Abstract
This paper portrays an unconventional state-of-the-art reservoir simulation study for an offshore field in the Arabian Gulf. The anticline shaped reservoir trap contains clastic flow units modeled with complex rock bodies deposited in a fluvial-tidal delta. The reservoir has highly permeable stacked braided sandstone channels overlain by heterogeneous stringer sands in tidal channels and bars interspersed with shale. While a conventional history matched model is valid at wellbores, clastic reservoirs usually present challenges for in-fill drilling prediction at inter-well locations due to the complex geometries of curvilinear sandstone rock bodies. A rock body based simulation model was used for history matching and was investigated for further production development scenarios. Rock bodies were constructed using a combination of object based approaches constrained to geometries and connectivity from analog satellite images. The nonlinear heterogeneity was modeled with a higher-order moment methodology, preserving the extreme permeability values observed in core data, and was calibrated to permeability and height (KH) from buildup well tests. The final simulation model was cross validated with recently gathered pressure data from Modular Dynamics Tester/Repeat Formation Tester (MDT/RFT) tests.
A previous history matched model based on older methodologies (i.e., Sequential Indicator Simulation (SIS)) was compared with our new rock body based simulation model for pressure, water cut, and the gas-oil ratio (GOR) matches. The history match of the linear SIS model was achieved only after time consuming, drastic and patchy "ad hoc" corrections of permeability around the wellbores. The inclusion of complex rock bodies to constrain our new model reduced uncertainty in the inter-well areas, and helped in achieving better history match that ensures reliable production forecast for the stringer sands. The paper comprises the numerical details, comparisons and validation relevant to the study. In addition, production scenarios were evaluated and compared. The rock bodies and higher-order heterogeneity based model revealed that by placing the wells with the adequate orientation and spacing, targeting the sand bodies is paramount to improve the recovery from the field.
