Mars Rocks Research Articles

Strain softening marly rock : Cavounidis, S; Sotiropoulos, E Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 2, P63–66. Publ Rotterdam, A A Balkema, 1979

Strain softening marly rock : Cavounidis, S; Sotiropoulos, E Proc 4th Congress International Society for Rock Mechanics, Montreux, 2–8 Sept 1979, Vol 2, P63–66. Publ Rotterdam, A A Balkema, 1979

Phase relations of a simplified Marly rock system with application to the Western Hohe Tauern (Austria)

The regional distribution of metamorphic mineral assemblages in Mesozoic carbonate rocks of the Western Hohe Tauern allows the mapping of isograds based on the appearance of biotite+calcite and biotite+zoisite+calcite. The latter isograd corresponds approximately to the thermal maximum of the alpidic metamorphism in the central part of this area. An estimate of P, T, Xfluid conditions can be obtained from phase relations among muscovite, biotite, chlorite, margarite, tremolite, zoisite, anorthite, quartz, calcite, and dolomite in the system K2O-CaO-MgO-Al2O3-SiO2-H2O-CO2 which approximates the composition of marls. Calculations based on various experimental and thermodynamic data have been made with emphasis on phase relations pertinent to a group of carbonate rocks with very low Fe and Na contents in non-opaque minerals. Significant and opposite deviations from the phase relations for stochiometric end member mineral compositions are due to the substitutions F-OH and Mg+Si-2Al. Consistency of observed and calculated phase relations is favoured by high F-contents. For the majority of carbonate rocks in the high metamorphic zone, maximum temperatures around 550° C, minimum pressures of 4–6 kb, and relatively low XCO2 values within the stability field of zoisite and of biotite+calcite+quartz are indicated.

Early Pleistocene Submarine Canyon, Boso Peninsula, Japan: ABSTRACT

The Boso submarine canyon was one of the first fossil canyons to be described. It is also one of the best exposed, because careful quarrying of the economically useful gravel fill has exposed the noneconomic marly rocks into which the canyon was cut. These country rocks (Umegase Formation) are gently dipping, cream-colored siltstones and mudstones. In contrast, the canyon fill (Higashi-higasa Formation) consists of brown to yellow sandstones with marked lenses of polymodal and polymictic conglomerates (with small pebbles of granites, basalts, cherts, and basic tuffs from the Chichibu terrane and much larger clasts of marlstone up to 1 m in diameter). There are also some boulder beds and armored mud balls and many early Pleistocene shelly fossils. End_Page 551------------------------------ Within the canyon-fill sediments, there are some unusual water-escape structures. The southern wall of the canyon is well exposed in a large quarry, where four steps occur in a vertical height of about 60 m. Upcanyon, these pass into fewer but higher steps. Small overhangs caused by protruding bedding surfaces are original features, as gravel fill still adheres to the marly walls. Canyon downcutting toward the east is shown by widening of the present outcrop of the fill in that direction, and eastward-moving paleocurrents are indicated by boulder imbrication. Rapid downcutting and filling is suggested by the well-preserved wall overhangs, and channeling within the fill sediments suggests that the deeply cut canyon was filled by several successive influxes of sediment. End_of_Article - Last_Page 552------------

Pilot Application of a Blocking Agent - Weyburn Unit, Saskatchewan

Channelblock is a gelatinous blocking agent that permanently reduces channeling in waterflooding operations. It diverts injection water into the tighter zones and thus effects higher waterflood recovery. The pilot operation described here illustrates a successful application on the edge of a fractured limestone reservoir. Introduction The Weyburn Unit is situated in southeastern Saskatchewan and encompasses an area of approximately 100 sq miles. The field was discovered in Jan. 1955 and was extensively developed by drilling 675 wells on 80-acre spacing (Fig. 1). A distinctive feature of this Mississippian Midale Beds pool and of other fields in the same part of the province is the presence of an anisotropic permeability system whose major axis is oriented northeast-southwest (Fig. 2). This fracture system, which was first recognized on the basis of oriented fracture cores, has been clearly identified by waterflood performance. Oil accumulation in this stratigraphic trap is found mainly in the Midale beds of the Charles formation of Mississippian age. The oil reservoir is subdivided into two distinct lithological units; the upper is the Marly limestone, and the lower is the Vuggy limestone (Fig. 3). The Marly rock is a microgranular carbonate characterized by fairly uniform porosity averaging 26 percent and low permeability averaging 4 md. The percent and low permeability averaging 4 md. The Vuggy is generally microcrystalline, fragmental limestone with extreme variations in pore size and in porosity-permeability distribution. Porosity averages porosity-permeability distribution. Porosity averages 11 percent and the permeability may vary between 0.1 and 4,000 md. Oil gravity varies with structural position from a low of 26 degrees API at the southern position from a low of 26 degrees API at the southern downdip limit to a high of 35.6 degrees API at the highest structural position to the north. An inverted nine-spot injection pattern was selected for waterflooding this type of limestone reservoir. Such a pattern was chosen because it could easily be converted to a line drive or a staggered line drive either by suspending the uneconomical on-trend wells or by converting them to water injection service. Flood Performance The waterflood scheme was implemented in June 1964. The angle that the fracture plane forms with the line connecting adjacent producers and injectors is the most important factor affecting the flood performance of each producer. performance of each producer. Fig. 4 shows that the performance of an on-trend well is characterized by a premature water breakthrough, rapid oil decline, and a sharp increase in water production. For this category of wells the estimated production. For this category of wells the estimated total waterflood recovery is approximately 8 to 12 percent of the original oil in place. percent of the original oil in place. Fig. 5 illustrates the performance of an off-trend well belonging to the same injection pattern. There was a gradual response to the flood for 2 or 3 years, and then there appears to have been a long subordinate phase. phase. The Marly zone is generally not fractured. In this zone the values of the factors governing the flood are as follows: mobility ratio, 0.32; Lorenz coefficient, 0.45; and permeability variance, 0.55. The Vuggy pay is fractured and has an average mobility ratio, Lorenz coefficient, and permeability variance of 1.75, 0.78, and 0.87, respectively. Furthermore, the water and residual oil saturations in the Vuggy are higher than in the Marly, resulting in a lower flushing efficiency. JPT P. 973

