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Peciko is a giant gas field located in offshore Mahakam delta, Indonesia. Hydrocarbons are accumulated in multi-layer reservoirs corresponding to several disconnected stacked distal mouth bars and occasional channels. The trap consists of a 4-way dip closure. The field is producing since 1999 and the reservoirs are depleted with strong variation from one layer to another. Building dynamic reservoir models of a mature field with ~90 layers in production and roughly 300 Geological Pressure Units (GPU), which are then updated regularly taking into account data of newly drilled wells, is very complex and time consuming. However, locating and quantifying the depletion are keys to identify the under-developed areas and to launch additional infill wells. In order to overcome the challenges, to save time and gain reactivity, an innovative workflow has been developed. This workflow encompasses dynamic data and synthesis from production history and allocation, and P/z analysis for pressure depletion modeling, all integrated in the static model. This static model then becomes the tool to support the collaborative works of geologists and reservoir engineers. It is observed that the pressure depletion is function of net sand stacking, stratigraphical units and gas production which is related to the well spacing. The depletion modeling is based on the pressures measured at wells and actualized to certain time then distributed for each layer in the static model using the net pay as geological constraint. Depletion decline rate is derived from formation pressure measurements & PLT data per layer. By predicting the current pressure, present hydrocarbon-in-place can be estimated and mapped. Gas material balance (P/z analysis) at well level is analyzed in association with well intervention activity (perforation, zone change, and water shut off) to quantify the remaining connected gas-in-place. Allocation layer by layer is then performed based on the production gain after intervention and reservoir properties / pressure or reservoir contribution from PLT results. The results are integrated in the static model through an iterative process and help to identify un-drained areas, thus revealing incremental resources for the future wells. The final result of this method is a remaining hydrocarbon-in-place stacked map used to define new development wells and their associated resources in Peciko field. The innovative automatic workflow involved an integration of many data and analysis from more than 100 wells with more than 90 producing layers that can be up-dated easily in reasonable time. The method is user friendly, straightforward and applicable to other fields.

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