Quantifying Compaction and Cementation in Deformation Bands in Porous Sandstones
K. L. Milliken, R. M. Reed, S. E. Laubach, 2005. "Quantifying Compaction and Cementation in Deformation Bands in Porous Sandstones", Faults, Fluid Flow, and Petroleum Traps, Rasoul Sorkhabi, Yoshihiro Tsuji
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Combined electron microbeam imaging techniques can be used to quantify cementation and compaction processes in deformation bands and their surround-ing host rocks. Mixed secondary and backscattered electron signals can be used to definitively identify pore space, whereas scanned cathodoluminescence can be used to discriminate between detrital and authigenic quartz. Classic deformation bands from three porous sandstone units, the Cambrian Hickory Sandstone of central Texas (two bands and two host rocks), the Pennsylvanian Tensleep Sandstone of Wyoming (one band and one host rock), and the Pennsylvanian Weber Sandstone of northwestern Colorado (one band and one host rock), were examined using these imaging techniques.
Cathodoluminescence images demonstrate that bands develop through a combination of grain-scale brittle processes and cementation. Point counting of scanning electron microscopy image mosaics reveals that the intergranular volume in deformation bands is higher than is apparent from transmitted light microscopy. Cementation equals or exceeds compaction as a cause of porosity decline in both deformation bands and host rocks. No evidence exists for significant pressure solution during band development. The intergranular volumes of host rocks in the range of 31-38% suggest that all of these samples have experienced burial of 2 km (1.2 mi) or less.
Contrasts in the compactional and cementational states of bands and surrounding host rocks possibly reflect the differing availability of quartz nucleation surfaces in these different parts of the rock. Preferential emplacement of cement in the bands can lead to divergent paths of compactional behavior in bands relative to host rocks during the postkinematic phase of their burial history.
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Japan National Oil Corporation (JNOC) (presently Japan Oil, Gas and Metals National Corporation) launched a multidisciplinary and international project on the Evaluation of Traps and Seals in 1997. The project ended in 2003. This publication resulted from that project and includes JNOC research articles as well as contributions from industry and academia. The 17 papers in this volume cover topics such as a method to estimate the amount of oil/gas accumulation using the concept of equivalent grain size in seal rock, and oil/gas migration to and spill-point geometry of petroleum traps; two case studies of fault seal assessment applied to normal faults in Tertiary clastic reservoirs in offshore Sarawak and offshore Gulf of Thailand; and physical analog studies of the development of extensional faults. This publication also contains a valuable bibliography of nearly 1000 additional articles and books published on fault traps, fault seal processes, and fault-related fluid flow in sedimentary basins, for use as a reference tool to delve into publications preceding this volume.