Isolation Of Kerogen And Bitumen

Isolation of kerogen and bitumen

Kerogen is the naturally occurring, solid, insoluble organic matter that occurs in source rocks and can yield oil upon heating. Kerogen is the portion of naturally occurring organic matter that is non
extractable using organic solvents. Typical organic constituents of kerogen are algae and woody plant material. Kerogens have a high molecular weight relative to bitumen, or soluble organic matter. Kerogens are described as Type I, consisting of mainly algal and amorphous (but presumably algal) kerogen and highly likely to generate oil; Type II, mixed terrestrial and marine source material that can generate waxy oil; and Type III, woody terrestrial source material that typically generates gas. Bitumen forms from kerogen during petroleum generation.

Bitumen is a naturally-occurring, inflammable organic matter formed from kerogen in the process of petroleum generation that is soluble in carbon bisulfide. Bitumen includes hydrocarbons such as asphalt and mineral wax. Typically, solid or nearly so, brown or black, bitumen has a distinctive petroliferous odor. Laboratory dissolution with organic solvents allows determination of the amount of bitumen in samples, an assessment of source rock richness.

Kerogen, complex waxy mixture of hydrocarbon compounds that is the primary organic component of oil shale. Kerogen consists mainly of paraffin hydrocarbons, though the solid mixture also incorporates nitrogen and sulfur. Kerogen is insoluble in water and in organic solvents such as benzene or alcohol.  kerogen is the organic matter that are deposited, it can be made up of different types. Example micro-organism, sea plants, land plants etc.

Different type of Kerogen produces different type of hydrocarbon

Type I Kerogen

This type of Kerogen comprises organic matter of microorganisms which is mostly from sea, they settle down at the bottom of the sea when they die and deposit. These type gives mostly oil and less gas.

Type II Kerogen

This comprises mostly of the sea plants and less animal so they care to generate oil and gas but mostly gas and less oil.

Type III Kerogen

This has the terrestial (land) plants and as you know coal is formed by the remains of plants so type 3 gives coal and less oil and gas comparative higher proportion.

Type IV Kerogen

This type of kerogen is oxidized and in order for the hydrocarbon generation the organic matter should not be oxidized or they will not produce the fuel. So the type 4 give inert gases as organic matter is oxidized and produce less gas, not economical.

Kerogens are of geochemical interest because they represent one of the most abundant forms of carbonaceous materials. The term “kerogen”, or “oil-former”, was originally given to the organic matter in oil shales, torbanite, kukersite, and others. Recently, broader usage has been made of the term in describing the insoluble organic material present in no reservoir sedimentary rocks and other rocks. The soluble organic materials associated with oil-shale kerogens are of particular interest because they are usually indigenous to the formation and have had little opportunity for migration because of the low porosity and low permeability of the formations.

By this classification, the term" kerogen rocks" describes sedimentary deposits containing insoluble organic kerogen which on distillation yields an oil equivalent to more than 50 percent of the organic content of the rock. Similarly, the term "kerogen coals" describes sedimentary materials containing organic matter which upon distillation yields an oil equivalent to more than 10 percent and less than 50 percent of the organic content. In the present discussion, the term "kerogen" will be used to describe the insoluble organic material present in kerogen rocks.  the term "bitumen" will be used to describe the soluble organic material present in the kerogen rock based upon solubility in a hydrocarbon solvent. Other nomenclature will be self-explanatory. For example, the material solubilized by methanol will be referred to as "methanol-soluble material".

The discussion covers the isolation of kerogen, bitumen, fatty acids, porphyrins, amino acids, and carbohydrates from kerogen rocks. The procedures as described are intended to be informative without any implication of recommended usage. Other methods are applicable and in some circumstances may be preferred. Likewise, the articles reviewed were chosen for the subject matter discussed and no attempt has been made to completely review the subject.

Isolation of kerogen

One important problem in kerogen constitutional studies is the isolation of unaltered kerogen from its associated mineral. The problem of the isolation of kerogen is complicated by extreme differences in mineral content and mineral.

Composition of the kerogen rock. Some kerogen rocks contain as little as 5 percent mineral while others may contain as much as 95 percent mineral. Some sediments are highly argillaceous while others highly calcareous. Some kerogen rocks contain large amounts of pyrite but others contain little pyrite.

 Pyrite is extremely difficult to separate from the organic material because of an apparent attraction for the kerogen. Thus, it is understandable that the best available separation techniques do not find universal application.

In studies of oil shale at the Bureau of Mines laboratory, techniques other than those to be described such as electrostatic, magnetic, ultrasonic, and flotation separations have been tried with only limited success.

