Better Understanding on Diagenetic Processes in the Low Productivity Reservoirs: An Opener Approach for Further Tambora G Zone Development Strategy

Tambora Field reservoir zone is sub-divided into D, E, F and G. Of the four zonation, Tambora G Zone has the lowest recovery factor. Based on this, the current study was intended to have better understanding of the diagenetic processes in low productivity reservoirs and its development strategy in that zone. Reduction of porosity and permeability due to different diagenetic intensity and causes are possible reasons for this condition. A new-improved petrology study was performed to understand the effects of diagenesis and the contribution of clay minerals which has led to worsening reservoir characteristics. In order to achieve better understanding of reservoir characteristics, integrated petrology analysis of petrography, XRD, SEM and CEC were performed. The results of detailed lithofacies analyses show that low productivity related to poor porosity and permeability is primarily caused by mechanical compaction and are worsened by chemical diagenesis related to isolated pore spaces, unconnected pore throats and depositional environment. Those affects the increase of diagenetic quartz-overgrowths, ferroan/iron-bearing and calcareous minerals. The occurrence of these minerals act as a pore-filling cement and are more developed in clean rather than shaly Sandstones. The most dominant diagenetic clay mineral in all lithofacies is recorded as kaolinite, followed by illite, chlorite and illite-smectite with this trend varying relative to depth and lithofacies. The effect of these factors is more intense when burial depth increases, and the depositional environment is increasingly distal as in the G Zone’s northeast area. Referring to this, and in order to minimize the risks of diagenetic minerals causing low productivity, the well placement strategy is addressed to the south and northwest compared to the northeast area. The proven result of applying this approach is the success story of drilling the TM-132 northwest well in 2019 that reached an initial gas rate production of around 3 MMscfd.