CN109612897B - Quantitative evaluation method for influence of sewage reinjection on physical properties and pore throat distribution of compact sandstone - Google Patents
Quantitative evaluation method for influence of sewage reinjection on physical properties and pore throat distribution of compact sandstone Download PDFInfo
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Abstract
The invention discloses a quantitative evaluation method for the influence of sewage reinjection on the physical properties and pore throat distribution of tight sandstone, which comprises the steps of firstly preparing a rock core and measuring the permeability by gas; preparing working fluid, vacuumizing the rock core to saturate the working fluid, and calculating the porosity of the rock core; testing nuclear magnetic resonance T2Performing spectrum to obtain the original pore throat distribution of the rock core sample; re-testing nuclear magnetic resonance T after core centrifugation2Performing spectrum to obtain pore throat distribution occupied by original immobile fluid of the rock core sample; injecting the treated sewage into the core; drying the water-injected rock core, measuring the permeability by gas, and saturating the water again to measure the porosity of the rock core; testing nuclear magnetic resonance T2Performing spectrum to obtain pore throat distribution of the rock core sample after water injection; re-testing nuclear magnetic resonance T after core centrifugation2Performing spectrum to obtain pore throat distribution occupied by immobile fluid after the water injection of the core sample; will measure T2And converting the spectrum into pore throat radius distribution, and quantitatively analyzing the influence of the sewage reinjection of the low-permeability sandstone reservoir on the physical property and the pore throat distribution of the reservoir.
Description
Technical Field
The invention belongs to the technical field of oil and gas field development, and particularly relates to a quantitative evaluation method for influences of sewage reinjection on physical properties and pore throat distribution of compact sandstone.
Background
The low-permeability oil fields in China are widely distributed, and low-permeability petroleum resources are rich in development in the length of a triple-fold system extension group of an Eldos basin from 6 to 7, a Quercong basin secondary-fold system reed ditch group, a Sichuan basin middle-lower Jurassystem and a chalk system mountain mouth group-spring head group of a Songlian basin. Low permeability reservoirs are generally flooded to maintain reservoir energy due to their low permeability, poor fluid supply, rapid formation pressure drop, and the like. With the development of oilfield flooding, especially in the later stage of flooding, a large amount of formation water is produced to the ground along with crude oil, and if the formation water is directly discharged, the environment is polluted, and if the formation water is discharged after treatment, the production cost of the oilfield is greatly increased. Particularly for northwest regions with deficient water resources, national environmental regulations and sustainable development of water resources require that sewage is treated and then re-injected into an oil layer to reduce discharge. Because the pore throat of a low-permeability reservoir is fine and is particularly sensitive to water quality, although most of oil field sewage is treated to a certain extent before reinjection, actual production finds that the reinjection of the sewage can cause reservoir damage and the water injection pressure is increased, so that the water flooding effect is influenced. The current research mostly focuses on indoor core damage evaluation, macroscopically analyzes the change of reservoir permeability caused by the water quality change of sewage, and does not microscopically research the pore throat blockage, pore throat distribution and movable fluid porosity change caused by injected water quality.
In the existing research, CN101973641A discloses a low-permeability/ultra-low-permeability oilfield oil extraction sewage reinjection treatment method. CN105130132A discloses a treatment process for reinjecting heavy oil sewage into a low-permeability oil field, CN101786739B discloses an oil extraction sewage treatment method for reinjecting oil field, and CN203050667U discloses a filtering device for produced sewage of an oil field development water injection well. In 2010, the indoor evaluation research of Bohai west oil field sewage reinjection is developed by Gao Bobo et al in Bohai west oil field sewage reinjection reservoir damage evaluation research and chemical protection measures in Bohai west oil field in marine oil product volume 30, No. 1, and compatibility of sewage and formation water is researched through computer prediction, static scaling experiments and dynamic scaling experiments. Shijing Ping et al, 2002, in the text of mineral rock, volume 22, 2, Experimental study on reinjection of Sewage into northern three zones of Marlin oil field, static experimental results of mixing sewage and formation water, and core flow experiments under simulated formation conditions, found that the injection of the produced sewage into the formation and the formation water mixed together also reduces the formation permeability, and the damage degree of the permeability increases with the increase of the sewage content. In the text of the research on the damage of the water absorption layer by the sewage reinjection of the Wang 27 fault block oil reservoir in the No. 6 of drilling and mining technology, 2007 Li Qiang et al, flow experiments of injected water and rock cores show that the quality of injected water does not reach the standard and the water injection technology is unreasonable, which are the root causes of the damage of the water absorption layer, including the exceeding of oil content and the exceeding of suspended insoluble solid phase particle size in water. In the text of the extra-low permeability oilfield water quality treatment and sewage reinjection of No. 2 of 31 st volume of oil and gas field ground engineering from Cao Xiao, 2012, aiming at the situation that a common filter is difficult to enable injected water to reach the injection standard, a double-layer expansion type fine filter is adopted for the treatment of the injected water, so that the problems of poor water quality and incomplete sewage reinjection are better solved. In 2016, in the research on evaluation of damage of reinjection of oilfield sewage to reservoirs with different permeabilities in the 4 th phase of the current chemical industry, Sun Ning et al analyze the damage degree of reinjection sewage to cores with different permeabilities through a core flow experiment, and determine the index requirement of the concentration of the reinjection suspended matters of the sewage in a research area. The method or the technology are all researches on damage of sewage reinjection on the permeability of a reservoir, and do not relate to evaluation of pore throat blockage caused by sewage reinjection.
