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Tunu is a mature giant gas field, located in swamp area of Mahakam delta. It covers an area of 75 km long and 15 km wide with enormous multi-layer sand-shale series deposited within a deltaic environment. The production commenced in 1990 and peaked in 1999 (1.5 Bcfd yearly average), with current production around 600 MMscfd, and nearly 1,200 wells drilled from 34 platforms. As the field is entering into the late stage of its life and number of new wells being drilled is decreasing, the field potential is now quite dependent on the existing perforation portfolio. Owing to the significant number of wells, with multi-layer reservoirs encountered by each well, the perforation portfolio needs to be managed in an efficient and detailed manner. An intensive well review has been performed, involving more than 9,000 reservoirs located in over 800 active wells. It commenced with an evaluation of perforation gain and its associated risks at reservoir level, which are then progressively summarized into higher levels; well, platform, and field. Perforation sequences are then defined for each well following a bottom-up perforation strategy while also adapting the risks of each reservoir. Ultimately, an organized reservoir chart is constructed where we can dynamically surveil the field perforation portfolio. Results of this intensive well review have enabled the shift of production forecast methodology from statistical toward deterministic approach. In the new approach, for instance, perforation sequences and time interval between the sequences in each well are deterministically determined on a well by well basis according to the aforementioned reservoir chart. Compared to the previous methodology, this new approach yields a better representation of the actual operations. Another area benefited by the results of the intensive well review is the optimization of well intervention planning. The identified workload is grouped together based on the remaining perforation portfolio of each platform while also respecting their location to define several well intervention clusters. Implementation of this clustering system optimizes perforation planning which reduces the time spent by perforation barges to travel from one platform to another, thus allowing more time for perforation.

Maintaining mature fields provides major challenges in which production and resources are decreasing, while the operations complexity is increasing. This condition leads to increasing project risk, rising cost, and eventually decreasing company’s profit. New development projects may become sensitive to cost. Low oil price environment has made the situation even more challenging. This paper will discuss the strategy being implemented in Mahakam to overcome the challenges as a mature asset. Having produced for more than 40 years, Mahakam fits perfectly in the category of mature, thus fundamental changes are needed for ensuring its sustainability. One of the main focus areas is cost effectiveness. Cost structure was investigated in order to identify the main cost drivers. Then, multiple workshops were held to discuss any possible solutions to improve the cost effectiveness. For capturing ideas from bigger audience, an online platform was created where employees can submit ideas. Lastly, a communication media is regularly distributed to maintain employee’s engagement to the program. Seven pillars in cost effectiveness have been identified for Mahakam to respond to the current situation; Budget accuracy, technical standardization and innovation, change of working philosophy, operations optimization, supply chain optimization and renegotiation, cooperation with other companies, and organizational right-sizing. Several initiatives under those pillars have been successfully implemented resulting in 20% reduction of operational cost in 2019 and will be sustained for the years to come without compromising safety. As the challenge facing mature fields is typically similar, the aforementioned approach will likely not only be applicable in Mahakam but also in other mature fields. Some adaptations might be needed to adjust with the specific characteristic of each individual field. Cost effectiveness will generate capability to continue future investment for sustaining the life of mature fields which is one of the key elements for securing energy supply in Indonesia.

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