Draft:Original research/Petrophysics

Petrophysics is the study of the parameters related to rocks. In the petroleum upstream industry, study focuses on the parameters involved in reserve estimation and fluid flow simulation (e.g. porosity, permeability, fluid saturations). This science is one of the major parts of reservoir study and reservoir characterization.

Petrophysics is the study of physical and chemical rock properties and their interactions with fluids.

Petroleums
Def. a "flammable liquid ranging in color from clear to very dark brown and black, consisting mainly of hydrocarbons, occurring naturally in deposits under the Earth's surface" is called a petroleum.

Sedimentary rocks
Def. "one of the major groups of rock that makes up the crust of the Earth; formed by the deposition of either the weathered remains of other rocks, the results of biological activity, or precipitation from solution" is called a sedimentary rock.

Saprolites
Def. "a chemically weathered rock" is called a saprolite.

Aeolianites
Def. a "rock formed from dune sand, often calcareous" is called an aeolianite.

Turbidites
Def. "sea-bottom deposits formed by massive slope failures where rivers have deposited large deltas" are called turbidites.

"Turbidites [shown in the image on the right] are sea-bottom deposits formed by massive slope failures where rivers have deposited large deltas. These slopes fail in response to earthquake shaking or excessive sedimentation load. The temporal correlation of turbidite occurrence for some deltas of the Pacific Northwest suggests that these deposits have been formed by earthquakes."

"Turbidites (interbedded with mudstones/siltstones) from the Ross Sandstone Formation Turbidite system of Namurian age in County Clare, Western Ireland. The sandstone beds were formed in a deep basin by turbidites coming from a delta area."

Marginal marines
The marginal marine sequence on the right has been dated to the Middle Triassic.

Limestones
The middle Triassic layers of alpine limestone in the image on the right were deposited on the bottom of a shallow sea.

Layered sediments
Def. secondary "rings or bands resulting from rhythmic precipitation in a gel, or within a fluid-saturated rock" are called Liesegang rings.

"The ruin marble structure of the Cretaceous/Paleogene fine-grained marly limestone from the Outer Flysch Belt of the Western Carpathians has a non-tectonic origin, according to structural and sedimentological evidence. Distinctive offsets of coloured red-brownish ferric oxyhydroxide bands are not due to displacements along rock-cutting fractures, as they superficially appear to be. Evidences for shear movement along these pseudo-faults were not observed. Band offsets result from different velocities of pervasively diffusing fluids, precipitating ferric oxyhydroxides in corridors bounded by sets of mineralised systematic joints. During rock weathering, calcite-filled joints operated as barriers for lateral fluid diffusion, but enabled longitudinal diffusion along healed joints."

Theoretical petrophysics
Def. the "physics of rock, especially rock that acts as a reservoir for petroleum or other fluids " is called petrophysics.

Electromagnetics
"Continuous measurements made in the field included dielectric profiling and electrical conductivity (related to the concentrations of neutral salts and acid)."

Lithification
Def. the "compaction and cementation of sediment into rock" is called lithification.

Def. a "subdivision of any stratigraphic unit that has characteristic lithologic features" is called a lithofacies.

Def. the "formation of sedimentary rock" is called lithogenesis.

Def. "an element that forms silicates or oxides and is concentrated in the minerals of the Earth's crust" is called a lithophile.

Bedrocks
Def. a "solid rock that exists at some depth below the ground surface" is called a bedrock.

"Bedrock is rock "in place", as opposed to material that has been transported from another location by weathering and erosion."

Usage notes

"In mountainous regions, bedrock can be seen at the surface. However, these occurrences are more properly called outcrops."

Petrology
Def. "the study of the origin, composition and structure of rock" or rocky objects is called petrology.

Petrochemistry
Many rocky objects are composed of oxide minerals. Oxygen has three known stable isotopes: 16O, 17O, and 18O.

"The stable isotopic compositions of low-mass (light) elements such as oxygen, hydrogen, [helium, lithium, beryllium, boron,] carbon, nitrogen, [fluorine, neon, sodium, magnesium, aluminum, silicon, phosphorus,] and sulfur are normally reported as "delta" ([δ]) values in parts per thousand (denoted as ‰ [per mille]) enrichments or depletions relative to a standard of known composition."

For 18O to 16O:


 * $$\delta ^{18}O = \Biggl( \frac{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{sample}}{\bigl( \frac{^{18}O}{^{16}O} \bigr)_{standard}} -1 \Biggr) * 1000\ ^{o}\!/\!_{oo}$$

The "ratio [by convention is] of the heavy to light isotope in the sample or standard."

