Deep etching pore acidification method applicable to high-calcium reservoirs

Abstract

The present invention discloses a deep etching pore acidification method applicable to high-calcium reservoirs, belonging to the technical field of oil and gas field production enhancement. The method includes: obtaining geological data; determining the construction displacement and construction pressure of the fluid injected into the well, and the fluid injected into the well includes an infiltration-enhancing etching pore acid, an etching pore precipitation liquid, and an aperture-expanding acid; determining the injection volume of the fluid injected into the well; injecting the infiltration-enhancing etching pore acid into the reservoir, and the infiltration-enhancing etching pore acid is composed of 3-10% of an infiltration enhancer and 90-97% of a pH-responsive phase change etching pore acid; injecting the etching pore precipitation liquid into the reservoir, and the etching pore precipitation liquid is a methanol or ethanol solution with a concentration higher than 80%; shutting in the well for 2-3 h; injecting the aperture-expanding acid into the reservoir, and the aperture-expanding acid is composed of an acid solution, a soluble consolidant, a comprehensive additive, and water; injecting a displacement fluid; shutting in the well and flowing back. The present invention can form complex, reticular, and multi-branched acid-etched wormholes in the reservoir, and can effectively support the acid-etching channels under high pressure, further improving the acidification effect of the reservoir, which is of great significance for the stimulation and transformation of high-calcium reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field production increase, and in particular relates to a deep pitting acidification method suitable for high-calcium reservoirs. Background Art

[0002] Increasing production is the main measure for oil and gas well transformation. Especially for high-calcium reservoirs, acid treatment is the most effective measure to increase production. High-calcium reservoirs refer to carbonate reservoirs or sandstone reservoirs with high carbonate content. Since carbonates react easily with acids, the simplest way to transform high-calcium reservoirs is to use a hydrochloric acid system: 2HCl + CaCO3 = CaCl2 + H2O +CO2

[0003] The mechanism of acidizing to increase production is that reservoir minerals and blockages are dissolved to form new oil and gas channels. However, the channels formed by acid etching may collapse and close under reservoir pressure, so the goal of acidizing operation is to form effective acid etching channels.

[0004] There are two types of existing acid treatment measures: acid fracturing and matrix acidification. Whether it is acid fracturing or matrix acidification, acid-etched holes, pits, trenches and other flow channels are formed in the reservoir by acid dissolving reservoir minerals. The reservoir has been under high pressure. After the construction is completed, the acid-etched channels will shrink or even close under high pressure, especially in reservoirs with low rock strength and loose mineral cementation. The acid-etched channels will gradually close or even disappear under reservoir pressure. Therefore, to improve the effect of acid treatment, two factors must be considered: on the one hand, the acid can efficiently dissolve reservoir minerals and form acid-etched channels; on the other hand, the channels formed by acid etching can be effectively maintained under high pressure in the reservoir.

[0005] The focus of acid treatment technology is on the development of acid systems and the adjustment of acid injection processes. The development direction of acid systems is mostly slow and high temperature resistant, mainly including autogenous acid, thickened acid, organic acid, variable viscosity acid, cross-linked acid, chelated acid, etc. The acid injection processes include alternating acid fracturing, pre-fluid acid fracturing, closed acid fracturing, etc. There are many factors that affect the effect of acid treatment, mainly the following two points: (1) The acid-carbonate mineral reaction rate is fast, and it is very easy to form acid wormholes, but the acid wormholes are easy to close under high pressure, especially when the reservoir minerals have high mud content and loose cementation, making it difficult for the acid erosion surface to support under high pressure; (2) Fast-reacting acid is easy to form a high-channel main hole near the wellbore, that is, to form a similar short and wide fracture, and slow-reacting acid forms a similar slender fracture. The short and wide fractures connect the reservoir area with a small area, and the slender fractures have a large affected area, but the slender fractures are easy to close under high pressure. How to form complex, network-shaped, multi-branched acid pores and effectively support the acid erosion area under high pressure is the goal pursued by carbonate rock acidizing technology.

