RU2660967C1 - Method of treating non-uniform permeability oil reservoir by injection of invert emulsion - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: invention relates to the development of oil fields and can find application in the development of an oil reservoir with heterogeneous permeabilities of flooded layers for regulating the input profile of a well and limiting the water inflow in the production well by equalizing the permeability heterogeneity of the formation. In the method for treating a non-uniform permeability oil reservoir by injection of an invert emulsion obtained by mixing the emulsifier and an aqueous solution in a certain proportion, an emulsifier consisting of an oxyethylated alkylphenol AF₉-6 and oleic acid in a ratio of 2:1, as well as a benzene-containing fraction, the total concentration of oxyethylated alkylphenol AF₉-6 and oleic acid in the emulsifier is 15–39 %, the rest is a benzene-containing fraction, as an aqueous solution, mineral water is used, before injecting the emulsion determine the allowable injection pressure and injectivity of the well, with injectivity below 250 m³/day emulsifier is mixed before pumping with mineralized water in a volume ratio of 2:1, and when the injectivity is above 250 m³/day – in a ratio of 1:2, with the injection in both cases conducted with pressure control, when the injection pressure is increased by 1.1–1.2 times from the initial pressure, the volume ratio of mineralized water in the emulsion is doubled to a ratio of 1:4, with a further increase in pressure of 1.1–1.2 times the ratio is increased to 1:10 and then successively doubled to 1:40, while the injection pressure should not exceed 0.95 of the allowable pressure.

EFFECT: increased formation coverage due to more uniform distribution of the emulsion along the reservoir, increased aggregative stability of the invert emulsion and improved rheological properties of the injected emulsion.

1 cl, 3 tbl, 2 ex

Description

The invention relates to the development of oil fields and can find application in the development of an oil reservoir with heterogeneous permeability waterfloods for regulating the injectivity profile of the injection well and limiting water inflows in the producing well by leveling the permeability heterogeneity of the formation.

Known emulsifier emulsifier, which is a mixture of esters of oleic, linolenic, linoleic, and resin acids contained in tall oil distillate, and triethanolamine, which is used to obtain invert emulsions (Emulsion is an emulsifier of invert emulsion drilling fluids / E.G. Kister and others] // RNTS. Drilling. - 1974. - No. 12. - S. 15-18).

The disadvantages of the invention include the fact that due to the high viscosity of both the emulsifier itself and the emulsion obtained on the basis of the emulsion, it is technologically difficult to pump the invert emulsion into the well in the cold season.

A known method of isolating water inflow in production wells (RF patent No. 24710600 C2, EV 33/138, publ. 12/27/2012. Bull. No. 24), including the injection of the inverse emulsion, characterized in that they use the inverse emulsion, including Neftenol NZ as an emulsifier or Neftenol NZ-TAT, and the injection of the reverse emulsion into the production well is alternated with the injection of water into it with the formation of several alternating layers of reverse emulsion and water in the well.

As a liquid hydrocarbon, a hexane fraction, stable gasoline, gas condensate, diesel fuel, and low-viscosity oil are used. Emulsifier Neftenol NZ is a hydrocarbon solution of acid esters of tall oil and triethanolamine.

The disadvantage of this method of isolating water inflow is the low aggregate stability of the invert microemulsion, which is easily destroyed under the influence of reservoir pressure, and the insulating ability of the emulsion decreases.

Closest to the proposed technical solution is a method of treating an oil reservoir by injection of an invert microemulsion (RF patent No. 2381250 C1, C09K 8/584, ЕВВ 43/22, publ. 02/10/2010 Bull. No. 4) obtained by mixing the emulsifier Neftenol and an aqueous solution of chloride calcium, characterized in that Neftenol NZ-TAT is used as Neftenol, it is pre-mixed with the specified aqueous solution in a volume ratio of 1: 1, and then the resulting coffee-with-milk emulsion is mixed with the remainder of the specified aqueous solution at their simultaneous injection in the following ratio of components, wt. %:

Neftenol NZ-TAT - 2.5-8.0;

calcium chloride - 0.3-12.0;

water is the rest.

