CN106883832A - A kind of controllable diverting agent of environment-friendly type and preparation method thereof - Google Patents

Abstract

The invention provides an environment-friendly controllable temporary plugging agent and a preparation method thereof. The temporary plugging agent is formed by mixing an organic and environmentally friendly synthetic stock solution and an inorganic functional reagent, wherein the synthetic stock solution is composed of polyvinyl alcohol, soluble starch, gelatin , sodium alginate, ammonium persulfate and water are mixed and stirred, and the auxiliary reagent is composed of anhydrous calcium chloride, anhydrous sodium sulfate, disodium edetate, sodium tetraborate and ammonium persulfate. The preparation method of the temporary plugging agent of the present invention is: adopt the solution polymerization method to prepare synthetic stock solution, then add gelation aid agent, realize the perfect combination of primary gel material on skeleton material, add secondary gel agent (primary gel agent again) ), to prepare the target product. The product developed by the invention has good plugging effect, controllable plugging time, good flowback performance, no pollution, few production procedures and low cost, and is suitable for industrialized production.

Description

A kind of environment-friendly controllable temporary plugging agent and preparation method thereof

technical field

The invention belongs to the technical field of shale gas exploitation, and in particular relates to an environment-friendly controllable temporary plugging agent and a preparation method thereof.

Background technique

Shale gas is a special kind of unconventional natural gas, which occurs in mudstone or shale. It has the characteristics of self-generation and self-storage, no gas-water interface, large-area continuous accumulation, low porosity, and low permeability. Generally, it has no natural productivity or Low production requires large-scale hydraulic fracturing and horizontal well technology for economical production, and the production cycle of a single well is long. As the earliest country in the world for the exploration and development of shale gas resources, the United States has formed mature evaluation methods and exploration and development technologies in North America, realized the industrial development of shale gas, and proved the effective development of shale gas resources theoretically and technically possibility. Therefore, accelerating the exploration and development of shale gas resources has become the common and eager desire of the world's major shale gas resource countries and regions.

The development of shale gas development technology can be roughly divided into five basic stages (taking the United States as an example):

1 Drill vertical wells and perform foam fracturing (large fluid volume, large displacement of 6.4 cubic meters per minute, with sand added; traditional fracturing fluid);

2 Drilling vertical wells, large-scale hydraulic fracturing technology (large fluid volume, large displacement 6.4 cubic meters per minute, 29% sand required; traditional fracturing fluid);

3 Drilling vertical wells, clean water fracturing or clean water and sand fracturing (Gaza 2.66-4.8%), can save 50%-60% of the cost compared with gel fracturing, and it has been the vertical well fracturing method since 1998;

4. In 1997, after the energy failure of the well initially fractured by gel, the recoverable reserves increased by 60% after secondary fracturing with clean water. The secondary fracturing technology was still relatively common until 2006;

5 Drill horizontal wells with a horizontal section length of 304.8-1066.8m, and perform fracturing with clean water and sand in stages. This technology began in 2003, and the "synchronous fracturing" technology was produced in 2006.

But generally speaking, the technical conditions for industrialized exploitation of shale gas in my country are not available now, which is mainly reflected in the following aspects:

(1) The shale geological conditions in my country are quite different from those of shale reservoirs successfully developed in foreign countries, and it is difficult to directly apply foreign effective technologies;

⑵We have not fully grasped the mature foreign technology;

(3) my country's natural environmental conditions are not suitable for foreign existing technologies;

(4) There are still many problems that need to be improved and developed in foreign effective technologies.

In view of the above problems, the steering fracturing process has been proposed at home and abroad. There are two types of diversion fracturing: intra-fracture diversion fracturing and inter-fracture diversion fracturing. Its core purpose is to increase the net pressure, force fractures to divert, and increase the volume of reservoir stimulation.

In-fracture diversion: According to the principle that the fluid flows in the direction of the least resistance, the temporary plugging agent particles first enter the high-permeability layer, and produce a "filter cake bridge plugging" effect on the large pores, primary fractures, hydraulic fracture walls and blastholes in the formation, making The pressure rises, forcing the fractures to divert and increasing the stimulated volume of the reservoir.

Inter-fracture diversion: By injecting fracturing fluid and proppant mixed with temporary plugging materials (fiber + large particle size temporary plugging agent - degradable), a temporary plug is formed at the opening of the first fracture, and the bottom hole pressure increases to force The liquid turns, and finally all the perforation clusters are reformed sequentially according to the fracture pressure from low to high.