[0006] As a non-renewable resource, the physical properties of oilfield reservoirs are getting worse and worse. Thin interbeds, shale, unconsolidated, and mixed sediments are all problems faced in oil production. Especially for high-calcium reservoirs, how to form complex, reticulated, and multi-branched acid-etched pores and maintain high permeability under high pressure is the key technology to improve the acidification effect and maintain the acidification validity period. Summary of the Invention

[0007] The purpose of the present invention is to provide a deep-etched pore acidification method applicable to high-calcium reservoirs. This method is easy to operate, can form complex, reticulated, and multi-branched acid-etched pores in the reservoir, achieve deep acid etching, expand the acid etching area, and effectively support the acid etching channels under high pressure, overcoming the deficiencies and defects of current reservoir acidification technologies. Especially for high-shale and loosely cemented high-calcium reservoirs, it solves the problems of reservoir collapse after acidification, inability to support acid etching channels, and acid fluid only acting in the near-well area. The present invention further improves the reservoir acidification effect and is of great significance for the stimulation and transformation of high-calcium reservoirs.

[0008] To achieve the above technical objectives, the present invention adopts the following technical solutions.

[0009] Reservoir minerals are divided into two categories, calcium component M Ca and silica component M Si , M Ca + M Si = 100%. The sum of the mass percentages of each component of dolomite, limestone, and siderite is M Ca , and the remaining component is silica component M Si . Silica component M Si is divided into shale component M m and hard silica component M q , M Si = M m + M q , and hard silica component M q is the sum of the mass ratios of quartz and feldspar in the mineral. Reservoirs with M Ca ≥50% are high-calcium reservoirs, reservoirs with M m ≥ 10% are high-shale limestone reservoirs, and reservoirs with M m <10% belong to conventional high-calcium reservoirs.

[0010] A deep-etched pore acidification method applicable to high-calcium reservoirs successively includes the following steps:

[0011] S1 Obtain geological data, including reservoir mineral components (calcium component M Ca , silica component M Si , shale component M m and hard silica component M q ), reservoir permeability K, and reservoir fracture pressure Pf and the average reservoir pressure P r and the well depth H.

[0012] S2 determines the construction displacement Q t and the construction pressure P t of the fluid injected into the well. The fluid injected into the well includes the permeability-increasing etching acid, the etching hole precipitation liquid, and the hole-expanding acid. The process is as follows:

[0013] S2-1 determines the construction displacement and construction pressure of the permeability-increasing etching acid injection

[0014] Using reservoir cores or artificial cores (the permeability of the artificial cores is close to that of the reservoir cores), core displacement experiments of the permeability-increasing etching acid are carried out with different flow rates respectively, and the flow rate-pressure difference relationship curve is obtained, and the displacement pressure inflection point P * and the displacement flow rate inflection point Q * are obtained, and the construction displacement Q t and the construction pressure P t of the permeability-increasing etching acid are obtained:

[0015]

[0016] S2-2 determines the construction displacement and construction pressure of the etching hole precipitation liquid and the hole-expanding acid injection

[0017] The construction displacement Q t of the etching hole precipitation liquid and the hole-expanding acid takes a value of 0.3 - 2 m 3 / min, which is related to the equipment parameters;

[0018] The construction pressure P t of the etching hole precipitation liquid and the hole-expanding acid is:

[0019]

[0020] where d is the core diameter, m;

[0021] D is the wellbore diameter of the well section where the fluid enters the well, m;

[0022] L is the length of the working well section, m;

[0023] ρ is the density of the fluid injected into the well, kg / m 3 ;

[0024] P λ is the injection pressure loss of the fluid injected into the well, MPa;

[0025] g is the acceleration of gravity, m / s 2 ;

[0026] λ is the friction coefficient of the fluid injected into the well;

[0027] d tis the pipe string diameter for injecting the fluid into the well (the tubing diameter for tubing construction and the casing diameter for casing construction), m;

[0028] H is the well depth, m.

[0029] S3 Determine the injection volume of the fluid into the well:

[0030] Permeability-increasing etching hole acid: determined by the length of the well section to be transformed, with a dosage of 0.5 - 2 m per meter 3 ;

[0031] Etching hole precipitation fluid: 0.3 - 0.5 times the volume dosage of the permeability-increasing etching hole acid;

[0032] Hole-expanding acid: determined by the length of the well section to be transformed, with a dosage of 2 - 6 m per meter 3 .

[0033] S4 Inject the permeability-increasing etching hole acid into the reservoir according to the construction pressure and construction displacement obtained in S2. The permeability-increasing etching hole acid is composed of 3 - 10% of a permeability-increasing agent and 90 - 97% of a pH-responsive phase-change etching hole acid. The permeability-increasing agent is methanol, ethanol or acetone. The pH-responsive phase-change etching hole acid is composed of the following components by weight percentage: 10 - 20% of an acid-generating agent, 10 - 30% of a hole-expanding agent, 1 - 2% of a coalescing agent, 0.5 - 10% of a pH regulator, and the balance is water.

