CN103820100B - Gelled acid used for acid fracturing of high-temperature fractured-vuggy type carbonate reservoir - Google Patents

Abstract

The invention relates to a thickening acid for acid fracturing of high-temperature fracture-cavity carbonate reservoirs. The weight percentage of each component is: hydrochloric acid (HCl): 20%; thickening agent (TP-1): 3% ; Corrosion inhibitor (MC50): 2%; Iron ion stabilizer (FL4‑7): 1.5%; Demulsifier (PRJ): 0.05%; Drainage aid (AD12): 1.5%; the rest is water. The invention has a temperature resistance of 130°C, good rheology and shear resistance, good compatibility and fluid loss control performance, and low friction resistance. Compared with ordinary acid (20% HCl), the acid-rock reaction speed can be reduced by 52 %. Under high temperature conditions, this system expands the treatment depth of the acid solution to the formation, improves the efficiency and success rate of acidification, and can effectively reduce pipe string corrosion and reservoir damage. It is easy to flow back, and has the ability to carry solid particles. The acid-dissolving time of the chemical agent is short, which is convenient for on-site preparation, and is very suitable for acid fracturing stimulation of high-temperature fractured-vuggy carbonate reservoirs.

Description

A thickening acid for acid fracturing of high-temperature fracture-cavity carbonate reservoirs

technical field

The invention relates to the acid fracturing stimulation technology for carbonate rock reservoirs, in particular to the thickening acid technology for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs.

Background technique

Acid fracturing is the most effective stimulation measure for the development of carbonate reservoirs, and its success depends on the effective length of acid-etched fractures and the conductivity of acid-etched fractures after acid fracturing. For high-temperature deep wells, in addition to being controlled by rock properties and in-situ stress fields, the effective acid-etched fracture length is mainly controlled by the acid-rock reaction rate and the fluid loss characteristics of acid fluid. The conductivity of acid-etched fractures depends on the closure stress of the formation, the compressive strength of the rock, the amount of acid-dissolved rock, and the irregularity of the acid-etched shape along the fracture surface. The current technical difficulties of high-temperature deep well acid fracturing are mainly concentrated in the following aspects: ①The well section is deeply buried and the construction friction is high. It is necessary to use an acid system with good resistance-reducing performance in order to increase displacement and reduce pump pressure, thereby reducing Requirements for wellhead devices and construction equipment; ②The reservoir temperature is high, and the acid-rock reaction speed is fast, so it is difficult to form long acid-etched fractures; ③Natural fractures and pores are relatively developed. For the acid system with good fluid loss performance, it is necessary to use high-viscosity prefluid to create fractures to reduce the subsequent acid fluid loss; ④ It is difficult to control the fracture height; ⑤ High closure pressure at the well depth is not conducive to maintaining high conductivity; ⑥ The pressure coefficient of the formation is low, and it takes a long time for the residual liquid to flow back after acid fracturing, so liquid nitrogen and high-efficiency drainage aids should be used to aid drainage; ⑦It is difficult to prevent corrosion, and the formation temperature is high, which requires high performance of corrosion inhibitors.

In view of the existing technical difficulties, the current research direction mainly focuses on the following three aspects: the technology of reducing the fluid loss of acid liquid during the acid fracturing process; the technology of reducing the reaction rate of acid rock during the injection process; the technology of improving the conductivity of acid-etched fractures.

The quality of acid fluid directly affects the acidizing effect, which is especially prominent in low-permeability, high-temperature deep well conditions. During acidification, the reaction between acid and rock occurs in porous media, which is a heterogeneous reaction. There are many factors that affect the flow and reaction of acid liquid in rock, including the mineral composition of rock, the composition and concentration of acid liquid, the reaction temperature of acid rock, and the construction pressure.

The development of high-performance acid liquid and the improvement of acidification efficiency have always been the subject of continuous exploration by oil exploration workers. Since the advent of acidizing technology, people have been trying to use various acid liquid systems for construction, and a lot of research work has been carried out in the development of retarded acids, including thickened acid, emulsified acid, foam acid, micellar acid, autogenous acid, etc. Acid and fluid loss acid and other slow acid systems.

Thickened acid acid fracturing refers to the acid system in which a non-crosslinked acid thickener is added to the acid solution to increase the viscosity of the acid solution. Thickened acid has a higher viscosity, which can control fluid loss, increase the width and length of cracks, so as to delay the reaction rate of acid rock, increase the penetration distance of active acid, reduce friction, increase construction displacement, and better realize Deep acidification transformation.

