Sand Body Trend Delineation Decrypting from Stratigraphic Dip Pattern Analysis: Case Study within a Fluvio-Deltaic Setting, East Kalimantan, Indonesia
Authors: Wu Ivan Zhia , Parashar Sarvagya , Andhika Banu , Syahdina Susan , Kurniawan Arrie , Wismoyo Yoga , Jannatan Muhammad Ardhyan 
Published: March 2021

During field development, a detailed understanding of reservoir geometry and associated sedimentary features within the sand sequence plays an important role in the effective recovery of hydrocarbon resources. Most aging fields encounter the common problem in well placement for effective production of the remaining hydrocarbon resources. The current example—onshore formation from Late Miocene in East Kalimantan—includes seismic data acquired during the 1970s and 1980s. Considering advancements and breakthroughs provided by current technology, the older information could provide a greater level of subsurface uncertainty. Geological challenges include comprehending geometry prediction and the continuity of the amalgamated distributary reservoir channels and the depositional architecture within a fluvio-deltaic environment in a structurally complex field. High-density borehole microresistivity image data from several wells in the study area were acquired to constrain and reduce the geological uncertainty resulting from poor control of subsurface imaging through the surface seismic data. Microresistivity imaging data were used to identify sedimentary features and to perform electrofacies analysis. The data are used for the structural reconstruction of sequences by decoding a different order of structural deformation and reconstructing the sediment transport direction at the time of deposition. The results are then incorporated within the regional geology context in the basin. The consistent shale/silt beddings in the studied wells indicate an overall structural dip trend of 10° toward the east. The structural deformation within the same section of these wells is identified by the characteristics in the rotation of the structural dips. This suggests the proximity of these wells in relation to the deformation plane of sub seismic features and helps refine the structural maps. During a later phase, the reservoir is correlated within the wells, and careful selection of a palaeocurrent indicator is established from the vertical distribution of the sedimentary beddings for paleogeography reconstruction. Based on this, the channel complex dispersal direction was observed to exhibit an overall easterly direction with complex migration, and the identified mouth bar sequences reveal more widespread geometry. The dispersion or variations observed in the studied wells are then correlated to the overall reservoir architecture within fluvio-deltaic settings. The case study demonstrates the applications of borehole microresistivity data and their importance in providing a high-resolution well-to-well correlation for sand body delineation within the targeted sequences. The results provide details about the structural complexity in the underlying subsurface litho-sequence and illustrate how behaviors change laterally from one well to another. This analysis helps develop a high-resolution geocellular model for the field.