When the pore throat distribution of the compact sandstone is researched by adopting the mercury intrusion method, the mercury intrusion saturation degree is often not 100%, so that the mercury intrusion data cannot reflect quite a lot of tiny pores in the compact sandstone, the adsorbed nitrogen is difficult to completely desorb in the nitrogen adsorption method, so that a core sample cannot be repeatedly measured, and the CT scanning method usually needs to cut a rock sample to damage the core sample.
Disclosure of Invention
The invention aims to provide a quantitative evaluation method for influences of sewage reinjection on physical properties and pore throat distribution of compact sandstone, which overcomes the defects in the prior art.
In order to achieve the purpose, the invention adopts the following technical scheme:
the quantitative evaluation method for the influence of sewage reinjection on the physical properties and pore throat distribution of the compact sandstone comprises the following steps of:
the method comprises the following steps: selecting a real sandstone core of a low-permeability reservoir, washing oil, drying, and then performing gas logging on the permeability of a core sample; preparing simulated formation water according to the mineralization degree and the ion composition of the oil field sewage; extracting the injected water, namely the treated sewage, of the operation area corresponding to the rock core;
step two: vacuumizing a rock core sample, saturating the simulated formation water at high pressure, and calculating the porosity and the pore volume of the rock core;
step three: testing the nuclear magnetic resonance T of the rock core sample obtained in the step two2Performing spectrum to obtain the original pore throat distribution of the rock core sample; then placing the rock core in a centrifugal device for centrifugation, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by original immobile fluid of the rock core sample;
step four: connecting the core sample obtained in the third step with a displacement process, setting an experimental temperature, and injecting an injection water sample retrieved on site into the core sample;
step five: drying the rock core sample obtained in the step four, and measuring the permeability by gas; then vacuumizing the core to saturate distilled water, and testing the porosity of the core;
step six: testing the nuclear magnetic resonance T of the rock core sample obtained in the fifth step2Performing spectrum to obtain pore throat distribution of the rock core sample after water injection; then placing the rock core in a centrifugal device for centrifugation, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by immobile fluid after the water injection of the core sample;
step seven: measuring the T before and after centrifugation measured in the third step and the sixth step2Spectra are plotted on two graphs, respectively, and T is plotted2Converting the spectrum into pore throat radius distribution;
step eight: according to measured T2And (3) spectrum and pore throat radius distribution curves, and quantitatively analyzing the distribution of the pore throat radius of the core after water flooding and the change of the porosity of the movable fluid.
Further, the core sample in the first step has a diameter of 2.5cm and a length of 4.0 cm.
Further, the pressure of the high-pressure saturation in the second step is 30 MPa.
Further, the centrifugation time in the third step and the sixth step is 120min, and the centrifugation speed is 9000 r/min.
Further, in step four, the injection rate was 0.1mL/min and the injection time was 24 hours.
Furthermore, in the fifth step, the drying temperature is 80 ℃, and the drying time is 24 hours.
Further, in the seventh step, the following formula is adopted to convert the nuclear magnetic resonance T into2Spectrum conversion pore throat radius:
in the formula: r is pore throat radius, mum;
T2transverse relaxation time measured for nuclear magnetic resonance, ms;
k is core permeability, mD.
