TOP 7 EXPLORATION TECHNIQUES FOR CRUDE OIL

The selection of a drilling site is a tricky and costly affair. Though some visible evidence of a hydrocarbon source, like seepage of oil and gas from the surface, the visual appearance of surface and vegetation, the presence of oil or gas in fountains or rivers, etc., are sometimes used in locating crude oil and gas reserves, and many ancient oil fields were discovered by these events. But, today, such fortunate events are very rare and sometimes may not always be suitable for commercial exploitation. Modern exploration techniques for petroleum use geophysical, geochemical, and geotechnical methods. Exploration of the surface of Earth can be useful for imaging or mapping sub-surface structures favorable for oil and gas accumulation. In the geophysical methods, gravimetric, magnetometric, seismic, radioactive, and stratigraphic studies of the surface are gathered.

exploration technique for crude oil 

 Chemical analysis of the surface soil and rocks is carried out by geochemical methods. Geotechnical methods, such as the mechanical properties of rocks and surfaces, are measured. Remote sensing from the satellite is the most recent development for a low-cost geological survey. Usual geophysical methods include gravimetric, magnetometric, seismic methods, and radioactive methods. Geochemical methods employ chemical analysis of the cuttings (rock samples cut by drilling bit) and core (a narrow column of rock taken from the wall of a drilled hole) of the drilled site

1-GRAVIMETRIC METHOD

The gravity of the earth’s surface varies with distance from the surface of Earth and the type of material, such as salt, water, oil, gas, or mineral matter. The measurement of a small variation of gravity or acceleration due to gravity is recorded with accuracy and the data are converted to retrieve a geological structure of the sub-surface of Earth. A gravimeter is a very sensitive instrument, usually a spring-type balance with high resolution and accuracy capable of detecting a minute variation in gravity. Porous and oil-containing rock layers and salt have a lower density compared to the surrounding non-porous and hard rock layers. Thus, a gravimetric curve is acquired and analyzed for the location of the deposit.

2-MAGNETOMETRIC METHOD

Earth has its magnetic field that varies from one location to another owing to the different structural materials of rocks and also the presence of solar-charged particles received by Earth. A variation of magnetic field strength is recorded by a sensitive instrument, called a magnetometer. Igneous non-porous rocks are found to be magnetic as compared to sedimentary rocks containing organic deposits. Thus, a magnetometric survey can also be used to locate oil deposits. Both the gravimetric and magnetometric methods are done simultaneously to predict a reproducible sub-surface structure. After the zone is confirmed by gravimetric and magnetometric surveys, a seismic survey is carried out for a clear image of the sub-surface structure.

3-SEISMIC SURVEY

This technique uses a sonic instrument over the desired site to correctly locate the prospective basin structure. In this method, a sound signal generated by the explosion method (explorers call them mini-earthquakes, which are artificially created by explosives) is transmitted through the earth’s surface under study, and reflected signals are detected by geophones located at specified positions. The frequency and time of the reflected signal vary with the density, porosity, and type of reflecting surface.

 Various rock deposits at different depths vary with density and porosity. Seismic reflection can measure this change as it travels below the surface. Computer simulation software is used for imaging the sub-surface structure. This is applied to all the surveys for fast and accurate prediction about the oil and gas reserve location, well before a site is finally selected for drilling operations. It is to be noted that exploration has to be deterministic, but the availability of oil and gas is estimated based on probability.

seismic survey

4-REMOTE SENSING METHOD

Solar radiation from the Earth’s surface varies in intensity and frequency depending on the sub-surface property. This observation is collected via satellite to predict the sub-surface structure. To image the sub-surface structure, historical geological data collected previously by gravimetric, magnetometric, and seismic surveys are used. The final image is obtained by geological imaging software (GIS). However, the remote sensing method is not applicable during nighttime or places incapable of reflecting solar radiation, like the ocean surface, which absorbs substantial amounts of solar radiation. However, extrapolation from the land surface in the vicinity of the sea can be accurately predicted but is not applicable for the deep-sea area. A radioactive or gamma-ray survey is also used in the exploration.

