RU2319727C1 - Composition for treatment of terrigenous reservoirs - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: invention relates to area of acid treatment of terrigenous reservoirs and unmuding of bottomhole formation zone. Acid composition contains 52.85-84.7% mud acid, 10-40% organic solvent mixable both with aqueous phase and with hydrocarbons, 0.2-2.0% surfactant, 5% acetic acid, and 0.10-0.15% hydrophobic silica "Polysil", said organic solvent being selected from isopropyl alcohol, butyl cellosolve, and liquid pyrolysis products. Composition exhibits lowered rate of interaction with reservoir rock, increased wettability of oil/water interface layers, high ability of washing out asphaltic-resinous paraffin deposits, high ability of removing iron hydroxide from treatment zone, and reduced corrosion activity.

EFFECT: improved performance characteristics.

2 cl, 4 tbl

Description

The present invention relates to the oil and gas industry, in particular to the field of acid treatment of terrigenous reservoirs and claying of the bottomhole formation zone.

It is known that terrigenous reservoirs are affected by a mixture of hydrochloric and hydrofluoric acids, called “clay acid” (P.M. Usachev. Hydraulic section of the reservoir. - M .: Nedra, 1986).

The interaction of hydrofluoric acid with silicate materials, quartz and kaolin of a terrigenous collector proceeds according to the reactions:

SiO ₂ + 4HF = SiF ₄ + 2H ₂ O

H ₄ AlSi ₂ O ₉ + 14HF = 2AlF ₃ + 2SiF ₄ + 9H ₂ O

Silicon fluoride formed as a result of the reaction, when interacting with water, in turn forms a silica hydrate, which, with a decrease in acidity, turns from sol to gel. To prevent the formation of silicic acid in the pore space, hydrofluoric acid is used only in a mixture with hydrochloric acid. The optimal content in the mixture is 3-5% HF and 8-15% HCl. Currently, in the industry produce finished clay acid containing 3-5% HF and 12-15% HCl.

Being an effective reagent for dissolving silicate materials and clays, clay acid, however, has a number of disadvantages, including:

- high rate of interaction with the reservoir rock, as a result of which the depth of acid penetration into the formation is reduced due to precipitation;

- poor wettability of the acid composition from the surface of the rocks of the boundary layers of oil and water due to the high surface tension;

- high corrosivity of the composition, adversely affecting oilfield equipment and cement stone.

To increase the permeability of acid solutions, improve oil washing properties, and also to slow down the rate of reaction with the rock, various surfactants of the type OP-10, Af ₉ -12, neftenol-VVD, ML-72, etc. are introduced into the composition. To reduce corrosion activity, they are introduced into clay acid corrosion inhibitors type SNPCH-6035, PB-5, etc.

However, the introduction of these reagents into the clay acid does not provide the necessary decrease in the rate of interaction of the acid solution with the reservoir rock.

In order to increase the coverage of the formation by acid exposure, numerous compositions and effective technological methods are known, which include preliminary blocking of highly permeable zones. This leads to the redistribution of the active acidic solution into the more colonized and less permeable sections of the bottom-hole formation zone (PZP). For these purposes, apply acid compositions thickened with biopolymers, polyacrylamide, CMC, guar gum, etc. (Express-inform. / VNIIOENG. Ser. "Oilfield business": Foreign experience. - Issue 23. - P.18-22) .

However, the introduction of water-soluble polymers into acidic compositions is often the cause of a decrease in well productivity or injectivity. The presence of high molecular weight compounds in the BCP that are firmly bonded to the walls of the filtration channels and to the surface of the mineral particles leads to a decrease in the permeability of the reservoir, and their dissolution and removal by conventional acidic solutions is difficult.

It is known that one of the effective methods of acidizing terrigenous reservoirs containing asphalt resinous paraffin deposits (AFS) is the preliminary injection of low-viscosity hydrocarbon solvents into the bottomhole formation zone.

Closest to the claimed invention (prototype) is a composition consisting of hydrochloric acid, hydrofluoric acid, an organic solvent, paraffin, nonionic surfactants and hydroxyethylene diphosphonic acid (OEDPK). The aromatic solvents used (toluene, AP-120/200 nefras, AO-130/150, etc.) dissolve and desorb the paraffin from the surface of the pore channels. The injection of the acid composition is preceded by treatment of the bottom-hole zone of the wells with a hydrocarbon suspension (diesel fuel or kerosene) containing sodium or potassium nitrite, or calcium and urea interacting with the acid composition with the release of heat and gaseous components (RF Patent RU No. 2181832).

