CN115745476A - Porous cement polymer composite material, preparation method and application thereof in enhancing permeability of natural gas hydrate reservoir - Google Patents

Abstract

The invention discloses a porous cement polymer composite material, a preparation method and its application in natural gas hydrate reservoirs to enhance permeability. No foaming agent is used, fine recycled concrete with uniform particle size is used as aggregate, and the porosity Fly ash and cement are mixed with cement, bamboo fibers or granules as auxiliary materials, and a certain amount of cationic polyacrylamide and water are mixed to prepare porous cement polymer composite slurry. After curing, the cement polymer composite with good permeability and strength is prepared. The material is used to enhance the cementation strength of natural gas hydrate reservoirs to form an artificial well wall, which can be used as a sand retaining medium. The method of retaining and modifying is used to alleviate sand production and prolong the production time, and improve its permeability and prolong its sand control time.

Description

Porous cement polymer composite material, preparation method and its application in natural gas hydrate Enhanced Permeability Application in Reservoirs

Technical field:

The invention relates to the technical field of natural gas hydrate exploitation, in particular to a porous cement polymer composite material, a preparation method and its application in enhancing permeability of natural gas hydrate reservoirs.

Background technique:

Natural gas hydrate is a cage-like crystal formed by lower hydrocarbons and water under high pressure and low temperature conditions. It is mainly distributed in deep-sea continental slopes and land permafrost zones with water depths greater than 300m. Marine natural gas hydrate resources account for about 10% of the world's total resources. 97%. The carbon content of proven gas hydrate deposits worldwide is about twice that of existing fossil fuels. Because of its wide distribution, large reserves, and cleanliness, natural gas hydrate is considered to be the next energy source with the most exploitation potential after shale gas, coalbed methane, and tight gas. The commanding heights of future energy strategies and the forefront of scientific and technological innovation that all countries strive for.

Marine natural gas hydrate layers generally occur in soft unconsolidated or weakly cemented sediments with a water depth of more than 800m and a depth of 400m below the seabed. The content is as high as more than 40%. Typical gas hydrates in my country mainly exist in argillaceous silt deposits in the form of dispersion or weak cementation. Gas hydrates themselves are cements, reservoir skeleton particles, and the average permeability of the reservoirs is only a few millidarcy. The reservoir distribution consists of hydrate layer, mixed layer and gaseous hydrocarbon layer from top to bottom. The physical parameters of the reservoir are shown in Table 1.

Table 1 Physical parameters of natural gas hydrate reservoirs

Such low-permeability soft reservoir characteristics have brought great challenges to the development of gas hydrates. The natural gas hydrate production process is a coupled complex process of changing the thermodynamic conditions in the gas hydrate stable zone, solid hydrate decomposition, liquid water migration, and natural gas production. So far, the proposed gas hydrate development technology methods mainly include: depressurization method, heating method, chemical potential difference driving method (including injection and _CO2 replacement, etc.) and solid-state fluidization method, etc., see Table 2.

Table 2

However, the current hydrate mining faces a long distance from commercialization. During the production process, the phase change of hydrate will lead to changes in the mechanical properties and porosity of the reservoir, and the in-situ formation stress will also be redistributed, which will easily induce a series of geological risks such as wellbore instability, wellbore sand production, formation subsidence and submarine landslides question. Among them, sand production is one of the bottlenecks restricting the safe and efficient mining of hydrates.

During the development of natural gas hydrate, the decomposition and formation of hydrate will further reduce the cementation strength of muddy silt, and muddy sand will be produced along with the produced liquid (a mixture of gas and water) during the production process. Sand production will increase the amount of sand settling in the wellbore, causing damage to downhole equipment such as electric submersible pumps, greatly increasing the production cycle or even stopping production, and the sand-liquid mixture that migrates up must be treated accordingly; The destruction of strata structure and the reduction of its strength redistribute the stress in the ground, which increases the risk of geological disasters. Therefore, how to prevent sand production in natural gas hydrate reservoirs, effectively increase reservoir strength, improve reservoir permeability, and improve gas production efficiency is the core problem to be solved to realize the industrialization of natural gas hydrates.

