Summary

Upper Cretaceous opoka marls, marls and clay limestones were examined as to their compression strength. On the basis of the results obtained during the examinations here considered and by means of photograpbical method applied for recording stresses and deformations, an analysis of the deformations of the rocks discussed has been made. It was ascertained that the rocks are characterized by elastic-plastic deformations, and that the magnitude of permanent deformations under the stresses from o to the boundary of proportionality is Considerable. The rocks under study are characterized by a distinct anisotropy of deformability. The anisotropy takes its origin already during the process of sedimentogenesis and continues during diagenesis and lithogenesis processes, particularly when vertical stresses in a rock massif are, during adequately long time, greater than lateral ones.

Resume

Les calcaires argileux et les marnes siliceuses etaient examinees au point de vue de leur resistance à la compression. À base des experiences de la resistance on a etudie des deformations des roches examinees. Les contraintes et les deformations etaient enregistrees photographiquement. En train de cette etude on a constate les deformations elastiques et plastiques des roches examinees, ce qu'est valable (selon toute probabilite) aussi pour les autres roches pareilles. L'etendue des deformations plastiques (permanentes) dans un intervalle des contraintes entre o et «la limite de proportionnalite» est assez grande. Les roches examinees se distinguent d'une anisotropic de deformation nette. Cette anisotropie prend sa naissance dejà pendant le processus de la sedimentogenèse, pour s'affermir pendant les processus diagenetiques et litogenetiques surtout dans le cas où dans un massif rocheux les contraintes perpendiculaires (verticales) sont par longtemps plus grandes que les contraintes laterals.

Zusammenfassung

Es wurden Druckfcstigkeitsuntersuchungen oberkretazischen Opoken-morgeln, Mergeln und tonigen Kalksteine durchgefuehrt. Auf der Basis dieser Untersuchungen wurde die Analyse der Deformationen durchgefuehrt; zur Registrierung der Spannungen und Verformungen verwendete man eine forographische Methode. Als Ergebnis wurde festgestellt, dass sich die Gesteine als elastischplastische Körper verhalten. Die Werte der bleibenden Verformung (d. h. des Plastizitatsmoduls) im Spannungsbereich zwischen 0 bis zur Elastizitetsgrenze sind gross. Die untersuchten Gesteine charakterisiert eine deutliche Verformungs-anisotropie. Die Anisotropie entsteht im Prozess der Diagenese und Lithogenese, besonders dann, wenn lùngere Zeit durch die senkrechten Spannungen im Gesteinsrnassiv grösser als die Horizontalspannungen sind.

During examinations of the deformability of rocks particular attention was paid to the deformability of the Upper Cretaceous clay limestones and marls, especially in an interval from 0 to the boundary of proportionality. Selection of these rocks for examinations was conditioned by their great macroscopical uniformity. However, a detailed analysis demonstrates that the rocks under consideration differ in numerous lithological features that may be discovered only after the detailed laboratory researches made to determine mineral composition, texture and structure. The material for examinations was taken from the Upper Cretaceous formations (Maestrichtian, Turonian) occurring at the natural exposures of the Lublin synclinorium. This is a part of a large marginal synclinorium running along the edge of a great pre-Cambrian Fennosarmatian platform. As a result of the complex research-petrographical methods applied to an apparently uniform Upper Cretaceous massif, the following lithological rock types have been distinguished:

  1. Marls - contents of calcium carbonate ranging from 50 to 75 percent., and those of amorphous silica from o to 5 per cent.

  2. Opoka marls - percentage of calcium carbonate ranging from 50 to 75, amorphous silica - from 5 to 25, and clay minerals and other aluminosilicates from 15 to 45 percent.

  3. Clay limestones - percentage of calcium carbonate ranging from 75 to 95, amorphous silica - from 0 to 5, and clay minerals and other aluminosilicates from 0 to 25 per cent.

The deformability examinations were made using hydraulic press of csB-29 type on cubic samples (5 cm × × 5 cm × 5 cm) cut out of the monoliths spatially oriented (top and bottom). The rock samples taken for examination were in air-dry state (mean humidity from 0.4 to 1.7%). The samples were examined one year after the time of their drawing out, i. e. after a time-span when no visible deformations caused by decompression were observed. The increase of pressure in hydraulic press during the compression of the samples examined amounts approximately to 10 kg/cm2/sec. The examinations were always made on spatially oriented samples, and the pressures were directed both perpendicularly and parallelly to their stratification. To analyse the deformations and to determine their magnitude during the process of uniaxial compression in an interval from 0 to the boundary of compression strength under laboratory conditions, a photographical method was applied that allowed for simultaneous measurements of a force acting on the sample, and of deformations of samples during the process of uniaxial compression. This, in turn, made possible to prepare the diagrams of dependence σ =f(Δh). Several diagrams obtained during examinations are presented on Figs. 1 and 2.

Keywords:
reservoir geomechanics, proportionality boundary, direction perpendicular, Upstream Oil & Gas, perpendicularly, laboratory examination, Reservoir Characterization, elastic-plastic deformation, direction parallel, compression
Subjects:
Reservoir Characterization, Reservoir geomechanics
This content is only available via PDF.
1966. LNEC (National Laboratory for Civil Engineering)
You can access this article if you purchase or spend a download.