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AAPG Annual Convention and Exhibition

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Tight Oil Unconventionals: Better Reservoir and Performance Understanding Resulting in a Novel Development Ranking Methodology Achieving Higher Recovery Through Dynamic Sweet-Spots Modeling

Abstract

The shale gas expansion of the early 2000's brought development focus to liquid-rich and tight oil plays. The major challenge was adapting shale gas understanding and technologies to the needs of tight oil resources. The production mechanism of a tight oil carbonate reservoir cannot be explained only by differences in stratigraphy, depositional environment and diagenesis. Traditional log analyses are challenging for interpretation of proper saturations. The hierarchy and patterns of natural fractures over approximately 8,300 square miles were characterized and modeled; their influence on stimulation, porosity preservation, rock types, flow mechanisms, and geomechanical properties were captured. Natural fracture trends identified on 3D seismic data were mapped as performance attributes and are found to correlate with many performance Previous HitindicatorsNext Hit such as lost circulation, depletion and anomalous pressures. The areas surrounding the high density fracture fairways are identified as potential sweet-spots. Geological Previous HitindicatorsNext Hit (porosity, Previous HithydrocarbonNext Hit pore-volume, fairway, fracture density, reservoir thickness), dynamic Previous HitindicatorsNext Hit (depletion, pressure, gas and water accumulation), and performance Previous HitindicatorsNext Hit (EUR, IP, linear flow slope, material balance attributes) are used to identify and rank the sweet-spots. The fracture fairways vertically segregate fluids (gas, oil and water) where gas and water accumulate in the upper and lower reservoir, respectively. Fracture corridors, on the other hand, have the most profound effect on productivity and vertical communication. A dramatic time-dependency is found in drilling sweet-spots - initial wells produce very high total fluids (and oil cuts), yet subsequent wells encounter pressure depletion of earlier wells and result in poor ultimate recoveries. As a result, wells that intercept rich Previous HithydrocarbonNext Hit-bearing zones with potentially higher performance Previous HitindicatorsNext Hit and less depletion effect, either by Previous HitdirectNext Hit placement or through hydraulic fracture extension, are better producers. A pilot well confirms the observed and modeled fluid movements in the fracture system and the effect of communication through the interaction of the natural and hydraulic fracture systems. Discretized geological, depletion and production Previous HitindicatorsTop translate these concepts into a rational ranking of future well locations by creating a simple and manageable database tool.