In this article we will get acquainted with the concept of reservoir pressure (RP). Here questions of its definition and meaning will be touched upon. We will also analyze the method of human exploitation. We will not bypass the concept of anomalous reservoir pressure, the accuracy of the measuring capabilities of the equipment and some individual concepts associated with the dominant in this text.
Introduction
Reservoir pressure is a measure of the amount of pressure created by the action of reservoir fluids and displaced on a certain breed of minerals, rocks, etc.
Fluids are any substances whose behavior during deformation can be described by using the laws of mechanics for fluids. The term itself was introduced into the scientific language around the middle of the seventeenth century. They denoted hypothetical liquids, with the help of which they tried to explain the process of rock formation from a physical point of view.
Reservoir identification
Before we startto the analysis of reservoir pressure, one should pay attention to some important concepts that are associated with it, namely: the reservoir and its energy.
Reservoir in geologists is called a body with a flat shape. At the same time, its power is much weaker than the size of the propagation area within which it operates. Also, this power indicator has a number of homogeneous features and is limited to a set of parallel surfaces, both small and large: roof - top and sole - bottom. The definition of the strength indicator can be determined by finding the shortest distance between the sole and the roof.
Reservoir structure
Layers can be formed from several layers belonging to different rocks and interconnected. An example is a coal seam with existing layers of mudstones. Often, the terminological unit "layer" is used to designate stratified accumulations of minerals, such as: coal, ore deposits, oil, and aquifers. The folding of layers occurs through the overlapping of various sedimentary rocks, as well as volcanogenic and metamorphic rocks.
Reservoir energy concept
Reservoir pressure is closely related to the concept of reservoir energy, which is a characteristic of the capabilities of reservoirs and the fluids contained in them, for example: oil, gas or water. It is important to understand that its value is based on the fact that all substances inside the reservoir are in a state of constant stress due torock pressure.
Species diversity of energy
There are several types of reservoir energy:
- pressure energy of reservoir fluid (water);
- energy of free and evolved gases in solutions with reduced pressure, such as oil;
- elasticity of compressed rock and fluid;
- pressure energy due to the gravity of matter.
During the selection of liquids, in particular gas, from the formation medium, the energy reserve is consumed to ensure the process of moving fluids, through which they can overcome forces opposing their movement (forces responsible for internal friction between liquids and gases and the rock, as well as capillary forces).
The direction of movement of oil and gases in the space of the reservoir, as a rule, is determined by the manifestation of new types of reservoir energy at the same time. An example is the appearance of the energy of elasticity of rock and fluid and its interaction with the potential of oil gravity. The predominance of a certain type of energy potential depends on a number of geological features, as well as the conditions in which a deposit of a particular resource is exploited. Correspondence of a specific form of energy, which is used to move liquids and gases, with the type of production well allows you to distinguish between different modes of operation of gas and oil deposits.
Importance of parameter
Reservoir pressure is an extremely important parameter that characterizes the energy potentialformations carrying water or oil and gas resources. Several types of pressure are involved in the process of its formation. All of them will be listed below:
- hydrostatic reservoir pressure;
- excess gas or oil (Archimedes force);
- pressure that occurs due to changes in the dimensional value of the volume of the tank;
- pressure due to the expansion or contraction of fluids, as well as changes in their mass.
Reservoir pressure includes two different forms:
- Initial - the initial indicator that the reservoir had before opening its reservoir underground. In some cases, it may be preserved, that is, not disturbed due to the impact of man-made factors and processes.
- Current, also called dynamic.
If we compare reservoir pressure with conditional hydrostatic pressure (pressure of a column of fresh liquid, vertical from the day surface to the measurement point), then we can say that the first is divided into two forms, namely, anomalous and normal. The latter is directly dependent on the depth of the formations and continues to grow, by approximately 0.1 MPa for every ten meters.
Normal and abnormal pressure
PD in the normal state is equal to the hydrostatic pressure of the water column, with a density equal to one gram per cm3, from the formation roof to the earth's surface vertically. Abnormal reservoir pressure is any formmanifestations of pressure that are different from normal.
There are 2 types of anomalous PD, which will be discussed now.
If PD exceeds hydrostatic, i.e., one in which the pressure of the water column has a density index of 103 kg/m3, then it is called abnormally high (AHPD). If the pressure in the reservoir is lower, then it is called abnormally low (ALP).