However, the use of such compositions for treating the bottomhole formation zone of production wells does not preclude the formation of iron hydroxide, insoluble fluorine compounds, and the release of corrosion inhibitors. It should also be noted that the known composition does not have a complexing ability to Fe ⁺³ ions of technogenic origin, which, as a rule, is a serious danger when carrying out acid treatments. In addition, the mixing of aqueous solutions of acids with aromatic solvents leads to the separation of 2 immiscible phases, which negatively affects the washing ability and removal of the boundary layers of oil and water from the surface of the pore channels.

The preliminary injection of a hydrocarbon suspension containing insoluble (in diesel fuel) nitrites of alkali metals provided for in the known invention does not provide an increase in the formation coverage by acid exposure.

The aim of the invention is the development of an acid composition having a solubility of silicate materials and clays, comparable with the prototype, but having a reduced rate of interaction with the reservoir rock, increased wettability of the boundary layers of oil and water, high washing ability from ARPD, the ability to remove iron hydroxide and reduced corrosion activity.

This goal is achieved by the fact that the composition for treating terrigenous reservoirs containing clay acid, an organic solvent and a surfactant contains as an organic solvent a substance miscible with both the aqueous phase and the hydrocarbon, and additionally acetic acid and hydrophobic Silica "Polysil" in the following ratio of components, wt.%:

- clay acid 52.85-84.7 - specified solvent 10-40 - surfactant 0.2-2.0 - acetic acid 5 - "Polisil" 0.10-0.15,

and as the specified solvent is isopropyl alcohol, butyl cellosolve, liquid pyrolysis products.

Acetic acid in the acid composition serves as a complexing agent, converting iron oxides into soluble salts. "Polysil" (RF Patent No. 2152967) is a hydrophobic silicon dioxide with a discrete particle size of 0.005-0.04 microns, forming a stable suspension in a mixture of acids and an organic solvent. Due to the ultrafine dispersion of Polysil solid particles, the suspension easily penetrates into the pore space and causes temporary blockage of highly permeable zones.

Adsorbed in the pore channels of the PZP, Polysil reduces the contact surface of the acid solution with the rock and thereby reduces the rate of interaction of the acid, which allows to increase the penetration depth of the reagent. In this case, hydrophobization of the pore space occurs, which provides easier removal of loose-bound water from the bottomhole zone.

Polysil also acts as a thickener for an acid solution acquiring pseudoplastic properties. Studies have shown that when creating a depression on the reservoir, it will be removed from the highly permeable and partially low permeable filtration channels, which increases the success of acid treatment of the well.

As surfactants, Neftenol-VVD, Sinol AN-1, Neftenol ML, OP-10, Af ₉ -12, etc. are used.

An increase in the content of organic solvent up to 40 wt.%, As well as the introduction of surfactants and Polysil in the acid composition, contributes to a noticeable (by an order of magnitude) decrease in the rate of interaction of the acid composition with the rock and a decrease in corrosion activity to oilfield equipment.

The presence of hydrophilic and hydrophobic groups in the organic solvent ensures its miscibility with the aqueous phase of the acid solution with the formation of a homogeneous liquid and allows it to be considered as a surfactant. This achieves yet another requirement for acidic compositions for the treatment of PZP - the possibility of high wettability and removal of adsorbed layers of oil and water from the rock surface.

Laboratory studies found that the selected hydrocarbon liquids dissolve up to 20% by weight of asphalt-resinous paraffin deposits (ARPD), which is at the level of the currently used ARPD solvents in the oil industry, such as SNPH, toluene, nephras. The hydrocarbons used are easily mixed with oil in any proportions, without forming emulsions and tars.

The following are specific examples of the effectiveness of the acid composition in treating a terrigenous reservoir.

Examples of specific performance.

Examples 1-3

The degree of interaction was determined on samples of a natural core of a terrigenous reservoir. In order to establish the rate of interaction of the proposed acid composition (I) with the rock, the reaction kinetics was studied.