The optimal viscosity of thickened acid is 30-40mPa.s, and the viscosity of barren acid should generally be between 5-10mPa.s, so as to facilitate flowback and carry solid particles in fractures, and reduce the secondary damage of acid fracturing to the formation . The frictional resistance of thickened acid is generally 60% of that of clear water, and that of emulsified acid in the external phase of oil is generally 100-150%. In the field application, the thickened acid is required to have good thermal stability, the viscosity-temperature effect of the fresh acid is not significant, the residual acid is completely broken, the viscosity is moderate, it must be easy to flow back, and it must also have the ability to carry solid particles.

Thickened acid is generally suitable for acid fracturing in medium-permeability reservoirs, and the length of acid-etched fractures is between 20-50m; in high-permeability formations, in addition to removing damage, thickened acid can also be used if a certain length of acid-etched fractures needs to be obtained. Thickened acid; be cautious when using thickened acid in reservoirs with low permeability and difficult flowback. Field tests and applications have been carried out mainly in Sichuan and Changqing gas fields in China, and good production increase effects have been achieved.

For acid fracturing of high temperature (above 120°C) fractured-cavity carbonate reservoirs like Tahe Oilfield, thickened acid should not only pay attention to whether it has good rheology, shear resistance and corrosion inhibition under high temperature in deep wells. , but also consider the fluid loss control performance of the acid, the corrosion of the string and the damage to the reservoir, the flowback effect and whether it has good compatibility, the acid dissolution time of the thickener, etc. In the preparation of high-temperature thickened acid, the following components should be considered:

Thickener: In the 1970s, thickened acid was used in industry, but it was not very common, mainly because it can maintain the viscosity of the necessary acidified liquid at high temperature (above 90°C) and high shear rate. quite little. After that, Halliburton Company of the United States developed a new type of copolymer of acrylamide and cationic monomer, which laid the foundation for the promotion of thickened acid technology. At present, BJ company has developed AG series of thickened acid, Dowell company has developed DSGA series of thickened acid, Halliburton company has developed SGA series of thickened acid; domestic Petroleum Exploration and Development Research Institute, Changqing Petroleum Exploration Institute and other units have also carried out thickened acid Chemical agent formulation research, but different products adapt to different temperatures, and the compatibility with other components is also different.

Corrosion inhibitor: It is the key to ensure the normal construction of acid fracturing. Improper selection of corrosion inhibitor will cause serious corrosion of the construction vehicle group and pipelines by the acid liquid, especially in high-temperature deep wells, and even normal construction cannot be guaranteed. Casing string corrosion will affect the normal production of operating wells. At the same time, the iron ions introduced by corrosion may also produce iron deposits in the reservoir, further aggravating the reservoir damage.

Iron ion stabilizer: During the acid fracturing process, the acid liquid reacts with the acid fracturing construction equipment, construction pipe strings and iron-containing minerals in the formation rocks to produce Fe ³⁺ and Fe ²⁺ . After acid fracturing, when the pH value of the residual acid is greater than 2.2, Fe ³⁺ ions will start to produce gelatinous ferric hydroxide precipitation, causing damage to the formation and reducing the acidizing effect. Therefore, it is necessary to add an appropriate amount of iron ion stabilizer to the acid solution to prevent the precipitation of Fe ³⁺ . At home and abroad, various substances that can form soluble chelates with iron ions or reduce Fe ³⁺ to Fe ²⁺ are used as iron ion stabilizers. When optimizing, it is necessary to choose the highest percentage of stable iron from a large number of products and have good compatibility with other components.

Demulsifier: During operation, due to the mixing of foreign fluid and formation fluid, an emulsion with oil or water as the external phase is often formed. These emulsions are generally larger than the pore throat size, often block the pores, increase the viscosity, reduce the effective flow capacity of the formation fluid, and cause damage to the reservoir. Therefore, the appropriate demulsifier must be screened to prevent the negative impact of acid liquid on the reservoir during the acid fracturing process.

Drainage aid: Added to the acid solution, it can reduce the surface tension of the acid solution, adjust the wettability of the rock, and facilitate the flowback of the remaining residual acid.

At present, domestic thickener products used in acid fracturing of high-temperature carbonate rock reservoirs above 120 °C mostly show shortcomings such as being greatly affected by shearing, weak acid viscosity-increasing ability, and long preparation time on site. It can overcome the above shortcomings, but it does not comprehensively consider the serious corrosion of the pipe string and the damage of the reservoir, the size of the friction resistance, and the effect of flowback under the high temperature condition of the deep well, and the formula is incomplete and perfect.

Therefore, starting from the completeness of the requirements, different types of products of each component are optimized, and a thickened acid for acid fracturing of high-temperature fracture-vuggy carbonate reservoirs is prepared. (Above 120°C) Expand the treatment depth of the acid solution to the formation, improve the efficiency and success rate of acidification, and at the same time effectively reduce the corrosion of the pipe string and the damage of the reservoir, easy to flow back, have the ability to carry solid particles, and low friction , The acid-soluble time of the thickener is short, which is conducive to on-site preparation.

