Analysis of Sedimentary Structures in Siliciclastic Reservoirs Through Interpretation of High-Resolution Micro-Resistivity Images and their Relationship with Fluid Mobility, Eastern Ecuadorian Basin

Abstract An operator has been facing unexpected production results from its main siliciclastic reservoirs. Variations in well-to-well behavior have created uncertainty in its projections. This study aimed to establish the relationship between sedimentary deposit geometry and reservoir fluid behavior through an integrated analysis of geological data acquired while drilling. The study focused on integrating geological and reservoir data obtained using logging-while-drilling (LWD) technology in two wells located within the same field. The analysis involved the identification and classification of sedimentary structures in a siliciclastic environment using manual interpretation of high-resolution micro-resistivity images. Fluid mobility was estimated using a formation-pressure-while-drilling sensor (FTWD) deployed in the same bottomhole assembly. The depth and orientation of the FTWD tool were correlated with the micro-resistivity image data to establish key relationships between sedimentary architecture and fluid dynamics. Image interpretation revealed sedimentary structures composed of thin beds as little as 0.4 in. thick, within reservoirs that appear homogeneous in standard triple-combo logs. The interpretation highlighted internal heterogeneity in the siliciclastic reservoirs, with the presence of high- and low-angle cross-bedding, parallel lamination, and more massive layers with thicknesses exceeding 30 cm. This heterogeneity indicates anisotropic behavior in terms of fluid flow. While reservoir pressure may remain relatively consistent within a single sand package, mobility is affected in areas with high lamination density or more complex depositional geometries, such as high-angle cross-bedding or structures that reduce lateral continuity, compared to simple, planar bedding. The integration of detailed image analysis with fluid mobility measurements has enhanced the understanding not only of the reservoir's internal structure but also of how that structure influences fluid dynamics. This integrated approach provides a key tool for reducing uncertainty in the characterization and development of siliciclastic reservoirs.