Surface Casing Perforation, A Promising and Reliable Solution for Producing Marginal Reserves of Shallow Reservoir Layer in Shallow Gas Prone Tunu Field
Authors: Putro R., W., S. 
Published: December 2020

In these difficult economic conditions, oil companies might accept higher challenges and risks to grasp only marginal gains. A new frontier in production methods to answer the challenge is by performing perforations in the surface casing, which is suited to fields with shallow gas such as the Tunu field, a shallow water field in the Mahakam Delta, East Kalimantan, Indonesia. This pioneering method has gone through detailed engineering studies as well as risk evaluations to validate it as a new production method. Detailed reviews of integrity, safety and operational aspects have been carried out by involving well control experts to ensure that all risks have been properly identified and mitigated. The operation begins with noise logging which aims to identify any potential cement integrity problems in the outer Annulus, and then proceeds with Annulus Cementing, Cement Logging, Perforation, Sand Consolidation and ends with Clean-Up. This operation involves 3 barges: a multipurpose barge, a testing barge and a waste containment barge. This configuration aims to minimize risks and as a part of the risk mitigation measures so that well killing operations, should they be required, could be done at any time. The operations took 51 days to complete starting from the preparation phase up to the well clean-up phase. The well clean-up shows that results exceeding the target with gas production rate of 2.6 Million Standard Cubic Feet per Day (MMSCFD) and a sand rate of only 1 cc/hr with a drawdown of 11 bars from the maximum 30 bars.Maximum drawdown is limited at 30 bars to avoid resin injection rupture which functions as a “filter” for unwanted unconsolidated sand from being produced also a the same time hydrocarbon enters from formation to inside production tubing. All operational phases have been conducted with robust engineering design and high operations standards so that the major risk of sustained annulus pressure and unintentional hydrocarbon flow to the surface could be avoided. Additionally, all precautions and risk mitigations identified during the project study have been applied throughout the job resulting in safe operations. Since the end of the operations until the production phase, the well remained intact with no integrity issue. Despite breaching the dual barrier philosophy, this job has been successfully completed without major well integrity concerns. The combination of surface casing perforation and sand consolidation has proven able to answer challenges and open up opportunities for safe production of sand prone reservoirs in shallow gas zones. The success of this pilot project proves that producing from shallow reservoirs across surface casing is operationally feasible and can be carried out in a safe manner. Other candidates are being prepared with improvements in engineering design and operational aspects to achieve maximum benefits with minimum operating cost. This paper aims to review challenges and strategies carried out starting from the detailed engineering study until operations execution which could be promising for future shallow reservoir production. Innovation of perforating the surface casing to unlock reserves in the shallow section is the first time this has been performed in the world. The context of frist time in the world since this method is specifically done in a very sensitive shallow gas prone field and targeting shallow gas pocket as reservoir.The breakthrough of this unconventional method of producing hydrocarbons will open new opportunities to enhance production especially in shallow gas prone fields worldwide.