The disadvantages of the method are that in the process of pumping emulsions, the filtration and reservoir characteristics of the formation (well) are not preliminarily evaluated — injectivity and allowable injection pressure. As a result of this, difficulties may arise in the process of emulsion injection due to the mismatch between the formation filtration parameters and the viscosity properties of the emulsion system. As a result of mixing the emulsion according to the “coffee with milk” prototype with the remaining part of the aqueous solution, a sharp increase in the viscosity of the injected emulsion occurs and the injection process is complicated, high injection pressure is required, which can lead to destruction of the integrity of the formation. In addition, due to its low mobility, a highly viscous emulsion loses its ability to penetrate deep into the formation and as a result, the formation coverage is reduced. Another disadvantage of this method is the low aggregative stability of the emulsion system (ES), which leads to the fact that the emulsion in the formation is easily destroyed by the applied voltage, and the coverage of the formation by the impact and, accordingly, the oil recovery efficiency are reduced.

The technical objectives of the proposed method for processing a heterogeneous permeability of an oil reservoir are: increasing the coverage of the reservoir due to a more uniform distribution of the emulsion over the reservoir, increasing the aggregate stability of the invert emulsion and improving the rheological properties of the injected emulsion due to the correctly selected ratio of emulsifier and water in accordance with the injectivity of the reservoir, preservation of reservoir properties of the reservoir by controlling the injection pressure.

Technical problems are solved by the method of processing a heterogeneous permeability of an oil reservoir by injection of invert emulsions obtained by mixing an emulsifier and an aqueous solution in a certain proportion.

What is new is that an emulsifier is used, consisting of oxyethylated alkyl phenol AF ₉ -6 and oleic acid in a 2: 1 ratio, as well as a benzene-containing fraction, the total concentration of oxyethylated alkyl phenol AF ₉ -6 and oleic acid in the emulsifier is 15-39%, the rest is a benzene-containing fraction, mineralized water is used as an aqueous solution, before injection of the emulsion, the permissible injection pressure and injectivity of the well are determined, when the injectivity of the well is below 250 m ³ / day, the emulsifier is mixed before injection with mineralized water in a volume ratio of 2: 1, and with an injection rate above 250 m ³ / day, in a ratio of 1: 2, while the injection in both cases is carried out with pressure control, with an increase in injection pressure of 1.1-1, 2 times from the initial double the volume ratio of saline water in the emulsion to a ratio of 1: 4, with a further increase in pressure 1.1-1.2 times, the ratio is increased to 1:10 and then subsequently doubled to 1:40, while the injection pressure does not must exceed 0.95 of the permissible pressure value.

As the emulsifier, invert emulsions, an emulsifier is used comprising oxyethylated alkylphenol AF -6 ₉ and oleic acid in the ratio 2: 1 at a total concentration of 15-39%, and the benzene fraction - the rest (RF Patent №2613975 C1 B01F 17/00, C09K 8/00 , C11D 1/04, C11D 3/43, published March 22, 2017, Bull. No. 9). The emulsifier is a clear liquid from light brown to brown in color with a density at 20 ° C of at least 0.750 g / cm ³ .

Mineralized (waste, produced) water with a salinity of 1 to 300 g / l is used as water.

SUMMARY OF THE INVENTION

In the development of oil fields, technologies are widely used based on pumping into the formation of stable hydrophobic (invert) emulsions prepared under surface conditions. Such emulsions are pumped into injection wells to even out the front of oil displacement by water, as well as for selective waterproofing in production wells.