[0034] The acid-generating agent is one or more of ammonium chloride, formaldehyde, methyl formate, ethyl acetate, glucono delta-lactone.

[0035] The hole-expanding agent is one or more of sodium benzoate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, pentasodium diethylenetriaminepentaacetate, tetrasodium glutamate diacetate, sodium fumarate, benzoic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, glutamate diacetic acid, fumaric acid.

[0036] The coalescing agent is one or more of ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol phenyl ether, propylene glycol tert-butyl ether.

[0037] The pH regulator is one or more of formic acid, acetic acid, sodium formate, sodium acetate.

[0038] The preparation of the permeability-increasing etching hole acid is as follows: Mix 10 - 20% of the acid-generating agent, 10 - 30% of the hole-expanding agent, 1 - 2% of the coalescing agent and water and stir evenly, and then add the pH regulator until the pH value of the solution is between 3 and 6.

[0039] S5 Inject the etch hole precipitation liquid into the reservoir according to the construction pressure and construction displacement obtained in S2, and the etch hole precipitation liquid is a methanol or ethanol solution with a concentration higher than 80%.

[0040] S6 Shut in the well for 2 - 3 h to form complex micro - wormholes in the reservoir.

[0041] S7 Inject the hole - enlarging acid into the reservoir according to the construction pressure and construction displacement obtained in S2. The hole - enlarging acid is composed of the following components by weight percentage: acid solution 10 - 20%, soluble consolidant 0 - 20%, comprehensive additive 3 - 5%, and the rest is water.

[0042] The acid solution is hydrochloric acid, acetic acid or formic acid; the soluble consolidant is one or more of oxalic acid, sodium oxalate, potassium oxalate, phosphoric acid, sodium phosphate, citric acid, sodium citrate; the comprehensive additive is composed of an inhibitor, a surfactant and a mutual solvent, all of which are conventional additives used in oilfield acidification.

[0043] The inhibitor is a commercially available inhibitor for oilfield acidification, such as aldehyde - ketone - amine condensate, alkynol, thiourea, imidazoline derivative.

[0044] The surfactant is a commercially available surfactant, such as fluorocarbon surfactant, quaternary ammonium salt surfactant.

[0045] The mutual solvent is a commercially available mutual solvent for oilfield acidification, such as ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, propylene glycol methyl ether.

[0046] Further, for conventional high - calcium reservoirs (M m <10%), no soluble consolidant is added to the hole - enlarging acid; for high - argillaceous limestone reservoirs, soluble consolidant is added to the hole - enlarging acid.

[0047] S8 Inject the displacement fluid.

[0048] S9 Shut in the well for 1 - 5 h and then flow back.

[0049] Further, the displacement fluid is a 3% NH4Cl solution, a 3% KCl solution or clear water, and the injection volume is 1.2 - 1.5 times the volume of the injection pipeline.

[0050] Further, when the reservoir temperature is higher than 120 °C, the shut - in time is 1 - 3 h; when the reservoir temperature is lower than or equal to 120 °C, the shut - in time is 2 - 5 h.

[0051] The present invention utilizes the synergistic effect of an extremely slow-reacting acid generation system (permeability-increasing etching pore acid) and a fast-reacting acid (pore-expanding acid) to form complex acid-etched wormholes in high-calcium reservoirs. The permeability-increasing etching pore acid, as a reservoir pretreatment fluid, reacts extremely slowly when contacting the rock, only generating extremely weak gas-liquid two-phase resistance (negligible), so the permeability-increasing etching pore acid enters the reservoir in a complex network seepage manner and slowly reacts with the calcium in the reservoir to form a complex acid-etched fine network. After further injecting the pore-expanding acid, the pore-expanding acid-rock reaction rapidly generates CO2 gas, forming a two-phase flow that causes the acid solution to more easily enter the acid-etched network formed by the pretreatment of the permeability-increasing etching pore acid, thereby forming a complex acid-etched wormhole network.