Compared with the prior art, the invention has the following beneficial technical effects:
compared with mercury intrusion method, nitrogen adsorption and CT scanning method, the nuclear magnetic resonance method for testing the radius distribution of the pore throats has the advantages of being capable of repeatedly measuring, not damaging rock core samples, being capable of accurately measuring the micro-nano pore throats and the like.
Drawings
FIG. 1 is a pore throat radius distribution before and after core flooding of example one;
fig. 2 is a pore throat radius distribution diagram before and after core flooding of example two.
Detailed Description
The following is further illustrated with reference to specific examples:
example one
In the embodiment, cores and injection water of JB oil field Y9 reservoirs in Ordos basin are selected, and the damage of incompatibility of the injection water and the formation water to the reservoirs is mainly considered.
A quantitative evaluation method for the influence of sewage reinjection on the physical properties and pore throat distribution of tight sandstone comprises the following steps:
the method comprises the following steps: drilling a core sample with the diameter of 2.5cm and the length of 4.0cm from the full-diameter core, washing with oil, drying, and measuring the permeability of the core with gas by 4.25 multiplied by 10-3μm2(ii) a Preparing simulated formation water according to the mineralization degree and the ion composition of the oilfield sewage, extracting the injected water of the operation area corresponding to the rock core, and showing the water quality analysis results of the formation water and the injected water in table 1.
Step two: vacuumizing a rock core sample, saturating the simulated formation water under high pressure, and calculating the porosity of the rock core to be 8.36%;
step three: testing the nuclear magnetic resonance T of the rock core sample obtained in the step two2Performing spectrum to obtain the original pore throat distribution of the rock core sample; then placing the rock core in a centrifugal device, centrifuging for 120min at a speed of 9000r/min, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by original immobile fluid of the rock core sample; according to T before and after centrifugation2The mobile fluid porosity was found to be 5.18% by spectral cumulative distribution.
Step four: placing the core sample obtained in the third step in a core holder, connecting a displacement process, setting an experiment temperature of 50 ℃, and injecting water into the core sample at an injection speed of 0.1 mL/min;
step five: placing the rock core sample obtained in the fourth step in a thermostat at 80 ℃ and drying for 24 hours, wherein the gas permeability is 2.86 multiplied by 10-3μm2(ii) a Then, vacuumizing the rock core to saturate distilled water, and testing the porosity of the rock core to be 6.26%;
step six: step five is to obtainObtained core sample test Nuclear magnetic resonance T2Performing spectrum to obtain pore throat distribution of the rock core sample after water injection; then placing the rock core in a centrifugal device for centrifugation for 120min, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by immobile fluid after the water injection of the core sample; according to T before and after centrifugation2The mobile fluid porosity was found to be 3.65% by spectral cumulative distribution.
Step seven: the T before and after centrifugation measured in the third step and the sixth step is calculated according to the following formula2The spectra were converted to pore throat radius distributions, see FIG. 1;
in the formula: r is pore throat radius, mum;
T2transverse relaxation time measured for nuclear magnetic resonance, ms;
k is core permeability, mD.
Step eight: and (4) quantitatively analyzing the distribution of the pore throat radius of the core after water flooding and the change of the porosity of the movable fluid according to the pore throat radius distribution curve.
TABLE 1 JB oilfield Y9 reservoir formation Water and injection Water ion compositions
TABLE 2 physical Properties before and after core flooding and Mobile fluid porosity
As can be seen from Table 2, the core had a reduced porosity and permeability after water flooding, the porosity being determined by8.36% to 6.26%, the reduction was 25.12%. The permeability is from 4.25X 10-3μm2Down to 2.86X 10-3μm2The reduction amplitude reaches 32.71%. The mobile fluid porosity decreased from 5.18% to 3.65%, with a decrease of 29.54%. As can be seen from FIG. 1, the pore throat radius distribution after water injection was changed, the number of pores (0.004 μm-0.11348 μm) was increased, and the porosity occupied was increased from 1.96% to 3.32%. The macropores (0.11348-9.869 μm) are reduced and the occupied porosity is reduced from 6.40% to 2.94%. For the analysis reason, although the injected water was treated from the sewage to a certain extent, it can be seen from Table 1 that the injected water after the treatment also contains Ca2+And Mg2+Thus, under certain temperature conditions, the mixture of injected water and formation water is easy to form calcium sulfate and calcium carbonate precipitates, and further a part of pore throats are blocked. Calcium sulfate and calcium carbonate precipitate block some large pore throats to form a large number of small pores, so that the pore throat distribution of the core is changed, namely, a part of large pores are reduced while more small pores are formed. Eventually, the permeability, porosity and mobile fluid porosity of the core are reduced.