However, at present, there are many problems with the general temporary plugging agents in China: 1. The plugging time is single, and cannot effectively change with the changes in the landform environment and construction needs; 2. The plugging effect of the temporary plugging agent is not ideal; 3. The temporary plugging After the plugging agent is completed, solid suspended matter remains in the flowback solution, which makes the flowback liquid more viscous and difficult to flow back. Some temporary plugging agents will also cause harm to the geological environment after being discharged; 4. The temporary plugging agent is not easy to process. Insufficient strength, poor pressure resistance and other related construction techniques cannot meet the standards. Therefore, it is particularly important to develop a new type of environmentally friendly and controllable temporary plugging agent.

Contents of the invention

The purpose of the present invention is to provide an environmentally friendly temporary plugging agent with high pressure bearing capacity, low density and easy processing. Compared with existing similar products, it has excellent plugging effect, good flowback effect, and controllable plugging time Advantages, and low cost, suitable for industrial production. In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

An environment-friendly controllable temporary plugging agent, which is compounded by a synthetic stock solution and a gel agent, and the synthetic stock solution is prepared by mixing polyvinyl alcohol (PVA), soluble starch, gelatin, sodium alginate, ammonium persulfate and water The gelling agent includes a gelling agent and a main gelling agent, wherein the gelling agent is compounded by anhydrous calcium chloride, anhydrous sodium sulfate, and disodium ethylenediaminetetraacetic acid (EDTA-2Na). The main gelling agent is compounded by sodium tetraborate and ammonium persulfate.

In the above scheme, the mass fraction of polyvinyl alcohol in the synthetic stock solution is 3-9%, the mass fraction of soluble starch is 2-6%, the mass fraction of gelatin is 1-6%, and the mass fraction of water is 70%, The balance is a mixture of sodium alginate and ammonium persulfate. The preparation of the synthetic stock solution follows the principle of uniformity in small quantities and multiple times.

In the above scheme, the mass ratio of anhydrous calcium chloride, anhydrous sodium sulfate, and disodium edetate in the gelling aid is 1-2:1-2:1-4.

In the above scheme, the mass ratio of sodium tetraborate and ammonium persulfate in the main gelling agent is 1-4:2.

In the above scheme, the temporary plugging agent is formed by mixing the synthetic stock solution, the co-gelling agent, and the main gelling agent in a mass ratio of 100:3-8:3-6. The whole gelation process involves secondary interpenetrating gelation and corrosion-inhibiting degelation.

The preparation method of the above-mentioned environment-friendly controllable temporary plugging agent comprises the following steps: (a) accurately weighing polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water according to the proportion, mixing and dissolving to obtain a synthetic stock solution; b) According to the ratio, anhydrous calcium chloride, anhydrous sodium sulfate, and disodium edetate are mixed and compounded to form a gelling aid, and sodium tetraborate and ammonium persulfate are compounded to form a main gelling agent for later use; ( c) Add the co-gelling agent into the homogeneous synthesis stock solution, add the main gelling agent into the mixed solution after a period of reaction, let it stand for cooling, and then heat-press and dry to obtain an environment-friendly and controllable temporary plugging agent.

The synthetic stock solution used in the present invention is a uniform composite component solution composed of polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and the like. In consideration of stability, viscosity and price, the selected gelling reagents include anhydrous calcium chloride, anhydrous sodium sulfate, disodium edetate, ammonium persulfate, sodium tetraborate, etc.

The invention adopts two gel formings to penetrate each other, and is prepared by wrapping additives such as corrosion inhibitors and viscosity reducers. Since the dissolution effect of gelatin is relatively appropriate and it is an amphoteric substance, gelatin is the first choice for the skeleton support of the temporary plugging agent; soluble starch has a relatively high viscosity, has good stability and cohesiveness, and can be blended with gelatin as a binder; EDTA-2Na is used as a complexing agent, reacts with anhydrous calcium chloride and gelatin, makes gelatin denatured in contact with chloride, slowly dissolves in water at low temperature, and provides good conditions for subsequent production; anhydrous calcium chloride and anhydrous Sodium sulfate water is used as a primary gelling agent (gelling aid) to stabilize EDTA-2Na so that it does not react too quickly with gelatin to ensure the dissolution rate; borax (primary gelling agent) and PVA undergo secondary gelation, PVA is well blended and associated with gelatin in the preparation of the stock solution, and when the stock solution is slowly and evenly poured into the aqueous solution of borax in the later stage of production, it will quickly gel with borax to form the main product temporary plugging agent.