In the proposed method, to increase the coverage of the formation by exposure, it is proposed to first pump the emulsion with a low viscosity, then pump the emulsion with an increasing viscosity. A low-viscosity emulsion easily penetrates into reservoirs with low permeability, due to which the radius of penetration increases, and previously not covered interlayers are involved in the development. Furthermore, the proposed method of processing an inhomogeneous oil permeability contributes to the aggregation stability of invert emulsions due properly chosen ratio of the emulsifier and water, and using an emulsifier consisting of ethoxylated alkyl phenol AF -6 ₉ and oleic acid in the ratio 2: 1, whereby the injected emulsion withstands repeated dilution with water in reservoir conditions with an increase in viscosity.

To increase the efficiency of oil recovery and increase the coverage of the reservoir by exposure, it is proposed to determine the allowable injection pressure and well injectivity before emulsion injection. Depending on the injectivity of the well, an initial ratio of emulsifier and saline water is selected. With a well injectivity below 250 m ³ / day, a 2: 1 ratio is selected, because with this ratio of emulsifier and water a low-viscosity emulsion is formed, the viscosity of which, for example, at a shear rate of 27 s ^-1 is 39 mPaПs (table 1). An emulsion with such a viscosity is easily pumped and, thanks to its hydrophobic properties, penetrates into low-permeability oil-saturated formations that were not previously covered by the impact. With further dilution of this emulsion with water to a ratio of 1: 1, the viscosity increases to a value of 184 mPa⋅s, which is an order of magnitude lower than the viscosity of the emulsion of the prototype under similar conditions - 1880 mPa⋅s. With an increase in injection pressure by 1.1-1.2 times from the initial, the volumetric ratio of mineralized water in the emulsion is doubled to a ratio of 1: 4 and then from 1:10 to 1:40, taking into account the pressure, which should not exceed 0.95 of the permissible pressure values.

When the injectivity of the well is above 250 m ³ / day, the ratio of the emulsifier and saline water is 1: 2, the emulsion viscosity in this case is 1080 mPa⋅s. The higher the injectivity of the well (formation), the higher the permeability of the formation or the greater the volume of washed zones of the formation, containing mainly water. Therefore, to create sufficient filtration resistance, contributing to an increase in reservoir coverage under these conditions, it is necessary to pump a more viscous emulsion obtained by mixing the emulsifier and water in a ratio of 1: 2. During emulsion injection, the injection pressure is constantly monitored. With an increase in injection pressure by 1.1-1.2 times from the initial one, the volume ratio of mineralized water in the emulsion is doubled to a ratio of 1: 4, while if the injection pressure increases by no more than 1.1-1.2 times, the ratio again increases water in the emulsion system to a value of 1:10. These operations can be repeated until the ratio of water in the emulsion system is 1:20, 1:40. The more water is contained in the invert emulsion, the higher its viscosity and the higher the filtration resistance created by the specified emulsion. To promote such a system in the formation, much more effort is required (increase the injection pressure), therefore, the injection pressure is controlled so that there is no violation of the integrity of the formation or the destruction of the emulsion system itself. The injection pressure should not exceed 0.95 of the permissible pressure values established by the geological service for this well.

Table 1 shows the values of the dynamic viscosity of the emulsion system according to the proposed method and the prototype based on the emulsifier Neftenol NZ-TAT obtained by diluting with water in ratios from 2: 1 and 1: 1 to 1:40

As can be seen from table 1, the initial viscosity of the emulsion systems is significantly different, the viscosity of the emulsion according to the prototype is 27 times higher than the viscosity of the emulsion system according to the proposed method with an emulsifier / water ratio of 2: 1 at the same shear rate of 5.7 s ^-1 , for example, 5440 mPa⋅s and 206 mPa⋅s, respectively. When the ratio of emulsifier and water in the emulsion according to the proposed method is equal to 1: 2, as for the case when the method is applied when the injectivity of the well is above 250 m ³ / day, the viscosity of the specified emulsion (3310 mPa⋅s) is still lower than the viscosity of the emulsion according to the prototype.

