Lessons Learnt from an Integrated Approach for Modeling a Tight Naturally Fractured Reservoir: A Case Study from Kuwait

Abstract The Najmah-Sargelu (NJSR) reservoir of west Kuwait is tight and highly pressured with matrix permeability in the range of 0.0001 to 0.1 mD. Because of the low permeability, oil production primarily depends on the wellbores intercepting natural fractures (NF). Future development of these complex reservoirs calls for a fit-for-purpose integrated reservoir modeling workflow, which incorporates inputs from all subject disciplines. The objective of this work scope was to understand why some wells produce with good rates while other wells do not produce anything, and to reconcile the differences in production between wells. This work presents lessons learnt in the integrated reservoir workflow for the tight Abduliyah-Dharif (AB-DF) field of west Kuwait. We developed a full-field 3D discrete fracture network (DFN) by coupling static and dynamic data such as petrophysics, borehole images, core analysis, 3D seismic, mud logs, drilling reports, PLTs and production test data. The resultant DFN provided the "DNA" for the initial dynamic modeling effort. A series of iterations were made between the dynamic model and DFN to ensure consistency with the completion and production observations. The petrophysical models used a fit-for-purpose approach for evaluation of the TOC (total organic carbon) and bitumen content in the Najmah kerogen interval. We have found that pervasive natural fracturing gives higher values of 3D seismic attributes such as discontinuity, curvature, and dip. For example, the DF wells showed enhanced production compared with their AB counterparts, and this is fully consistent with the much greater activity in 3D seismic natural fracture attributes and the higher density of natural fractures from the borehole images in DF wells versus AB wells. However, in the areas of low to moderate natural fracturing, the 3D seismic attributes are much less obvious indicators of natural fracturing. They become more subtle, as other factors start to play a more important part such as the way the wells are completed and whether the main producing naturally fractured intervals are below the resolution of the 3D seismic. These factors were observed particularly in AB-NJSR reservoir where four (4) completed wells are presented in this paper, each one with different production outcomes. Tight, naturally fractured carbonate reservoirs such as the NJSR are becoming an increasingly important resource in an operator's portfolio. One of the advantages of the NJSR over other unconventional plays is the large natural fracturing that can be present in some intervals. If this is combined with drilling and fit-for-purpose completion and stimulation particularly in areas with few natural fractures, these reservoirs can exceed their production potential. Unlocking these reserves requires a holistic approach to understand and integrate data from multiple sources. This paper provides a reference for future integrated efforts in similar reservoirs.