CN111484653A

CN111484653A - Xanthan gum composite gel for underbalanced drilling and preparation method and application thereof

Info

Publication number: CN111484653A
Application number: CN202010391664.0A
Authority: CN
Inventors: 林梅钦; 王柳; 杨子浩; 张娟; 董朝霞
Original assignee: China University of Petroleum Beijing
Current assignee: China University of Petroleum Beijing
Priority date: 2020-05-11
Filing date: 2020-05-11
Publication date: 2020-08-04
Anticipated expiration: 2040-05-11
Also published as: CN111484653B

Abstract

The invention discloses a xanthan gum composite gel for underbalanced drilling, a preparation method and application thereof, belonging to the field of oilfield chemistry. The invention adopts xanthan gum as polymer, chromium acetate as cross-linking agent, starch, nano-silica, montmorillonite and laponite as toughening material to prepare xanthan gum composite gel; the xanthan gum composite gel has good viscoelastic property, adhesion and pressure resistance, can meet the requirements of a gel valve in an underbalanced drilling site, and has good application prospect.

Description

Xanthan gum composite gel for underbalanced drilling and preparation method and application thereof

Technical Field

The invention relates to the field of oilfield chemistry, in particular to a xanthan gum composite gel for underbalanced drilling and a preparation method and application thereof.

Background

From a worldwide exploration format, the possibility of finding large, large oil and gas fields on land and offshore is becoming less and less, while the state of the art horizontal and comprehensive economic evaluation has led to less exploration and development of deep sea oil and gas resources. In order to meet the demand of the world economic development on petroleum, the key points of the petroleum exploration and development are transferred to medium and small oil fields, oil fields under complex geological surface conditions, unconventional oil and gas resources, and the transformation and excavation of the medium and later oil fields. In China, special oil and gas resources are distributed in large oil fields in China, and the reserves of the special oil and gas resources account for more than one third of the total proven reserves. In the drilling process of a conventional oil field, the oil deposit is polluted and blocked due to long-term overbalanced drilling, and a part of oil fields enter the low-pressure oil field category due to the descending of pressure in the middle and later periods of development, so that the underbalanced drilling technology is widely applied with unique advantages.

The drilling by the underbalanced drilling technology has the following characteristics: the damage to the stratum can be reduced to a certain extent, the hydrocarbon reservoir is protected, and the yield of the hydrocarbon reservoir is increased; meanwhile, the stratum condition can be dynamically monitored in the drilling process, so that the efficiency is improved, the cost is saved, the occurrence probability of a well leakage event is reduced, the risk of differential pressure drill sticking is reduced, and the cost is saved. However, the underbalanced drilling technology has some disadvantages in practical application, the snubbing unit needs a lot of time to install equipment before use, and needs a lot of time to realize the tripping and the drilling operation in the use process, and in addition, the device can not realize safe snubbing operation in the screen pipe completion process. The downhole casing valve is mainly imported, the cost is high, and in addition, the drilling tool can damage the downhole casing valve due to well deviation in the drilling process, so that the control system fails.

To address these problems with underbalanced completions, gel valve technology has been proposed. After a section of gel is injected into the well bore, the gel can form gel inside the well bore and is fixed at a certain height inside the well bore by virtue of the adhesion force of the gel and the wall of the well bore, so that the valve fixing function is realized. And secondly, the gel valve seals an oil-gas layer at the lower part of the gel valve and drilling fluid at the upper part in the shaft, so that the gel valve and the drilling fluid are prevented from contacting, and the effects of sealing and isolating are achieved. And finally, after drilling is completed, a gel breaker can be added to realize gel breaking and flowback of the gel valve, and meanwhile, the gel breaking time and the gel breaking strength can be adjusted to realize valve opening.

The mechanical strength of the pure polymer gel can not meet the requirements of field application, so the mechanical strength of the gel valve is enhanced by adding the toughening material. The traditional polyacrylamide gel usually adopts an oxidation gel breaker, and oxygen is continuously generated in the gel breaking process, is enriched and is easy to explode. Therefore, the gel valve is prepared by adopting the biopolymer, and the biological enzyme gel breaker can be adopted in the gel breaking process, so that the safety of gel breaking can be ensured, the gel breaking agent can be naturally degraded, and the gel valve is free from environmental pollution. Therefore, gel valves made of biopolymers have become a focus of research.

Disclosure of Invention

The invention provides a xanthan gum composite gel for under-balanced drilling, a preparation method and application thereof, wherein the xanthan gum is used as a polymer, chromium acetate is used as a cross-linking agent, and starch, nano silicon dioxide, montmorillonite and laponite are used as toughening materials to prepare the xanthan gum composite gel; the xanthan gum composite gel has good viscoelastic property, adhesive force and pressure resistance.

The invention firstly provides a xanthan gum composite gel, which is prepared from the following raw materials: based on the total mass of the raw materials, the mass percent of the xanthan gum is 1-4%; the mass percent of the cross-linking agent is 0.2-0.5%; the mass percent of the toughening agent is 0-10 percent but not 0; the balance of water; the toughening agent is selected from at least one of laponite, starch, nano silicon dioxide and montmorillonite.

In the xanthan gum composite gel, the mass percent of the xanthan gum can be 2-4%; specifically, it may be 3%.

The number average of the xanthan gumMolecular weight (M)_n) Can be 300-1800 ten thousand, specifically 1000-1800 ten thousand, more specifically 1500-1800 ten thousand or 1800 ten thousand.

The cross-linking agent is chromium acetate.

The mass percentage of the cross-linking agent can be 0.3-0.5%, and specifically can be 0.4%.

The mass percentage of the toughening agent can be 1-10%, 3-10%, 5-10%, 7% or 10%.

The water is deionized water.