Channelblock Pilot-Area Application, Weyburn Unit, Saskatchewan

Abstract The results of treating a pilot area located on the east edge of the Weyburn Unit with Channelblock* are discussed in this paper. Channelblock is obtained by mixing polymer in low concentrations 0.05 to 0.1%) withwater and adding an "activator", which greatly changes the characteristics of the injected water to a gel-like material This gelled polymer gradually penetrates and adsorbs itself on the walls of the highly permeable streaks or fractures, thus diverting large quantities of water into tighter zones and resulting in a higher waterflood recovery. Introduction THE WEYBURN UNIT is situated in southeastern Saskatchewan and encompasses an area of approximately 100 square miles. The field was discovered in January, 1955 and was extensively developed during subsequent years by drilling 675 wells on 80-acre spacing (Fig. 1). A distinctive feature of this Mississippian Midale Beds pool and of other fields located in the same part of the Province is the presence of an anisotropic permeability system) with the major axis of permeability oriented in a northeast direction (Fig-2). This fracture system, which was first recognized an the basis of oriented fracture cores, has been clearly identified by waterflood performance. Oil accumulation in this stratigraphic trap is found mainly in the Midale Beds of the Charles Formation of Mississippian age. It is subdivided into two distinct lithological units; the lower is called the "Vuggy" limestone and the upper is called the "Marly" limestone (Fig 3). The Marly rock is a micro granular carbonate characterized by fairly uniform porosity and low permeability. The Vuggy rock is generally a microcrystalline, frag-mental limestone with extreme variations in pore size and in porosity- permeability distribution. Oil gravity varies with structural position from a low of 26 °API at the southern downdip limit to a high of 35.6 °API at the highest structural position to the north~ An aquifer of modest dimensions is generally present along the edges of the field. An inverted nine-spot injection pattern was selected for water-flooding this type of limestone reservoir because of the flexibility of this pattern, allowing for the conversion to a staggered line drive or a line drive when the on-trend wells along the fracture plane water out and the flood front moves toward the off-trend wells. Since the implementation of the waterflood injection scheme in June, 1964, the on-trend producers ha.ve generally shown early breakthrough ollowed by a rapid productivity decline, a sharp increase in water production and what appears to be a very short waterflood productive life. The flood performance of the off-trend and corner wells is essentially affected by their degree of stratification. This unfavourable waterflood performance has been substantially improved in a pilot "rea of the field by the use of Channelblock chemicals. It is the object of this paper to give a description of the treatment and a detailed presentation of the results obtained. GEOLOGY The Weyburn field is situated along the northeastern flank of the Wilnston Basin in southeastern Saskatchewan.

Die Entstehung der Poljen und ihre Stellung in der Karstabtragung, auf Grund von Beobachtungen im Taurus

