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At the time of deposition, sands in high energy environments commonly have porosities of 40 to 55%. This depositional porosity is reduced following burial by cementation and compactional processes. In sands with a high percentage of ductile grains, ductile grain deformation can be a major compactional process and can have an appreciable effect on porosity and reservoir characteristics. To test the significance of this process, a series of sands were manufactured containing variable percentages (5 to 50%) of ductile grains mixed with equal-sized quartz. These mixtures were compressed in a biaxial compression system at pressures of from 4,000 to 20,000 psi (27,580 to 137,900 kPa), simulating burial to depths of up to 20,000 ft (6,096 m). As expected the results showed a neg tive correlation between porosity and pressure for samples with the same ductile content. A strong negative correlation was also apparent, however, between porosity and ductile grain content in samples compressed at the same pressure. Porosity values of medium-grained sands compressed to 10,000 psi (68,950 kPa) ranged from 24% in sands with 20% ductile grains to 9% in sands with 50% ductile grains. In samples compressed to 20,000 psi (137,900 kPa), porosity values ranged from 9% in sands with 10% ductile grains to 1% in sands with 50% ductile grains. Experimentation with other types of ductile grains and grain sizes indicates these variables are also significant but do not alter the basic relation between ductile grain content and porosity. These data suggest it may be possible, with kno ledge of ductile grain content from outcrop or shallow well samples, to predict porosity reduction due to ductile grain deformation in deeper, downdip reservoirs. The data may also have application in determining depth at which cementation occurred.
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