In view of the two key problems of extremely low permeability and severe sand production caused by muddy silt in hydrate reservoirs, some scholars in my country have given suggestions to focus on hydraulic fracturing and supplementary near-well reservoir reconstruction. However, hydraulic fracturing cannot solve the problem that the mechanical strength of the reservoir itself is not enough to produce sand when the hydrate is exploited. Sand production is one of the key factors restricting the efficient and safe mining of hydrates. The measures currently proposed are basically based on the sand control methods of conventional unconsolidated sandstone oil and gas reservoirs. At present, the main conventional sand control methods include gravel packing and mechanical sand control method combined with various screens, chemical sand control method and composite sand control method combining chemical sand control and mechanical sand control. Chemical sand control methods are mainly divided into artificial cemented formation method and artificial borehole wall method. The artificial cementation method is to use cement to cement the loose sand grains in the loose sandstone strata at the contact points of the sand grains, so as to achieve the purpose of sand control and enhance the mechanical strength of the loose sandstone strata. The chemical sand consolidation agent for conventional unconsolidated sandstone oil and gas reservoirs uses inorganic cements such as silicic acid and calcium silicate or organic cements such as phenolic resins, urea-formaldehyde resins, epoxy resins, and polyurethanes to cement the sand grains together to increase the cementation strength. The artificial wellbore method is to squeeze resin-coated sand, cement mortar, etc. into the hollow of the wellbore to form an artificial wellbore with a certain degree of permeability, which can cement the formation and form a formation sand-retaining medium for sand control. The chemical sand control method of conventional oil and gas reservoirs is better than the mechanical sand control method for fine silt sand control, but it will damage the permeability of the reservoir. At the same time, the organic sand consolidation agent is easy to age and has a short validity period.

However, hydrate reservoirs in sea areas are dominated by muddy fine silt, with a median particle size of 10-16 μm, which is finer than conventional unconsolidated sandstone oil and gas reservoirs. The shale content is as high as 25%-50%, and the sediment cementation is weak or Uncemented, and the sand production is more serious after the phase change is induced during the mining process. The weak cementation of conventional high-shale fine silt sand makes the sand control of hydrate reservoirs more difficult than that of conventional unconsolidated sandstone oil and gas reservoirs, and puts forward higher requirements for sand control media and sand control technology. At present, the research on sand control of natural gas hydrate reservoirs is still in its infancy, mainly focusing on the mechanism of sand production, the law of sand migration and plugging of different sand retaining media. In 2020, Ning Fulong et al. proposed that for such low-permeability argillaceous silt hydrate reservoirs, the traditional idea of "blocking and preventing" becomes "consolidating and reforming", that is, improving the permeability of the reservoir while strengthening the hydrate reservoir. Rate.

In the construction of underground engineering, grouting technology is often used to reinforce the weak stratum and seal the groundwater. The grouting materials in the grouting technology are divided into granular materials and organic chemical materials. Granular materials mainly include cement slurry, cement-sodium silicate double slurry, superfine cement slurry, clay slurry, etc. This type of grouting material has the advantages of low cost, wide material source, simple grout preparation and simple grouting process, so it is widely used in underground projects. Organic chemical materials mainly include polyacrylamide, polyurethane, polyacrylate, epoxy resin, etc. These materials have low viscosity and are easy to inject into small cracks or pores, but the cost is high, the process is complicated and has an impact on the environment. The application is subject to certain restrictions. The grout infiltrates and diffuses in the formation under a certain pressure or reaches the splitting pressure to split and spread or fill in the cracks. However, the current grouting slurry will reduce the permeability coefficient of the underground rock and soil after it condenses.

Combining the soft rock reinforcement in underground engineering and the sand consolidation technology of conventional unconsolidated sandstone oil and gas reservoirs, aiming at such low permeability (several millidarcy) and unconsolidated muddy silt gas hydrate reservoirs, academician Sun Youhong proposed a Double-effect (increased permeability) polyurethane slurry for seabed hydrate reservoirs, application and application method, the prepared porous polyurethane slurry can be rapidly dispersed in the temperature and pressure environment of seabed hydrate reservoirs after splitting and diffusing under formation fracture pressure Solidification forms a stable, porous support network framework with high conductivity and high strength, and can have a strong cementation effect with sediments, which not only improves the mechanical strength of the reservoir, but also increases the stability of the reservoir. The permeability of the reservoir can be improved to realize the double-increasing reconstruction of the natural gas hydrate reservoir-enhanced permeability enhancement, which is conducive to the safe and efficient development of natural gas hydrate.