"Various isotope standards are used for reporting isotopic compositions; the compositions of each of the standards have been defined as 0‰. Stable oxygen and hydrogen isotopic ratios are normally reported relative to the SMOW standard ("Standard Mean Ocean Water" (Craig, 1961b)) or the virtually equivalent VSMOW (Vienna-SMOW) standard. Carbon stable isotope ratios are reported relative to the PDB (for Pee Dee Belemnite) or the equivalent VPDB (Vienna PDB) standard. The oxygen stable isotope ratios of carbonates are commonly reported relative to PDB or VPDB, also. Sulfur and nitrogen isotopes are reported relative to CDT (for Cañon Diablo Troilite) and AIR (for atmospheric air), respectively."

"Ordinary water consists of slightly different kinds of so-called isotopic water molecules of equal chemical properties but different masses: a light one (H2O16), which occurs most frequently by far in natural waters, and quite a few heavier ones, of which the H2O18 and the [deuterium, D) HDO16 components occur in concentrations of approximately 2000 and 320 ppm (parts per million) water molecules, respectively. Due to slightly different vapour pressures and rates of reaction, the concentrations of the isotopic components change somewhat during phase-shifts in the natural water cycle".

Ice "cores contain a wealth of information on past climates in the form of a great number of parameters, of which some are listed below:"
 * 1) Concentrations of the oxygen-18 and deuterium components of water in the ice give information about the cloud temperature and precipitation at the time of deposition,
 * 2) the content of air in bubbles reveals the altitude of the then ice surface,
 * 3) the concentrations of carbon dioxide and methane in the air bubbles tell about the greenhouse effect in past atmospheres,
 * 4) the chemical composition of the ice itself gives information about other aspects of the chemistry in past atmospheres,
 * 5) dust and calcium concentration tell about the violence and frequency of the storms that carried dust from ice free areas to the inland ice, and
 * 6) the acidity of the ice indicates the fall-out of volcanic acids and thereby past volcanic activity.

Inclusions
"A sliver of Antarctic ice [in the image at the right reveals] the myriad enclosed tiny bubbles of air. Air bubbles trapped in ice hundreds or even thousands of years ago are providing vital information about past levels of greenhouse gases in the Earth's atmosphere." The image at the left shows the crystals and air bubbles in polarized light which varies with grain orientation.

"The only visible inclusions in glacier ice are the air bubbles, particularly as far as 14C, 10Be, and the greenhouse gases CO2 and methane are concerned [...]. The invisible inclusions, micro particles and chemical impurities, had potential to reveal other interesting facets of the environment of the past".

Invisible "inclusions in the ice, especially dust and strong acids [...] are deposited with the snow. During interglacial time most of the dust comes from spring-dry areas in North America, and most of the strong acids always originate from volcanic eruptions in the northern hemisphere."

A "Coulter counter [...] measures the concentration and size distribution of microscopic dust particles in the ice, which render information about the origin of the dust and the frequency and strength of the storms that bring it to Greenland."

The "Crête core [contains] the fall-out of insoluble dust particles from the continents tops in early summer. Therefore, a continuous profile of the dust concentration along an ice core would allow a year by year dating by counting summer maxima downward from the surface, just like counting δ-maxima. Counting dust maxima may even extend the dating further back in time, because dust does not diffuse like the isotopic components of water"

"Greenland ice deposited through the glaciation contains up to 100 times more dust than post-glacial ice. The summer maxima drown more or less in the high background values that are caused partly by dryer and more stormy climate then, partly by vast areas north of Siberia being drained due to lowering of the sea level, which creates a most efficient source of dust. In contrast, the dust counting method works also on glacial ice in Antarctica, where the air has always contained very little dust. There is simply no large ice-free land areas nearby that may serve as sources of dust."

A "method for detecting great volcanic eruptions in the past [included] a series of conventional acidity (pH) measurements on ice samples deposited about A.D. 1783, when the Icelandic volcano Laki had a giant eruption. As expected, the 1783 layer was highly acid owing to fall-out of sulphuric acid. The volcano emitted sulphur dioxide (SO2) into the higher atmosphere, where it was quickly converted into tiny droplets of diluted sulphuric acid. Soon after they have fallen down into the lower atmosphere they are washed out by precipitation".

Layered sediments
Def. "a pair of sedimentary layers, a couplet, that form in an annual cycle as the result of seasonal weather changes" is called a varve.

"Typically formed in glacial lakes a varve couplet consists of a coarser grained summer layer formed during open-water conditions, and a finer grained winter layer formed from deposition from suspension during a period of winter ice cover. Many varve deposits contain hundreds of couplets."

