Wortel gas field is located within the Sampang Production Sharing Contract (PSC) near Madura Island, approximately 43 miles from Surabaya, the second largest city of Indonesia. It was put into production in January 2012.
The Oyong field and the Jeruk field are the other two discoveries which lie within the Sampang PSC. The Wortel offshore gas field has been developed as a tie-back to Oyong oil and gas field.
Government approval for the development of shallow-water Wortel offshore gas field was given in December 2009.
Project partners with roles in the Sampang Production Sharing Contract (PSC)
Santos Sampang, a wholly-owned subsidiary of Australian energy company Santos, is the operator of the Sampang PSC. Its share in the PSC is 45%.
Singapore Petroleum Company (SPC) and Cue Energy Resources are the other two partners holding 40% and 15% interest respectively.
Discovery and field development of the Wortel gas field
Drilling of appraisal well one (Wortel-1) in September 2006 led to the discovery of Wortel gas field. The well had encountered a gross gas column of 141m over the 1,242-1,383m interval in the early Pliocene Mundu formation limestone.
A drill stem test showed that the flow rate of natural gas, through a 56/64" choke, was 18.5 million cubic feet a day.
A second appraisal well (Wortel-2) was drilled in October 2006 using the Sedco 601 drilling rig. It was drilled to a depth of 1,421m. The development, however, was not encouraging as the second well failed to encounter substantial hydrocarbons in fault block ‘C’.
The Wortel 2D seismic survey was conducted in the fourth quarter of 2007. It was designed to extract additional infill seismic data over the gas discovery and three nearby exploration leads.
The third development well, Wortel-3, is drilled to a depth of 2003m and Wortel-4 to 2,271m. Both the wells were drilled in January 2012 using a COSL Boss jack-up drilling rig. Hook-up and commissioning work were completed later in the same month.
Infrastructure of the offshore gas production facility near Madura Island
The Wortel offshore gas production facility comprises of two gas wells, a remote-controlled wellhead platform and a 6.2-mile subsea gas pipeline to the Oyong field, which is operational since 2007. The field development costs were estimated at $105.1m.
The Wortel-Oyong gas pipeline was commissioned in January 2012. The Wortel platform topsides were constructed in a fabrication yard. These were then transported to the site and were installed in the same month.
Gas production is exported to the Grati processing plant through an existing gas pipeline for processing and onward sale.
Gas reserves and production at the Indonesian field
In December 2009, the Wortel gas field was estimated to have had recoverable gas reserves of approximately 150 billion cubic feet. At the end of 2011, proved and probable gas reserves were estimated to be 103.2 billion cubic feet.
Santos’ share in the proved and probable gas reserves is eight million barrels of oil equivalents (mmboe).
Wortel and Oyong fields together are estimated to produce 90 terajoules (TJ) of gas each day.
In March 2012, Santos reported that gas production rate on Wortel field has gradually increased to approximately 52.75TJ a day.
Gas produced at Wortel is sold to PT Indonesia Power. The sales agreement between the two parties was signed in November 2010.
Pipelines used for exporting and transporting produced gas
Gas produced from Wortel field is first transported to the existing Oyong wellhead platform through an underwater gas pipeline. From here, a multiphase pipeline is used to export the gas to an onshore gas processing facility near the Grati power plant.
A geophysical survey was conducted to identify the best conditions for the pipeline on the selected route. The length of the pipeline from Oyong to Grati is 37 miles and the diameter is 14in. Corrosion tolerance is 300.
The pipeline has a life of 15 years and was designed as per the American Society of Mechanical Engineers (ASME) B31.8 code.