Cap rock integrity assessment is one of the corner stones for heavy oil field development where thermal, water flooding, or other Enhanced Oil Recovery (EOR) related fluid injection operation is involved. In this paper, we present our recent work related to cap rock in a heavy oil field in Northern Kuwait. The cap rock in our field is unique in many aspects compared to other heavy oil fields around the world, in that it is very shallow in burial depth, highly unconsolidated with high porosity and permeability and very ductile in terms of geomechanical properties. Furthermore, there are multiple pay reservoirs separated by different mudstone layers, so the term of cap rock becomes somewhat vague and complicated by itself. The unique properties of the cap rock in our field call for unique core analysis approaches and put up exciting challenges to petrophysical data acquisition and interpretation. A special core analysis approach has been adopted to provide mudstone porosity and permeability that is different from either the Gas Research Institute (GRI) shale analysis or the more conventional routine core analysis suitable for clastic rocks. Integrated study has been performed to understand these special attributes of the mudstones in this field, using core analysis, downhole wireline and surface mini frac measurements, which are all used as inputs into geomechanical model initiation.

Based on integrated study, we have established the fracture gradient of different layers of mudstone intervals, gain initial understanding of the rock property of mudstones in this field, and identified data and information gaps that need to be closed by further data collection and study. In the end, we have made recommendations on future mini frac data collection and core analyses for shallow unconsolidated ductile mudstones.

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