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.
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| 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 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:
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| 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:
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| 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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