RU2827721C1 - Hydraulic fracturing fluid based on synthetic gelling agent and surface water, method of its preparation and method of treating formation using said fluid - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: group of inventions relates to production using hydraulic fracturing technology of productive oil formations. Method of hydraulic fracturing using a liquid for hydraulic fracturing based on a synthetic gelling agent—anionic water-soluble polymer of polyacrylamide and surface water, hydraulic fracturing fluid contains polyacrylamide hydrolysed with 2-ethylhexylacrylate—polyprop-2-enamide hydrolysed with 2-ethylhexylprop-2-enoate. Fluid is prepared for hydraulic fracturing in hydration unit—blender. First, said water is dosed into the blender vessel in amount of 88.0 to 95.0 wt.%, the mixer is switched on with revolutions from 1,000 to 1,700 rpm and demulsifier is introduced in amount of 1.0 wt.% with constant stirring. Then, using a screw dispenser, said gelling agent is poured into the blender in an amount of approximately 3.0 to 10 wt.%, stirring until complete hydration of said gelling agent. Proppant in amount of 700 kg per 1 m³ of polymer liquid is discharged into the obtained polymer liquid—aqueous polymer solution. Then a polymer destructor is added through the same screw feeder in amount of 1.0 wt.%, the obtained mass is stirred until a homogeneous suspension is obtained. Further, the fluid for hydraulic fracturing from the blender enters the productive formation, performing hydraulic fracturing of the formation.

EFFECT: reduced time of operations, reduced impact on environment, uniform distribution of injected fluid along the whole length of fracture created during hydraulic fracturing, deeper penetration of proppant particles.

7 cl, 10 dwg, 1 tbl, 3 ex

Description

The invention relates to the oil and gas industry, in particular to production using hydraulic fracturing (HF) technology of productive oil formations. More specifically, the invention relates to technological compositions used to increase the permeability of productive formations by implementing hydraulic fracturing (HF), and can be used to prepare fluid for hydraulic fracturing of a formation from alternative (non-natural) synthetic gelling agents and using sources of surface water such as, for example, rivers, streams, reservoirs, lakes, ponds and others. In particular, the invention relates to a method for preparing a fluid for hydraulic fracturing a formation based on a synthetic gelling agent and surface water, as well as to a method for treating a formation using a fluid for hydraulic fracturing a formation based on a synthetic gelling agent and surface water, including adding proppant to the above-mentioned fluid and performing hydraulic fracturing of the formation, thereby forming a stable suspension that prevents the settling of proppants granules in an aqueous solution. A fluid for hydraulic fracturing a formation, a method for preparing a fluid for hydraulic fracturing a formation, and a method for treating a formation using it in hydrocarbon production are proposed.

State of the art

A technical solution and method for stabilizing an aqueous solution of polyacrylamide are known (see patent for invention No. 2466160 under class C08L 33/26 (2006.01) E21B 43/22 (2006.01), filed 10.05.2011, published 10.11.2012 “Method for stabilizing an aqueous solution of polyacrylamide”).

However, in the known method, the preparation of fluid for hydraulic fracturing consists of preparing a solution and maintaining the rheological properties of aqueous solutions of polyacrylamide for a long time, as well as increasing the efficiency of using the resulting solution by stabilizing its dynamic viscosity. The technical result of the method for stabilizing an aqueous solution of polyacrylamide is obtained by preparing a solution of polyacrylamide in water with a concentration of 0.15 to 0.30 wt.% by dispersion at an angular velocity of 14,000 rpm to 17,000 rpm.

The main disadvantages of the above invention are that the distilled water used to prepare the solution does not have a mineral composition, therefore, it does not affect the rheological properties of the aqueous solution, and, as a result, the stability time of the solution under real conditions is difficult to predict, and the indicated mass concentrations of the aqueous solution will be weakly expressed or will not have sand-bearing capacity at all due to the low concentration of the polymer.

A hydraulic fracturing fluid and a method for its preparation are known (CN 108559477, published 21.09.2018, IPC: C09K 8/60, C09K 8/66, C09K 8/68), which use a synthetic gelling agent, a dispersant, a chelating agent, a clay stabilizer, a structural stabilizer, a destructor, and high-salinity water, which provide low viscosity of the fluid for easy removal from the formation. Common features of the known and claimed hydraulic fracturing fluids and the method for its preparation are the use of a synthetic gelling agent and a destructor. However, in the technical solution under consideration, the components used are used as stabilizers and neutralizers of salts, which can affect the quality of the prepared hydraulic fracturing fluid, which significantly increases the cost of the work.