Compared with the prior art, the present invention has the following beneficial effects: (1) The raw materials sodium alginate, soluble starch, gelatin, etc. used in the preparation of the temporary plugging agent all have good biocompatibility, and the sources of raw materials are environmentally friendly, and the temporary blocking agent It can be completely dissolved in water and discharged in time with the flowback liquid, will not be left in the formation, and will not cause harm to the environment; (2) The plugging effect is good, the flowback effect is excellent, and the viscosity of the solution after dissolution is as low as 5.3204mPa·s , less than 50mPa·s; (3) The plugging time is controllable, and the dissolution time of the temporary plugging agent prepared by different ratios of gels is different; (4) The preparation process is simple, the cost of raw materials is low, and it is suitable for industrial production.

Description of drawings

Fig. 1 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention to ordinary fine sand;

Fig. 2 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention for medium sand;

Fig. 3 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention to sand mixing A;

Fig. 4 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention to coarse sand;

Fig. 5 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention to the mixed sand B;

Fig. 6 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention to the mixed sand C;

Fig. 7 is the plugging performance curve of the temporary plugging agent prepared in Example 1 of the present invention for sand mixing D.

detailed description

In order to enable those skilled in the art to fully understand the technical solutions and beneficial effects of the present invention, further description will be given below in conjunction with specific examples.

Example 1

An environment-friendly controllable temporary plugging agent, which is compounded from synthetic stock solution and auxiliary and main gelling agents. In terms of parts by mass, the synthetic stock solution consists of 9 parts of polyvinyl alcohol, 3 parts of soluble starch, 6 parts of gelatin, 70 parts of water, 12 parts of sodium alginate and ammonium persulfate in total; the gelling aid is composed of anhydrous calcium chloride 1 part, 1 part of anhydrous sodium sulfate, 3 parts of EDTA-2Na, the main gelling agent is composed of 3 parts of sodium tetraborate and 2 parts of ammonium persulfate. When preparing, first mix and dissolve polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water according to the ratio to obtain a uniform synthetic stock solution, then add the gelling aid to the synthetic stock solution and react for about 10 minutes, then add The main gelling agent, stop the reaction after the desired sample is formed, take it out and dry it for later use.

Example 2

An environment-friendly controllable temporary plugging agent, which is compounded from synthetic stock solution and auxiliary and main gelling agents. In terms of parts by mass, the synthetic stock solution consists of 9 parts of polyvinyl alcohol, 3 parts of soluble starch, 6 parts of gelatin, 70 parts of water, 12 parts of sodium alginate and ammonium persulfate in total; the gelling aid is composed of anhydrous calcium chloride 2 parts, 2 parts of anhydrous sodium sulfate, 3 parts of EDTA-2Na, the main gelling agent is composed of 3 parts of sodium tetraborate and 2 parts of ammonium persulfate. When preparing, first mix and dissolve polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water according to the ratio to obtain a uniform synthetic stock solution, then add the gelling aid to the synthetic stock solution and react for about 10 minutes, then add The main gelling agent, stop the reaction after the desired sample is formed, take it out and dry it for later use.

Example 3

An environment-friendly controllable temporary plugging agent, which is compounded from synthetic stock solution and auxiliary and main gelling agents. In terms of parts by mass, the synthetic stock solution consists of 9 parts of polyvinyl alcohol, 3 parts of soluble starch, 6 parts of gelatin, 70 parts of water, 12 parts of sodium alginate and ammonium persulfate in total; the gelling aid is composed of anhydrous calcium chloride 2 parts, 2 parts of anhydrous sodium sulfate, 4 parts of EDTA-2Na, the main gelling agent is composed of 4 parts of sodium tetraborate and 2 parts of ammonium persulfate. When preparing, first mix and dissolve polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water according to the ratio to obtain a uniform synthetic stock solution, then add the gelling aid to the synthetic stock solution and react for about 10 minutes, then add The main gelling agent, stop the reaction after the desired sample is formed, take it out and dry it for later use.

In order to fully understand the relevant properties of the temporary plugging agent prepared in Example 1 of the present invention, corresponding tests were carried out respectively.

(1) Viscosity test

Test conditions: the instrument is a NDJ-1 rotary viscometer, the No. 1 rotor, the shear rate is 60 rpm, and the coefficient is 1. The test method is as follows: take 1.0g sample in the laboratory, put it in a jar with a stopper, add 300ml of water, and observe the dissolution in a constant temperature drying oven at 85°C. The experiment found that the sample dissolved after 4 hours, and the measured apparent viscosity was 5.3204mPa·s, which was slightly higher than the viscosity of tap water at room temperature of 1.0050mPa·s, indicating that the flowback performance of this temporary plugging agent is very good.