In the xanthan gum composite gel, the nano silicon dioxide, the montmorillonite and the laponite are all nano-scale.

The invention also provides a preparation method of the xanthan gum composite gel, which comprises the following steps: and uniformly mixing the xanthan gum, the toughening agent and water, then adding the cross-linking agent, and gelling to obtain the xanthan gum composite gel.

In the above preparation method, the method further comprises the step of dissolving the xanthan gum in water and then standing; the standing time is 12-36h, and specifically can be 24 h.

In the preparation method, the temperature of the gel forming is 40-90 ℃, and particularly can be 50 ℃; the time is 6-36h, specifically 24 h.

The application of the xanthan gum composite gel provided by the invention in underbalanced drilling also belongs to the protection scope of the invention.

The xanthan gum composite gel is used for a gel valve in underbalanced drilling.

According to the invention, starch, nano silicon dioxide, montmorillonite or laponite are added into xanthan gum as toughening materials, so that the rheological property, the compression property, the adhesion and the pressure resistance of the composite gel are improved. The xanthan gum composite gel can meet the requirements of a gel valve in an underbalanced drilling site, and has a good application prospect.

Drawings

FIG. 1 is a graph of the elastic and viscous moduli of a starch-xanthan gum complex gel; wherein a is the elastic modulus of the starch-xanthan gum composite gel, and b is the viscous modulus of the starch-xanthan gum composite gel.

Fig. 2 is a graph of compressive stress-strain curves for a starch-xanthan gum complex gel.

Fig. 3 is a graph of the adhesion of a starch-xanthan gum complex gel.

FIG. 4 is a graph of the viscous modulus versus the elastic modulus of a silica-xanthan gum complex gel; wherein a is the elastic modulus of the silica-xanthan gum composite gel, and b is the viscous modulus of the silica-xanthan gum composite gel.

Fig. 5 is a graph of compressive stress-strain curves for a silica-xanthan gum complex gel.

Fig. 6 is a graph of silica-xanthan gum complex gel adhesion.

FIG. 7 shows the viscous modulus and elastic modulus of a montmorillonite-xanthan gum composite gel; wherein a is the elastic modulus of the montmorillonite-xanthan gum composite gel, and b is the viscous modulus of the montmorillonite-xanthan gum composite gel.

Fig. 8 is a graph of compressive stress-strain of a montmorillonite-xanthan gum composite gel.

FIG. 9 is a graph of the adhesion of a montmorillonite-xanthan gum composite gel.

FIG. 10 is a graph of the viscous modulus and elastic modulus of a laponite-xanthan gum complex gel; wherein a is the elastic modulus of the laponite-xanthan gum composite gel, and b is the viscous modulus of the laponite-xanthan gum composite gel.

Fig. 11 is a graph of compressive stress-strain curves for a laponite-xanthan gum complex gel.

FIG. 12 is a graph of adhesion of a laponite-xanthan gum complex gel.

Detailed Description

The present invention is described in further detail below with reference to specific embodiments, which are given for the purpose of illustration only and are not intended to limit the scope of the invention.

The experimental procedures in the following examples are conventional unless otherwise specified.

Materials, reagents and the like used in the following examples are commercially available unless otherwise specified.

Xanthan gum M used in the following examples_n1800 ten thousand; chromium acetate is analytically pure and purchased from Beijing, modern Oriental Fine Chemicals, Inc.; the starch is analytically pure and purchased from Tanshino chemical reagents, Inc. of Tianjin; the nano silicon dioxide is nano grade and is purchased from Zhejiang Yudao chemical Co Ltd; montmorillonite is nano-scale and is purchased from Zhejiang Uuda chemical Co.Ltd; laponite was analytically pure and purchased from Tanshino Chemicals Co., Ltd.

The following examples the mechanical properties of xanthan gum complex gels were tested as follows:

1. rheological Property test

The rheological property of the xanthan gum composite gel is characterized by using a German Haake rheometer, a PP20 plate-plate geometric measurement system is selected, and the plate interval is set to be 1 mm. Taking a proper amount of xanthan gum composite gel, firstly carrying out frequency scanning, setting the stress scanning range to be 0.1-250Pa and the frequency to be 1Hz, selecting a proper stress value in a linear viscoelastic region of the composite gel, then fixing the stress and the frequency, and measuring the change of the viscoelasticity of the composite gel along with time under the condition. The temperature was maintained at 25 ℃ throughout the test.

2. Test of pressure resistance

The pressure resistance of the composite gel is measured by adopting a pressure resistance device shown in the specification and attached figure 1 in patent 201610963885.4 (polymer gel for well killing and a preparation method and application thereof) to simulate the condition of the composite gel in a stratum, and the maximum pressure value which can be borne by the composite gel is measured.

3. Stress-strain performance test

The stress-strain performance test adopts a TA.XT texture analyzer. Injecting the prepared composite gel base liquid into a cylindrical mold, putting the cylindrical mold into a constant-temperature drying oven at 50 ℃ for 24 hours, taking the cylindrical mold out of the mold, putting the cylindrical mold in the center of a texture tester testing platform, and uniformly compressing the cylindrical mold at a speed of 0.5mm/s by adopting a 50kg weight induction element until the strain degree is 90%, namely compressing the composite gel to 90% of the original height.

4. Adhesion test

The instrument adopted for the adhesion test is a gel macroscopic adhesion force measuring device (Z L201710916930.5). The composite gel base liquid prepared according to the composite gel formula shown in tables 1-4 is injected into a base of the adhesion force measuring device, so that the lower surface of the cylinder is just contacted with the upper surface of the gel base liquid, the cylinder is placed into a constant temperature drying box at 50 ℃ after being completely sealed, the temperature is kept for 24h, the texture instrument is operated to correct the weight and the distance, then the adhesion force measuring device is fixed on the base of the texture instrument, the experimental mode is a stretching mode, the stretching speed is 0.5mm/min, the test is started, in the test process, the force arm of the texture instrument pulls the cylinder of the mold to ascend at a constant speed, the bottom of the cylinder is gradually separated from the upper surface of the composite gel, and the force required when the cylinder is completely separated is observed and recorded.

