CN104390902B - Method for analyzing pore distribution of sediment by virtue of saturation change of gas hydrate - Google Patents
Method for analyzing pore distribution of sediment by virtue of saturation change of gas hydrate Download PDFInfo
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- CN104390902B CN104390902B CN201410668860.2A CN201410668860A CN104390902B CN 104390902 B CN104390902 B CN 104390902B CN 201410668860 A CN201410668860 A CN 201410668860A CN 104390902 B CN104390902 B CN 104390902B
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Abstract
The invention belongs to the field of geological exploration and resource development of gas hydrates and relates to a method for analyzing the pore distribution of sediment by virtue of the saturation change of a gas hydrate. According to the method, the gas hydrate is generated in the sediment by virtue of pressurization temperature reduction. In the decomposition process of the generated gas hydrate, the temperature remains unchanged. In a mode of gradually reducing the pressure, the hydrate is promoted to be gradually decomposed. The signal strength of water in the sediment in each decomposition stage and the pore distribution situation of the decomposed hydrate are measured by virtue of nuclear magnetic resonance imaging equipment. The size and total quantity of pores occupied by the gas hydrate decomposed in each stage are determined by virtue of the temperature and pressure of each decomposition stage, so that the pore distribution characteristics of the sediment are calculated and described by virtue of an image shot by nuclear magnetic resonance imaging. The method has the advantage that under the condition that the natural core structure is not destroyed, the internal porosity distribution characteristics of the sediment can be clearly identified by virtue of the generation decomposition process of the hydrate. The method is easy to operate.
Description
Technical field
The invention belongs to gas hydrate geological prospecting and development of resources field are and in particular to utilize gas hydrate to one kind
The method of thing saturation degree mutation analysis deposit distribution of pores.
Background technology
With the increasingly depleted of conventional fossil fuel resource, the discovery of gas hydrates is undoubtedly the huge of energy field
Break through.In nature, gas hydrates are distributed mainly in halmeic deposit or the permafrost of land-based area, to exploitation and utilization
Bring great difficulty.Accurate quarter to the microphysics property such as the particle diameter distribution of deposit, sedimentary structure and pore structure
Picture can obtain reliable geologic data data, and developing for natural gas hydrate exploration provides significant data to support.
The method of the analysis deposit commonly used at present has the side such as intrusive mercury curve, x-ray diffraction, thin section identification, ESEM
Method, although these can more clearly identify the pore structure characteristic of deposit.But due to gas hydrates in nature
Deposit is mostly dispersed, would generally destroy natural sediment structure, impact test accuracy in conventional method test process.
Because hydrate a little has corresponding relation in balancing each other under specified temp pressure and deposit porosity between, so utilizing
Gas hydrate saturation degree changes, and in the case of not changing deposit formalness and internal structure, studies deposit hole
Degree distribution, is a kind of convenient and effective method.
From the point of view of gas hydrate forming process, hydrate substitutes the water in deposit hole, forms hydrate deposit,
Hydrate may suspend in a fluid it is also possible to contact or cementing sedimentary particle in hole.These microcosmic occurrence status and
Saturation degree change and rock core particle diameter and its arrayed feature have relation closely, to the pore structure of deposit, permeability
Deng physical parameter, there is crucial effect, have also been changed the propagation of seismic wave simultaneously, thus to the geophysical exploration of hydrate and
Resource assessment has material impact.
Content of the invention
The invention provides a kind of method of utilization gas hydrate saturation degree mutation analysis deposit distribution of pores, it is easy to
The exploration of natural gas hydrate resources, exploitation.
The present invention is lowered the temperature by pressurization, so that gas hydrate is generated in deposit.Dividing after gas hydrate generates
In solution preocess, keeping temperature is constant, using gradually reducing pressure mode, promotes hydrate progressively to decompose, and utilizes nuclear magnetic resonance
Imaging (mri) equipment measures the signal strength signal intensity of water and the distribution of pores feelings having decomposed hydrate in each catabolic phase deposit
Condition, in conjunction with the temperature and pressure of each catabolic phase, determine pore size that the gas hydrate of each stage decomposition occupies and
Hole total amount, thus the image shooting with reference to Magnetic resonance imaging calculates and depicts the porosity distribution of deposit.