The question of the origin of karst poljes still remains open despite certain advances achieved during recent decades. Observations in the western part of the middle Taurus between Lake Beysehir and the Mediterranean coast near Manavgat, especially in the neighbourhood of Akseki, and also west and north of Antalya in the western Taurus, have shown that there the real reason for the formation of karst plains is to be found in the deposition of insoluble debris in concave relief forms within the limestone area. The source of these alluvial deposits are the sandy and marly rocks which were incorporated into the limestone massif by the folding process. The polje basins are always situated in vales which were once sections of a genuine valley network and which were formed before the fractures in the limestone had become active in the karst hydrography (as understood by Otto Lehmann). In many cases, but not always, major guiding lines of this valley mesh are tectonically determined. After genuine karst formation has set in (i. e. underground drainage), and when the drainage has ceased to run in one direction, closed circumference karst hollows with nonsoluble rocks in their catchment area function as vessels for the deposition of the waste material of these rocks. As long as the infilling continues the deposits take on a fan shape. These fans make the limestone basic layer impermeable so that the water of the streams causing the deposit disappears at the lower end of the fans into the cracks in the limestone, where then pronounced karst erosion takes place. The limestone slopes forming the frame recede with a cliff-like lower section. The fan surface, i. e. the polje surface, occupies the area where the limestone mountain frame was pushed back by corrosion, and the alluvial plain stretches nearly horizontally across the remaining limestone strata. These may dip in any direction. lt is thus that a karst pediment surface, thinly covered with alluvial material, is originated. The conical fan shape of the polje bottom can only be preserved while insoluble deposits are brought into the polje. Once an appreciable supply of such material ceases, the polje bottom gradually assumes an almost plain or gently undulating surface as is the case for instance in many of the !arge poljes of the Dinaric karst. Polje formation is thus neither linked with a karst water table nor, as a rule, with the sea level. The formation is initiated and continued by local causes, as for example the occurrence of water transportable impermeable rocks within the limestone region or at its margins, and the existence within the limestone region of local areas of deposition for the waste products of such rocks. Generally speaking polje formation cannot therefore be considered as a definite stage in a karst erosion cycle, nor can it be linked with peneplain formation as understood by W. M. Davis. It appears that the formation of enclosed poljes is a peculiarity of the periodically dry sub-tropics and the middle latitudes, whereas in the humid and intermittently humid tropics, as well as in the permanently humid sub-tropics with hot summers, formation of karst plains usually occurs in relation to the level of surface streams.

Remarkable Fossil Oysters from Syria

IN examining a series of more than one hundred specimens of Ostrea (Exogyra) flabellata, Goldfuss, from the Middle Cretaceous of Lebanon, I was struck with the marked reproduction in the free upper valves of the figures of other shells to which the lower valves have been attached. These specimens were all collected in the same place, a hill near Bhamdun, Mount Lebanon, Syria. They have been freed by weathering from a soft marly rock exceedingly rich in fossils. Specimens of Ostrea, Plicatula, Pecten and Anomia have the shell well preserved. Many others, including species of Cardium, Trigonia, Corbula, Isocardia, Cytherea, Leda, Nucula, Cerithium, Alaria, Melo, Pterocera, Turritella, Natica and others are preserved only as casts. Consequently the shell to which the oyster was attached has usually disappeared, except in those cases in which it was attached to one of its own species. More than half of the specimens have the two valves united and free from adhesions, so that they are capable of exhibiting the phenomenon referred to. More than nine-tenths of these show more or less clearly in the upper valve the figure impressed upon the lower valve by the shell to which the latter adhered.

On the Physical Relations of the Reptiliferous Sandstone near Elgin

Abstract R eferring to Sir R. Murchison’s sections of the Elgin district, published in the Quart. Journ. Geol. Soc. No. 59, pp. 424 and 428, which show a conformable sequence of strata from the Old Red Sandstone of Foths to the yellow sandstone and cornstone of Lossiemouth and Burgh Head, the author first stated that the siliceous marly rocks, or so-called “cornstones” of Glassgreen, Linksfield, Spynie, Inveragie, and Lossiemouth are in reality very dissimilar to the cornstones of Foths and Cothall; and he then pointed out the improbability of the so-called cornstone of Glassgreen continuing to dip north-westwardly under the sandstone of the Quarry-wood Ridge, especially as near Linksfield it is, at different spots, seen to dip away from that ridge. Evidence also of a break in the strata at the Bishop Mill quarries was advanced to show that the sandstone beneath this “cornstone” (presumed to be the Reptiliferous sandstone) is probably brought by a fault against the lower or Holoptychian sandstone, which latter towards Spynie the author thinks is surmounted by the Reptiliferous sandstone, and this last conformably by a marly siliceous rock or so-called “cornstone.” Beyond Spynie Loch, northward, the author supposed that another fault had again brought up the sandstone with Stagonolepis and Hyperodapedon at Lossiemouth. Beyond this a cornstone-like rock is again seen to cover the sandstone. The author then referred to the probable Liassic and Triassic character of the shales at Linksfield, and dwelt upon the suggestion that had been offered as to the probability of the layer of boulder-clay beneath the shales having been due to the mass of shales being a portion of a cliff in the glacial period, and having then slipped from a higher level. Regarding these shales as having been removed merely by a slip from their original site, and as conformably over-lying the calcarco-siliceous rock and sandstone beneath, Mr. Symonds expressed his belief that this sandstone, shifted by a fault against the Holoptychian sandstone at Quarry-wood, must be the Reptiliferous sandstone and of Triassic age. Lastly he remarked that the pebble-beds and sandstone, track-marked and rippled, of Burgh Head are far more like the Triassic conglomerates of England than like the Old Red rocks of Cothall and Foths.