Example 1 preparation of xanthan gum complex gel

A certain mass of deionized water is taken by balance and put into a beaker, a certain mass of xanthan gum is put into the beaker, stirred by a stirrer at the rotating speed of 300r/min for 4h, and kept stand for 24h for standby. And then adding a certain amount of toughening agent into a beaker containing xanthan gum, continuing stirring, adding a crosslinking agent of chromium acetate after uniform dispersion, uniformly stirring, placing into a drying oven at a constant temperature of 50 ℃ for 24 hours, observing the gelling condition, and testing the performance of the gelling condition. The amounts of each substance added in the preparation of the xanthan gum complex gel are shown in tables 1 to 4.

TABLE 1 starch-Xanthan Gum composite gel formulation

TABLE 2 silica-Xanthan Gum composite gel formulations

TABLE 3 montmorillonite-xanthan gum composite gel formulations

TABLE 4 laponite-xanthan gum composite gel formulations

EXAMPLE 2 Properties of starch-Xanthan Gum composite gel

1. Rheological properties of starch-xanthan gum composite gel

Through rheological property tests, the characteristics of the material can be predicted, and the elastic modulus (namely storage modulus), the viscous modulus (namely loss modulus) and the loss factor (namely the ratio of the loss modulus to the storage modulus) of the composite gel are mainly tested. In order to clarify the influence of the starch content on the viscoelasticity of the gel system, the viscoelasticity and the loss factor of the gels of different systems are measured by a Haake rheometer, and the results are shown in FIG. 1 (the preparation and the formula of the starch-xanthan gum composite gel are shown in example 1 and Table 1). The test conditions were: at 25 ℃ with a stress of 10Pa and a frequency of 1 Hz.

As can be seen from a in fig. 1, the elastic modulus of the starch-xanthan gum composite gel after the starch is added is enhanced, the elastic modulus of the starch-xanthan gum composite gel is increased from 14.82Pa to 22.69Pa with a small increase when the amount of the added starch is 1% to 5%, the elastic modulus of the starch-xanthan gum composite gel is sharply increased to 64.13Pa when the content of the added starch is increased to 7%, and the elastic modulus of the starch-xanthan gum composite gel is increased to a maximum value of 5002Pa with an increase of two orders of magnitude when the amount of the added starch is 10%.

As can be seen from b in fig. 1, the viscous modulus of the starch-xanthan gum composite gel increases after the starch is added, and when the starch is added at a low concentration, i.e., the amount of the added starch is 1% to 7%, the viscous modulus of the starch-xanthan gum composite gel increases to a small extent, only from 2.626Pa to 17.45 Pa. While the viscosity modulus of the starch-xanthan gum composite gel is 677.3Pa when the content of the added starch is 10%, and the increase is two orders of magnitude. This indicates that the elastic modulus and viscous modulus of the starch-xanthan gum complex gel are positively correlated with the amount of starch added. The viscous modulus of the starch-xanthan gum composite gel reaches a maximum value when the amount of starch added is 10%. Moreover, the elastic modulus of the starch-xanthan gum composite gel is far greater than the viscous modulus, which shows that the starch-xanthan gum composite gel is a viscoelastic fluid mainly with elasticity, and when the starch-xanthan gum composite gel is compressed, the starch-xanthan gum composite gel mainly generates elastic deformation and shows more elastic solid properties.

2. Compression performance of starch-xanthan gum composite gel

The compressive stress-strain test is to observe the stress and deformation conditions of the composite gel in a compressed state so as to judge whether the composite gel can meet the design requirement of compressive strength. Fig. 2 is a compressive stress-strain curve of a starch-xanthan gum composite gel system with a starch content of 1% to 10% at a compression degree of 90%.

As can be seen from fig. 2, the stress required for compression of the starch-xanthan gum complex gel gradually increased from 40435mN to 60623mN as the content of starch added increased. When the amount of starch added is 7%, the stress value required for the degree of compression of the starch-xanthan gum complex gel to be 90% is 60623mN at the maximum, and the stress required for compression is reduced to 58402mN instead as the starch content continues to increase. This is probably because the starch particles have smaller particles and larger specific surface area, and the contact area with the system is increased with the further increase of the content of the starch particles, so that the surface defects of the composite gel are filled, and the added starch is excessive, so that the structure of the starch-xanthan gum composite gel becomes fluffy, and the stress required by the compression of the starch-xanthan gum composite gel is reduced.

As can also be seen from fig. 2, the compressive stress-strain test curve of the starch-xanthan gum composite gel can be divided into three parts, the degree of compression of the first part is 0-60% (low degree of compression), and the stress required for reaching the corresponding degree of compression is small, and the addition of starch has no influence on the compressive stress of the starch-xanthan gum composite gel, and in the process, the deformation amount of the starch-xanthan gum composite gel is small, and the starch-xanthan gum composite gel is compressed to 100% -40% of the original height, and the energy required to be stored is small; the degree of compression of the second part is 60-80%, the second part is compressed at a constant speed continuously, and the required stress is increased slowly; the third part has a compression degree of 80-90%, the required stress rises sharply after compression is continued, and the maximum compression stress of the starch-xanthan gum composite gel with the starch content of 7% can be found by comparing test curves of different starch addition amounts.