(2) Core displacement experiment of temporary plugging agent

2.1 Fill 0-2mm quartz sand (fine sand) into a sand-packing tube with a diameter of 20 cm and a length of 60 cm, inject the shale gas prepared above into the core tube with an environment-friendly controllable temporary plugging agent, and drive the core into the core tube. The temperature of the replacement device was set at 85°C and 8 MPa, and the fluid loss was observed and recorded every 30 minutes to further investigate the plugging capacity of the temporary plugging agent. The results are shown in Figure 1 and Table 1 respectively.

Table 1. The plugging performance of ordinary fine sand by environment-friendly controllable temporary plugging agent in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 3 0 0 0 0 0 0 0 100

It can be seen from Table 1 and Figure 1 that the environmental-friendly controllable temporary plugging agent for shale gas development prepared in Example 1 has a 100% plugging effect on fine sand with a small particle size (0-1 mm), and the plugging effect is 100% within the specified dissolution time. After the blockage is removed, the flowback effect is good.

2.2 Fill the gravel (medium sand) with an average particle size of 2-5 mm into a sand-packing tube with a diameter of 20 cm and a length of 60 cm, and inject the shale gas prepared above into the core tube with an environment-friendly controllable temporary plugging agent. Set the temperature of the core displacement device at 85°C and 8 MPa, observe and record the fluid loss every 30 minutes, and further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 2 and Figure 2.

Table 2. Plugging performance of environment-friendly controllable temporary plugging agent for medium sand in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 0.2 0.2 0 0 0 0 0 100

It can be seen from Table 2 and Figure 2 that the use of environmentally friendly and controllable temporary plugging agents in shale gas development is not ideal for plugging medium-sized (1-3mm) medium sand in the first 30 minutes before the sample swells. The plugging rate is 100%, and the plugging is removed after the specified dissolution time, and the flowback effect is good.

2.3 Fill fine sand with fine sand (mixed sand A) into a sand-packing tube with a diameter of 20 cm and a length of 60 cm, and inject the shale gas developed above into the core tube with an environmentally friendly and controllable temporary plugging agent. The temperature of the core displacement device was set at 85°C and 8 MPa, and the fluid loss was observed and recorded every 30 minutes to further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 3 and Figure 3.

Table 3 The plugging performance of environmental-friendly controllable temporary plugging agent for sand mixing A in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 3.5 7 4 3 3 3 8 100

It can be seen from Table 3 and Figure 3 that the plugging of mixed sand A with an environmentally friendly and controllable temporary plugging agent in shale gas development is not ideal before the sample is swollen in the first 30 minutes, and the plugging rate is over 90% after the swelling is completed , and quite stable, and after the specified dissolution time, the blockage is removed, and the flowback effect is good.

2.4 Fill the 5-10mm gravel (coarse sand) into the sand-packing tube with a diameter of 20 cm and a length of 60 cm, inject the shale gas developed above into the core tube with an environment-friendly controllable temporary plugging agent, and drive the core into the core tube. The temperature of the replacement device was set at 85°C and 8 MPa, and the fluid loss was observed and recorded every 30 minutes to further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 4 and Figure 4.

Table 4. Plugging performance of environmental-friendly controllable temporary plugging agent for coarse sand in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 8 5 3 2 15 27 100 100

It can be seen from Table 4 and Figure 4 that the plugging of large particle size coarse sand (5-10 mm) by environmental-friendly controllable temporary plugging agent in shale gas development is not ideal before the sample swells in the first 30 minutes, and the swelling After completion, the plugging rate is more than 90%. Due to the large particle size of the coarse sand and the large gaps between the gravels, the contact area between the temporary plugging agent and water is large, the temporary plugging agent dissolves quickly, and the later dissolution speed is accelerated. And after the specified dissolution time, the blockage is removed, and the flowback effect is good.

2.5 Fill fine sand and coarse sand (mixed sand B) into a sand-packing tube with a diameter of 20 cm and a length of 60 cm, and inject the shale gas prepared above into the core tube with an environmentally-friendly controllable temporary plugging agent. The temperature of the displacement device was set at 85°C and 8 MPa, and the fluid loss was observed and recorded every 30 minutes to further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 5 and Figure 5.

Table 5. Plugging performance of environment-friendly controllable temporary plugging agent for sand mixing B in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 6 2 2 2 2 9 9 100

It can be seen from Table 5 and Figure 5 that the plugging of mixed sand B with an environmentally friendly and controllable temporary plugging agent for shale gas development is not ideal before the sample swells in the first 30 minutes, and the plugging rate is over 90% after the swelling is completed , and relatively stable, after the specified dissolution time, the blockage is removed, and the flowback effect is good.

