| Title | Evaluation of Production Multilateral Well in Salak Geothermal Field, Indonesia |
|---|---|
| Authors | Peter PETER, Yudi Indra KUSUMAH, Andrew RYDER |
| Year | 2015 |
| Conference | World Geothermal Congress |
| Keywords | multilateral, formation stability, wellbore integrity, well deliverability, economic benefit |
| Abstract | In late 2012, Chevron Geothermal and Power Operations Indonesia (GPO-I) drilled the first multilateral production well in the Salak Geothermal Field, Indonesia. Multilateral wells have the potential to reduce significantly the number of future make-up wells required to maintain full generation of 377 MWe at Salak. The goals of drilling a moderate- to high-inclination forked well were to reduce the cost of producing from the steam cap reservoir by penetrating more of the fracture network in the steam cap, and maximize deliverability of steam with low (less than 2.0 wt.%) non-condensable gas (NCG). The most critical aspect of planning the multilateral well was selecting the interval for the unsupported open-hole junction for the forked leg. Geological and mechanical criteria were used to guide the selection process. To avoid potential production interference with the adjacent offset well, the trajectory of the original hole (OH) was turned 75 degrees (Az. 278-353 degrees; Incl. 55 degrees) to achieve the planned trajectory. Sonic scanner (Modular Sonic Imaging Platform, MSIP) and gamma ray (GR) logs were run in the 17-1/2 inch hole to confirm competent formation at the interval selected for the open-hole junction. A bridge plug and retrievable whipstock were used for sidetracking the forked leg (FL) from the original hole. Both legs were completed with 10-3/4 inch perforated liners; a scab liner was installed across the milled window in the 13-3/8 inch casing to protect the integrity of the original hole (OH). The deliverability of the well was calculated using Chevron in-house geothermal wellbore simulator, with a modified workflow to introduce the additional pressure loss in the upper section of the wellbore, and estimate the potential impact that either leg might act as a thief zone. Based on the initial flowtest results, the well is expected to deliver 455 klb/hr (57.4 kg/s) of dry steam at commercial wellhead pressure. A full production flow-test cannot be conducted at this time due to limitation of the available surface facility capacity at the well pad. Drilling results and initial well evaluation have demonstrated the technical feasibility and economic benefit of multilateral wells at Salak. The better-than-expected results of the steam cap multilateral well indicate, however, that drilling two single-penetration wells would have delivered a higher steam rate. Ongoing work involves further evaluation of the additional pressure loss in the wellbore, and potential for increased interference between the OH and FL. |