Example two
This example selects cores and injection water from a reservoir in the deldos basin HB oilfield C6 and mainly looks at the damage to the reservoir from insoluble solid phase particles in the injection water.
A quantitative evaluation method for the influence of sewage reinjection on the physical properties and pore throat distribution of tight sandstone comprises the following steps:
the method comprises the following steps: drilling a core sample with the diameter of 2.5cm and the length of 4.0cm from the full-diameter core, washing with oil, drying, and measuring the permeability of the core by gas to be 3.46 multiplied by 10-3μm2(ii) a In order to separately examine the damage of insoluble solid phase particles injected into water to a reservoir stratum, deionized water, namely distilled water is adopted as simulated formation water. And extracting the injected water of the operation area corresponding to the rock core, wherein the water quality analysis result of the injected water is shown in a table 1.
Step two: vacuumizing a rock core sample, saturating the simulated formation water under high pressure, and calculating the porosity of the rock core to be 6.28%;
step three: testing the nuclear magnetic resonance T of the rock core sample obtained in the step two2Spectrum, obtainingOriginal pore throat distribution of a core sample; then placing the rock core in a centrifugal device, centrifuging for 120min at a speed of 9000r/min, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by original immobile fluid of the rock core sample; according to T before and after centrifugation2The mobile fluid porosity was found to be 4.17% by spectral cumulative distribution.
Step four: placing the core sample obtained in the third step in a core holder, connecting a displacement process, setting an experiment temperature of 50 ℃, and injecting water into the core sample at an injection speed of 0.1 ml/min;
step five: placing the rock core sample obtained in the fourth step in a thermostat at 80 ℃ and drying for 24 hours, wherein the gas permeability is 2.05 multiplied by 10-3μm2(ii) a Then, vacuumizing the rock core to saturate distilled water, and testing the porosity of the rock core to be 4.59%;
step six: testing the nuclear magnetic resonance T of the rock core sample obtained in the fifth step2Performing spectrum to obtain pore throat distribution of the rock core sample after water injection; then placing the rock core in a centrifugal device for centrifugation for 120min, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by immobile fluid after the water injection of the core sample; according to T before and after centrifugation2The mobile fluid porosity was found to be 3.02% by spectral cumulative distribution.
Step seven: the T before and after centrifugation measured in the third step and the sixth step is calculated according to the following formula2The spectra were converted to pore throat radius distributions, see FIG. 2;
in the formula: r is pore throat radius, mum;
T2transverse relaxation time measured for nuclear magnetic resonance, ms;
k is core permeability, mD.
Step eight: and (4) quantitatively analyzing the distribution of the pore throat radius of the core after water flooding and the change of the porosity of the movable fluid according to the pore throat radius distribution curve.
TABLE 3 HB oilfield C6 reservoir injection Water quality analysis
| Analysis item | Analysis results | Industry Standard |
| Oil content (mg/L) | 4.26 | ≤5 |
| Insoluble solid phase particles (mg/L) | 35.6 | ≤1 |
| Median particle size (μm) | 3.48 | ≤1 |
| Total iron content (mg/L) | 0.27 | ≤0.5 |
TABLE 4 physical Properties before and after core flooding and Mobile fluid porosity
As can be seen from Table 4, the porosity and permeability of the cores after water injection were both reduced, from 6.28% to 4.59%, with a reduction of 26.91%. The permeability is 3.46 multiplied by 10-3μm2Down to 2.05X 10-3μm2The reduction amplitude reaches 40.75 percent. The mobile fluid porosity decreased from 4.17% to 3.02%, with a decrease of 27.58%. As can be seen from FIG. 1, the pore throat radius distribution after water injection was changed, the number of pores (0.001 μm to 0.029 μm) was increased, and the occupied porosity was increased from 2.24% to 3.61%. The macropores (0.029-20.46 μm) are reduced, and the occupied porosity is reduced from 4.04% to 0.98%. The analysis reason is shown in table 3, although the oil content and the total iron content are both below the industry standard, the content of the treated water-insoluble solid phase particles and the median value of the particle size greatly exceed the industry standard, and the particles can block some large pore throats, so that a large number of small pores are formed, and the pore throat distribution of the rock core is changed. Eventually, the permeability, porosity and mobile fluid porosity of the core are reduced.