The technical scheme is that
A kind of method of utilization gas hydrate saturation degree mutation analysis deposit distribution of pores, the deposit being analysed to
Vacuumize in the core chamber putting into vacuum pressed saturation device, add deionized water to soak deposit, to rock core in core chamber
Room applies certain external pressure, and depending on external pressure is according to the loose of deposit and compactness extent, this pressure enables deposit to fully absorb
Deionized water；It is placed in inhaling after water saturated deposit takes out in basket, source of the gas, constant temperature bath, data acquisition monitoring system are equal
It is connected with Magnetic resonance imaging, the basket that will be equipped with deposit is placed in Magnetic resonance imaging, is passed through methane or titanium dioxide
The gases such as carbon, open constant temperature bath, so that temperature in basket is reduced, set the temperature of constant temperature bath according to gas with various, make gas complete
Full generation gas hydrate；After gas hydrate generates in deposit hole completely, keep temperature-resistant in basket,
Progressively it is depressured, a part of gas hydrate decomposes；Continue to be depressured and decompose completely until gas hydrate, be depressured 0.2mpa every time,
Once press every ten minutes falls；According to phase balance condition under different aperture radius for the gas hydrate, anti-correspondence can be released
Decomposition pressure and at a temperature of the deposit pore-size that occupies of gas hydrate.
According to the signal strength signal intensity of water in each catabolic phase deposit of Magnetic resonance imaging record, can through processing and converting
Obtain the intensity value of each catabolic phase remnants hydrate, so as to calculate the percentage of the void content of decomposition gas hydrate
The image that Magnetic resonance imaging shoots records the distribution of pores position of deposit to ratio simultaneously.
Deposit pore size according to each catabolic phase and void content obtain the distribution of pores frequency histogram of deposit,
Distribution of pores frequency histogram is combined with distribution of pores location drawing picture, can intuitively find out the porosity distribution of deposit.
The present invention in the case of not destroying deposit structure, using the generation decomposable process of gas hydrate, Neng Gouqing
Chu's ground identification deposit wood interior porosity distribution characteristics, and quantitative description has been carried out to it, compensate for directly being become with nuclear magnetic resonance
As gaging hole porosity is distributed the inadequate shortcoming of resolution ratio.This method is equally applicable to nature natural gas hydrate deposit hole and divides
The test of cloth.The pore structure of deposit reflects the microphysics property of rock, because its structure is sufficiently complex, how to characterize
Its seepage flow mechanism is most important to recognizing for pore structure distribution characteristics, and the method that the present invention provides is simple to operate, convenient effective,
Can effectively solve the problem that this problem in laboratory conditions, also the exploration for gas hydrates and exploitation offer technology are managed simultaneously
By support.
Brief description
Fig. 1 is each catabolic phase distribution of pores location drawing.
Fig. 2 is porosity distribution figure.
Fig. 3 is distribution of pores frequency histogram.
Specific embodiment
Describe the specific embodiment of the present invention below in conjunction with technical scheme in detail.
Embodiment
Deposit after pressurization saturation in vacuum pressed saturation device is placed in basket, basket is put in nuclear-magnetism
In resonance image-forming and connect the pipeline of source of the gas, constant temperature bath, data acquisition monitoring system, open valve, using gas injection pump
Into basket, injection methane gas closes valve to 3.3mpa.Standing three to four hours, makes methane fully dissolve in water.
After pressure stabilisation open constant temperature bath again, make temperature in basket drop to 274.15k.Pressure sensor and thermocouple can be in real time
Pressure and temperature data in collection core holding unit, by data acquisition monitoring system it is observed that the change of pressure and temperature
Change situation, Magnetic resonance imaging also can the change in signal strength of water and deposit distribution of pores feelings in real time record deposit hole
Condition.When pressure declines suddenly, show have methane hydrate to generate in a large number, at this moment continue to keep design temperature, treat that methane is hydrated
Thing generates completely.
It is possible to be progressively depressured decomposition after methane hydrate generates completely.Maintain the temperature at 274.15k not
Become, be progressively depressured, a part of methane hydrate can first decompose, usually the hydrate in fine pore first decomposes, in macrovoid
Decompose after hydrate, continue to be depressured and decompose completely until methane hydrate, each Amplitude of Hypotensive is 0.2mpa, drops every ten minutes
Once press.With the decomposition of hydrate, Magnetic resonance imaging can record the aperture position image of methane hydrate decomposition, such as schemes
Shown in 1, black represents solid, and grey represents the water after methane hydrate decomposes.
