Compaction Of Sedimentary Rocks Research Articles

Permeability, porosity and pore geometry evolution during compaction of Neogene sedimentary rocks

Permeability k is expressed as a product of the hydraulic radius Rh (=pore volume Vp/sample surface area S) squared, porosity ϕ, and a nondimensional geometrical factors 1/G. G is often assumed constant depending on the model, partly because its measurement is difficult. We propose a method to measure G without assuming any microstructural model, and present its evolution during compaction of sedimentary rocks that are too fine-grained to observe and quantify microstructures. We measured S, k, Vp, and grain volume Vg during compaction with confining pressure up to 100 MPa of diatomaceous mudstone from Koetoi Formation (Kdm, ϕ = 0.53–0.64) and siliceous mudstone from Wakkanai Formation (Wsm, ϕ = 0.28–0.33), Horonobe, Japan. They are similar sedimentary rocks, but are different in the grade of diagenesis. Vp and S yield Rh, and thus we can estimate G. G for Kdm remains nearly constant during compaction and varies from 1.3 to 6, whereas G for some samples from less porous Wsm increases irreversibly with compaction from about 0.1 to 10. The increase in G by 2 orders of magnitude probably indicates the change in the dominant fluid conduit from concentrated flow along fractures to pervasive flow.

Stress-Driven Phase Transformation and the Roughening of Solid-Solid Interfaces

The application of stress to multiphase solid-liquid systems often results in morphological instabilities. Here we propose a solid-solid phase transformation model for roughening instability in the interface between two porous materials with different porosities under normal compression stresses. This instability is triggered by a finite jump in the free energy density across the interface, and it leads to the formation of fingerlike structures aligned with the principal direction of compaction. The model is proposed as an explanation for the roughening of stylolites-irregular interfaces associated with the compaction of sedimentary rocks that fluctuate about a plane perpendicular to the principal direction of compaction.

Study of petroleum generation by compaction pyrolysis—I. Construction of a novel pyrolysis system with compaction and expulsion of pyrolyzate from source rock

A compaction pyrolysis system was developed to simulate changes of source rocks during the course of burial and subsidence in a sedimentary basin. This system can reproduce a number of phenomena that previous methods could not achieve. With programmed temperature and pressure controllers, the system can simulate the following facets of sediment diagenesis in the natural system: 1. (a) Increase in temperature, overburden pressure, and fluid pressure during burial and subsidence of a formation. 2. (b) Petroleum generation from thermal degradation of kerogen. 3. (c) Expulsion of interstitial and bound water during compaction of sedimentary rocks. 4. (d) Expulsion of oil and gas generated. 5. (e) Phase changes of clay minerals, zeolites, and silica minerals due to increases in temperature and pressure. In addition, comparison of compaction pyrolysis with non-compacting hydrous pyrolysis shows the following: 1. (1) The composition of gas from compaction pyrolysis was similar to that of natural gases, containing only small proportions of unsaturated hydro-carbons. In contrast, gas from hydrous pyrolysis contain 5–10% unsaturated hydrocarbons. 2. (2) Both compaction and hydrous pyrolysis produced oils resembling crude oil in the natural system. 3. (3) While macerals after hydrous pyrolysis showed abundant holes by evaporation of volatile products by pyrolysis, macerals after compaction pyrolysis showed fewer holes. However, in samples from compaction pyrolysis, deformation from compaction was observed. 4. (4) During the compaction pyrolysis experiment, expulsion of oil and gas from source rock (compaction cell) was observed with the increase in fluid pressure and fluid volume. In summary, compaction pyrolysis permits a more realistic reproduction of natural phenomena, as a result of which a more detailed study of petroleum generation and migration is possible.

Parallel Plate Interaction in Clay-Water Systems

TWO RANGES MAY BE DISTINGUISHED IN THE DISCUSSION OF THE INTERACTION BETWEEN PARALLEL CLAY PLATES IN A CLAY-WATER SYSTEM, I.E. A SHORT RANGE AND A LONG RANGE. IN PRACTICE, THESE REGIONS DOMINATE THE PROBLEMS ENCOUNTERED IN FOUNDATION ENGINEERING /LONG RANGE INTERACTION/ AND IN THE STUDY OF THE COMPACTION OF SEDIMENTARY ROCKS /SHORT RANGE INTERACTION/. THE QUANTITATIVE TREATMENT OF THE LONG RANGE INTERACTION /OR OSMOTIC SWELLING/ DEALS WITH THE EVALUATION OF THE ELECTRIC DOUBLE LAYER REPULSION AND OF THE VAN DER WAALS ATTRACTION FORCES AND OTHER POSSIBLE SOURCES OF ATTRACTION. THE TREATMENT OF THE SHORT RANGE INTERACTION INVOLVES THE EVALUATION OF VAN DER WAALS, ELECTROSTATIC AND ADSORPTION FORCES. THE NET EFFECT OF THESE THREE FORCES IS ACCESSIBLE TO MEASUREMENT FROM ADSORPTION-DESORPTION ISOTHERMS OF WATER VAPOR ON AN EXPANDABLE CLAY. AN ANALOGOUS TREATMENT CAN BE GIVEN FOR CLAY-ORGANIC-HYDROCARBON SYSTEMS, AND APPLIED TO THE PROBLEM OF RETENTION OF HYDROCARBONS BY SOURCE ROCKS. /AUTHOR/

Density, Porosity, and Compaction of Sedimentary Rocks

An efficient laboratory method of obtaining the bulk volume of a chunk sample of rock is explained. The relation between depth of burial and the density, porosity, and compaction of different types of sediment is discussed and data are presented. These relations can be expressed by exponential equations. Compaction as a cause of structure is substantiated by computation and data. A table is given showing the relation in north-central Oklahoma between depth of burial, height of buried hills, and closure resulting from compaction. An approximate idea of the depth of material eroded from a given area may be obtained by density or porosity studies.