Claims (6)
1. The quantitative evaluation method for the influence of sewage reinjection on the physical properties and pore throat distribution of the compact sandstone is characterized by comprising the following steps of:
the method comprises the following steps: selecting a real sandstone core of a low-permeability reservoir, washing oil, drying, and then performing gas logging on the permeability of a core sample; preparing simulated formation water according to the mineralization degree and the ion composition of the oilfield produced water; extracting the injected water of the operation area corresponding to the rock core;
step two: vacuumizing a rock core sample, saturating the simulated formation water at high pressure, and calculating the porosity and the pore volume of the rock core;
step three: testing the nuclear magnetic resonance T of the rock core sample obtained in the step two2Performing spectrum to obtain the original pore throat distribution of the rock core sample; then placing the rock core in a centrifugal device for centrifugation, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by original immobile fluid of the rock core sample;
step four: connecting the core sample obtained in the third step with a displacement process, setting an experimental temperature, and injecting an injection water sample retrieved on site into the core sample;
step five: drying the rock core sample obtained in the step four, and measuring the permeability by gas; then vacuumizing the core to saturate distilled water, and testing the porosity of the core;
step six: testing the nuclear magnetic resonance T of the rock core sample obtained in the fifth step2Performing spectrum to obtain pore throat distribution of the rock core sample after water injection; then placing the rock core in a centrifugal device for centrifugation, removing the movable water in the rock core, and testing the nuclear magnetic resonance T again2Performing spectrum to obtain pore throat distribution occupied by immobile fluid after the water injection of the core sample;
step seven: measuring the T before and after centrifugation measured in the third step and the sixth step2Spectra are plotted on two graphs, respectively, and T is plotted2Converting the spectrum into pore throat radius distribution;
using the following formula2Spectrum conversion pore throat radius:
in the formula: r is pore throat radius, mum;
T2transverse relaxation time measured for nuclear magnetic resonance, ms;
k is core permeability, mD;
step eight: according to measured T2And (3) spectrum and pore throat radius distribution curves, and quantitatively analyzing the distribution of the pore throat radius of the core after water flooding and the change of the porosity of the movable fluid.
2. The method for quantitatively evaluating the influence of sewage reinjection on the physical properties and pore throat distribution of the tight sandstone according to claim 1, wherein the core sample in the step one has a diameter of 2.5cm and a length of 4.0 cm.
3. The method for quantitatively evaluating the influence of sewage reinjection on the physical properties and pore throat distribution of the tight sandstone according to claim 1, wherein the pressure of high-pressure saturation in the second step is 30 MPa.
4. The method for quantitatively evaluating the influence of sewage reinjection on the physical properties and pore throat distribution of the tight sandstone according to claim 1, wherein the centrifugation time in the third step and the centrifugation speed in the sixth step are 120min and 9000 r/min.
5. The method for quantitatively evaluating the influence of sewage reinjection on the physical properties and pore throat distribution of the tight sandstone according to claim 1, wherein the injection speed in the fourth step is 0.1mL/min, and the injection time is 24 hours.
6. The method for quantitatively evaluating the influence of sewage reinjection on the physical properties and pore throat distribution of the tight sandstone according to claim 1, wherein in the fifth step, the drying temperature is 80 ℃ and the drying time is 24 hours.
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| CN110715888B (en) * | 2019-05-30 | 2022-04-22 | 西南石油大学 | Method for measuring size distribution change of sulfur deposit pores of high-sulfur-content gas reservoir core |
| CN110231268B (en) * | 2019-05-31 | 2022-07-22 | 大庆油田有限责任公司 | Method for analyzing oil-water occurrence pore size distribution of rock of tight reservoir |
| CN111006985B (en) * | 2019-11-11 | 2023-05-26 | 中国石油天然气股份有限公司 | Quantitative evaluation method for pore throat effectiveness of dense reservoir of land lake basin under geological conditions |
| CN114858678B (en) * | 2021-02-04 | 2024-06-25 | 中国石油天然气股份有限公司 | Core imbibition parameter measurement method for unconventional oil reservoir |
| CN114994283B (en) * | 2022-06-01 | 2024-09-24 | 国家石油天然气管网集团有限公司 | Pore throat structure change analysis method for gas storage |
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