Abstract
In this paper, we characterized the natural fracture systems and inferred the state of in situ stress field through an integrated study in a very complex and heterogeneous fractured carbonate reservoir. Relative magnitudes and orientations of the in-situ principal stresses in a naturally fractured carbonate heavy oil field were estimated with a combination of available data (World Stress Map, geological and geotectonic evidence, outcrop studies) and techniques (core analysis, borehole image logs and Side View Seismic Location). The estimates made here using various tools and data including routine core analysis and image logs are confirmatory to estimates made by the World Stress Map and geotectonic facts. NE-SW and NW-SE found to be the dominant orientations for maximum and minimum horizontal stresses in the study area. In addition, three dominant orientations were identified for vertical and sub-vertical fractures atop the crestal region of the anticlinal structure. Image logs found useful in recognition and delineation of natural fractures. The results implemented in a real field development and proved practical in optimal well placement, drilling and production practices. Such integrated studies can be instrumental in any E&P projects and related projects such as geological CO2 sequestration site characterization.
Highlights
Carbonate reservoirs are usually naturally fractured and are known as Naturally Fractured Carbonate Reservoirs (NFCRs).NFCRs are responsible for over 1/3 of the current global conventional oil production; dominantly in the prolific Persian Gulf Basin
The study area has gone through two different tectonic events which their interaction has shaped up the current complex fracture systems and in situ stresses in the region
Ductile strata with lower fracturing intensities are located below and above this depth interval. This finding implies subdividing the studied section based on the geomechanical properties or some measure of “strength” of the rock units:
Summary
Carbonate reservoirs are usually naturally fractured (diagenetically or tectonically pre-fractured or pre-sheared rock masses) and are known as Naturally Fractured Carbonate Reservoirs (NFCRs). Understanding the structural fabric of the sedimentary basins and rock densification, Evaluation of stress and pressure controlled hydrocarbon migration episodes in exploration activities (paleo-stresses), Calculation of mud-weight windows for safe drilling (blow-out prevention), Determination of optimum drilling trajectories to reduce borehole instability in shales, Evaluation of horizontal well placement in reservoirs with horizontal permeability anisotropy arising from stressed natural fracture fabric, Casing shoe depth choice in mildly and strongly over-pressured regimes, Casing design including casing-rock interaction potential during production leading to shear or parting, Design of cementing operations to avoid drilling fluids losses (in both natural and induced fractures), Well completion design to manage or exclude sand, Design of hydraulic fracture installations, Assessment of compaction potential and magnitude, Evaluation of potential fault reactivation, Thermal stress calculations in thermal EOR or cold water flooding, Microseismic monitoring data interpretation, Interpretation of acoustical wave velocity and quality changes in 4-D seismic surveys or tomographic surveys, Design and evaluation of liquid and solid deep well waste disposal, Site characterization for geological CO2 storage. Such studies can be instrumental for optimal field development, well placement, hydraulic fracture design and reservoir simulation practice in this class of complex and heterogeneous reservoir
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