The closest in technical essence and achieved effect to the claimed method for producing a fluid for hydraulic fracturing based on a synthetic gelling agent and selected as the closest analogue (prototype) is the technical solution and method for preparing a fluid for hydraulic fracturing based on a synthetic gelling agent and highly mineralized water (See patent for invention No. 2760115 under class C09K 8/62 (2021.08) E21B 43/26 (2021.08), declared 06.11.2020, published 22.11.2021 "Fluid for hydraulic fracturing based on a synthetic gelling agent and highly mineralized water, a method for its preparation and a method for treating a formation using it").

However, in the known method of preparing fluid for hydraulic fracturing, highly mineralized formation (Cenomanian) and bottom water are used.

The main disadvantage of the above invention is that formation water (Cenomanian) has an unstable mineral composition, depending on the deposit and depth of occurrence, which greatly complicates the selection of recipes and, with a high probability, for its normal use, it will be necessary to introduce additional stabilizing additives. Bottom water, being water contaminated with oil products and accumulated during the storage of watered oil products in tanks or pumped into wells artificially to maintain reservoir pressure, has an even more unstable mineral composition and, as a rule, has dissolved iron oxide (III) in its composition. With this type of water, it is necessary to have a whole line of stabilizing additives that stop the harmful effect of the mineral composition of the water.

Disclosure of invention

The objective of the proposed invention is to create a fluid for hydraulic fracturing based on a synthetic gelling agent and surface water, a method for preparing a fluid for hydraulic fracturing based on a synthetic gelling agent and surface water, and a method for treating a formation using it, ensuring the sand-bearing capacity of the working fluid necessary for work using hydraulic fracturing technology.

The set task is achieved by preparing a liquid using alternative (not natural origin) synthetic gelling agents using surface water sources (rivers, streams, reservoirs, lakes, ponds and others), and the anionic water-soluble polymer Polyprop-2-enamide hydrolyzed with 2-ethylhexylprop-2-enoate (Polyacrylamide hydrolyzed with 2-ethylhexyl acrylate) in the form of a hydrated powder is used as a polymer.

The stated task is also solved by using a liquid obtained by the above-mentioned method and by using the considered fluid for hydraulic fracturing of a formation based on a synthetic gelling agent and surface water, with subsequent addition of proppant to the above-mentioned fluid for hydraulic fracturing of a formation, and carrying out hydraulic fracturing of the formation, thereby forming a stable suspension that prevents the settling of proppant granules in an aqueous solution.

The technical result that allows solving this problem is a method for feeding a powdered polymer of a synthetic gelling agent into a surface water flow in hydration units, due to which there is no need to separately use tanks for preparing and hydrating the polymer, the time of operations is reduced; chemical stabilizing reagents used to stabilize the mineral composition of water during hydraulic fracturing operations are abandoned, which reduces the impact on the environment; uniform viscosity gain during injection of a liquid-sand mixture (lower at the wellhead than in the perforation zone), as a result of which uniform distribution of liquid is ensured along the entire length of the crack created during hydraulic fracturing, ensuring deeper penetration of proppant particles into the crack due to better fluidity; obtaining optimal rheological properties regardless of the source of surface water and its chemical composition.

The above technical result is achieved by a method of hydraulic fracturing a formation using a fluid for hydraulic fracturing a formation based on a synthetic gelling agent - an anionic water-soluble polymer polyacrylamide and water containing a demulsifier, a polymer destructor and a proppant, wherein:

fracturing fluid contains polyacrylamide hydrolyzed with 2-ethylhexyl acrylate - Polyprop-2-enamide hydrolyzed with 2-ethylhexyl prop-2-enoate, surface water,

the preparation of the fluid for hydraulic fracturing is carried out in a hydration unit - a blender, first the said water is dosed into the blender vat in an amount of 88.0 to 95.0 wt.%, the mixer is turned on with revolutions from 1000 to 1700 rpm and with constant stirring the demulsifier is introduced in an amount of 1.0 wt.%, then using a screw dispenser the said gelling agent is poured into the blender vat in an amount of approximately 3.0 to 10 wt.%, stirred until the said gelling agent is completely hydrated,

proppant is unloaded into the resulting polymer liquid - an aqueous polymer solution in the amount of 700 kg per 1 m3 of polymer liquid, then a polymer destructor is added through the same screw dispenser in the amount of 1.0 wt.%, the resulting mass is mixed until a homogeneous suspension is obtained,

Then the fracturing fluid from the blender enters the productive formation, performing hydraulic fracturing of the formation.