2.6 Fill medium sand and coarse sand (mixed sand C) into a sand-packing tube with a diameter of 20 cm and a length of 60 cm, inject the shale gas prepared above into the core tube with an environment-friendly controllable temporary plugging agent, and core The temperature of the displacement device was set at 85°C and 8 MPa, and the fluid loss was observed and recorded every 30 minutes to further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 6 and Figure 6.

Table 6. Plugging performance of environment-friendly controllable temporary plugging agent for sand mixing C in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 18 6 5 6 6 100 100 100

It can be seen from Table 6 and Figure 6 that the plugging of mixed sand C with environmentally friendly and controllable temporary plugging agent in shale gas development is not ideal before the sample swells in the first 30 minutes, and the plugging rate after swelling is over 82% , After a period of extrusion, the plugging rate reaches about 94%, and it is relatively stable; after the specified dissolution time, the blockage is removed, and the flowback effect is good.

2.7 Fill fine sand, medium sand and coarse sand (mixed sand D) into the sand packing pipe with a diameter of 20cm and a length of 60cm, and inject the environmental-friendly controllable temporary plugging agent for shale gas development prepared above into the core pipe , set the temperature of the core displacement device at 85°C and 8 MPa, observe and record the fluid loss every 30 minutes, and further investigate the plugging capacity of the temporary plugging agent. The results are shown in Table 7 and Figure 7.

Table 7. Plugging performance of environmental-friendly controllable temporary plugging agent for sand mixing D in shale gas development

time (h) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 Filtration loss (ml) 100 15 6 6 5 5 100 100 100

It can be seen from Table 6 and Figure 6 that the plugging of mixed sand D with environmental-friendly controllable temporary plugging agent in shale gas development is not ideal in the first 30 minutes before the sample is swollen, and the plugging rate is over 85% after the swelling is completed , After a period of extrusion, the plugging rate reaches about 94%, and it is relatively stable; after the specified dissolution time, the blockage is removed, and the flowback effect is good.

Embodiments of the present invention have been described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementations, and the above-mentioned specific implementations are only illustrative, rather than restrictive, and those of ordinary skill in the art will Under the enlightenment of the present invention, without departing from the gist of the present invention and the protection scope of the claims, many changes can be made, and these all belong to the protection of the present invention.

Claims (6)

1. a kind of controllable diverting agent of environment-friendly type, is formed by synthesizing stoste and gel compounding, it is characterised in that：The synthesis stoste Mixed by polyvinyl alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water, the gel includes helping gel Agent and main gel, wherein help gel to be formed by anhydrous calcium chloride, anhydrous sodium sulfate, disodium ethylene diamine tetraacetate compounding, it is main Gel is formed by sodium tetraborate, ammonium persulfate compounding.

2. the controllable diverting agent of a kind of environment-friendly type according to claim 1, it is characterised in that：Polyethylene in the synthesis stoste The mass fraction of alcohol is 3-9%, and the mass fraction of soluble starch is 2-6%, and the mass fraction of gelatin is 1-6%, the matter of water Amount fraction is 70%, balance of sodium alginate and ammonium persulfate mixture.

3. the controllable diverting agent of a kind of environment-friendly type according to claim 1, it is characterised in that：It is described to help anhydrous chlorine in gel It is 1-2 to change calcium, anhydrous sodium sulfate, the mass ratio of disodium ethylene diamine tetraacetate：1-2：1-4.

4. the controllable diverting agent of a kind of environment-friendly type according to claim 1, it is characterised in that：Tetraboric acid in the main gel Sodium, the mass ratio of ammonium persulfate are 1-4：2.

5. the controllable diverting agent of a kind of environment-friendly type according to claim any one of 1-4, it is characterised in that：The diverting agent by Synthesize stoste, help gel, main gel according to 100：3-8：The mass ratio of 3-6 is mixed.

6. the preparation method of the controllable diverting agent of a kind of environment-friendly type, it is characterised in that comprise the following steps：A () is claimed by proportion speed Weight northylen alcohol, soluble starch, gelatin, sodium alginate, ammonium persulfate and water, mixed dissolution obtain synthesizing stoste；B () is by matching somebody with somebody Gel is helped than mixing to be re-dubbed anhydrous calcium chloride, anhydrous sodium sulfate, disodium ethylene diamine tetraacetate, by sodium tetraborate, over cure It is standby that sour ammonium is re-dubbed main gel；C () will help gel to be added in homogeneous synthesis stoste, will be main after reaction a period of time Gel is added in mixed solution, stands the hot pressing controllable diverting agent of drying environment-friendly type after cooling.