Abstract

Interdisciplinary data integration is key to top-quartile Well Reservoir Field Management (WRFM). In our field case, results from annual well-intervention activities were analyzed and integrated with production data and the regional-to-reservoir scale geological understanding of this carbonate gas field to improve the delineation of the gas-water contact (GWC) development and allow timely water shut off (WSO) at the optimal depths in the reservoir, while at the same time utilizing reservoir heterogeneities (such as horizontal baffles) to delay water breakthrough (WBT).

The carbonate gas field is located in Central Luconia, with over 30 years of production history. Some wells have seen significant WBT and the field experiences an uneven rise of the GWC with production. To improve the GWC prediction, reservoir characterization work was aimed to capture the key heterogeneities that matter for flow: baffles vs. high-permeability conduits to water movement. As such, geological characterization focused on low-porosity zone correlation and platform margin & slope deposit interpretation along the flanks of the field, respectively.

In order to understand the baffling nature of rock facies to fluid flow, low porosity zones were mapped across the field initially on seismic and well logs. In core, two types of low-porosity layers were observed: flooding- and exposure-related low-porosity layers. Both types of low-porosity layers show similar log signatures, but behave very differently during production (Warrlich et al., 2014). Flooding-related low-porosity layers are extensive and composed of fine-grained, argillaceous material. They form baffles that are capable of delaying water rise for several years. Exposure-related low-porosity layers, on the other hand, are composed of cemented, brittle limestones and are often associated with karsts and fractures. Their baffling capacity is limited and can even act as high-permeability conduits speeding up the GWC rise, when connected to karst dissolution.

Platform margin and depositional-slope deposits were observed on seismic in the flanks of the field. These are inclined beds of potentially permeable deposits that have been shed from the carbonate platform during sea-level highstands. Commonly the strongest progradation and best-developed slope deposits are located on the leeward side, i.e. platform-top shedding and transport in the main paleo-current direction. Due to their inclined nature, they dip directly into the water leg and thus can act as conduits for water during production.

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