Contents of the invention

The technical problem to be solved by the present invention is to provide a thickened acid for acid fracturing reformation of high-temperature fracture-vug carbonate reservoirs with a complete formula in view of the above-mentioned defects of the prior art, which can meet the design requirements of acid fracturing and as soon as possible Possible reduction of various damages.

The present invention is achieved by adopting the following technical solutions:

A thickening acid for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs, characterized in that the thickening acid comprises, by weight percentage: hydrochloric acid, 20%; thickening agent, 3%; corrosion inhibitor agent, 2%; iron ion stabilizer, 1.5%; demulsifier, 0.05%; drainage aid, 1.5%; the balance is water.

The thickened acid used for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs is characterized in that the thickened agent is TP-1, which uses acrylamide and other two temperature-resistant and salt-resistant monomers as The synthetic monomer is synthesized by inverse emulsion polymerization, with a density of 0.99-1.05g/cm ³ , a molecular weight of 8-11 million, and a solid content of 30%. The viscosity of the acid solution prepared by TP-1 and 20% HCl is 37mPa.s at 130°C.

The thickening acid for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs is characterized in that the corrosion inhibitor is a high-temperature-resistant imidazoline derivative MC50, which is composed of 2-aminoethyl heptadecene The base imidazoline reacts with sodium chloroacetate. Implement SY/T5885-95 standard, at 45°C, the average corrosion inhibition rate of 2% MC50 corrosion inhibitor is 0.253g/m ² h.

The thickening acid for acid fracturing of high-temperature fractured-vuggy carbonate reservoirs is characterized in that the iron ion stabilizer is erythorbic acid FL4-7. Implementation of SY/T6571-2003 standard, under the condition of PH=3.5, 1.5% FL4-7 stabilized iron content reaches 86%.

The thickened acid for acid fracturing of high-temperature fractured-vuggy carbonate rock reservoirs is characterized in that the demulsifier is biological demulsifier PRJ. The demulsification rate of PRJ reached 100% at 0.05% concentration for 10 minutes.

The thickened acid used for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs is characterized in that the drainage aid is a quaternary ammonium salt type cationic surfactant dodecyl dimethyl chloride Ammonium AD12, under normal temperature conditions, the interfacial tension of 1.5% AD12 is 0.9mN/m.

The above-mentioned raw materials are sold in the market.

Aiming at the characteristics of acid fracturing of high-temperature fractured-cavity carbonate rock reservoirs, in order to fully meet the requirements, a complete thickened acid formula is obtained through the optimization of each component. Compared with the prior art, the present invention Has the following advantages:

The thickened acid has a temperature resistance of 130°C, has good rheology and shear resistance, and has good compatibility and fluid loss control performance. Compared with ordinary acid (20% HCl), the acid-rock reaction rate can be reduced by 52%. Under high temperature conditions, the treatment depth of the acid solution to the formation is expanded, the efficiency and success rate of acidification are improved, and at the same time, it can effectively reduce the corrosion of the pipe string and the damage of the reservoir, easy to flow back, have the ability to carry solid particles, and have low frictional resistance , the acid-dissolving time of the thickener is short, which is conducive to the on-site preparation to meet the acid fracturing stimulation of high-temperature fracture-cavity carbonate reservoirs.

Description of drawings

In order to illustrate the embodiments and test examples of the present invention more clearly, the following briefly introduces the accompanying drawings that are used in the description of the embodiments and test examples. In the attached picture:

Figure 1 is the viscosity measurement curve of thickened acid (20% HCl) prepared with different thickeners (shear rate 170S ^-1 );

Figure 2 is the shear stability curve of thickened acid at different temperatures.

detailed description

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the embodiments of the present invention will be further described in detail below in conjunction with the accompanying drawings. Here, the exemplary embodiments and descriptions of the present invention are used to explain the present invention, but not to limit the present invention.

Example

A thickening acid for acid fracturing of high-temperature fracture-cavity carbonate rock reservoirs, characterized in that the thickening acid comprises, by weight percentage: hydrochloric acid, 20%; thickening agent, 3%; corrosion inhibitor agent, 2%; iron ion stabilizer, 1.5%; demulsifier, 0.05%; drainage aid, 1.5%; the balance is water.

The preparation process is as follows: first dilute industrial hydrochloric acid to a concentration of 20%, then add 1.5% iron ion stabilizer FL4-7, 0.05% demulsifier PRJ, 1.5% Drainage aid AD12, then add 3% thickener TP-1, at room temperature, mix evenly and swell for about 2 hours, the thickener can be fully dissolved and thickened in the formula acid solution, finally add 2% Corrosion inhibitor MC50, made into thickened acid after fully stirring.