 

5-GEOCHEMICAL METHODS

Inorganic contents of surface or shallow cuttings or core are sampled and analyzed for inorganic materials, such as salts and carbonates, which are frequently associated with hydrocarbons. Organic contents or the presence of organic matter are detected by heating a sample in a crucible and the loss of mass of the sample is an indication of the presence of organic matter. The ratio of organic mass to inorganic matter in a sample is used to ascertain the presence of hydrocarbons. Total organic carbon is defined as the carbon present in the organic matter in the sample which is different in inorganic carbon from carbonates. Core samples are examined for porosity, permeability, salt content, organic content, and many other physical and chemical properties.

6-Radioactive:

Equipment and procedures involving radioactive materials have been used within the hydrocarbon exploration and production industry for many years, as well as in other industries and the public health sector. Tracers are routinely used in both the drilling and flow enhancement (stimulation by fracturing) of wells. They may be either chemical or radioactive. There are a considerable number of different radioactive materials used, utilizing either beta or gamma forms of radiation.

There are several purposes to which tracers are applied. In situ logging is used to detect the location of gamma-emitting radioactive tracers (and hence for example the location of the cement, packing, drilling muds, perforating changes, and/or fracturing proppants, or to provide proof of clean-up, depending upon the purpose and means of utilization), while sampling of return/produced fluids for either beta-emitting or chemical tracers is used as a means of evaluating flows and formation clean-up.

 Matters such as well integrity, the precise placement of equipment or identification of target formations, and the extent of fracturing fluid penetration, can be assessed using tracers. It should be noted that not all field operators in Taranaki use radioactive tracers, and likewise, not all uses of radioactive tracers relate to fracturing. As noted above such tracers can be an integral part of a conventional well drilling operation.

 

7-STRATIGRAPHY

Correlations are established between wells, fossils, rock and mud properties, before and during drilling operations for the final prediction, and this technique is known as stratigraphy. But it is important to remember that prediction from exploration may not be correct as far as the location and amount of deposit are concerned. It may happen that the drilling operation may not yield oil or the yield may not be sufficient at the explored site and that the expenditure borne by this work is irrecoverable. Hence, a more accurate determination of the location and economic deposit should be done before investing money in good construction. After confirmation from the test drilled hole, final construction is carried out.

 

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why does oil go up to the surface?:

 

The answer to this question is pressure, or more precisely, the pressure difference between the bottom of the well and the surface. It is known that the pressure on the surface of the earth is one atmospheric pressure, and the pressure at the bottom of the well is much more, so the oil flows from the high-pressure area, which represents the bottom of the well, to the low-pressure area, which represents the wellhead on the surface. If this condition is not met, the flow of oil will stop naturally, indeed there is a set of forces is responsible for the pressure at the bottom of the well.

why does oil go up to the surface?

 

Downhole Pressure (BHP):

There are three types of pressures: stratigraphic pressure (rock pressure), stock pressure, and aggregate pressure.

1- Layer pressure: It is the weight of the upper rocks, the greater the depth, the greater the pressure of the layers, and the greater the density of the rock, the greater the pressure of the layers.

2- Stock pressure: It is the pressure resulting from the weight of oil, gas, or water, or all of them, on the rock particles.

3- Total pressure: It is the sum of both rock pressure and stock pressure. And this total pressure pushes the oil in the well to a certain level until the pressure fades and becomes equal to atmospheric pressure, and this level is usually below the surface of the earth.

the presence of other forces that push oil upward, namely: Pushing forces of the dissolved gas, Force of water, The gas dome's thrust forces, Mixed gas thrust forces, One or more of these four forces are usually available in any oil field, no matter how different its size and the depth of its oil reservoir, and the presence of any kind of these propulsive forces in any field has a close relationship with the specifications of the reservoir and the stock of oil. These forces are called the natural forces in which the primary production stage takes place.

