Oil is produced at the Horn Mountain field (Gulf of Mexico, Mississippi Canyon blocks 126 and 127) from two middle Miocene reservoirs (M and J Sands). Reservoir facies are characterized as sand-filled channels and associated overbank deposits and are positioned in combination structural-stratigraphic traps. Prior to initial production, several barriers and baffles were identified in both reservoirs by integrating geological, geophysical, petrophysical, pressure, PVT and geochemical data and petroleum- filling history. A Compartmentalization Risk Matrix was developed to facilitate and visualize the integrated evaluation of compartmentalization.

During production, reservoir surveillance is a vital task aimed at understanding how petroleum is produced from a reservoir. In addition to traditional surveillance technologies, we applied time-lapse geochemistry (TLG) to visualize the petroleum sweep by monitoring changes in fluid composition and fingerprints across reservoirs. For this technology, appraisal and preproduction fluid samples are first analyzed to map fluid types across a static reservoir. Then, a surveillance program in which fluid samples are taken from producing wells at regular time intervals is designed and executed. The production samples are geochemically “fingerprinted” and compared with preproduction fluids from the same well and surrounding wells. At Horn Mountain, interpretation of geochemical data allowed us to infer oil movement across the M Sand and helped to reevaluate reservoir models and reduce risks in managing reservoir performance. In the J Sand, an untapped compartment was identified, and an additional producer was justified for future drilling. TLG results are consistent with and complementary to other surveillance data available to date. Our study demonstrates that TLG is a safe and cost-effective technology that reduces uncertainties associated with other reservoir surveillance methods and appears to be a valuable technique for reservoir management.

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