The selection of thickener is an important point in the preparation of thickened acid. Figure 1 shows the viscosity measurement curves (shear rate 170S ^-1 ) of thickened acid (20% HCl) prepared with different thickeners in the temperature range of 30°C-130°C and other components are the same. It can be seen from the figure that under the same temperature and acid concentration conditions, TP-1's ability to increase acid viscosity is significantly better than CTl-6 and VY-101, and it is better than DSGA at high temperature. The viscosity of the thickened acid prepared by TP-1 decreases slowly with the increase of temperature. When the temperature reaches a certain height, the viscosity increases and then decreases. At a constant temperature of 130°C, TP-1 thickened acid can still maintain a certain viscosity, which will help the acidified reactant residue to flow back to the ground along with the residual acid. At room temperature, TP-1 thickener can be fully dissolved and thickened in the formula acid solution at 114 minutes to form a stable thickened acid.

test case

The present invention further evaluates the acid dissolution time, thermal stability, rheology, shear stability, compatibility and retardation of the thickened acid used for acid fracturing of high-temperature fracture-cavity carbonate reservoirs prepared in the examples , see standard SY/T6214-1996, some test results are as follows:

Table 1 Effect of acid dissolution time on viscosity of thickened acid (25°C)

Table 2 Thermal stability of thickened acid (170S ^-1 )

Table 3 Test data of the relationship between thickener concentration and acid viscosity (30°C, 170S ^-1 )

Thickening acid concentration, % 1 2 3 3.5 Static viscosity of acid liquid, mPa.s 26 36 48 53

The impact test data of table 4 shear rate on the apparent viscosity of viscosifying acid

Figure 2 shows the apparent viscosity of thickened acid during continuous shearing for 120 minutes at a shear rate of 170S-1 at 25°C, 90°C, and 130°C. It can be seen from the figure that under the three temperature conditions, the viscosity decreases by 1.7%, 16.3% and 24.3% respectively, and the viscosity results after shearing still meet the site construction standards (the site construction standard is that the acid viscosity is not less than 20mPa.s) , with good shear stability.

Table 5 Compatibility of thickener and corrosion inhibitor at 590°C

Table 6 Determination of Corrosion Inhibition Rate of Corrosion Inhibitor MC50

Table 7 Compatibility of iron ion stabilizer and thickener

sample name Exterior Iron ion concentration mg/l State after mixing and dissolving acetic acid Transparent liquid 2000 The yellow-green becomes lighter, and no insoluble matter such as precipitate appears EDTA White powder 2000 The yellow-green becomes lighter, and no insoluble matter such as precipitate appears citric acid white crystals 2000 The yellow-green becomes lighter, and no insoluble matter such as precipitate appears isoascorbic acid white crystals 2000 The yellow-green color disappears immediately, and no insoluble matter such as precipitate appears

Table 8 Reaction rate of acid liquid and carbonate core

The test results show that the thickened acid has a temperature resistance of over 130°C, good rheology and shear resistance, good compatibility and fluid loss control performance, and low friction, which can effectively delay the acid-rock reaction rate and expand the acid-rock reaction rate. The treatment depth of the liquid to the formation can improve the efficiency and success rate of acidification, and at the same time, it can effectively reduce the corrosion of the pipe string and the damage of the reservoir. It is easy to flow back and has the ability to carry solid particles. It is formulated to meet the acid fracturing stimulation of high-temperature fractured-cavity carbonate reservoirs.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the scope of the present invention. Protection scope, within the spirit and principles of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims (1)

1. a kind of viscous acid of high temperature fracture-cavity type carbonate reservoir acid fracturing is it is characterised in that described viscous acid, and by weight hundred Divide and include than meter：Hydrochloric acid, 20%；Thickening agent, 3%；Corrosion inhibiter, 2%；Ferrous stability, 1.5%；Demulsifier, 0.05%； Cleanup additive, 1.5%；Balance of water；Described thickening agent is TP-1, and it selects acrylamide and other 2 kinds of temperature-resistant anti-salt monomers to make Adopt the method synthesis of inverse emulsion polymerization, density 0.99-1.05g/cm for synthon³, molecular weight 800-1100 ten thousand, admittedly contain Amount 30%；Described corrosion inhibiter is high temperature resistant imidazolidine derivatives MC50, by 2- amine ethyl 17 carbon mono alkenyl imidazoline and chloroethene Sour sodium reaction generates；Described ferrous stability is arabo-ascorbic acid FL4-7；Described demulsifier is biological demulsifying agent PRJ；Described Cleanup additive is the double dodecyl dimethyl ammonium chloride AD12 of quaternary ammonium salt cationic surfactant.