3. Adhesion of starch-xanthan gum composite gel

The gel valve realizes well killing by utilizing the mechanical strength of the gel valve and the adhesion force of the gel valve and the wall of a shaft pipe. Thus, in addition to the need to enhance the mechanical properties of the composite gel itself, there is also a need to increase the adhesion of the composite gel to the wellbore wall.

Fig. 3 is a graph of the adhesion of a starch-xanthan gum complex gel. As can be seen from fig. 3, the adhesion of the starch-xanthan gum complex gel was significantly enhanced after the addition of the starch granules. The adhesion of the starch-xanthan gum complex gel can reach a maximum of 13495mN when the amount of starch is 10%, while the adhesion of the starch-xanthan gum complex gel is only 8667mN when the amount of starch is 1%. By comparison, it can be seen that the starch-xanthan gum complex gel has significantly increased adhesion to the tube wall by the addition of starch. Meanwhile, in the adhesion test process of the starch-xanthan gum composite gel, the whole process can be divided into three stages. The first stage is that the texture analyzer slowly lifts the upper part of the test element, and the adhesive force is gradually increased; the second stage is that the upper part of the test element is pulled on the upper surface of the starch-xanthan gum composite gel, and the adhesive force is increased to the maximum value; the third stage is that the starch-xanthan gum composite gel is separated from the test element, the contact area is gradually reduced, and finally the complete separation is realized. The adhesion of the composite gel reached a maximum in the first stage when 1% -5% starch was added, at which point the adhesion of the starch-xanthan composite gel to the test element wall was increased. When the amount of the added starch is 7 to 10 percent, the adhesion of the starch-xanthan gum composite gel reaches the maximum value in the second stage, the adhesion of the starch-xanthan gum composite gel to the upper part of the test element is increased, and the tensile property of the starch-xanthan gum composite gel is reflected from the other side, the increase of the amount of the added starch also enables the tensile property of the starch-xanthan gum composite gel to be obviously improved, the starch-xanthan gum composite gel is not easy to break from the middle, and therefore the starch-xanthan gum composite gel is not easy to break.

4. Compressive strength of starch-xanthan gum composite gel

When the gel valve is applied on site, 300m of composite gel is injected into the shaft, so that the aim of balancing the pressure inside the stratum and the ground pressure is fulfilled, and the well killing is realized. The pressure test is used for simulating the field application condition and testing the maximum pressure which can be borne by the composite gel.

Table 5 shows the compressive strength values of the starch-xanthan gum composite gels with different contents, and it can be seen from table 5 that the compressive strength of the xanthan gum and chromium acetate composite gel is 14.5MPa without adding starch, which cannot meet the requirements of field application. When the amount of starch added was 1%, the compressive strength of the starch-xanthan gum composite gel increased sharply to 30.2MPa, which is about 2 times the compressive strength of the gel without the addition of starch. It can be seen that the addition of starch granules increases the compressive strength of the starch-xanthan gum complex gel. When the content of the starch in the starch-xanthan gum composite gel is continuously increased to 7%, the compressive strength of the starch-xanthan gum composite gel is only slightly increased to 49.6 MPa. When the amount of starch added was increased to 10%, the compressive strength of the starch-xanthan gum composite gel reached a maximum, increasing to 98.0MPa, which is about 7 times the compressive strength of the gel without the addition of starch.

TABLE 5 compressive Strength of starch-Xanthan Gum composite gels

Example 3 Properties of silica-Xanthan Gum composite gels

1. Rheological properties of silica-xanthan gum composite gels

A German Hakker rheometer is adopted to represent the rheological property of the silicon dioxide-xanthan gum composite gel, namely the viscoelasticity of the silicon dioxide-xanthan gum composite gel at normal temperature. Fig. 4 is a graph showing the viscoelasticity of a silica-xanthan gum complex gel (see example 1 and table 2 for the preparation and formulation of the silica-xanthan gum complex gel), wherein a in fig. 4 is a graph showing the elastic modulus of the silica-xanthan gum complex gel, and b in fig. 4 is a graph showing the viscosity modulus of the silica-xanthan gum complex gel. The test conditions were: at 25 ℃ with a stress of 10Pa and a frequency of 1 Hz.

As can be seen from a in fig. 4, the elastic modulus of the silica-xanthan gum composite gel gradually increases as the amount of the silica nanoparticles added increases, and the elastic modulus of the silica-xanthan gum composite gel reaches a maximum of 14730Pa when the amount of the silica nanoparticles added reaches 10%. Without the addition of silica nanoparticles, the elastic modulus of the xanthan/chromium acetate gel was only 15.65Pa, at which point the elastic modulus of the gel was at a minimum. After 1% silica nanoparticles were added, the elastic modulus of the silica-xanthan gum composite gel rapidly increased to 91.53Pa, which is 6 times the elastic modulus of the gel without silica nanoparticles. The content of silica nanoparticles added was continuously increased, and when the added amount reached 5%, the elastic modulus of the silica-xanthan gum complex gel was increased to 674.6 Pa. When the amount added reached 10%, the elastic modulus of the silica-xanthan gum complex gel at this time reached a maximum of 14730 Pa. Compared with a blank test without adding silica nanoparticles, the blank test shows that after the nano silica is added, the elastic modulus of the silica-xanthan gum composite gel is obviously increased, and when the silica-xanthan gum composite gel is elastically deformed, the energy required to be stored is larger, so that the elasticity enhancement of the silica-xanthan gum composite gel is reflected.