Domestic scholars are thus inspired to develop foamy water glass slurry. Water glass slurry is used as the main agent, and admixtures such as foaming agent and foam stabilizer are added to adjust the property and properties to a certain extent, so that it can cement the reservoir to form a porous structure and achieve the purpose of enhancing seepage stability. Foamed concrete is an internally porous cement lightweight material formed by physically foaming the solution prepared by foaming agent and water and cement slurry, stirring evenly, pouring and curing. Since the cement lightweight material introduces a large number of tiny foams during the preparation process, these bubbles are evenly distributed in the cement paste, resulting in a much lower bulk density than ordinary concrete. The hardened porous cement/concrete contains a large number of pores. It is used in soft soil foundation backfill, cavity filling, tunnel collapse control, water leakage sealing and other projects. The post-bonding effect is good but the consolidation strength is not great.

Although the porous and high-permeability grout is injected into the stratum through "consolidation and reformation", after penetrating into the stratum with a certain radius, it can consolidate part of the fine silt and sand in the reservoir, increase the permeability of the reservoir, and produce gas and liquid. A certain channel is provided, which can alleviate sand production in hydrate reservoirs to a certain extent. However, during the production of hydrates, fine silt and sand will still be mixed with the produced gas and liquid under the production pressure difference.

Invention content:

The purpose of the present invention is to provide a kind of porous cement polymer composite material, preparation method and its application in enhancing permeability of natural gas hydrate reservoir, without using foaming agent, using fine recycled concrete with uniform particle size as aggregate, Porous fly ash and cement are used as cement, bamboo fibers or particles are used as auxiliary materials, and a certain amount of cationic polyacrylamide and water are mixed to prepare porous cement polymer composite slurry, which is squeezed into the hole hole and penetrates a certain radius under a certain pressure. For natural gas hydrate reservoirs, the cement-polymer composite material with good permeability and strength prepared after solidification is used to enhance the cementation strength of natural gas hydrate reservoirs and form artificial well walls, which can be used as sand retaining media. The method is to alleviate sand production and prolong the production time, and improve its permeability and prolong its sand control time.

A kind of porous cement polymer composite material, with uniform particle size of 1-3mm fine recycled concrete as aggregate, porous fly ash and cement as cement, bamboo fiber particles as auxiliary materials, plus cationic polyacrylamide and Water composition; By total mass percentage is 100%, the mass fraction of bamboo fiber particles is 7%-8%, the mass fraction of cationic polyacrylamide is 1%, aggregate and cement are collectively referred to as ash, and the water-cement ratio is (0.3 -0.6):1, the mass ratio of aggregate to cement is 3:(1～1.5).

Preferably, based on 100% of the total mass percentage, the mass fraction of bamboo fiber particles is 8%, the mass fraction of cationic polyacrylamide is 1%, and the water-cement ratio is 0.5:1.

The preparation method of the porous cement polymer composite material comprises the following steps: stirring the aggregate and the cement for 3-8 minutes, adding bamboo fiber particles, cationic polyacrylamide and water, stirring and mixing, then filling the mold into a mold for curing and demoulding get.

The present invention also protects the application of the above-mentioned porous cement polymer composite material in natural gas hydrate reservoirs to enhance permeability, comprising the following steps: stirring the aggregate and cement, adding bamboo fiber particles, cationic polyacrylamide and water, and then stirring The slurry is mixed and squeezed into the hole hole to penetrate the natural gas hydrate reservoir with a certain radius under a certain pressure. After curing, the cement-polymer composite material with good permeability and strength is prepared to enhance the cementation strength of the natural gas hydrate reservoir and Improve its permeability to form an artificial well wall.

After the slurry is injected into the natural gas hydrate reservoir, the strength is greatly increased. In addition, the prepared cement-polymer composite material has a relatively uniform particle size, and the formed pores have a relatively uniform size and good permeability. The added bamboo fiber polymer will also increase the permeability to the reservoir cement. Cationic polyacrylamide can flocculate ultra-fine mud and silt, and the flocs formed have high permeability and do not affect the flow of gas and liquid. Therefore, the prepared cement-polymer composite material with good permeability and strength is used to strengthen natural gas. The cementation strength of the hydrate reservoir can be improved, the permeability can be improved, and the sand control time can be extended.