Anomalous PD is located in an isolated type system. At present, there is no unequivocal answer to the question about the genesis of APD, since here the opinions of experts differ. Among the main reasons for its formation are such factors as: the process of compaction of clay rocks, the phenomenon of osmosis, the catagenetic nature of the transformation of the rock and organic compounds included in it, the work of tectogenesis, as well as the presence of a geothermal environment in the bowels of the earth. All of these factors can become dominant among themselves, which depends on the structure of the geological structure and the historical development of the region.
However, most researchers believe that the most important reason for this or that reservoir formation and the presence of pressure in it is the temperature factor. This is based on the fact that the thermal coefficient of expansion of any fluid in an isolated rock is many times greater than that of the mineral series of components in the rock.
Setting the ADF
APD is established as a result of drilling in various wells, both on land and in water areas. It's connected withcontinuous search, exploration and development of gas and/or oil deposits. They are usually found in a fairly wide depth range.
Where it is extremely deep at the bottom, anomalous high reservoir pressure (from four km or more) can be found more often. Most often, such pressure will exceed the hydrostatic pressure, approximately 1.3 - 1.8 times. Sometimes there are cases from 2 to 2.2; in such cases, they are most often unable to achieve an excess of geostatic pressure exerted by the weight of the overlying rock. It is extremely rare to find a case in which at a great depth it is possible to fix an AHRP equal to or greater than the value of the geostatic pressure. It is assumed that this is due to the influence of various factors, such as: an earthquake, a mud volcano, an increase in the s alt dome structure.
The positive component of AHRP
AHRP has a beneficial effect on the reservoir properties of the reservoir rock. Allows you to increase the time interval for the exploitation of gas and oil fields, without using secondary expensive methods in the course of this. It also increases the specific gas reserve and well flow rate, tries to preserve the accumulation of hydrocarbons and is evidence of the presence of various isolated areas in the oil and gas basin. Speaking about any form of PD, it is important to remember what it is formed from: reservoir pressure of gas, oil and hydrostatic pressure.
HAP sites that have been developed at great depths, especially those with regional distribution, contain a significant supply of suchresource like methane. He stays there in a state of solution, which is contained in superheated water, with a temperature of 150-200 ° C.
Some data
Man can extract methane reserves and use the hydraulic and thermal energy of water. However, there is also a downside here, because AHRP often become a source of accidents that occurred during the drilling of a well. For such zones, a weighting method is used during the drilling process, the purpose of which is to prevent a blowout. However, the applied fluids can be absorbed by formations of two pressures: hydrostatic and abnormally low.
In the course of understanding the process of extracting oil and gas resources through the installation of rigs, it is necessary to know about the presence of the concept of bottomhole formation pressure. It is the pressure value at the bottom of an oil, gas or water well that performs the process of work. It should be lower than the reservoir impact value.
General information
PD is constantly changing as the reservoir spreads and the depth of oil or gas deposits increases. It also increases due to the increase in the thickness of the aquifer. This pressure is compared only with any one plane, namely the level, the initial position of the oil-water contact. Indicators of devices such as pressure gauges show results only for reduced zones.
If we talk specifically about the formation pressure of a well, then these words mean the amount of accumulation of minerals located in the voids of the earth. The reason for this phenomenon was the accidental opportunity for the main part of the reservoir to come to the surface. The process of drinking the reservoir is carried out thanks to the holes formed.
SPPD
Reservoir pressure maintenance system is a technological complex of equipment that is required to carry out work on the preparation, transportation and injection of an agent that performs the force necessary to penetrate into the reservoir space with oil. Now let's get straight to the specifics.
Reservoir pressure maintenance is performed by a system including:
- objects for various types of injections, such as water into the reservoir;
- preparation of suction water to the state of conditions;
- supervision of water quality in RPM systems;
- monitoring the implementation of all safety requirements, as well as checking the level of reliability and tightness in the device of the field water conduit operation system;
- use of closed water treatment cycle;
- creating the possibility to change the parameters responsible for the mode of water injection from the well cavity.
SPPD contains three main systems: injection for a well, pipeline and distribution systems, and for injection of an agent. Also included is equipment to prepare the agent operated for injection.
Reservoir pressure formula: Рpl=h▪r▪g, where
h is the level of the height of the liquid column that balances the PD, r is the value of the fluid density inside the well, g isacceleration in free fall m/s2.