[0052] The mechanism analysis of the present invention is as follows:

[0053] First, the permeability-increasing etching pore acid is a weak acid system, and the reaction rate is extremely low or does not react when contacting the reservoir rock (if it does not react, no CO2 gas is formed, and no interfacial resistance of the gas-liquid two-phase flow is formed). A small amount of alcohol in the permeability-increasing etching pore acid system helps it enter each microchannel in the reservoir, that is, enter the complex seepage network;

[0054] Second, after the acid generator in the system is injected into the reservoir, it slowly releases acid to combine with the pore-expanding agent to form solid-phase organic acid particles. The coalescing agent further promotes the coalescence of the solid-phase organic acids into large particles. At the same time, the injected etching pore precipitation liquid accelerates the coalescence of the solid-phase organic acids into large particles and precipitation and growth. Due to the growth of the solid-phase particles, it has an effective temporary plugging and diversion function during the liquid injection process, improving the efficiency of forming a complex seepage network;

[0055] Third, the already formed solid-phase organic acid slowly reacts with the calcium minerals in the reservoir to form a complex fine network with seepage ability. At the same time, the solid-phase organic acid also gradually reacts into dissolved salts to achieve self-cleaning;

[0056] Fourth, conventional acid will rapidly react with the carbonate rock in the reservoir to generate CO2, resulting in extremely large resistance due to the gas-liquid two-phase flow during the acid injection process. Especially in low-permeability areas, due to the capillary force, the two-phase resistance is greater. At this time, the acid solution will only form a single acid-etched channel along the large pores and main fractures. However, based on the pretreatment of the permeability-increasing etching pore acid in the present invention, the injected pore-expanding acid will enter the complex fine network to form a complex acid-etched wormhole network with high seepage ability, achieving a high improvement ratio;

[0057] Fifth, after the reservoir rock is dissolved by acid, the mechanical properties of the rock decrease, resulting in the reservoir being prone to collapse. Especially in high-argillaceous limestone reservoirs, after acid treatment, the clay is loose and migrates, resulting in poor acidification effect or short effective period. The soluble consolidant in the pore-expanding acid combines with the calcium ions after the acid reaction to form a hard support framework, consolidating some clay minerals. That is, the fast-reacting acid expands the pores, and the soluble consolidant supports the acid-etched pores to form a complex acid-etched wormhole network and can maintain a long-term support effect.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] 1. By utilizing the synergistic effect of various materials, on the basis of pre-treating with the permeability-increasing etching acid, the pore-expanding acid enters the complex fine network to form a complex acid-etched wormhole network with high seepage capacity, expanding the area affected by the acid etching effect and increasing the improvement ratio of acid treatment;

[0060] 2. By using the soluble consolidant, a consolidated framework is formed with the calcium salt after reacting with the acid during the shut-in time, which is equivalent to forming a support for the complex acid-etched wormhole network after acid etching, effectively supporting the acid etching channels under the reservoir pressure and extending the effective period of acidification;

[0061] 3. The present invention is applicable to the acidification reconstruction construction of high-calcium reservoirs, especially for reservoirs with loose, porous and high shale content, and has better reconstruction effects. Brief Description of the Drawings

[0062] Figure 1 is a process flow chart of a deep pore etching acidification method applicable to high-calcium reservoirs.

[0063] Figure 2 is the CT morphology diagram after the experiments on Cores C1, C2 and C3.

[0064] Figure 3 is the CT morphology diagram of Cores D1 and D2 before and after the experiments. Detailed Embodiments

[0065] The present invention will be further described below with reference to the drawings and examples to facilitate the understanding of those skilled in the art of the present technology. It should be clear, however, that the present invention is not limited to the scope of the specific embodiments, and for those of ordinary skill in the art of the present technology, all changes within the spirit and scope of the present invention defined and determined by the appended claims are within the scope of protection. Embodiment

[0066] A porous homogeneous high-calcium outcrop core was selected for a core flow displacement experiment. The experimental core M Ca = 95%, which is a conventional high-calcium core with a core length of 8 cm and a diameter of 2.54 cm.

[0067] Pore-expanding acid: 15% HCl + 1% oil-based imidazoline + 1% fluorocarbon surfactant + 1% ethylene glycol monobutyl ether + 82% water.

[0068] Permeability-increasing etching acid: 5% ethanol + 9.5% ammonium chloride + 9.5% formaldehyde + 14.25% sodium fumarate + 1.9% ethylene glycol monoethyl ether + 57% water + 2.85% acetic acid, with a pH value between 3 and 4.

[0069] Etching pore precipitation solution: 80% ethanol solution.

[0070]

[0071] Note: 3% NH4Cl solution is used to test the permeability of the core, does not chemically react with the core, has no effect on the core structure, and the injection volume is based on the stability of the experiment during the test. K0 and K1 are the core permeabilities before and after the experiment respectively.