Separation techniques

Should ideally remove all mineral matter from the organic kerogen without fractionating the kerogen into dissimilar components or altering the kerogen chemically. At the present time this has not been accomplished. The methods to be described consist of the modified

1.      Quass

2.      Sink-float,

3.      Acid digestion

4.      Pyrite removal.

A common kerogen isolation method involves hydrochloric and hydrofluoric acid extractions, which remove carbonate and silicate mineral phases, respectively

Hydrochloric acid extractions

The isolation of the insoluble fraction of oil shale organic, kerogen, has been attacked with many methods, both chemical and physical, by previous workers. The present work attempts to combine these techniques into a simple method which produces material representative of kerogen in situ. The isolation technique involves an acid wash with hydrochloric acid for removal of carbonates, Soxhlet extraction with a mixture of methanol and toluene for removal of soluble organics (bitumens)

Hydrofluoric acid extractions

hydrofluoric acid treatment for removal of silicates, and reduction with lithium aluminum hydride for removal of pyrites. The ash content of the resulting kerogen is roughly 5 %, comparable to methods employing substantially longer contact times and higher temperatures. The elemental analysis of the product is similar to that of kerogen isolates in the literature. The yield of kerogen is considerably higher than that obtained by physical isolation methods.

Isolation of bitumen

Organic solvents

The method of isolation exploits the different solubility of bitumen in organic solvents. We treat the rock sample with organic solvents (we use a 9:1 mixture of methanol: DCM) to isolate the bitumen, which is soluble

Silica column fractionation

perform an isotopic analysis on the bitumen, to get a bulk carbon isotopic composition, and further analyses the bitumen using pyrolysis. With the bitumen, we continue to isolate using silica column fractionation.

Gravity isolation

It involves the isolation of bitumen from sand using water-based gravity isolation. Although plant configurations vary across the operators. In order to isolate the bitumen droplets, the bitumen must first be liberated from the sand grain. Once liberated (which mostly occurs during Hydrotransport), the hydrophobic (water-fearing) bitumen will seek to attach itself to any free air bubbles. This aerated bitumen droplet is relatively light and will float to the top of the gravity isolation vessel. The coarse sand particles contained in the slurry are heavy and will immediately sink to the bottom.

Question 2. Describe pyrolysis

Pyrolysis a type of geochemical analysis in which a rock sample is subject to controlled heating in an inert gas to or past the point of generating hydrocarbons in order to assess its quality as a source rock, the abundance of organic material in it, its thermal maturity, and the quality of hydrocarbons it might generate or have generated. Pyrolysis breaks large hydrocarbon molecules into smaller molecules. This process is used to determine the quality of shale as a source rock and is instrumental in evaluating shale gas plays.

Pyrolysis is the decomposition of organic matter by heating in the absence of oxygen. Organic geochemists use pyrolysis to measure richness and maturity of potential source rocks. In a pyrolysis analysis, the organic content is pyrolyzed in the absence of oxygen, then combusted. The amount of hydrocarbons and carbon dioxide released is measured. The most widely used pyrolysis technique is Rock-Eval.

In Rock-Eval pyrolysis, a sample is placed in a vessel and is progressively heated to 550°C under an inert atmosphere. During the analysis, the hydrocarbons already present in the sample are volatized at a moderate temperature.

This process converts kerogen in oil shale into shale oil by pyrolysis, hydrogenation, or thermal dissolution. Therefore, Shale oil is an unconventional oil produced from oil shale rock fragments by pyrolysis, hydrogenation, or thermal dissolution. Different geochemical scales, such as vitrinite reflectance, pyrolysis Tmax, and biomarker maturity ratios can be used to indicate the level of thermal maturity of organic matter.

The amount of hydrocarbons is measured and recorded as a peak known as S1. Next pyrolyzed is the kerogen present in the sample, which generates hydrocarbons and hydrocarbon-like compounds (recorded as the S2 peak), CO2, and water The CO2 generated is recorded as the S3 peak. Residual carbon is also measured and is recorded as S4.

Question 3. Describe Geochemical methods

Geochemical method is a method of petroleum exploration that utilizes systematic measurements of one or more chemical properties of a naturally occurring material. The materials analyzed most commonly are rock, soil, stream and lake sediment, natural waters, vegetation and soil air.

Geochemical methods used in exploring for oil and natural gas are based on the premise that hydrocarbons migrate upward from subsurface petroleum accumulations and produce anomalous patterns near the surface.

Geochemical exploration techniques are both direct or indirect.

·         Direct techniques require analysis of microquantities of hydrocarbons that occur in the free state in the soil interstices or that are adsorbed on the fine-grained portions of the soil.

·         Indirect geochemical methods are based on the detection, in near-surface soils or in vegetation, of inorganic alteration products that result from upward migration of hydrocarbons.

Geochemical Methods are based on the assumption that the hydrocarbon found in an oil pool tent to migrate upwards because of their lower density, some of these hydrocarbon molecules may eventually reach the surface. In the proved oil/gas fields, the samples of surface are likely to have a comparatively high percentage of hydrocarbon content.  Similarly, higher than average chloride content could be expected around the edges of an oil pool left by the water which has migrated and evaporated.