The natural forces of the reservoir:

Petroleum reservoirs can have primary permeability, which is also known as matrix permeability, and secondary permeability. Matrix permeability originated at the time of deposition and lithification (hardening) of sedimentary rocks. Secondary permeability resulted from the alteration of the rock matrix by compaction, cementation, fracturing, and solution, Oil reservoirs exhibit a wide range of environmental conditions which can affect byproducts such as biosurfactants, such as temperature, pressure, pH, salinity, and oxygen levels. These are significant factors that can determine the success or failure of biosurfactants.

 Dissolved gas forces:

These driving forces are formed when the dissolved gas is released from the oil and expands. This expansion of the gas creates a force that presses the oil, and the oil is pushed from the layers to the bottom of the well and thus upwards. With this type of propulsion, 5 to 15% of the total oil in the reservoir can be extracted.

Water forces:

These driving forces are formed as a result of the expansion of the water reservoir, which presses the bottom of the oil reservoir and pushes it upwards. With this type of propulsion alone, more than 25 percent of the total oil in the reservoir can be extracted.

Gas dome thrust forces:

Gas is always on top of the oil because it is lighter, so it puts pressure on the oil and pushes it to the bottom of the well. The greater the volume of the gas stock located above the oil stock, and the more the gas is expandable, the pressure of the bottom of the well does not decrease except gradually in this case despite the increase in production. 15 to 30 percent of the oil can be extracted by pushing and expanding gas.

Mixed gas thrust forces:

A huge kinetic force arises in the reservoir if the oil is mixed with the gas and is not dissolved in it, due to the absence of harmony between the two mixtures, and the oil in such a case is in a permanent downward movement while the mixed gas is in a permanent upward movement, and as a result of this movement the oil and gas rush From the layers to the bottom of the well, and thus to the surface. In this type of reservoir, i.e. reservoirs of oil and gas mixed with gas, the reservoir maintains its pressure as long as the amount of produced oil is subject to precise engineering control. in the reservoir.

Powers created for oil production:

By studying the types of oil pushing forces, it becomes clear that there must be high pressure in the reservoir to ensure the continuation of oil extraction from the bottom of the wells to the surface, and this reservoir pressure decreases as the intensity of production increases. At the present time, we cannot extract more than 50 percent of the oil in the reservoir, at most. That is why scientific institutes and international oil companies study increasing production from reservoirs and spend a lot on this type of research, taking advantage of what is new in the world of technology to try to extract the remaining large percentage of oil underground. These studies focus on studying the following cases of the reservoir:

Try to maintain the existing pressure if it is observed to continue to decrease, attempting to find new driving forces in the event of stopping or declining productivity, and is called the secondary production stage, trying to find new drilling methods to reach the largest possible area of ​​the oil reservoir, and the latest of these methods is the horizontal drilling method, the effectiveness of the forces created to extract oil depends on the characteristics of the reservoir such as the depth, tendencies, homogeneity of the reservoir and the properties of its rocks, as well as on the nature and type of oil and the method of its displacement to the surface.

stay Under pressure:

For the oil to continue flowing during the initial production stage, the natural forces must be maintained to keep the downhole pressure high. In the case of deterioration of pressure in several wells, each well is treated separately after diagnosing the disease or the cause that led to the decline in the production capacity of the well, which is usually the result of clogging the pores of the oil-producing rocks around the bottom of the well in most cases. To open these pores, water, compressed gas, or an oil derivative such as propane is pumped into the well, according to what the simulation study of nature in the laboratory has concluded. To maintain pressure sometimes requires closing the well or reducing its productivity for a certain period.

Secondary production stage:

secondary production stage

When production stops or decreases in many of the field's wells, it turns some of the wells into pumping wells after an integrated engineering study of the oil field, and as a result of this study, the locations of the pumping wells are determined. This study includes full knowledge of the rocky formation of the reservoir and the size of the oil stock to be removed economically. It also looks at the possibility of benefiting from the feature of gravity, and this can only be achieved in reservoirs with tilted layers.