[0072] Compare the data of the permeability improvement effect of cores numbered C1, C2, and C3 before and after the experiment. That C1 is better than C2 indicates that the reaming acid has a stronger acid dissolution ability than the permeability-increasing etching pore acid. That C3 is much higher than the sum of the improvements of C1 and C2 indicates that the synergistic effect of the permeability-increasing etching pore acid and the reaming acid greatly improves the effect of improving the core permeability.

[0073] Figure 1 The core morphologies after the experiments of C1, C2, and C3 are shown. The core improved by the reaming acid shows a main wormhole channel, and the core improved by the permeability-increasing etching pore acid shows a multi-dispersed fine network channel. Further using the reaming acid on the basis of the improvement by the permeability-increasing etching pore acid can form enlarged complex pores.

[0074] Example 2

[0075] Select the core of the carbonate rock reservoir in J Oilfield for core flow displacement experiment. M Ca = 79%, M Si = 21%, M q = 18%, M m = 3%. The core of this reservoir is a conventional high-calcium core. The core length is 5 cm and the diameter is 2.54 cm.

[0076] Reaming acid: 15% HCl + 1% oil-based imidazoline + 1% fluorocarbon surfactant + 1% ethylene glycol monobutyl ether + 82% water.

[0077] Permeability-increasing etching pore acid: 10% ethanol + 9% glucono-delta-lactone + 9% pentasodium diethylenetriaminepentaacetate + 0.9% ethylene glycol monobutyl ether + 1.8% acetic acid + 69.3% water, pH is between 4 - 5.

[0078] Etching pore precipitation solution: 80% ethanol solution.

[0079]

[0080] Note: 3% NH4Cl solution is used to test the permeability of the core, does not chemically react with the core, has no effect on the core structure, and the injection volume is based on the stability of the experiment during the test. K0 and K1 are the core permeabilities before and after the experiment respectively.

[0081] Compare the data of the improvement effect of the permeability before and after the core experiments with the numbers D1 and D2. That D2 is better than D1 indicates that the synergistic effect of the permeability-increasing etching acid and the pore-expanding acid greatly improves the improvement effect of the core permeability.

[0082] Figure 2 They are the core morphologies before and after the D1 and D2 experiments. The initial states of D1 and D2 are dense and there are almost no connected pores. After acid treatment, they show excellent acid connectivity effects. After the pore-expanding acid treatment, the D1 core shows main wormhole channels and erodes out from the side of the core. After the combined action of the permeability-increasing etching acid and the pore-expanding acid on the D2 core, an enlarged complex pore network is formed in the core and part of it penetrates the interior of the core.

[0083] Example 3

[0084] Taking the engineering transformation of Well X1 in Oilfield B as the implementation object, use the deep etching pore acidification method applicable to high-calcium reservoirs for transformation. The specific steps are as follows:

[0085] S1 Obtain the geological data of Well X1 in Oilfield B. The mineral components of this reservoir: the calcium component M Ca = 76.3%, the silica component M Si = 23.7%, the shale component M m = 13.5%, the hard silica component M q = 10.2%. The target well reservoir is a high-shale limestone reservoir. The average gas logging permeability of the reservoir K = 750 mD, the fracture pressure of the reservoir P f = 28 MPa, the average reservoir pressure P r = 13 MPa, the well depth H = 1200 m, and the reservoir temperature T = 70°C.

[0086] S2 Determine the construction pressure P t and the construction displacement Q t of the fluid injected into the well. The process is as follows:

[0087] S2-1 Determine the construction displacement and construction pressure of the permeability-increasing etching acid injection

[0088] Use the core sampled from the reservoir and set different flow rates for the core displacement experiment of the permeability-increasing etching acid to obtain the flow rate-pressure difference relationship curve, and obtain the inflection point of the displacement pressure P* = 0.6 MPa and the inflection point of the displacement flow rate Q* = 2.6 ml / min. The diameter of the wellbore in the injection interval D = 0.2 m, the length of the operation interval L = 100 m, the diameter of the core d = 0.025 m, and the diameter of the string d t = 0.1 m. Calculate that the construction displacement Q t of the permeability-increasing etching acid injection is not greater than 0.33 m 3 / min. Permeability-increasing etching pore acid: λ = 2.15, ρ = 1250 kg / m 3 , P λ = 7.9 MPa, the calculated construction pressure P for injecting the permeability-increasing etching pore acid t shall not be greater than 6.5 MPa;

[0089] S2-2 Determine the construction displacement and construction pressure for injecting the etching pore precipitation liquid and reaming acid

[0090] The construction displacement of the etching pore precipitation liquid and reaming acid is 1.5 m 3 / min;

[0091] Etching pore precipitation liquid: λ = 0.095, ρ = 900 kg / m 3 , P λ = 5.2 MPa, the construction pressure P of the etching pore precipitation liquid t is greater than 7.4 MPa and less than 22.4 MPa;

[0092] Reaming acid: λ = 0.12, ρ = 1100 kg / m 3 , P λ = 8.03 MPa, the construction pressure P of the reaming acid t is greater than 7.83 MPa and less than 22.83 MPa.