The results were compared with the prototype (II): Composition, wt.% I II III (prototype) (clay acid) one. Hf 3.0 3.0 3.0 2. Hcl fifteen fifteen fifteen 3. OEDFK - 5 - four. Butyl cellosolve twenty - - 5. Toluene - twenty - 6. Neonol AF ₉ -12 1,0 1,0 1,0 7. CH ₃ COOH, 98% conc. 5,0 - - 8. "Polisil" 0.1 - - 9. Water rest rest rest

For comparison, in parallel, studies were conducted on the rate of interaction of commodity clay acid of composition (III) with the rock. In the experiments, crushed rock samples of the North Kislor deposit with a clay content of 12.6% dried to constant weight were used.

Samples of samples (about 2 g) were poured with acid solutions in an amount of 25 ml and kept at room temperature for 15 minutes to 1 hour. After a predetermined time, the precipitate was filtered on a paper filter, washed until neutral and dried to constant weight. The processing efficiency was evaluated by the degree of dissolution of the precipitate as m ₂ / m ₁ , where m ₁ and m ₂ are the weight of the dried precipitate before and after treatment, respectively. The results are shown in tables.

As can be seen from the tables, the dissolution rates of samples with compositions I-III differ markedly. The reaction rate of acidic compounds (V ₀ ) with bentonite clay, defined as tg of the angle of inclination at the initial coordinate point, is (% solution / min):

for compositions: I - 0.5; II - 1.5; III - 7.5.

From the data obtained, it can be seen that the initial rate of interaction of the acid compositions I and II with the terrigenous rock of the collector is significantly lower than for commercial clay. Among the considered compositions, the proposed acid composition (V _0-I <V _0-II 3 times) has the lowest dissolution rate of terrigenous rocks. As indicated above, a decrease in the rate of interaction of the acid composition with the rock is an extremely important factor in the processing of low permeability reservoirs.

Examples 4-5

Table 1 shows comparative data on the solubility of the acid compositions I and II when interacting with bentonite clay, previously moistened with hydrocarbon.

Table 1 The solubility of bentonite clay known and proposed acid compositions for 6 hours at 20 ° C Experience number Acid composition The degree of dissolution of the oil-saturated sample of bentonite clay four. I 55.0 5. II (prototype) 43.5

As can be seen from the table, the proposed acid composition is 1.3 times more effective in dissolving an oil-saturated sample of bentonite clay compared to the prototype. In addition, studies have shown that the proposed acid composition I dissolves iron oxides more efficiently than the prototype, due to the presence of acetic acid in the acid composition. So the introduction of 10% by weight of F ₂ O ₃ into the acid compositions leads to the complete dissolution of iron oxides with composition I at 60 ° C for 15 minutes, and composition II for more than 24 hours.

Examples 6-11

The composition of the acid composition - the concentration of acids, their ratio, the content of the hydrocarbon solvent and its nature affect the rate of interaction with terrigenous rock of the reservoir and corrosion activity.

The corrosion activity of the developed acid composition was checked by standard methods on metal plates (steel 3) at room temperature and atmospheric pressure.

A 10 × 15 × 3 steel plate 3 was cleaned, washed in warm water, degreased with acetone or alcohol, and dried to constant weight. The plate was suspended on a nylon filament in a glass so that when the glass was filled with an acid solution, the end face of the plate was approximately 10 mm below the liquid level. The beaker was filled with an acidic composition, and the plate remained in this solution for a fixed time. After a predetermined time, the plate was removed from the acid, thoroughly washed in running water with a soft brush and repeatedly rinsed with hot distilled water. Moisture was removed from the surface with filter paper and the plate was dried to constant weight.

The corrosion rate was calculated by the formula

V = q / 10 ⁻⁴ · S · t,

where V is the corrosion rate, g / m ² hour;

q is the mass loss of the plate as a result of corrosion, g;

S is the surface subjected to corrosion, m ² ;

t is the duration of the test, hours.

The results obtained on the corrosion activity and on the solubility of natural core samples of the North Kislor deposit with clay content of 12.6% in acid compositions of various compositions are shown in table 2.

When comparing the results obtained, it is seen that the proposed acid composition containing up to 40 wt.% Organic solvent, in corrosion activity is 2.5-3 times lower than the known composition. With an increase in the concentration of acids in the composition, a decrease in the content of hydrocarbon solvent occurs, which, in turn, leads to a noticeable increase in the corrosion activity of the composition. In this case, due to a decrease in the washing ability, the degree of dissolution of the sample moistened with oil practically does not increase (cf. Example 7 and 8).

The decrease in the content of the mixture of acids in the composition leads to a noticeable decrease in the solubility of the sample (example 11), while the corrosion activity of the acid composition decreases slightly.