The beneficial effects of the present invention are as follows:

1) Different from the way that porous polyurethane, water glass and concrete use foaming agent to prepare high-permeability porous slurry and inject it into low-permeability soft soil gas hydrate reservoir, the present invention does not use foaming agent to uniformly Fine recycled concrete with particle size is used as aggregate, porous fly ash and cement are used as cement, bamboo fibers or particles are used as auxiliary materials, and a certain amount of cationic polyacrylamide and water are mixed to prepare porous cement polymer composite slurry, which is prepared after curing The cement-polymer composite material with good permeability and strength is used to enhance the cementation strength of natural gas hydrate reservoirs to form an artificial well wall, which can be used as a sand retaining medium, and the method of retaining and modifying is used to alleviate sand production and prolong the production time , and improve its permeability and prolong its sand control time.

2) The particle size of the cement polymer composite material prepared by the present invention is relatively uniform, the size of the formed pores is relatively uniform, and it has good permeability. The added bamboo fiber polymer will also increase the permeability to the reservoir cement. Cationic polyacrylamide flocculates ultra-fine mud and silt sand, and the flocs formed have high loose permeability and do not affect the flow of gas and liquid. Therefore, the prepared cement-polymer composite material with good permeability and strength is used to enhance natural gas hydration. It can improve the cementation strength of the reservoir, improve its permeability, and prolong its sand control time.

Description of drawings:

Fig. 1 is a schematic diagram of the principle of the medium sand retaining test of the present invention.

Detailed ways:

The following is a further description of the present invention, rather than a limitation of the present invention.

Sample Preparation Example 1: Preparation of Porous Cement Polymer Composite Slurry:

Use a 8-10 mesh sieve to sieve fine recycled concrete aggregates with a particle size of about 2mm, take 42.3kg of fine recycled concrete, 4.23kg of porous fly ash and 14.108kg of cement and stir for 5 minutes with a concrete single horizontal shaft, add 8kg of bamboo fiber Granules, 1 kg of cationic polyacrylamide and 30.33 kg of water were fully dissolved and then stirred for 5 minutes to prepare a porous cement polymer composite slurry.

Comparative example 1:

Referring to Sample Preparation Example 1, the difference is that no fly ash, bamboo fiber particles and cationic polyacrylamide were added in the preparation of the porous cement polymer composite slurry.

Comparative example 2:

Referring to Sample Preparation Example 1, the difference is that no bamboo fiber particles and cationic polyacrylamide are added in the preparation of the porous cement polymer composite slurry.

Comparative example 3:

Referring to Sample Preparation Example 1, the difference is that no cationic polyacrylamide is added in the preparation of the porous cement polymer composite slurry.

The simulated rock samples of the reservoir are obtained by manual sample preparation according to the grain size distribution curve and shale content of seabed sand samples. Reservoir simulation rock samples were cemented with 20 mesh, 40 mesh, 100 mesh, 200 mesh, 500 mesh, 1000 mesh montmorillonite and illite, and quartz clay. The shale content is 40.2%, and the median particle size of the sample is 11 μm. It is high-mud fine siltstone, and its particle size and physical properties are basically consistent with those of unconsolidated sediments in the reservoir.

Example of performance test

1. Determination of coagulation time

Adopt viscometer method to carry out viscosity test to sample preparation embodiment 1, comparative example 1-3 slurry material, when slurry viscosity reaches 100cp, the time that slurry loses fluidity substantially is primary gel time. See Table 3 for the results.

2. Preparation of rock samples

Fill the well-stirred mortar of Preparation Example 1 and Comparative Example 1-3 into the Ф50mm*100mm circular rigid mold respectively and compact it initially. Use a pressure testing machine to pressurize at a pressure of 3.0MPa for 30s. After curing for 2 hours under 3% salt water, the mold was demoulded. Put the sample after demoulding into a high-pressure reactor and place it in a 3% saline environment at 10°C-20°C for 3 days and 30 days, and then prepare rock samples for testing compressive strength and permeability. See Table 3 for the results.