[0093] S3 Determine the injection volume of the fluid entering the well:

[0094] Permeability-increasing etching pore acid: The dosage per meter is 1 m 3 , and the total dosage is 100 m 3 ;

[0095] Etching pore precipitation liquid: 0.3 times the volume dosage of the permeability-increasing etching pore acid, and the total dosage is 30 m 3 ;

[0096] Reaming acid: The dosage per meter is 3 m 3 , and the total dosage is 300 m 3 .

[0097] S4 Inject the permeability-increasing etching pore acid into the reservoir according to the construction pressure and construction displacement obtained in S2: 5% ethanol + 4.75% ammonium chloride + 4.75% formaldehyde + 4.75% glucono-delta-lactone + 4.75% sodium fumarate + 9.5% glutamic acid diacetic acid + 0.95% ethylene glycol monobutyl ether + 1.9% acetic acid + 63.65% water, pH is between 4 - 5.

[0098] S5 Inject the etching pore precipitation liquid into the reservoir according to the construction pressure and construction displacement obtained in S2: 80% ethanol solution.

[0099] Shut in for 3 h at S6 to form complex micro-wormholes in the reservoir.

[0100] Inject reaming acid into the reservoir according to the construction pressure and construction displacement obtained in S2: 12% HCl + 6% oxalic acid + 1% oil-based imidazoline + 1% fluorocarbon surfactant + 1% ethylene glycol monobutyl ether + 79% water.

[0101] Inject displacement fluid: 3% NH4Cl, 1.3 times the volume of the injection pipeline, with a dosage of about 12.2 m 3 .

[0102] Shut in for 5 h at S9 and flow back.

[0103] Field B is a newly developed oilfield. In the initial stage, measures such as conventional acidification technology and diversion acidification technology were adopted. Due to the poor physical properties of the reservoir, the improvement effects were all poor. After adopting the deep etching pore acidification method for high-calcium reservoirs, the improvement multiple of a single well reached 6.8 times, and the stable production continued for more than 3 months after the improvement.

[0104] Example 4

[0105] Taking the engineering transformation of Well Z1 in Oilfield J as the implementation object, use the deep etching pore acidification method applicable to high-calcium reservoirs for transformation. The specific steps are as follows:

[0106] Obtain the geological data of Well Z1 in Oilfield J. The mineral components of this reservoir: calcium component M Ca = 81.9%, silica component M Si = 18.1%, shale component M m = 2.8%, hard silica component M q = 15.32%. The target well reservoir is a high-calcium reservoir. The average gas logging permeability of the reservoir K = 46 mD, the fracture pressure of the reservoir P f = 75 MPa, the average reservoir pressure P r = 51 MPa, the well depth H = 4600 m, and the reservoir temperature T = 125 °C.

[0107] Determine the construction pressure P t and construction displacement Q t of the fluid injected into the well. The process is as follows:

[0108] Determine the construction displacement and construction pressure of the permeability-increasing etching acid injection

[0109] Use the reservoir sampling core, set different flow rates for the core displacement experiment of the permeability-increasing etching acid respectively, obtain the flow rate-pressure difference relationship curve, and obtain the inflection point P * = 7.1 MPa of the displacement pressure and the inflection point Q *= 0.9 ml / min, the wellbore diameter D of the section where the fluid enters the well is 0.2 m, the length L of the operation section is 150 m, the core diameter d is 0.025 m, and the pipe string diameter d t = 0.1 m. The construction displacement Q of the acid injection for increasing permeability and corroding holes is calculated t not greater than 0.173 m 3 / min. Acid for increasing permeability and corroding holes: λ = 2.15, ρ = 1300 kg / m 3 , P λ = 8.67 MPa. The construction pressure P of the acid injection for increasing permeability and corroding holes t is not greater than 6.97 MPa;

[0110] S2-2 Determine the construction displacement and construction pressure of the corroded hole precipitation liquid and the reaming acid injection

[0111] The construction displacement of the corroded hole precipitation liquid and the reaming acid is 2 m 3 / min;

[0112] Corroded hole precipitation liquid: λ = 0.095, ρ = 900 kg / m 3 , P λ = 17.7 Mpa. The construction pressure P of the corroded hole precipitation liquid t is greater than 27.3 MPa and less than 51.3 MPa;

[0113] Reaming acid: λ = 0.12, ρ = 1100 kg / m 3 , P λ = 27.37 Mpa. The construction pressure P of the reaming acid t is greater than 27.77 Mpa and less than 51.77 Mpa.