According to the stated method, rivers, streams, reservoirs, lakes, and ponds can be used as a source of surface water.

According to the claimed method, the loaded components of the hydraulic fracturing fluid in the blender are in constant motion to ensure hydration of the gelling agent.

According to the claimed method, the hydraulic fracturing fluid enters the production formation from the blender vat through a low-pressure line, then after the pumps into a high-pressure line, from which the fluid enters the production formation through perforation holes or, for multi-stage hydraulic fracturing of the formation, through a frac port via a pump-compressor pipe lift.

According to the claimed method, the synthetic gelling agent can be taken in an amount of 4.0 wt.%.

According to the claimed method, the synthetic gelling agent can be taken in an amount of 6.0 wt.%.

According to the stated method, additional effective polymer additives can be used, if necessary.

The above-mentioned technical result is also achieved by means of a fluid for hydraulic fracturing based on a synthetic gelling agent and surface water, including a synthetic gelling agent, a demulsifier, a destructor and a proppant, wherein the powdered polymer of the synthetic gelling agent is an anionic water-soluble polymer Polyprop-2-enamide hydrolyzed with 2-ethylhexylprop-2-enoate (Polyacrylamide hydrolyzed with 2-ethylhexyl acrylate) in the form of a hydrated powder, and it is prepared by any of the above-mentioned methods.

Brief description of the drawings

Figure 1 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is given for Example (Composition) 1 in Table 1.

Figure 2 shows the change in fracturing fluid viscosity with changing shear rate at elevated temperature for Example (Composition) 1 in Table 1.

Figure 3 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is given for Example (Composition) 2 in Table 1.

Figure 4 shows the change in fracturing fluid viscosity with changing shear rate at elevated temperature for Example (Formulation) 2 in Table 1.

Figure 5 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is given for Example (Composition) 3 in Table 1.

Figure 6 shows the change in fracturing fluid viscosity with changing shear rate at elevated temperature for Example (Formulation) 3 in Table 1.

Figure 7 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is given for Example (Composition) 4 in Table 1.

Figure 8 shows the change in fracturing fluid viscosity with changing shear rate at elevated temperature for Example (Formulation) 4 in Table 1.

Figure 9 shows the rheological profile for a fracturing fluid at a shear rate of 100 s ^-1 , the composition of which is given for Example (Composition) 5 in Table 1.

Figure 10 shows the change in fracturing fluid viscosity with changing shear rate at elevated temperature for Example (Formulation) 5 in Table 1.

Implementation of the invention

The claimed method is carried out as follows.

The preparation of the fluid for hydraulic fracturing is carried out in a hydration unit (a special blender), which is filled with surface water in a volume corresponding to the working volume of the blender, then with the mixing device turned on, the demulsifier is dosed, for example, but not necessarily at 1500-3000 rpm, then a dry synthetic gelling agent is loaded, while the anionic water-soluble polymer Polyprop-2-enamide hydrolyzed with 2-ethylhexylprop-2-enoate (Polyacrylamide hydrolyzed with 2-ethylhexyl acrylate) is used as such a polymer gelling agent in the form of a hydrated powder in an amount of, for example, but not necessarily, at least 4.0 kg per 1 m ³ of surface water, and mixed until complete hydration of the polymer for, for example, but not necessarily, at least 3 minutes, after hydration in a hydration unit (special blender) The destructor is dosed and, if necessary, other polymer-effective additives can be added.

Below is a more detailed example of one of the particular embodiments of the claimed method for preparing a fluid for hydraulic fracturing based on a synthetic gelling agent and surface water. This example is provided solely for the purpose of a clearer understanding of the claimed method and cannot be interpreted to narrow/limit the scope of legal protection of the claimed method. In this case, the recipe for each specific well is selected individually, depending on the reservoir conditions and technical equipment of the service company.

