Fracture-permeability development in organically-rich sediments through methane generation

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Title: Fracture-permeability development in organically-rich sediments through methane generation
Author: Monroe, John Napier
Abstract: The result of methane generation in low -permeability rock matrices is fracturepermeability development . Such expansion is the result of methane generation which , in turn , is the result of burial of organic matter under euxinic conditions . The fracturepermeability -development process has been demonstrated in the laboratory using a microwave oven to generate gas (water vapor ) in well -indurated , low -permeability sedimentary rocks . The process has been quantified through modeling constrained by principles of chemistry and physics . The modeling process is applied to both shales and limestones and relates sediment expansion to sediment organic carbon content converted to methane . The model shows that the quantity of organic carbon required to be converted into methane for microfracture development is small compared to the amount commonly contained in hydrocarbon source rocks . A wide variety of fracture -producing mechanisms proposed to explain natural fracture development in hydrocarbon reservoirs is acknowledged . However , fracturepermeability -development that appears to occur selectively in low -permeability , organically -rich sequences has received much less attention . Additionally , unabsolved anomalies that persist when current explanations are applied call attention to the need for alternative explanations . The fracture permeability , including the distribution and orientation of those fractures , which some reservoirs exhibit seem to defy explanation until now . A better understanding of fracture -permeability development and related aspects of petroleum maturation will remain illusive until the methane -generation fracture -permeability process , which until now has not been adequately quantified , is fully appreciated . Sediment expansion through methane generation in low -permeability rock matrices explains fracture -permeability development in many naturally -fractured hydrocarbon reservoirs including cleat permeability in coalbed methane reservoirs . Evidence is presented for the importance of this fracture permeability process in producing the natural fractures in low -permeability matrix sediments ofthe Frio Formation (Oligocene ) ; i .e . , the Frio Formation's geopressured shales ; and the low -permeability matrix sediments ofthe Spraberry Formation (Leonardian ) , the Clear Fork Formation (Leonardian ) , the Strawn Formation (Pennsylvanian ) , and the Austin Chalk Formation (Upper Cretaceous ) .Fracture -permeability development through methane generation is of utmost importance to the migration of liquid and gaseous hydrocarbons out of source beds into reservoir beds .
URI: http : / /hdl .handle .net /2346 /13105
Date: 1999-12


Monroe, John Napier Fracture-permeability development in organically-rich sediments through methane generation. Doctoral dissertation, Texas Tech University. Available electronically from http : / /hdl .handle .net /2346 /13105 .

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