[0114] S3 Determine the injection volume of the fluid entering the well:

[0115] Acid for increasing permeability and corroding holes: The dosage per meter is 1.2 m 3 , and the total dosage is 180 m 3 ;

[0116] Corroded hole precipitation liquid: 0.5 times the volume dosage of the acid for increasing permeability and corroding holes, and the total dosage is 90 m 3 ;

[0117] Reaming acid: The dosage per meter is 5 m 3 , and the total dosage is 750 m 3 .

[0118] S4 Inject the permeability-increasing etching acid into the reservoir according to the construction pressure and displacement obtained in S2: 10% ethanol + 9% glucono delta-lactone + 9% pentasodium diethylenetriaminepentaacetate + 0.9% ethylene glycol monobutyl ether + 1.8% acetic acid + 69.3% water, with pH between 4 and 5.

[0119] S5 Inject the etching pore precipitation liquid into the reservoir according to the construction pressure and displacement obtained in S2: 80% ethanol solution.

[0120] S6 Shut in the well for 2 h to form complex micro-wormholes in the reservoir.

[0121] S7 Inject the pore-expanding acid into the reservoir according to the construction pressure and displacement obtained in S2: 20% HCl + 2% oil-based imidazoline + 1% fluorocarbon surfactant + 1% ethylene glycol monobutyl ether + 76% water.

[0122] S8 Inject the displacement fluid: 3% NH4Cl, 1.3 times the volume of the injection pipeline.

[0123] S9 Shut in the well for 3 h and then flow back.

[0124] Oilfield J is a newly developed oilfield. In the initial stage, conventional treatment measures such as clean acidification and gelled acidification were adopted, and the improvement ratio was about 5 times. After adopting the deep etching pore acidification method for high-calcium reservoirs, the improvement ratio of a single well reached 8.3 times.

Claims

1. A deep etching hole acidification method applicable to high-calcium reservoirs, which successively includes the following steps: S1 Obtain geological data, including reservoir mineral components, reservoir permeability K, reservoir fracture pressure P f , average reservoir pressure P r and well depth H; S2 Determine the construction displacement Q of the fluid injected into the well t and the construction pressure P t , where the fluid injected into the well includes permeability-increasing etching acid, etching hole precipitation liquid, and hole-expanding acid; S3 Determine the injection volume of the fluid injected into the well. S4 Inject the permeability-enhancing etching hole acid into the reservoir according to the construction pressure and construction displacement obtained in S2. The permeability-enhancing etching hole acid is composed of 3-10% of a permeability enhancer and 90-97% of a pH-responsive phase-change etching hole acid. The permeability enhancer is methanol, ethanol or acetone. The pH-responsive phase-change etching hole acid is composed of the following components by weight percentage: 10-20% of a raw acid agent, 10-30% of a pore-expanding agent, 1-2% of a coalescing agent, 0.5-10% of a pH regulator, and the rest is water. The raw acid agent is one or more of ammonium chloride, formaldehyde, methyl formate, ethyl acetate, glucono delta-lactone. The pore-expanding agent is one or more of sodium benzoate, disodium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, pentasodium diethylenetriaminepentaacetate, tetrasodium glutamate diacetate, sodium fumarate, benzoic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, glutamate diacetic acid, fumaric acid. The coalescing agent is one or more of ethylene glycol monoethyl ether, ethylene glycol monopropyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, diethylene glycol monohexyl ether, propylene glycol n-butyl ether, dipropylene glycol n-butyl ether, dipropylene glycol monomethyl ether, tripropylene glycol monomethyl ether, propylene glycol phenyl ether, propylene glycol tert-butyl ether. The pH regulator is one or more of formic acid, acetic acid, sodium formate, sodium acetate. S5 Inject the etching hole precipitation liquid into the reservoir according to the construction pressure and construction displacement obtained in S2. The etching hole precipitation liquid is a methanol or ethanol solution with a concentration higher than 80%. S6 Shut in the well for 2-3 h to form complex micro-wormholes in the reservoir. S7 Inject the pore-expanding acid into the reservoir according to the construction pressure and construction displacement obtained in S2. The pore-expanding acid is composed of the following components by weight percentage: 10-20% of an acid solution, 0-20% of a soluble consolidant, 3-5% of a comprehensive additive, and the rest is water. The acid solution is hydrochloric acid, acetic acid or formic acid. The soluble consolidant is one or more of oxalic acid, sodium oxalate, potassium oxalate, phosphoric acid, sodium phosphate, citric acid, sodium citrate. The comprehensive additive is composed of an inhibitor, a surfactant and a mutual solvent, all of which are conventional additives used in oilfield acidification. S8 Inject a displacement fluid. S9 Shut in the well for 1-5 h and flow back.