Examples 12-13

To test the solubility of silicate materials and clays in close to reservoir conditions on bulk models, filtration studies were performed to measure the permeability of samples treated with the proposed acid composition.

The experiments were carried out in the following sequence:

As a reservoir model, a bulk model with a length of 470 mm and an inner diameter of 30 mm filled with quartz sand containing 4.36% dry bentonite clay was used. The model was connected to a BPS-805 installation, flooded with Cenomanian water and allowed to stand for 12 hours to completely swell the clay. After determining the pore volume, one pore volume of oil was pumped into the bulk model of the reservoir and the pumping of Cenomanian water was continued until the stabilization regime was reached.

Having determined the residual oil saturation and Cenomanian water permeability, two pore volumes of acid composition were pumped into the reservoir model and, after exposure to the reaction for 8 hours at a temperature of 40 C, Cenomanian water permeability was re-determined.

Similar work was carried out on a bulk model of the reservoir with similar filtration characteristics, where instead of the developed composition, the composition obtained from the prototype was used. The results of filtration studies are shown in table 3.

As can be seen from the data in table 3, processing the bulk model of the reservoir with the proposed acid composition compared with the prototype increases the permeability of the sample by 1.2 times, although the concentration of clay acid in both cases was the same.

Table 3 The change in the permeability of the bulk model of the reservoir after injection of acid compositions at 75 ° C No. at measure The acid composition, wt.% The initial permeability, μ ₁ , MD Pore volume,% Residual oil saturation,% Ultimate
permeability, μ ₂ , MD μ ₂ / μ ₁ clay acid - 73.5 12. OEDFK -15 butyl cellosolve - 10 106.5 19.0 39.68 345 3.24 AF ₉ -12 - 1.5 (prototype) clay acid - 73.35 13. butyl cellosolve - 20 98.2 17.8 42.37 410 4.18 AF ₉ -12 - 1.5 acetic acid - 5 "Polisil" - 0.15

Examples 14-15

The effectiveness of the use of hydrophobic silica in the acid composition, which acts as a thickener, was evaluated by filtering the acid compositions through a sample of a fractured-pore collector. In order to block highly permeable cracks, 0.15% by weight of Polysil was introduced into the acid composition. As test samples, cores of a fractured-porous reservoir with close permeability and pore volume were selected.

The effect of Polysil on the filtration process was evaluated by the change in injection pressure and pH of the filtered fluid. The results of the study are shown in table 4.

Table 4 The effect of the composition of the acid composition on the change in pressure and pH of the medium during filtration at 75 ° C Example No. Composition, parts by weight Permeability, MD V _time % Pumping time, min P pumping, MPA pH of the filtered medium fourteen clay acid - 84.0
butyl cellosol - 10 310 22.4 5 0.11 1.9 10 0.11 1.9 Neftenol-VV - 1.0
CH ₃ COOH - 5 fifteen 0.09 1.8 fifteen clay acid - 83.85
butyl cellosol - 10
Neftenol-VV - 1.0
CH ₃ COOH - 5
"Polisil" - 0.15 298 20.8 5 0.11 1.9 10 0.13 2,4 fifteen 0.19 3.3

As can be seen from the data in table 4, the presence in the composition of “Polysil” (example 15) leads to an increase in the pumping pressure of the acid composition, which is due to the partial blocking of highly permeable zones by discrete particles of chemically modified silica (compare with example 14). This leads to a redistribution of the active acid solution into less permeable sections of the reservoir model. An increase in the interaction surface contributes to a more effective neutralization of the acid, which is expressed in a change in the pH of the medium (see table 4). Filtration studies showed that the introduction of more than 0.15 wt.% “Polysil” into the acid composition leads to a noticeable colmatation of the pore space and an increase in pumping pressure.

Claims (2)

1. A composition for treating terrigenous reservoirs containing clay acid, an organic solvent and a surfactant surfactant, characterized in that it contains as an organic solvent a substance miscible with both the aqueous phase and the hydrocarbon, and additionally acetic acid and hydrophobic Silica "Polysil" in the following ratio of components, wt.%: Clay acid 52.85-84.7 Specified Solvent 10-40 Surfactant 0.2-2.0 Acetic acid 5 "Polisil" 0.10-0.15 2. The composition according to claim 1, characterized in that it contains isopropyl alcohol, butyl cellosolve, liquid pyrolysis products as the specified solvent.