through cased hole and less than 2 metres of reservoir section perforated. This is in contrast to the previous DST at Mako South-1 which saw a substantially larger section tested in open hole. This provides a valid completion alternative for field development,” he said.
Two well campaign
As previously reported, Tambak-2, the initial well of the two well campaign, was a 13.5 km step out from the original Mako South-1 discovery well. Tambak-2 encountered 10 m of high-quality gas-bearing reservoir intra-Muda sandstones, representing a better developed reservoir than seen in the discovery well. It also confirmed a common gas-water contact and pressure system across the Mako structure, which covers an area of some 350 sq km (OGJ Online, Oct. 25, 2019).
Tambak-2 was drilled to a total depth of 1,544 m TVD subsea, encountering several sand bodies in the Lower Gabus section, with associated gas shows while drilling. Individual sand bodies were 3-15 m in thickness with average porosities of 5-15%. Following wireline logging, pressure surveying, and fluid sampling, a petrophysical evaluation concluded that these sandstones contained low gas saturation levels of between 20-30% and is likely to represent residual gas. The sandstones were of very poor reservoir quality, having very low permeabilities of 1-3 md.
An independent review by Gaffney Cline & Associates previously ascribed gross 2C resources of 276 bcf (48.78 MMboe) of recoverable dry gas in Mako field with gross 3C resources of 392 bcf (69.3 MMboe) representing additional field upside. Coro Energy estimates the campaign has demonstrated a gross resource addition of at least 100 bcf.
Conrad Petroleum Ltd., Singapore, operates the Duyung PSC, which covers 890 sq km in 60-100 m of water in the Riau Islands province, with a 76.5% participating interest. Other participating interests are held by Coro Energy PLC, 15%, and Empyrean Energy PLC, 8.5%.