2. The deep etching pore acidification method applicable to high-calcium reservoirs according to claim 1, characterized in that In the step S1, the reservoir mineral components refer to the calcareous component M Ca , the siliceous component M Si , the argillaceous component M m , and the hard silicon component M q .

3. The deep etched hole acidification method applicable to high calcium reservoirs according to claim 1, characterized in that, The process of step S2 is as follows: S2-1 Determine the construction displacement and construction pressure for injecting the permeability-enhancing etching hole acid. Using reservoir cores or artificial cores, core displacement experiments of acid for increasing permeability and etching pores are carried out with different flow rates respectively, the flow rate - pressure difference relationship curve is obtained, and the inflection point P of the displacement pressure is obtained. * And the inflection point Q of the displacement flow rate * , and the construction displacement Q of the acid for increasing permeability and etching pores is obtained t And the construction pressure P t : ； S2-2 Determine the construction displacement and construction pressure for injecting the etching hole precipitation liquid and the pore-expanding acid. The construction displacement Q of the etching hole precipitation liquid and the reaming acid t Take the value of 0.3 - 2 m 3 / min, related to the equipment parameters; Construction pressure P of etch hole precipitation liquid and hole expansion acid t : ； In the formula, d is the core diameter, m; D is the wellbore diameter of the well section into the well, m; L is the length of the operation well section, m; ρ is the density of the fluid entering the well, kg / m 3 ; P λ is the injection pressure loss of the fluid injected into the well, MPa; g is the acceleration due to gravity, m / s 2 ; λ is the friction coefficient of the fluid injected into the well; d t The diameter of the string for injecting fluid into the well, m; H is the well depth, m.

4. The deep etched hole acidification method applicable to high calcium reservoirs as described in claim 1, characterized in that, The step S3 includes: Permeability-increasing etching acid: Determined by the length of the modified section, with a dosage of 0.5 - 2 m per meter 3 ; Etching hole precipitation liquid: 0.3-0.5 times the volume dosage of the permeability-enhancing etching hole acid. Reaming acid: Determined by the length of the section to be modified, with a dosage of 2 - 6 m per meter 3 .

5. The deep etching pore acidification method applicable to high-calcium reservoirs according to claim 1, characterized in that, In step S4, the permeability-enhancing etching hole acid is prepared as follows: Mix 10-20% of the raw acid agent, 10-30% of the pore-expanding agent, 1-2% of the coalescing agent and water and stir evenly, and add the pH regulator until the pH value of the solution is between 3 and 6.

6. The deep etched hole acidification method applicable to high calcium reservoirs as described in claim 1, characterized in that, In the step S7, for conventional high-calcium reservoirs, no soluble consolidant is added to the reaming acid; for high-argillaceous limestone reservoirs, a soluble consolidant is added to the reaming acid.

7. The deep etched hole acidification method applicable to high calcium reservoirs according to claim 1, characterized in that In the step S7, the corrosion inhibitor is an aldehyde-ketone-amine condensate, an alkynol, a thiourea, or an imidazoline derivative, the surfactant is a fluorocarbon surfactant or a quaternary ammonium salt surfactant, and the mutual solvent is ethylene glycol monobutyl ether, diethylene glycol monobutyl ether, or propylene glycol monomethyl ether.

8. The deep etched pore acidification method applicable to high calcium reservoirs according to claim 1, characterized in that In the step S8, the displacement fluid is a 3% NH4Cl solution, a 3% KCl solution, or water, and the injection volume is 1.2 - 1.5 times the volume of the injection pipeline.

9. The deep etching pore acidification method applicable to high-calcium reservoirs according to claim 1, characterized in that In the step S9, when the reservoir temperature is higher than 120°C, the shut-in time is 1 - 3 h; when the reservoir temperature is lower than or equal to 120°C, the shut-in time is 2 - 5 h.

Images