3. Test of compressive strength:

Put the wet rock sample of Ф50*100mm into the NYL-60 uniaxial stress tester to test the compressive strength, put the rock sample into the compression container with the compression section of 50mm*50mm, The center of the tool and the center of the pressure plate of the tester are geometrically aligned, and the load is uniformly loaded at a rate of 2400N/s until the rock sample is destroyed, and the failure load F is recorded. The compressive strength R _c is calculated by the following formula:

R _c =F/A

F-breaking load (N); A-stress area (mm ² )

4. Penetration test:

Refer to the national petroleum and natural gas industry standard SY/T "Test Method for Relative Permeability of Two-phase Fluids in Rocks", put a wet rock sample of Ф50*100mm*100mm into the core holder of the rock permeameter to test the permeability of the rock sample. Use a rubber seal with a certain outer diameter for sealing, the ring pressure is 1.2-1.4MPa, open the water supply system, keep the overflow and constant water head constant, wait for the flow to stabilize, and count the outlet flow for 5 minutes. The permeability coefficient is calculated by Darcy's formula, and then converted into permeability:

Among them, K is the permeability coefficient (cm/s); Q is the seepage flow rate in 5 minutes; L is the seepage length (cm); A is the seepage cross-sectional area (cm ² ); H is the water head difference (cm); t is the seepage time (s ). The results are shown in Table 3.

table 3

Among them, the simulated rock samples of the reservoir are obtained by manual sample preparation according to the grain size distribution curve and shale content of seabed sand samples. Reservoir simulation rock samples were cemented with 20 mesh, 40 mesh, 100 mesh, 200 mesh, 500 mesh, 1000 mesh montmorillonite and illite, and quartz clay. The shale content is 40.2%, and the median particle size of the sample is 11 μm. It is high-mud fine siltstone, and its particle size and physical properties are basically consistent with those of unconsolidated sediments in the reservoir.

It can be seen from Table 3 that compared with Comparative Example 1, adding fly ash will slightly reduce the compressive strength of the composite material, but increase the permeability of the composite material. Compared with Comparative Example 3 and Comparative Example 2, Adding hydrophilic bamboo fiber does not increase the compressive strength much, but the permeability increases by 20%. The analysis may be that on the one hand, the hydroxyl group of bamboo fiber can form hydrogen bond with hydration cement, while the hydrophilic elongated fiber is water Provide percolation channels. In Example 1 where cationic polyacrylamide is added, the amide group can also form hydrogen bonds with some hydroxyl groups of bamboo fibers, and high molecular weight cationic polyacrylamide increases the flow resistance of water. Therefore, on the basis of Comparative Example 3, although the permeability has decreased, the compressive strength has increased. It can be seen that the fly ash and hydrophilic bamboo fiber of the present application act synergistically, and the prepared cement-polymer composite material significantly improves permeability with a slight increase in strength, and has good permeability and strength. After adding cationic polyacrylamide, fly ash and hydrophilic bamboo fiber are synergistic, and the prepared cement-polymer composite material improves strength with a slight increase in permeability.

5. Sand retaining simulation test

Using a sand-retaining simulation test device (see Dong Changyin, Zhou Bo, Song Yang, etc., Sand-retaining simulation test and evaluation method of sand control media in natural gas hydrate reservoirs, Journal of China University of Petroleum (Natural Science Edition), 2020, 44(5): 79 -88), its principle is shown in Figure 1. Example 1 and Comparative Examples 1-3 prepared 4 kinds of sand retaining media for simulated displacement experiments using the same pump flow rate, silt volume and silt volume content. As the water-carrying sand displacement proceeds, the sand retaining media are gradually blocked, achieving While retaining sand, it causes a decrease in fluidity and permeability. A certain concentration of argillaceous siltstone was mixed into the water by an automatic sander, and the permeability was tested for 3d and 30d with different sand retaining media. The permeability of the sand retaining medium at 3d and 30d was calculated by Darcy's formula. See Table 4 for the results.