In the 0min moment, image represents and starts the state before being depressured after methane hydrate generates completely, then begins to be depressured,
The image in 10min moment is the image after step-down decomposition for the first time, and the position by blacking ash is exactly the position of decomposition of hydrate
Put.So, reduced a pressure every ten minutes under temperature constant state, until methane hydrate decomposes completely it is possible to obtain
A series of methane hydrates decompose the image of position, i.e. different size aperture position distribution map.In order to apparent find out various
The adjacent image being depressured twice can be done subtraction, after being depressured each time, have methane hydrate by the position of size distribution of pores
The aperture position decomposed, as shown in Figure 2.
According to phase balance condition under different aperture radius for the methane hydrate, corresponding decomposition pressure and temperature counter can be released
The deposit pore-size that the lower methane hydrate of degree occupies.Magnetic resonance imaging can record water in each catabolic phase deposit
Signal strength signal intensity, can be calculated the intensity value of each catabolic phase remnants hydrate through formula (1).
Note: s in formulaw0For initial water saturation, it is 1 in this experiment；i0And iiRepresent initial time and the mi in i moment respectively
Value.
Test shared by the methane hydrate of each catabolic phase pressure, corresponding pore-size and every stage decomposition obtaining
Void content percentage is as shown in table 1.The corresponding pressure found according to each catabolic phase and at a temperature of pore-size, in conjunction with by
The void content that saturation degree obtains can make the distribution of pores frequency histogram of deposit, as shown in Figure 3.
The characteristic quantity of each catabolic phase of table 1
| Time (min) | 0 | 10 | 20 | 30 |
| Pressure (mpa) | 3.3 | 3.1 | 2.9 | 2.7 |
| Pore-size (nm) | — | 60 | 200 | 300 |
| Remaining hydrate concentration | 0.3123 | 0.2783 | 0.0122 | 0 |
| Void content | — | 10.89% | 85.21% | 3.90% |
Fig. 3 is combined with Fig. 2, can intuitively find out the porosity distribution of deposit.By distribution of pores frequency histogram
As can be seen that the hole of 200nm side-to-side dimensions is at most, the void content of other two size is less, and the deposition of this experiment is described
The distribution of pores of thing is more uniform.
Claims (2)
1. a kind of method of utilization gas hydrate saturation degree mutation analysis deposit distribution of pores it is characterised in that
(1) deposit being analysed to is put in the core chamber of vacuum pressed saturation device and is vacuumized, and adds go in core chamber
Ionized water soaks deposit, applies external pressure according to the loose of deposit and compactness extent to core chamber, external pressure makes deposit abundant
Absorb deionized water；
(2) be placed in inhaling after water saturated deposit takes out in basket, source of the gas, constant temperature bath, data acquisition monitoring system all with
Magnetic resonance imaging connects, and the basket that will be equipped with deposit is placed in Magnetic resonance imaging, is passed through gas, opens constant temperature bath,
So that temperature in basket is reduced, set the temperature of constant temperature bath according to gas with various, make gas generate gas hydrate completely；
(3) after gas hydrate generates in deposit hole completely, keep temperature-resistant in basket, be progressively depressured,
A part of gas hydrate decomposes, and continues to be depressured and decomposes completely until gas hydrate；Step-down 0.2mpa every time, every ten minutes
Fall is once pressed；
(4) phase balance condition under different aperture radius by gas hydrate, anti-release corresponding decomposition pressure and at a temperature of gas
The deposit pore-size that gas hydrate occupies；
(5) in each catabolic phase deposit of Magnetic resonance imaging record water signal strength signal intensity, through process obtain each decomposition rank
The intensity value of the remaining hydrate of section, is calculated the percentage of the void content of decomposition gas hydrate, Magnetic resonance imaging
The image shooting records the distribution of pores position of deposit simultaneously；
(6) the deposit pore size according to each catabolic phase and void content, obtains the distribution of pores frequency histogram of deposit,
Distribution of pores frequency histogram is combined with distribution of pores location drawing picture, the porosity distribution observing deposit directly perceived.
2. method according to claim 1 is it is characterised in that described gas is methane or carbon dioxide.
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| CN101458218B (en) * | 2008-12-28 | 2011-02-02 | 大连理工大学 | Carbon dioxide oil-displacing nmr imaging detection device |
| CN102062742B (en) * | 2010-12-15 | 2012-09-05 | 大连理工大学 | Sand-filling type clamp fastener for nuclear magnetic resonance imaging |
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