A polymer solution is prepared using surface water from any source, for example, a hydropolymer composition in the form of an aqueous solution, where the surface water is dosed into a hydration unit (hereinafter referred to as a blender) equipped with a stirrer in an amount of approximately 88.0 to 95.0 wt.%. This range is provided solely for a specific example and the choice of this range does not affect the achievement of the declared technical result. The stirrer is turned on with revolutions depending on the type and model of the blender used in specific cases in the approximate range from 1000 to 1700 rpm and, with constant stirring, a demulsifier is introduced in an amount of 1.0 mass. %, then using a screw dispenser, pour a synthetic gelling agent (polymer) into the blender vat in an amount of approximately 3.0 wt.% to 10 wt.%, the mixing time directly depends on the temperature of the water used, the type and model of the blender used in the work, but not more than 180 seconds until complete hydration of the polymer is achieved, proppant granules are unloaded into the resulting aqueous polymer solution one by one, in accordance with the pumping program, in an amount of 700 kg per 1 m3 ^of polymer liquid, then, through the same screw dispenser, add a polymer destructor in an amount of 1.0 wt.%, the resulting mass is mixed for approximately 3 minutes until a homogeneous suspension is obtained. Next, the liquid with proppant from the blender tank enters the low-pressure line, then after the pumps, into the high-pressure line, from which, via the tubing lift, the liquid enters the productive formation through perforations (for multi-stage hydraulic fracturing (MSHF) through the frac port).

The above ranges of values (rev/min of the stirrer, mass % of polymer and polymer granules, seconds and minutes of mixing, etc.) are also given solely for a specific example, and the choice of these values/ranges does not directly affect the achievement of the declared technical result. Thus, the choice of mass % of polymer is determined by the range of mass % of water and the need to obtain the final 100 mass %. The declared method may use different values/ranges of the above quantities.

The main essence and novelty of the invention are based on the use of surface water to obtain a polymer liquid without the use of stabilizing additives.

Below are explanations of the use of synthetic gelling agents in hydrocarbon production. The polymer synthetic fluid is prepared in a hydration unit, a demulsifier is introduced, then proppant is added to the fluid flow alternately with the destructor, and the finished mixture is pumped into the well using a pump.

Confirming examples in terms of the use of proppant in hydrocarbon production.

Example No. 1.

To prepare the hydraulic fracturing fluid, at high speeds of 1700 rpm, surface water of 95 wt.%, a synthetic gelling agent in an amount of 3.0 wt.% are continuously fed into the hydration unit vat in the calculated amount, adding proppant in an amount calculated at 700 kg per 1 m3 ^of polymer fluid, a polymer destructor in an amount of 1.0 wt.% and a demulsifier in an amount of 1.0 wt.%. The mixing system is designed in such a way that the loaded components of the hydraulic fracturing fluid and proppant are in constant motion to ensure hydration of the gelling agent. After a specified time, the resulting hydraulic fracturing fluid with proppant is fed into the low-pressure line. During injection in the operational mode, the viscosity and temperature of the hydraulic fluid are monitored.

Example No. 2.

To prepare the hydraulic fracturing fluid, at high speeds of 1700 rpm, surface water of 94 wt.%, a synthetic gelling agent in an amount of 4.0 wt.% are continuously fed into the hydration unit vat in the calculated amount, adding proppant in an amount calculated at 700 kg per 1 m3 ^of polymer fluid, a polymer destructor in an amount of 1.0 wt.% and a demulsifier in an amount of 1.0 wt.%. The mixing system is designed in such a way that the loaded components of the hydraulic fracturing fluid and proppant are in constant motion to ensure hydration of the gelling agent. After a specified time, the resulting hydraulic fracturing fluid with proppant is fed into the low-pressure line. During injection in the operational mode, the viscosity and temperature of the hydraulic fluid are monitored.

Example No. 3.

To prepare the hydraulic fracturing fluid, at high speeds of 1700 rpm, surface water of 92 wt.%, a synthetic gelling agent in an amount of 6.0 wt.% are continuously fed into the hydration unit vat in the calculated amount, adding proppant in an amount calculated at 700 kg per 1 m3 ^of polymer fluid, a polymer destructor in an amount of 1.0 wt.% and a demulsifier in an amount of 1.0 wt.%. The mixing system is designed in such a way that the loaded components of the hydraulic fracturing fluid and proppant are in constant motion to ensure hydration of the gelling agent. After a specified time, the resulting hydraulic fracturing fluid with proppant is fed into the low-pressure line. During injection in the operational mode, the viscosity and temperature of the hydraulic fluid are monitored.