"The ruin marble structure of the Cretaceous/Paleogene fine-grained marly limestone from the Outer Flysch Belt of the Western Carpathians has a non-tectonic origin, according to structural and sedimentological evidence. Distinctive offsets of coloured red-brownish ferric oxyhydroxide bands are not due to displacements along rock-cutting fractures, as they superficially appear to be. Evidences for shear movement along these pseudo-faults were not observed. Band offsets result from different velocities of pervasively diffusing fluids, precipitating ferric oxyhydroxides in corridors bounded by sets of mineralised systematic joints. During rock weathering, calcite-filled joints operated as barriers for lateral fluid diffusion, but enabled longitudinal diffusion along healed joints."

Fossils
"Microscopic shells in seafloor sediment collected from Blake Ridge. The large, round shell at the top left of the image is a planktonic pteropod about 0.25mm across. The triangular shell immediately underneath is a benthic, or bottom dwelling, foraminifer, Bolivina. All other larger shells, including the pink one (Gloobigerinoides), are planktonic foraminifers. The planktonic shells have fallen from the surface waters to the seafloor."

Geochronology
Shallow cores, or the upper parts of cores in high-accumulation areas, can be dated exactly by counting individual layers, each representing a year. These layers may be visible, related to the nature of the ice; or they may be chemical, related to differential transport in different seasons; or they may be isotopic, reflecting the annual temperature signal (for example, snow from colder periods has less of the heavier isotopes of H and O). Deeper into the core the layers thin out due to ice flow and high pressure and eventually individual years cannot be distinguished. It may be possible to identify events such as nuclear bomb atmospheric testing's radioisotope layers in the upper levels, and ash layers corresponding to known volcanic eruptions. Volcanic eruptions may be detected by visible ash layers, acidic chemistry, or electrical resistance change. Some composition changes are detected by high-resolution scans of electrical resistance. Lower down the ages are reconstructed by modeling accumulation rate variations and ice flow.

Dating is a difficult task. Five different dating methods have been used for Vostok cores, with differences such as 300 years per meter at 100 m depth, 600yr/m at 200 m, 7000yr/m at 400 m, 5000yr/m at 800 m, 6000yr/m at 1600 m, and 5000yr/m at 1934 m.

Different dating methods makes comparison and interpretation difficult. Matching peaks by visual examination of Moulton and Vostok ice cores suggests a time difference of about 10,000 years but proper interpretation requires knowing the reasons for the differences.

Sediment cores
Sediment cores may be obtained "by drilling or jack-hammering a steel rod or shoving a hand auger or hollow "push core" into a beach or marsh or water bottom, and pulling up sediment samples for analysis."

"You can think of a sediment core as being more or less a tape recorder of time. Within that sediment core, we work with proxies, or environmental proxies, and these can be very simple measures of grain size or composition or some organic geochemical property or maybe pollen."

"There are environments that preserve storm records that are buried in the sea bed, so that you can go down through time and actually develop a record of the intensity and frequency of cyclonic storms. That's something that's pretty high up on the radar for coastal inhabitants. Kind of understanding the pattern of these storms through time helps us to understand what might be coming down the pike."

"You take a sediment core through a barrier island and under that is marsh, bay, marsh, mainland. You have maybe an old forest, roots. Looking back in time at that location, hundreds of thousands of years ago, you get this vertical succession of these different layers."

Stratigraphy
"The time scale to the right [in the diagram at the right] gives calculated ages in millennia. It has later been changed, particularly beyond 60.000 years. The double arrows show probable simultaneous events. In the coldest part of the glaciation, the climate obviously varied much more violently in Greenland than in Antarctica, probably due to strongly shifting ice cover in the North Atlantic Ocean. Note also the difference at the termination of the glaciation."

An "ice dating method based on the radioactive 36Cl/10Be ratio [ref.11.8 has been applied to Dye 3. The] hydrogen peroxide concentration varies seasonally [ref.11.9] and may thus be used as an additional way of annual layer identification [The image at the left] shows δ-profiles along the deepest c.300 m, of the surface to bedrock ice cores from Dye 3 and Camp Century. The 10 double arrows point at common features suggesting layers of simultaneous deposition. Down to arrow No. 1 the two records are obviously similar indicating that the abrupt δ-shifts during late glacial time are outcomes of events common for the entire ice cap. Below arrow No. 1, however, the two records do not agree in detail. Probably, the Dye 3 core does not reach continuously as far back in time (90,000 years at most) as the Camp Century core, which is not surprising in view of the hilly bedrock upstream. The very deepest part may be of Eemian origin, though, i.e. from the last interglaciation some 125,000 years ago, but the stratigraphy is hardly undisturbed."

"Down to a depth of 2750m the two profiles [in the figure at the lower right] are essentially identical, but they are different in ice from the Eem period. The layer sequence is disturbed in the GISP2 core. Is this also the case for the GRIP core?"