As can be seen from b in fig. 4, the viscous modulus of the xanthan/chromium acetate gel increased with the addition of silica after the silica nanoparticles were added, increasing from 2.393Pa, which is the viscous modulus when silica nanoparticles were not added, to 1933Pa, and increasing by three orders of magnitude the viscous modulus of the silica-xanthan composite gel. When the amount of silica added was 10%, the viscous modulus of the silica-xanthan gum complex gel increased to a maximum of 1933 Pa. Comparing the graphs a and b in fig. 4, the elastic modulus is always much greater than the viscous modulus, which shows that it is a viscoelastic fluid mainly based on elasticity, and when the silica-xanthan gum complex gel is compressed, the silica-xanthan gum complex gel is mainly subjected to elastic deformation, and shows more elastic solid properties.

2. Compressibility of silica-xanthan gum composite gels

Analyzing the compressive stress-strain curve of the silica-xanthan gum complex gel after adding different amounts of silica nanoparticles in fig. 5, it can be seen that the blank test without adding silica nanoparticles is compressed to 90% of the original height, and the stress value is 39053.94mN, which is the minimum stress value. The 1% of silica nanoparticles are added on the basis of a blank test, the compression stress value of the silica-xanthan gum composite gel is increased to 56801.46mN, only the 1% of silica nanoparticles are added, the silica-xanthan gum composite gel is compressed to the same height, the stress is obviously increased, and the toughness of the silica-xanthan gum composite gel is obviously increased. The amount of silica nanoparticles added was increased further, and the silica-xanthan gum complex gel had a compressive stress value of 57684.29 mN. When the amount of the silica nanoparticles added reached 5%, the stress value of the silica-xanthan gum complex gel was 87857.01 mN. When the amount added reached 7%, the stress value of the silica-xanthan gum complex gel reached a maximum of 112545.14 mN. Continuing to increase the amount of silica, the stress value of the silica-xanthan gum composite gel decreased instead. Summarizing the above rule, it is found that when the amount of added silica is 1% to 7%, the stress value of the silica-xanthan gum composite gel gradually increases while the compression ratio is the same, and the stress value decreases inversely as the amount of silica continues to increase.

3. Adhesion of silica-xanthan gum complex gels

Fig. 6 is a graph of adhesion curves for silica-xanthan composite gels incorporating varying amounts of silica nanoparticles. As can be seen from fig. 6, when no silica nanoparticles are added, the adhesion of the xanthan gum/chromium acetate gel is 9604mN, and the adhesion of the composite gel to the upper wall of the device is minimal, and the device can be separated by pulling slightly. When 1% of silicon dioxide nanoparticles are added in the blank test, the adhesive force between the silicon dioxide-xanthan gum composite gel and the component is increased to 9932mN, but the increase amplitude is smaller, the relationship with the added amount of silicon dioxide is smaller, the silicon dioxide nanoparticles dispersed on the surface of the composite gel are fewer, and the increase value of the friction force is smaller. Continuing to increase the amount of silica nanoparticles in the silica-xanthan complex gel, when the content reached 3%, it was seen that the adhesion curve of the silica-xanthan complex gel had two peaks, reaching a maximum of 14557mN at the second peak. The first peak value occurs in the stage that the silicon dioxide-xanthan gum composite gel and the upper wall of the component are pulled, the adhesion value is continuously increased to the peak, the adhesion force is gradually reduced along with the separation of the silicon dioxide-xanthan gum composite gel and the peripheral wall surface of the component in the later stage, when the silicon dioxide-xanthan gum composite gel and the peripheral wall surface of the component are completely separated, namely the silicon dioxide-xanthan gum composite gel is only adhered to the upper wall surface and the bottom of the component, and the adhesion force of the silicon dioxide-xanthan gum composite gel is reduced to the minimum. The texture analyzer continuously pulls the elements on the components upwards, the silicon dioxide-xanthan gum composite gel and the upper and lower bottom surfaces of the components are pulled, the adhesion force value of the silicon dioxide-xanthan gum composite gel is gradually increased, when the adhesion force value reaches the maximum value, the silicon dioxide-xanthan gum composite gel and the components begin to be separated, the adhesion force is gradually reduced until the components are completely separated, the adhesion force value at the moment is leveled, and the adhesion force value is the gravity value of the elements on the upper portions of the components. When the amount of the silicon dioxide in the silicon dioxide-xanthan gum composite gel is 5%, the adhesion value between the silicon dioxide-xanthan gum composite gel and the component is increased sharply, the adhesion at the moment reaches the maximum value of 40842mN, the adhesion curve has only one peak value, and the adhesion occurs in the first stage. Similarly, at a silica content of 7%, the peak also occurred in the first stage, but the adhesion value began to decrease, continuing to increase the amount of silica nanoparticles added, and continuing to decrease the adhesion value to 21482 mN.

4. Compressive strength of silica-xanthan gum composite gel

Table 6 shows the silica-xanthan gum composite gel compressive strength values. As can be seen from Table 6, the 300m xanthan gum/chromium acetate gel without silica nanoparticles has a pressure resistance value of 14.47MPa, which is lower than 25MPa required for field application, and cannot meet the production requirements. After 1% of nano silicon dioxide particles are added, the compressive strength value of the silicon dioxide-xanthan gum composite gel reaches 25.09MPa, is basically doubled, and can meet the field application requirement, which shows that the compressive strength value of the silicon dioxide-xanthan gum composite gel can be obviously increased after the silicon dioxide is added. When the amount of silica added was increased further and the amount added was 3%, the compressive strength of the 300m silica-xanthan gum composite gel was 37.00MPa, and the increasing tendency was similar to the former. The amount of added silica was 5%, and the compressive strength of the silica-xanthan gum composite gel was 45.07 MPa. Similarly, when the addition amount of the silicon dioxide in the composite gel is 7% and 10%, the compressive strength of the silicon dioxide-xanthan gum composite gel can reach 48.17MPa and 57.77MPa respectively.