The idea of ​​the secondary stage of production is summed up by pumping liquids or gases with high pressure, higher than the pressure of the bottom of the well, and this liquid or gas is pushed to the bottom of the well and then to the reservoir rocks, and the oil is displaced through the pores of the rocks to the nearest producing well. There are several models for distributing production wells and pumping wells, such as the model of spreading pumping wells between production wells, and the model of assembling pumping wells in a sector of the field or on the edge of the reservoir so that oil can be trapped from all sides and force it to move towards wells intended for production.

 Water is usually pumped at this stage, due to its availability, low costs, and the ability of water to push oil and fill the place from which oil is displaced. And sometimes some chemicals are added with the pumped water to help it perform its role as a material (polymer). Sometimes the water is pumped hot to raise the temperature of the oil and reduce its viscosity and make it easy to move to where it is intended.

Pumping water or something else in the secondary stage of production increases the productivity of the reservoir until it sometimes reaches what was produced in the first phase with the pressure of the natural reservoir before it collapses. But these pumping costs are very expensive because the quantities of pumped water are very large and need desalination, pumping equipment, and continuous monitoring, and it may be necessary to dig several pumping wells to complete the project. Therefore, a broad and serious study is required, not only of the reservoir, but of water sources, methods of desalination, and how to transport it to the optimal sites for pumping water to extract the largest economic amount of oil commensurate with the pumping costs.

horizontal drilling:

horizontal drilling

Horizontal drilling is considered the most important modern technical method that contributed to the attempt to increase oil recovery from the reservoir.

The horizontal drilling method differs from the traditional drilling method (vertical and inclined) in that the first penetrates a larger area of ​​the reservoir and more oil reserves flow from the well towards the surface. In other words, the difference between the two methods is production from a straight line by horizontal drilling method instead of production from one point. from the reservoir. Therefore, a well dug by the horizontal drilling method is geometrically equivalent to several wells drilled traditionally. The feasibility of horizontal drilling lies in the possibility of reaching the oil trapped in the pores of the rocks and isolated by water or gas, as well as in oil reservoirs of small thickness.

As science progresses and research continues, man can increase the percentage of the amount of oil production lying underground, and perhaps in the future, man will be able to extract every drop of oil in the reservoir, even though this is impossible according to the information and capabilities available at present.

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crude oil definition

Petroleum is a fossilized mass that has accumulated below the earth’s surface from time immemorial. Raw petroleum is known as crude (petroleum) oil or mineral oil, It is a mixture of various organic substances and is the source of hydrocarbons, such as methane, ethane, propane, butane, pentane, and various other paraffinic, naphthenic, and aromatic hydrocarbons, Various petroleum products, such as gaseous and liquid fuels, lubricating oil, solvents, asphalts, waxes, and coke, are derived from refining crude oil. Many lighter hydrocarbons and other organic chemicals are synthesized by thermal and catalytic treatments of these hydrocarbons. Refineries produce cooking gas (liquified petroleum gas or LPG), motor spirit (also known as petrol or gasoline), naphtha, kerosene, aviation turbine fuel (ATF), high-speed diesel (HSD), lubricating base oils, wax, coke, bitumen (or asphalt), etc.

In a petrochemical plant (where one or more petrochemicals are produced) or in a petrochemical complex (where many petrochemical products are produced), pure hydrocarbons or other organic chemicals with a definite number and type of constituent element or compound are produced from the products in refineries. Thus, petrochemicals are derived from petroleum products obtained from refineries products from a petrochemical complex are plastics, rubbers, synthetic fibers, raw materials for soap and detergents, alcohols, paints, pharmaceuticals, etc. Since petroleum is the mixture of hundreds of thousands of hydrocarbon compounds, there is a possibility of synthesizing many new compounds. 

crude oil definition 

what is crude oil made of?:

The compounds in crude petroleum oil are essentially hydrocarbons or substituted hydrocarbons in which the major elements are carbon at 85%–90% and hydrogen at 10%–14%, and the rest with non-hydrocarbon elements—sulfur (0.2%–3%), nitrogen (< 0.1–2%), oxygen (1%–1.5%), and organometallic compounds of nickel, vanadium, arsenic, lead, and other metals in traces (in parts per million or parts per billion concentration) inorganic salts of magnesium chloride, sodium chlorides, and another mineral salts are also accompanied with crude oil from the well either because of water from formation or water and chemicals injected during drilling and production.