The emulsion of the prototype has unsatisfactory rheological properties, which significantly complicate the injection process. An emulsion with such a viscosity is more difficult to pump, it is necessary to create additional energy costs like increasing the injection pressure, especially when the injectivity of the well is below 250 m ³ / day, which can destroy the integrity of the formation. In addition, the emulsion according to the proposed method withstands 40-fold dilution with water, while maintaining its technological properties, the emulsion of the prototype at this degree of dilution is stratified into water and the hydrocarbon phase.

It is known that the flow rate of concentrated invert emulsions in a porous medium decreases sharply over time even when maintaining a constant pressure drop, the so-called dynamic locking effect is created. Due to the fact that the viscosity of the injected emulsion according to the proposed method increases gradually, it is able to penetrate into a much larger pore space, starting from small pores. As a result, redistribution of subsequent filtration flows occurs and the reservoir coverage increases, which leads to an increase in oil recovery.

To evaluate the effectiveness of the emulsion composition by the method of laboratory testing of technologies for stimulating the formation through injection wells, it is possible through efficiency parameters such as resistance factor (FS) and residual resistance factor (OFS). FS is the ratio of the coefficient of mobility of water before exposure to the coefficient of mobility of the emulsion composition in a porous medium. OFS is the ratio of water mobility before exposure to water mobility after exposure to enhanced oil recovery (EOR) methods.

Table 2 shows the main conditions and test results on Devonian cores of the filtration properties of the proposed hydrophobic emulsion compositions. The increase in the coverage factor is judged by the value of the total SFC: the higher the SFS, the greater the coverage coefficient of the formation by the impact.

As can be seen from table 2, the experiments were carried out both with the same ratio of emulsifier and saline water, and with an increase in the ratio of water in the emulsion system. The first three series of experiments were carried out on cores with a permeability below 0.250 μm ² , therefore, the initial ratio of emulsifier and water in the injected emulsion was 2: 1. In experiments in which the ratio of emulsifier and water varied from 2: 1 to 1: 1, higher values of the residual resistance factor were obtained than in experiments with a constant ratio of emulsifier and water 2: 1. This indicates that an emulsion of variable composition with gradually increasing viscosity penetrates more evenly into the pore space of the core and increases the coverage of the formation by exposure.

When the emulsion was pumped with an emulsifier / water ratio of 1: 1, the injection pressure increased from 1.9 atm to 2.57 atm, the pressure increase exceeded 1.1-1.2 from the initial one, so further emulsion was stopped.

A series of experiments numbered 4-8 was carried out with core permeability above 250 μm ² , and the initial ratio of emulsifier and water in the injected emulsion was 1: 2. In this case, experiments 4-5 were carried out with the injection of emulsions of constant composition, and subsequent experiments 7-8 with a varying ratio of emulsifier and water (with an increase in the proportion of water in the emulsion) with control of the injection pressure to an acceptable value.

Comparison of the effectiveness of emulsion formulations from the injection method shows that when emulsion is injected with a constant ratio of emulsifier and water, the residual resistance factor is 1.5-6.6 times lower than OFS values when emulsion is injected with an increase in the ratio of water in emulsion from 1: 2 to 1: four. All investigated emulsion systems of variable composition, according to the proposed method, have high values of the residual resistance factor in the range from 6.8 to 28.8, exceeding the OFS values of the prototype by 2.4-10.1 times. Such high rates of residual resistance factor indicate a significant penetration of the emulsion into the pore space of the core as a result of injection of an invert emulsion by this method. Emulsions with constant ratios of emulsifier and water, respectively 2: 1 and 1: 4, also exceed the OFS values of the prototype 1.1-2.7 times.