TABLE 6 strength resistance of silica-Xanthan Gum composite gels

EXAMPLE 4 Properties of montmorillonite-xanthan Complex gel

1. Rheological property of montmorillonite-xanthan gum composite gel

Fig. 7 is a graph showing the viscoelasticity of a montmorillonite-xanthan gum composite gel (see example 1 and table 3 for the preparation and formulation of the montmorillonite-xanthan gum composite gel), wherein a in fig. 7 is a graph showing the elastic modulus of the montmorillonite-xanthan gum composite gel, and b in fig. 7 is a graph showing the viscosity modulus of the montmorillonite-xanthan gum composite gel. The test conditions were: at 25 ℃ with a stress of 10Pa and a frequency of 1 Hz.

As can be seen from a in fig. 7, the elastic modulus of the gel without montmorillonite is only 15.65Pa, and the elastic modulus of the montmorillonite-xanthan gum composite gel with 1% montmorillonite added is increased to 55.49Pa, which is 3.55 times of the elastic modulus of the xanthan gum/chromium acetate gel without montmorillonite added. When the amount of the montmorillonite added is increased continuously and is 3%, the elastic modulus of the montmorillonite-xanthan gum composite gel at the moment is 332.6Pa, the elastic modulus is rapidly increased to 21.25 times of the elastic modulus of the xanthan gum/chromium acetate gel, and the increase amplitude is rapidly increased. When the amount of the montmorillonite added is 5 percent and 7 percent respectively, the elastic modulus of the montmorillonite-xanthan gum composite gel is 965.3Pa and 1097Pa respectively, and the difference between the two is small. When the added amount reaches 10%, the elastic modulus of the montmorillonite-xanthan gum composite gel is sharply increased to 4400Pa, and the elastic modulus of the montmorillonite-xanthan gum composite gel is 281.15 times of the elastic modulus of the gel without the montmorillonite. This shows that the elastic modulus of the montmorillonite-xanthan gum composite gel is obviously increased after the montmorillonite is added.

It can be seen from b in fig. 7 that, after the montmorillonite is added, the change rule of the viscous modulus of the montmorillonite-xanthan gum composite gel is consistent with the change rule of the elastic modulus, that is, the viscous modulus of the montmorillonite-xanthan gum composite gel after the montmorillonite is added is obviously increased, and the viscous modulus of the montmorillonite-xanthan gum composite gel is continuously increased along with the increase of the adding amount, from the initial 2.404Pa to 920.3Pa, the viscous modulus is increased by 382.82 times. Meanwhile, by comparing all the measured data, the elastic modulus of the montmorillonite-xanthan gum composite gel is always larger than the viscous modulus of the composite gel, which indicates that the montmorillonite-xanthan gum composite gel is a viscoelastic solid with elasticity as the main component.

2. Compression performance of montmorillonite-xanthan gum composite gel

FIG. 8 is a graph of compression-stress strain curves of montmorillonite-xanthan gum composite gels after different contents of montmorillonite are added. It can be seen from the figure that the stress value for compressing to the same degree is continuously increased with the increase of the added montmorillonite amount, when the added montmorillonite amount is 7%, the stress value of the montmorillonite-xanthan gum composite gel reaches the maximum value of 87082mN, and when the added montmorillonite amount is continuously increased, the stress value of the montmorillonite-xanthan gum composite gel is reduced to 80258mN instead. Meanwhile, the stress value of the gel after the montmorillonite is added under the same compression degree is compared with the stress value of the gel without the montmorillonite, and the compressive stress-strain value of the montmorillonite-xanthan gum composite gel is increased after the montmorillonite is added, namely the mechanical strength of the montmorillonite-xanthan gum composite gel is enhanced after the montmorillonite is added. It was concluded that this phenomenon may occur because montmorillonite toughens two structures, one intercalated and one exfoliated. According to the intercalation polymerization method adopted by the method, the added xanthan gum polymer is inserted into the lamellar structure of the montmorillonite, and with the increase of the addition amount of the montmorillonite, the amount of the xanthan gum inserted into the lamellar structure of the montmorillonite is reduced, the distance between the lamellar structure layers of the montmorillonite is smaller and smaller, and the compressive stress-strain value of the montmorillonite-xanthan gum composite gel is larger and larger.

3. Adhesion of montmorillonite-xanthan gum composite gel

FIG. 9 is a graph of the adhesion of montmorillonite-xanthan gum composite gels after various amounts of montmorillonite were added. As can be seen from fig. 9, the adhesion value of the xanthan gum chromium acetate gel when no montmorillonite is added is 9793mN at the lowest, the adhesion value of the montmorillonite-xanthan gum composite gel gradually increases with the increase of the addition amount of montmorillonite, and when the addition amount of montmorillonite reaches 10%, the adhesion value of the montmorillonite-xanthan gum composite gel is 20857mN at the highest, which is about 2 times of the adhesion value of the xanthan gum/chromium acetate gel when no montmorillonite is added. After the montmorillonite is added, the adhesion between the montmorillonite-xanthan gum composite gel and the stainless steel test element is obviously increased. Meanwhile, as can be seen from fig. 9, after the adhesion test is performed on all the montmorillonite-xanthan gum composite gels, the adhesion curve has only one peak value, and the peak value occurs in the first stage, that is, the stage of separating and pulling the montmorillonite-xanthan gum composite gels from the upper portion of the tested component.