The implementation of the method for preparing a working fluid from a synthetic gelling agent and its rheological properties are also illustrated by specific examples (See Table 1).

Table 1 - Implementation of the method for preparing a working fluid from a synthetic gelling agent on surface water and its rheological properties

Parameter Compound Composition 1 (Fig. 1) Composition 2 (Fig. 3) Composition 3 (Fig. 5) Composition 4
(Fig. 7) Composition 5
(Fig. 9) 65°C 85°C 90°С 100°С 85°C 1 2 3 4 5 6 Synthetic gelling agent, kg/ ^m3 3.0 3.0 3.0 4.0 6.0 Encapsulated breaker, kg/ ^m3 0.3 0.3 0.1 0.1 0.15 Stability time, min (more than 20 cP) 70 90 60 65 135

Data analysis shows that the claimed hydraulic fracturing fluid based on a synthetic gelling agent, prepared on surface water, can be used under various reservoir conditions.

The above examples serve to illustrate the invention and should not be construed as limiting the invention.

As can be seen from figures 1, 3, 5, 7, 9, all the obtained hydraulic fracturing fluids retain viscosity above 20 cP at various temperatures for at least 60 minutes. Then the gel is destroyed and the viscosity drops.

Figures 2, 4, 6, 8, 10 show the results of testing the hydraulic fracturing fluid for sensitivity to changes in shear rate. As can be seen from the graphs, recovery after the first cycle of shear loads occurs in less than 60 seconds, after the second cycle also in less than 60 seconds, after the third cycle also in less than 60 seconds.

Thus, the presented data confirm the achievement of the technical result for the hydraulic fracturing fluid and the method of its preparation.

Claims (12)

1. A method of hydraulic fracturing a formation using a hydraulic fracturing fluid based on a synthetic gelling agent - an anionic water-soluble polymer polyacrylamide and water containing a demulsifier, a polymer destructor and a proppant, characterized in that fracturing fluid contains polyacrylamide hydrolyzed with 2-ethylhexyl acrylate - polyprop-2-enamide hydrolyzed with 2-ethylhexyl prop-2-enoate, surface water, the preparation of the fluid for hydraulic fracturing is carried out in a hydration unit - a blender, first the said water is dosed into the blender vat in an amount of 88.0 to 95.0 wt.%, the mixer is turned on with revolutions from 1000 to 1700 rpm and with constant stirring the demulsifier is introduced in an amount of 1.0 wt.%, then using a screw dispenser the said gelling agent is poured into the blender vat in an amount of approximately 3.0 to 10 wt.%, stirred until the said gelling agent is completely hydrated, proppant is unloaded into the resulting polymer liquid - an aqueous polymer solution in the amount of 700 kg per 1 m3 ^of polymer liquid, then a polymer destructor is added through the same screw dispenser in the amount of 1.0 wt.%, the resulting mass is mixed until a homogeneous suspension is obtained, Then the fracturing fluid from the blender enters the productive formation, performing hydraulic fracturing of the formation. 2. The method according to paragraph 1, in which rivers, streams, reservoirs, lakes, and ponds are used as a source of surface water. 3. The method according to claim 1, in which the loaded components of the fracturing fluid in the blender are in constant motion to ensure hydration of the gelling agent. 4. The method according to item 1, in which the hydraulic fracturing fluid enters the production formation from the blender tank through a low-pressure line, then after the pumps into a high-pressure line, from which the fluid enters the production formation via a lift of tubing through perforation holes or, for multi-stage hydraulic fracturing of the formation, through a frac port. 5. The method according to claim 1, wherein said gelling agent is used in an amount of 4.0 wt.%. 6. The method according to claim 1, wherein said gelling agent is used in an amount of 6.0 wt.%. 7. A fluid for hydraulic fracturing based on a synthetic gelling agent and surface water, comprising a synthetic gelling agent, a demulsifier, a polymer destructor and a proppant, wherein the powdered polymer of the synthetic gelling agent is an anionic water-soluble polymer polyprop-2-enamide hydrolyzed with 2-ethylhexylprop-2-enoate, and it is prepared by the method according to any one of paragraphs 1-6.