ORIGIN OF HYDROCARBONS:

The word petroleum is derived from the Latin words for rock (petra) and oleum (oil), it is found in the form of gas and/or liquid phases in porous rock structures. Both gases and liquids are rich mixtures of organic components consisting of carbon and hydrogen and hence are known as hydrocarbons in general. Usually, these are available in the sub-surface of Earth in the porous rocks known as sedimentary basins. In the majority of the basins, gas, oil, and water coexist under pressure with methane gas at the cap, and oil is sandwiched between the gas and water.

origin of oil

 Physical properties of crude oil:

Crude oil is classified as a paraffinic base, naphthenic base, or asphaltic base, according to the prevalence of the hydrocarbon groups. But various physical properties are required in addition to this classification to characterize a crude oil. API gravity is expressed as the relationship developed by the American Petroleum Institute:

API = 141.5/s − 131.5

where is the specific gravity of oil measured concerning water, both at 60°F (15.5°C), Since oil is lighter than water, API gravity is always greater than 10. The lighter the oil, the larger the API gravity. However, gravity is not the only measurement of crude oil, but a mere indicator of lightness. Since crude oil is, in fact, a mixture of various hydrocarbons varying from gases to semi-solid asphalts, it is convenient to separate these into various boiling fractions rather than as individual chemical species. Crude is distilled in a laboratory distillation apparatus and the boiling fractions are collected. Boiling fractions are a mixture of hydrocarbons.

 boiling in a certain range of temperatures. For a particular crude oil, each boiling fraction separated has a certain average boiling point. A characterization factor of crude oil has been related with the average (molal average) boiling point (TB in Rankine) of all the fractions separated and its specific gravity:

CF = (TB)1/3 /s.

Characterization factor (CF) is universally accepted as the identity of crude oil and its products. Various other properties, such as molecular weight, density, viscosity, and thermodynamic properties, are available for any oil product if its characterization factor is determined. Since crude oil is always associated with water and settleable solids, it is essential to determine the relative amount of bottom sludge and water (BSW) after the necessary settling period. Water is separated by the solvent extraction method in the laboratory. Ultimate analysis of crude oil is a method to determine the amount of carbon, hydrogen, and other constituent elements in it. Combustion of crude oil yields ashes of metallic oxides that are analyzed for the metallic components present in crude oil.

Hydrocarbon groups:

Compounds solely made of carbon and hydrogen are called hydrocarbons. These hydrocarbons are grouped in general into 4 groups paraffin, naphthene, aromatics, and olefins. Crude oil contains these hydrocarbons in different proportions, except olefins, which are produced during processing.

 

1.  Paraffins: Paraffins are saturated hydrocarbons, a saturated hydrocarbon is a compound where all four bonds of a carbon atom are linked to four separate atoms. Examples are methane, ethane, propane, butane, pentane, hexane, with the generic molecular formula of CnH2n+2, where n is the number of carbon atoms in that compound. The homologous series of these hydrocarbons are called alkanes.

paraffin hydrocarbons

 

2.  Naphthene: are cyclic saturated hydrocarbons with the general formula, like olefins, of CnH2n, also known as cyclo-alkanes. Since they are saturated, they are relatively inactive, like paraffins, naphthenes are desirable compounds for the production of aromatics and good quality lube oil base stocks.

