Publications

Tambora field, discovered in 1974, is an old, mature oil & gas field situated in a swamp area at the apex of the Mahakam delta. The reservoirs consist of Middle to Upper Miocene-aged fluvio-deltaic sequences. The hydrocarbon trapping system in Tambora north is mainly controlled by the structural trap, whilst a stratigraphic trap is dominant in the southern part of the field. As per Q1 2016, 126 wells have been drilled in Tambora field, in which 50 wells are currently actively producing. Tambora is a multilayer field mainly consisting of stacked deltaic reservoirs subdivided into four main productive zones (D, E, F and G respectively, from top to bottom). The sandstone reservoirs are mainly formed by distributary channel deposits, along with some delta front mouth bars. The west-east trending distributary channels are mostly found in Tambora North, whilst in Tambora South the channel orientation is mostly northwest-southeast. Reservoir quality is variable, clean sands have porosities between 8% - 30% and permeability up to several hundreds of mD. Compared to other fields in the Total acreage, the facies succession of Tambora and Handil fields are more proximal than the reservoirs produced in Tunu, Peciko, Bekapai and Sisi-Nubi. Tunu and Peciko are dominated by delta front sediments whilst the Sisi-Nubi field is mostly prodelta-shelf deposits. Core from well TM-62 (drilled in 2006) has been cut in the interval MF11_12 to MF11_20 over the reservoirs G54A, G54B, and G55A. A total of 51m of core (3979 - 4029.6 mTMD) provides insights into the complete depositional processes responsible for the accumulation of the G sand reservoirs. The overall succession coarsens upwards, which records a classical prograding deltaic system. Coarser sandstone of a distributary channel rests upon delta front mouth bar deposits. Distributary channel sandstone, of some 10m thick, shows intermittent abandonment. The mouth bar deposits range in thickness from 1-2 m. Tambora G Zone is the deepest productive zone in the field, and has some production problems which can be attributed to compaction through reduction of pore space. The low production rate in the G Zone is caused by low porosity and permeability, mainly due to grain compaction to the pore network. The second parameter is clay filling & bridging of pores with clay (kaolinite/illite). An integrated analysis on thin section, SEM and XRD on core sample from the TM-62 well show evidence of a complex diagenetic history, including: Siderite crystallization, Kaolinite/Chlorite crystallization, Silicification, Dolomite Crystallization and Compaction (pressure dissolution/Quartz overgrowths). A strong understanding on reservoir properties, as well as on sedimentary facies and depositional environments, will lead to a pragmatic strategy to handle the low poro - perm reservoirs in the G Zone of Tambora Field.