Materials
Many materials can appear in an ice core. Layers can be measured in several ways to identify changes in composition. Small meteorites may be embedded in the ice. Volcanic eruptions leave identifiable ash layers. Dust in the core can be linked to increased desert area or wind speed.

Isotopic analysis of the ice in the core can be linked to temperature and global sea level variations. Analysis of the air contained in bubbles in the ice can reveal the palaeocomposition of the atmosphere, in particular CO2 variations. There are great problems relating the dating of the included bubbles to the dating of the ice, since the bubbles only slowly "close off" after the ice has been deposited. Nonetheless, recent work has tended to show that during deglaciations CO2 increases lag temperature increases by 600 +/- 400 years. Beryllium-10 concentrations are linked to cosmic ray intensity which can be a proxy for solar strength.

There may be an association between atmospheric nitrates in ice and solar activity. However, recently it was discovered that sunlight triggers chemical changes within top levels of firn which significantly alter the pore air composition. This raises levels of formaldehyde and NOx. Although the remaining levels of nitrates may indeed be indicators of solar activity, there is ongoing investigation of resulting and related effects of effects upon ice core data.

Ice cores
An ice core is a cylindrical sample of a rocky object consisting mostly of water ice. As shown in the image at the right, the long axis is in the direction of the coring into the object from its outer surface.

An ice core is taken with a hollow drill supported by a rig.

Technology
A Petrophysics Laboratory conducts dielectric spectrographic analysis of rock samples including core samples and powdered drill cuttings.

Coring
A core is collected by separating it from the surrounding material.

A diagram showing the components of a drill is at the right. The coring end of the drill has knives attached as shown in the image at the left. The drill above the knives is a hollow steel tube. The inner tube holds the ice core and the outer tube collects the cuttings or shavings from the action of the knives.

To power and stabilize the drill for coring, a rig such as in the photo at the second left is used.

The length of the drill barrel determines the maximum length of a core sample. Collection of a long core record requires many cycles of lowering a drill assembly, cutting a core 4–6 m in length, raising the assembly to the surface, emptying the core barrel, and preparing another assembly for drilling.

"Boring ice to depths in excess of about 300 meters requires a fluid with a density closely matched to that of ice to prevent lithostatic pressure from causing plastic collapse of the borehole; the latter frequently results in loss of the drilling equipment. The fluid, or mixture of fluids, must simultaneously satisfy criteria for density, low viscosity, frost resistance, as well as workplace safety and environmental compliance over both the short term (e.g., fire hazard and acute toxicity) and long term (chronic toxicity, local and global environmental degradation). The fluid must also satisfy other criteria, for example those stemming from the analytical methods employed on the ice core."

"A number of different fluids and fluid combinations have been tried in the past. Since GISP2 (1990-1993) the US Polar Program has utilized a single-component fluid system, n-butyl acetate, but the toxicology, flammability, aggressive solvent nature, and longterm liabilities of n-butyl acetate raises serious questions about its continued application."

"The European community, including the Russian program, has concentrated on the use of two-component drilling fluid consisting of low-density hydrocarbon base boosted to the density of ice by addition of halogenated-hydrocarbon (s.l.) densifier. Many of the proven densifier products are now considered too toxic, or are no longer available due to efforts to enforce the Montreal Protocol on ozone-depleting substances."

In April 1998 on the Devon Ice Cap filtered lamp oil was used as a drilling fluid. In the Devon core it was observed that below about 150 m the stratigraphy was obscured by microfractures.

When the drill barrel is filled, the barrel is removed from the rocky object and maneuvered, oriented, or tilted, as in the third image at the left, so that the ice core may be released, being performed in the image on the lowest left.

"A VIMS field crew [assembled in the image on the right] collects sediment cores on the landward side of the Plum Island barrier island in May 2014. These cores were collected with a Geoprobe drill rig [shown] and went as much as 60 feet below the surface of the island. Cores were collected in 4 feet sections and brought back to VIMS for processing."

A sediment core sample extracted for the ANtarctic geological DRILLing program known as ANDRILL is shown on the right. Sediment and rock core were extracted from the ocean floor under the Ross Ice Shelf during the 2006-2007 austral summer.

Logs
Def. the "analysis and recording of the strata penetrated by the drill of an oil well as an aid to exploration" is called well logging.

In the image on the right, the cabin contains a place for operators and electronics. The reel of wire is used for lowering and recovering of sensors.

In the image on the top left, the temperature of the earth is measured at discrete locations in a well bore.

In the second image on the left, the impedance logs are inverted from amplitude measured at discrete locations in a well bore.

Hypotheses

 * 1) Sedimentary rocks carrying petroleum must have a hard cap rock and hard bedrock.
 * 2) Sediment occurs from the action of rocky, liquid, gaseous, and plasma objects.