4. Compressive strength of montmorillonite-xanthan gum composite gel

Table 7 shows compressive strength values of the montmorillonite-xanthan gum composite gel measured by simulating the state of the composite gel in the wellbore during field application. As can be seen from Table 7, the pressure resistance of the montmorillonite-xanthan gum composite gel is continuously enhanced by continuously increasing the addition of the montmorillonite. When montmorillonite is not added, the compressive strength value of the xanthan gum/chromium acetate gel is 14.47MPa, and after the test is finished, the bottom of the composite gel can be seen to slide upwards a little, which shows that the adhesion force of the composite gel and the wall of the test tube is small, and the gel is slowly separated from the tube wall under the condition of pushing of lower gas. Meanwhile, large bubbles on the upper surface of the gel are seen to swell, which also indicates that the gel is not strong enough to bear the impact of high-strength airflow, so that the gas breaks through from the middle part of the gel. 1% of montmorillonite particles are added into the xanthan gum/chromium acetate gel, and the compressive strength of the montmorillonite-xanthan gum composite gel with the thickness of 300m is increased to 58.24MPa through test calculation and is rapidly increased to 4 times of the original value. Along with the increase of the content of the added montmorillonite, the compressive strength of the montmorillonite-xanthan gum composite gel of 300m is continuously increased. When the amount of the montmorillonite added is 10 percent, the compressive strength value of the montmorillonite-xanthan gum composite gel of 300m is 105.51MPa, and the compressive strength of the montmorillonite-xanthan gum composite gel is the maximum at the moment and is 7.29 times of the compressive strength value of the gel without the montmorillonite added. After the montmorillonite is added, the compressive strength of the montmorillonite-xanthan gum composite gel is enhanced, on one hand, the self strength of the montmorillonite-xanthan gum composite gel is enhanced because the viscous modulus and the elastic modulus of the montmorillonite-xanthan gum composite gel are increased, and on the other hand, the adhesion force of the montmorillonite-xanthan gum composite gel and the pipe wall is increased.

TABLE 7 compressive Strength of montmorillonite-Xanthan Gum chromium composite gels

EXAMPLE 5 Properties of laponite-Xanthan Gum composite gel

1. Rheological property of laponite-xanthan gum composite gel

FIG. 10 is a graph showing the viscoelasticity of a laponite-xanthan gum complex gel (see example 1 and Table 4 for preparation and formulation of a laponite-xanthan gum complex gel); where a in fig. 10 is an elastic modulus of the laponite-xanthan gum composite gel, and b in fig. 10 is a viscous modulus of the laponite-xanthan gum composite gel. The test conditions were: at 25 ℃ with a stress of 10Pa and a frequency of 1 Hz.

As can be seen from a in fig. 10, the elastic modulus of the laponite-xanthan gum composite gel gradually increases as the amount of added laponite increases, and the elastic modulus of the laponite-xanthan gum composite gel reaches a maximum of 123.1Pa when the amount of added laponite nanoparticles reaches 10%. Without the addition of laponite nanoparticles, the elastic modulus of the xanthan/chromium acetate gel was only 15.6Pa, at which point the elastic modulus of the gel was at a minimum. After 1% of the laponite nanoparticles were added, the elastic modulus of the laponite-xanthan gum composite gel rapidly increased to 63.7Pa, which is about 4 times the elastic modulus of the gel without the addition of laponite nanoparticles. The content of added laponite was continuously increased, and when the added amount reached 5%, the elastic modulus of the laponite-xanthan gum composite gel was increased to 86.9 Pa. When the amount added reached 10%, the elastic modulus of the laponite-xanthan gum complex gel reached a maximum of 123.1Pa at this time. Compared with a blank test without adding the laponite nanoparticles, the method has the advantages that after the nano laponite is added, the elasticity modulus of the laponite-xanthan gum composite gel is obviously increased, and when the laponite-xanthan gum composite gel is subjected to elastic deformation, the energy required to be stored is larger, so that the elasticity enhancement of the laponite-xanthan gum composite gel is reflected.

As can be seen from b in fig. 10, after adding the laponite particles, the viscous modulus of the xanthan/chromium acetate gel increased with the addition of laponite, from the elastic modulus of 2.4Pa without adding laponite nanoparticles to 49.1Pa, and the viscous modulus of the laponite-xanthan composite gel increased by one order of magnitude. When the amount of added laponite was 10%, the viscous modulus of the laponite-xanthan gum complex gel increased to a maximum of 49.1 Pa. Comparing the graphs a and b in fig. 10, it can be seen that the elastic modulus is always much greater than the viscous modulus, which indicates that the laponite-xanthan gum composite gel is a viscoelastic fluid with elasticity as the main component, and when the laponite-xanthan gum composite gel is compressed, the laponite-xanthan gum composite gel mainly undergoes elastic deformation, and exhibits more elastic solid properties.

2. Compression performance of laponite-xanthan gum composite gel

Fig. 11 is a compressive stress-strain curve of a laponite-xanthan gum composite gel system having a laponite content of 1% to 10% at a compression degree of 90%.

As can be seen from fig. 11, as the content of added laponite increases, the stress required for compression of the laponite-xanthan gum complex gel gradually increases from 39224mN to 131918 mN. When the added amount of the laponite is 7%, the compression degree of the laponite-xanthan gum composite gel is 90%, and the required stress value is maximum and is 131918 mN; continuing to increase the laponite content, the stress required for compression was instead reduced to 125268 mN. The reason for this is probably that the particle size of the laponite is smaller, the specific surface area is large, and the contact area with the system is increased with the further increase of the content of the laponite, so that the surface defect of the laponite-xanthan gum composite gel is filled, and the added laponite is excessive, so that the structure of the laponite-xanthan gum composite gel becomes fluffy, and the stress required by compression of the laponite-xanthan gum composite gel is reduced.

