Publications

Gas from the Ruby Field, located in the Sebuku Production Sharing Contract Area, Makassar Strait will be developed from Late Oligocene carbonate debris flow reservoirs. Reservoir facies are predominantly matrix- and clast-supported breccias. After the successful discovery and appraisal of the Ruby Field, a subsequent exploration well targeting an adjacent feature (NW Ruby-1) was unexpectedly dry. The results of NW Ruby-1 were a surprise as previous work indicated that this was a favorable structural location to drill. As a result, a comprehensive dry hole analysis was conducted to compare and contrast the successful and nonsuccessful debris-flow deposits. Analysis suggests that a valid present-day trap has been tested by NW Ruby-1, with sufficient seal present within the well. Furthermore, a viable mature source rock is interpreted to exist in the area. Therefore, reservoir quality, fluid migration, and the timing of vertical and lateral seal emplacement were studied in detail to determine possible factors for well failure. Cathodoluminescence petrography and stable carbon and oxygen isotopic analyses, which supplement basic petrographic studies, have proven valuable in resolving the paragenesis and relative timing of porosity development. Results indicate that the Late Oligocene debris flow carbonates have a complex depositional framework, experiencing a multistage diagenetic evolution (both pre-dating and post-dating the emplacement of the debris flows).The later dissolution event is the more important for porosity enhancement. Unlike the Ruby Field, the NW Ruby-1 well did not undergo * Mubadala Petroleum, Indonesia extensive late dissolution.87Sr/86Sr data are interpreted to be rock-buffered, indicating diagenesis associated with low-Sr basinal fluids. This is consistent with Sr-lean pore fluids generally associated with continental coal-rich shales. There are two likely scenarios for hydrocarbon charge of the Ruby debris-flow lobe: fault-mediated charge access or lateral up-dip migration along carrier beds. Seismic data show faults within the Ruby Field lobe, predating seal emplacement, which may have allowed charge access without compromising the seal. In comparison, NW Ruby-1 appears unfaulted, precluding vertical migration of hydrocarbons into the feature via the same access mechanism. In addition, well log correlation calibrated with seismic data indicates that the NW Ruby and Ruby lobes are separated by coeval shale, deposited between the lobes, which acted as a lateral seal. Moreover, the NW Ruby lobe was sealed before the Ruby lobe, isolating NW Ruby from lateral hydrocarbon migration as well. The corresponding lack of both vertical and lateral access to late-stage basin-derived brines are reflected in the lack of late diagenesis in NW Ruby- 1, and are consistent with the lack of hydrocarbon charge.