Compartmentalization Study in a Mature Field Using 3-D PSDM Seismic, Well Logs and Reservoir Data

Abstract

Compartmentalization is defined as the geological segmentation of once continuous reservoirs into isolated compartments. It is a complex subsurface uncertainty that is the product of the combination of stratigraphic architecture, structural architecture, fault permeability and diagenesis. This paper will discuss a process that was developed to integrate geophysical, geological and reservoir data to study compartmentalization in a mature field located in Trinidad. A set of seismic, well log, petrophysical, and well test data was integrated to construct a 3D structural model to study two compartmentalized/baffled reservoirs in Dolphin Field, Trinidad. This integration of various data was used to develop a practical and efficient methodology of studying compartmentalized reservoirs. Material Balance analysis has proven that there is poor connectivity between select wells within the same reservoir of Dolphin field due to the existence of likely barriers or baffles that affect pressure communication and flow, dividing the reservoirs into various compartments. Compartments were defined for two unconsolidated Pleistocene Reservoirs within the field’s E and G sands. In order to determine the geometry and extension of these partitions in E and G sands, re-interpretation of the seismic 3D PSDM data was done, applying seismic attributes to enhance the visualization of the data. Additionally, all suites of well logs were analyzed to define the geologic markers of interest and assess evidence of compartmentalization. Well correlations were revised to assess lateral changes that could represent a reservoir fluid confinement. Furthermore, reservoir data was evaluated in order to determine areal and vertical connectivity, and analyze the formation fluids to estimate the Gas-Water Contact on the wells. A new structural model was generated from the 3D seismic interpretation, which resulted in defining different compartments along the top of the structures. Faults framing these areas were characterized by calculating Shale Gouge Ratio (SGR) and Shale Smear Factor (SSF) for defining possible sealing faults. The values obtained for SGR and SSF fell within the range of a ‘good seal’ for each fault (> 40%), therefore they were deemed likely flow barrier/baffles. Juxtaposition (evaluated on the Allan diagrams) was analyzed along every fault to determine the lateral continuity of the seal. Integration of different data provided a significant benefit to the study of possible compartmentalization/baffling of select reservoirs in Dolphin field. Seismic attributes application enhanced structural modeling and provided evidence of compartmentalization in both sands. SGR, SSF results and Allan Diagrams determined the sealing properties of the confining faults. Formation Tester logs (e.g. MDT) assessed the existence of different Gas-Water Contacts on several wells. Integration of similar data and following this processes workflow could prove to be a viable means of identifying compartmentalization in other analog fields throughout the region.