As can be seen from fig. 11, the compressive stress-strain test curve of the laponite-xanthan gum composite gel can be divided into three parts, the degree of compression of the first part is 0% to 60% (low degree of compression), and the stress required for reaching the corresponding degree of compression is small, and the laponite is added to the laponite-xanthan gum composite gel, so that the compressive stress of the laponite-xanthan gum composite gel is basically not influenced, and in the process, the deformation amount of the laponite-xanthan gum composite gel is small, and the laponite-xanthan gum composite gel is compressed to 100% to 40% of the original height, so that less energy needs to be stored; the degree of compression of the second part is 60-80%, the second part is compressed at a constant speed continuously, and the required stress is increased slowly; the third part has a compression degree of 80-90%, the required stress rises sharply after compression is continued, and meanwhile, the compressive stress of the laponite-xanthan gum composite gel with the laponite content of 7% is the largest through comparing test curves of different laponite addition amounts.

3. Adhesion of laponite-xanthan gum composite gel

FIG. 12 shows the adhesion of a laponite-xanthan gum complex gel, measured by adding laponite to the xanthan/chromium acetate gel. As can be seen from fig. 12, the adhesion of the laponite-xanthan gum complex gel was significantly enhanced after the addition of the laponite particles. The adhesion of the laponite-xanthan gum complex gel can reach a maximum value of 18958mN when the laponite is added in an amount of 7%, while the adhesion of the xanthan gum/chromium acetate gel is only 9331mN when the laponite is not added. When 1% of the laponite particles are added in the blank test, the adhesion between the laponite-xanthan gum composite gel and the components is increased to 9380mN, but the increase amplitude is smaller, the relationship with the added laponite quantity is smaller, the laponite particles dispersed on the surface of the laponite-xanthan gum composite gel are smaller, and the increase value of the friction force is smaller. The comparison shows that the adhesion between the laponite-xanthan gum composite gel and the pipe wall can be obviously increased by adding the laponite. Meanwhile, in the adhesion testing process of the laponite-xanthan gum composite gel, the whole process can be divided into three stages. The first stage is that the texture analyzer slowly lifts the upper part of the test element, and the adhesive force is gradually increased; the second stage is that the upper part of the test element is pulled against the upper surface of the composite gel, and the adhesion force is increased to the maximum value; the third stage is that the composite gel is separated from the test element, the contact area is gradually reduced, and finally the composite gel is completely separated. The adhesion of the laponite-xanthan gum complex gel reached a maximum in the first stage when the amount of added laponite was 1% -5%, 10%, where the adhesion of the complex gel to the test element wall increased. When the added amount of the laponite is 7%, the adhesion of the laponite-xanthan gum composite gel reaches the maximum value in the second stage, and the adhesion of the laponite-xanthan gum composite gel to the upper part of the test element is increased, and meanwhile, the tensile property of the laponite-xanthan gum composite gel is reflected from the other aspect, the increase of the added amount of the laponite also enables the tensile property of the laponite-xanthan gum composite gel to be remarkably improved, the laponite-xanthan gum composite gel is not easy to break from the middle, and the laponite-xanthan gum composite gel is not easy to break.

4. Compressive strength of laponite-xanthan gum composite gel

Table 8 shows the compressive strength values of the laponite-xanthan gum composite gel, and it can be seen from Table 8 that the compressive strength of the 300m xanthan gum/chromium acetate gel is 14.5MPa without adding laponite, which cannot meet the requirements of field application. When the amount of added laponite was 1%, the compressive strength of the 300m laponite-xanthan gum composite gel was drastically increased to 28.4MPa, which is about 2 times the compressive strength of the gel without adding laponite. At this time, it can be seen that the compressive strength of the laponite-xanthan gum composite gel is increased by adding the laponite particles. When the content of the laponite in the laponite-xanthan gum composite gel is continuously increased to 7%, the compressive strength of the 300m laponite-xanthan gum composite gel is sharply increased to be 164.9MPa at the maximum value, which is about 11 times of the compressive strength of the composite gel without adding the laponite. When the amount of added laponite was increased to 10%, the compressive strength of the 300m laponite-xanthan gum composite gel was rather reduced to 99.1 MPa.

TABLE 8 compressive Strength of laponite-Xanthan Gum composite gels

Claims

1. A xanthan gum composite gel is prepared from the following raw materials: based on the total mass of the raw materials, the mass percent of the xanthan gum is 1-4%; the mass percent of the cross-linking agent is 0.2-0.5%; the mass percent of the toughening agent is 0-10 percent but not 0; the balance of water;

the toughening agent is selected from at least one of laponite, starch, nano silicon dioxide and montmorillonite.

2. The xanthan gum complex gel of claim 1, wherein: the mass percentage of the xanthan gum is 3%;

the number average molecular weight of the xanthan gum is 300-1800 ten thousand; specifically 1800 thousands;

the water is deionized water.

3. The xanthan gum complex gel according to claim 1 or 2, wherein: the cross-linking agent is chromium acetate;

the mass percentage of the cross-linking agent is 0.4%.

4. The xanthan gum complex gel according to any one of claims 1-3, wherein: the mass percentage of the toughening agent is 5% -10%.

5. The xanthan gum complex gel according to any one of claims 1-4, wherein: the nano silicon dioxide, the montmorillonite and the laponite are all nano-scale.

6. A process for the preparation of xanthan gum complex gel according to any one of claims 1 to 5 comprising the steps of: and uniformly mixing the xanthan gum, the toughening agent and water, then adding the cross-linking agent, and gelling to obtain the xanthan gum composite gel.

7. The method of claim 6, wherein: the method further comprises the step of dissolving the xanthan gum in water and then standing.

8. The method of claim 7, wherein: the standing time is 12-36 h.

9. The production method according to any one of claims 6 to 8, characterized in that: the temperature for gelatinizing is 40-90 ℃, and specifically can be 50 ℃; the time is 6-36h, specifically 24 h.

10. Use of the xanthan gum complex gel of any one of claims 1 to 5 in underbalanced drilling.