naphthene hydrocarbons

3.  Aromatics: often called benzenes, are chemically very active as compared to other groups of hydrocarbons. Their general formula is CnH2n-6. These hydrocarbons in particular are attacked by oxygen to form organic acids. Naphthene can be dehydrogenated to aromatics in the presence of a platinum catalyst. Lower aromatics, such as benzene, toluene, and xylenes, are good solvents and precursors for many petrochemicals. Aromatics from petroleum products can be separated by extraction with solvents such as phenol, furfurol, and diethylene glycol.

aromatics hydrocarbons

 

4.  Olefins: are unsaturated hydrocarbons, i.e., the double bond is present between the two carbon atoms in the formula. The generic formula is CnH2n, and the lowest member of this homologous series is ethylene, C2H4. This series is known as alkenes. these are highly reactive and can react to themselves to mono olefins Olefins are not present in crude oil, but they are produced by thermal and catalytic decomposition or dehydrogenation of normal paraffins.

olefin hydrocarbons

Complex Hydrocarbons:

Crude oil also contains a large number of hydrocarbons that do not fall into the category of paraffin, olefins, naphthenes, or aromatics, but maybe the combined group of any two or more groups of paraffin, naphthenes, or aromatic hydrocarbons. By joining two or more naphthene rings or combining naphthene and aromatic rings, paraffin “n” chains with aromatic rings (alkyl-aromatics), etc., a vast array of complex hydrocarbons may be formed, examples of these compounds are decalin, naphthalene, and diphenyl. Heavier fractions of crude oil contain these types of hydrocarbons, multinuclear (multi-ring) aromatics or polynuclear aromatics (PNA) are well known in crude oil and its residual products.

 

polynuclear hydrocarbons

Non-Hydrocarbons or Hetero-Atomic Compounds :

Common hetero atoms in hydrocarbons are sulfur, oxygen, nitrogen, and metallic atoms. Sulfur compounds are present in crude oil as mercaptans, mono- and disulfides with the general formula R-SH, R-S-R1, R-S-S-R1, where R and R1 are the alkyl radicals. Mercaptans are very corrosive whereas mono- and disulfides are not. Examples of cyclic sulfur compounds are thiophenes and benzothiophene.

 

hetero-atomic hydrocarbons

1.    Hydrogen sulfide (H2S): gas is associated with crude oil in dissolved form and is released when heated. H2S is corrosive at high temperatures and in the presence of moisture. Crude oil that contains large amounts of H2S is called sour crude. Sulfur present in petroleum fuel products also forms various oxides of sulfur (SOx) during combustion, which are strong environmental pollutants H2S can be removed from gases by absorption in an amine solution. the sulfur atom is very stable and non-reactive. As a result, sulfur from heavier petroleum cannot be removed without a destructive reaction, such as severe thermal or catalytic reactions. Nowadays, sulfur is recovered during refining and sold as a product. Sulfur also has a poisoning effect on various catalysts.

 

2.    Nitrogen compounds: hydrocarbons are usually found in the heavier parts of crude oil. These are responsible for color and color instability and poisoning of certain catalysts. Nitrogen in petroleum fuels causes the generation of oxides of nitrogen (NOx), which are also strong pollutants in the atmosphere. Nitrogen can be eliminated from petroleum products by catalytic hydrogenation. Like sulfur, nitrogen in the heavier parts of petroleum cannot be removed without severe cracking or hydrogenation reactions.

 

3.    Oxygen compounds: crude oil may contain oxygen-containing compounds, such as naphthenic acids, phenols, and cresols, which are responsible for corrosive activities. Oxygen also acts as a poison for many catalysts. This can be removed by catalytic hydrogenation. Excess oxygen compounds may even lead to explosions.

 

4.    Metallic compounds: of vanadium, nickel, lead, arsenic, etc., are also found in crude oil. Vanadium and nickel are found in the form of organometallic compounds mostly in the heavier fractions of crude oil where the metal atoms are distributed within the compound in a complex form called porphyrins. Petroleum fuels containing these metallic compounds may damage the burners, lines, and walls of the combustion chambers.

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