Geochemical method is still in an experimental stage and requires extremely precise analysis technique. It is interesting for an oil explorer because of its direct approach.  The geochemical methods generally used are: -

Micro gas survey:

The area under investigation is divided into profiles. The interval of the profiles is decided, depending upon the work and generally the distance of 2 kms taken. The laying of the profiles is just the same as is being done in case of seismic survey. The samples of the circulating mud were collected at 5 to 10m interval from exploratory wells. After the samples were collected they were taken to the laboratory for degassing.

Gas Logging:

Gas Logging which is one of the geochemical methods of prospecting for hydrocarbons is a continuous method unlike other geophysical methods. Therefore, on exploratory wells where there may be a danger of blow out, application of gas logging is a boon. It records gas shows which are present in the mud in the form of micro concentrations.

Hydro chemical surveys:

This method analyses formation water properties as it is closely involved in the primary mechanism that causes the accumulation, preservation and destruction of oil and gas fields. Water serves as a vehicle in transporting the hydrocarbons from their source bed to a trap, where they accumulate.

Organo - Hydro Chemical Survey:

Natural gases are understood to diffuse into edge waters only a few kilometers from petroleum accumulation. Aquifers overlying oil/gas pools show anomalous concentration of gaseous hydrocarbons. Dissolved organics have significantly high concentration in interstitial waters in source rocks during primary migration and in water expelled during clay mineral digenesis.

Define petrography for oil and gas exploration and describe basic microscopic organic analysis

Petrography is the examination of rocks in thin section. Rock samples can be glued to a glass slide and the rock ground to 0.03-mm thickness in order to observe mineralogy and texture using a microscope. (A petrographic microscope is a transmitted-light polarizing microscope.) Samples of sedimentary rock can be impregnated with blue epoxy to highlight porosity.

A petrographic analysis is an in depth investigation of the chemical and physical features of a particular rock sample. A complete analysis should include macroscopic to microscopic investigations of the rock sample.

A petrographic analysis is critical when trying to learn about a rock, reservoir, or formation of interest. The scale of investigation depends on the importance of the particular sample of interest. To fully describe and characterize a rock takes varying stages of analysis beginning with an outcrop or hand sample

The petrographic microscope provides a direct visual means of observing and measuring the chemical and physical properties of sedimentary rocks. Through its use the geologist is able to study the details and relationships of a sediment that have a direct bearing on the majority of our exploration problems. Petrographic information is being used effectively now to supplement other types of geological and engineering data in the following ways:

(a)   to assist in the interpretation of depositional environments, textural trends and facies patterns by revealing the primary character of the rock, i,e., composition, texture and fabric;

(b)   by showing the secondary changes that the rock has undergone since deposition such as mineral alteration, the development of solution cavities, fracturing and cementation;

(c)   by providing a visual method of analysing porosity and its relationship to both the primary character and the secondary changes;

(d)   by revealing the age relationship between cementation, fracturing and porosity development with respect to the times of fluid movement and to the time of oil accumulation, and

(e)   by providing detailed mineralogical data that can be applied statistically toward the identification and correlation of specific sedimentary bodies.

Micro analytical instrument to analyze the organic constituents of particulates and inhomogeneous samples with spatial resolution of approximately 40 pm. this method, two-step laser desorption/laser ionization mass spectrometry (L2MS), uses an Infrared laser to volatilize constituent molecules intact and an ultraviolet law to ionize desorbed molecules in a selective manner with little or no fragmentation.

Although the elemental analysis of particulates and samples that are inhomogeneous on a microscopic scale is a highly- developed technology, the organic analysis of such samples presents a challenge because of thermal fragility. To take advantage of sensitive gas-phase techniques, such as mass spectrometry, the sample must be volatilized; however, traditional evaporation methods, such as resistive heating, often result in decomposition rather than volatilization of thermally labile compounds. Moreover, the smaller the sample size or the finer the heterogeneity, the greater the need for highly localized heating.

In recent years several sensitive techniques for the organic analysis of microscopic quantities of solid samples have been developed. Methods, such as secondary ionization mass spectrometry (SIMS) and laser microprobe mass analysis (LAMMA), cause the ejection of ions from the sample by bombardment with a high-energy beam consisting of ions in the former method and photons in the latter. The ion and laser beams can be focused onto the sample, enabling microscopic analysis of samples. Briggs has demonstrated the use of static or low-dose SIMS for the microanalysis of heterogeneous polymeric surfaces, while Gillen et have successfully applied dynamic or high-dose SIMS to the analysis of organic molecules deposited on a conducting surface.

Scanning Electron microscope (SEM)

SEM is a type of electron microscope that produces images of a sample by scanning it with a focused beam of electrons. The electrons interact with atoms in the sample, producing various signals that contai information about the samples surface topography and composition.

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