Table 4

It can be seen from Table 4 that after the silt flowing in one direction has passed through the different sand-retaining media of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1 for 3 days, the permeability of the sand-retaining media has a large increase. Decline, but the permeability of the media of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1 still has 1500mD, 1300mD, 1000mD, and 1200mD respectively. It shows that the porous sand retaining media with high permeability such as Comparative Example 1, Comparative Example 2, Comparative Example 3 and Example 1 still have good seepage property after a certain amount of quicksand 3d. After the silt and sand flowed in one direction passed through the different sand retaining media of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Example 1 for 30 days, the permeability of the media in Comparative Example 1, Comparative Example 2, and Comparative Example 3 was only several mD, while Example 1 still has 400 mD. It shows that the porous sand-retaining media with high permeability of Comparative Example 1, Comparative Example 2 and Comparative Example 3 have poor permeability after flowing through a certain amount of quicksand for 30 days, while Example 1 still has good permeability. This is because in the initial stage (3d), although the permeability of the four kinds of sand retaining media has dropped significantly, they still have good seepage capacity. However, under a certain pressure difference, the fine sand in the flow of fine silt and sand is easier to pass through the sand retaining medium of Comparative Example 1, Comparative Example 2, and Comparative Example 3, and some mud and sand will pass through the middle barriers of Comparative Example 1, Comparative Example 2, and Comparative Example 3. For sand medium rock samples, some fine silts migrate longer distances in the sand retaining medium, and some of them are blocked in the rear part of the sand retaining medium, while some mud will slowly form on the surface of the sand retaining medium with certain permeability. Therefore, at this time (3d) still has good water seepage, but the sand retaining media in Comparative Example 1, Comparative Example 2, and Comparative Example 3 have poor sand retaining effects. With the prolongation of time (30d), the thin layer of mud cake is gradually filled, and has almost no seepage capacity under constant pressure difference. However, in Example 1, because the added cationic polyacrylamide can flocculate negatively charged mud and sand, in the initial stage (3d) the fine powder mud sand with a finer particle size flocculates into looser and larger coarse particles, blocking the surface of the medium to form infiltration The filter cake with a large rate will gradually form loose flocculated particles inside the medium, so it has good permeability at the beginning and can block most of the quicksand. As time goes on, the formed flocculated coarse mud cake has a relatively high The fine mud cake has a higher permeability, so the sand retaining medium of Example 1 has better water flow seepage capacity than the sand retaining media of Comparative Example 1, Comparative Example 2, and Comparative Example 3 after 30 days. Since the flocculation of cationic polyacrylamide will flocculate the fine silt from the reservoir into coarse silt during the production process, so Example 1 not only has better sand retaining ability as the sand retaining medium, but also with the prolongation of production time, the relative The sand-retaining media prepared in Comparative Example 1, Comparative Example 2, and Comparative Example 3 have better seepage capacity, have less impact on water flow seepage capacity, and can greatly prolong the production time of hydrate reservoir produced fluid.

Claims (4)

1. a kind of porous cement polymer composite material, it is characterized in that, be the fine regenerated concrete of 1-3mm with uniform particle diameter as aggregate, porous fly ash and cement are cementing agent, bamboo fiber particle is auxiliary material, add Composed of cationic polyacrylamide and water; based on the total mass percentage of 100%, the mass fraction of bamboo fiber particles is 7%-8%, and the mass fraction of cationic polyacrylamide is 1%; the aggregate and cement are collectively referred to as ash, The water-cement ratio is (0.3-0.6):1, and the mass ratio of aggregate to cement is 3:(1-1.5). 2. porous cement polymer composite material according to claim 1, is characterized in that, by total mass percentage is 100%, bamboo fiber particle massfraction is 8%, and the massfraction of cationic polyacrylamide is 1%, The water-cement ratio is 0.5:1. 3. the preparation method of the described porous cement polymer composite material of claim 1 is characterized in that, comprises the following steps: aggregate and cement are stirred 3-8 minute, add bamboo fiber particle and cationic polyacrylamide and water and then It is stirred and mixed, then filled into a mold, maintained and solidified, and then released from the mold. 4. The porous cement polymer composite material of claim 1 is used in the enhanced permeation enhancement of natural gas hydrate reservoir, it is characterized in that, comprising the following steps: aggregate and cement are stirred, adding bamboo fiber particles and cationic polypropylene Amide and water are then stirred and mixed to obtain a slurry, which is squeezed into the hole hole and penetrates a certain radius of the gas hydrate reservoir under a certain pressure to form an artificial wellbore wall.

Images