Introduction

The Mako gas field lies in the Duyung PSC of the West Natuna Basin, which is considered one of the largest prolific and proven hydrocarbons basins in Asia.

The Duyung PSC covers an area of 1,145km² and is strategically located approximately 20km from gas export and oil production facilities. Water depths ranging from 60m to 100m.

The Mako gas field is a large gas accumulation covering 340km² of the Duyung PSC, located at a depth of 1,700ft. The field reservoir lies in a large north-east to south-west elongated anticline measuring 47km-long and 16km-wide.

It contains sandstones within the Intra Muda formation of the Plio-Pleistocene age. The field is estimated to contain 705 billion cubic feet (bcf) of gas initially in place (GIIP) with an upside potential of 1,317bcf. The field’s proven and probable recoverable resources are estimated to be 433bcf and 646bcf respectively.

The Mako gas field has been appraised by three wells, namely Cakalang-1, Tenggiri-1 and Mako-1, which established the presence of gas and examined the field’s petrophysical characteristics.

However, three wells themselves were not flow tested. A fourth well, Mako South-1, was drilled in June 2017 to a total depth of 1,707ft by the COSL Seeker jack-up rig. The well encountered 23ft of net pay in the Intra Muda formation. It was tested and flowed at the rate of 10.9 million cubic feet per day with high-quality gas containing 100% methane. The gas showed no presence of contaminants such as CO2 and H2S.

The Mako gas field is planned to be developed using vertical wells. The developers have signed a heads of agreement with a regional utility for the sale of the entirety of the gas produced at the field.

A gas sales agreement (GSA) is planned to be negotiated between WNEL and the regional utility, which will finalise the terms of the arrangement. The final investment decision and the GSA are expected to be completed by second half of 2019. WNEL is also expected to sign agreements for access to the West Natuna Transport System, which will enable the transportation of gas recovered from the field to Singapore.

WNEL completed the re-processing of 2009 2D seismic data to identify the various geological features under the Mako gas field. An evaluation of the data identified the Mako Deep exploration prospect at depths between 2,000ft and 6,000ft. Mako Deep is expected to contain large quantities of recoverable oil and gas reserves, along with sand packages similar to those encountered by the Tenggiri-1 well. Further seismic analyses and examinations of the drill cutting recovered from the Tenggiri-1 well are currently ongoing in order to delineate and de-risk the prospect. The prospect is planned to be drilled in 2019 to examine its potential.

Development Plan

The operator's current field development plan envisages an inial four well development scheme, a small plaorm with compression facilies and an addional four wells as a second phase to be drilled later in the field's life. The plateau producon rate is envisaged to be up to 90 MMscf/d.

A series of prospects both beneath and above the Mako field have been mapped. Of parcular note is the Tambak (formerly 'Mako Deep') prospect, a Lower Gabus structure that sits beneath the northern end of the Mako field. The target interval within Tambak exhibits seismic amplitude brightening, conformable with structural closure. The prospect has a prospecve resource range of 200 to 300 Bcf with a mid-case 250 Bcf and a CoS of 45%. At the southern end of the field, over the structure's crest, sits the Mako Shallow prospect. This again shows a very strong direct hydrocarbon indicators on seismic, conformable with closure in shallow Muda sandstones. The Shallow Muda prospect has potenal to add a further 100 Bcf of recoverable resources and a very high CoS of 75%. A drilling campaign is being planned for 2019 and a test of the Tambak prospect is expected to be a part of the 2019 Work Programme.

Operator

Coro Energy(United Kingdom): 15%

West Natuna Exploration(WNEL)(Indonesia): 85%

Contractor

China Oilfield Services Ltd (COSL)(China): COSL Drilling provided its COSL Seeker drilling rig for the drilling of the Mako South-1 appraisal well.