The emulsion according to the proposed method in laboratory conditions is prepared as follows: the calculated volume of natural produced water with a salinity of 180 g / l is gradually introduced into the calculated volume of the emulsifier. The ratio of emulsifier and water in this case can be 2: 1, 1: 2, depending on the permeability of the test core. For better emulsification, the studied compositions were mixed using an RW-20 paddle type electric drive mixer (IKA Werke, Germany) at a speed of 500 rpm for five minutes. The values of dynamic viscosity were determined on a Rheomat RM-180 reoviscimeter (Mettler Toledo, Switzerland) at room temperature in the shear rate range (Dr) of 5.4-1280 s ^-1 . It was found that aqueous solutions of the emulsifier according to the proposed method after intensive mixing are stable inverse emulsions. The maximum dilution at which the prepared emulsions remain stable is 1:40.

An emulsion according to the prototype is prepared as follows: a coffee with milk emulsion is preliminarily prepared in 50 cm ^{3 of} Neftenol NZ-TAT emulsifier; 50 cm ^{3 of an} aqueous solution of 0.33% (by weight) calcium chloride solution is introduced. The resulting emulsion has a name due to the corresponding color “coffee with milk”.

Case Studies

To implement a technology based on a hydrophobic emulsion in field conditions, pumping units (HA) of the CA-320 type, tankers (AC) and a tank for preparing a working solution are required.

Example 1. Preliminarily, according to field studies, the injectivity of the selected well and the permissible injection pressure are determined. Well 1 is developing an oil reservoir with a thickness of 5 m and a porosity of 20%. The injectivity of the well 230 m ³ / day at a pressure on the water pipe of 8.0 MPa. Mineralization of water for the preparation of the composition is 110 g / l (density - 1070 kg / m ³ ). Allowable injection pressure is 13.5 MPa.

Since the injectivity of the well below 250 m ³ / day, the initial ratio of emulsifier and water is taken 2: 1. The emulsion is prepared either in volumetric containers of the AT or in the tanker of the AC. The calculated amount of emulsifier and mineralized water, for example 4 m ^{3 of} emulsifier and 2 m ^{3 of} mineralized water with a density of 1070 kg / m ^{3, is} pumped into the measured capacity of the NA or in the AC. The emulsion is mixed using a pumping unit, for 30 minutes until a homogeneous composition is obtained in a volume of 6 m ³ .

Then the resulting emulsion is pumped into the well. Injection pressure increased and stabilized at 8.3 MPa. The pressure increase does not exceed 1.1-1.2 times, so the next portion of the emulsion composition is prepared with an increased water content relative to the emulsifier with a ratio of 1: 1. 3 m ^{3 of} emulsifier and 3 m ^{3 of} mineralized water are pumped into a measured container. Everything is mixed up. The resulting emulsion is pumped into the well. Injection pressure increased to 8.9 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content relative to the emulsifier with a ratio of 1: 2. 2 m ^{3 of} emulsifier and 4 m ^{3 of} mineralized water are pumped into a measured container. Everything is mixed up. The resulting emulsion is pumped into the well. Injection pressure increased to 9.6 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content of 1: 4. To do this, 1.2 m ^{3 of} emulsifier and 4.8 m ^{3 of} mineralized water are pumped into the measured capacity by the pumping unit. Everything is mixed up. The resulting emulsion is pumped into the well. Injection pressure increased to 10.6 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content of up to 1:10. To do this, 0.5 m ^{3 of} emulsifier and 5.5 m ^{3 of} mineralized water are pumped into the measured capacity by the pumping unit. Injection pressure increased to 12.9 MPa. The pressure increase exceeds 1.2 times and besides, the pressure value is 0.96 of the permissible. Further emulsion pumping is stopped. After the emulsion system is pumped, 5-10 m ³ + volume of tubing are pumped into the formation.

Example 2. Preliminarily, according to field studies, the injectivity of the selected well and the permissible injection pressure are determined. Well 2 is developing an oil reservoir with a thickness of 8 m and a porosity of 22%. Well injectivity - 450 m³/ day at a pressure of 8.0 MPa in the water supply. Mineralization of water for the preparation of the composition - 170 g / l (density -1120 kg / m³) Allowable injection pressure is 15.0 MPa. Since the injectivity of the well is above 250 m³/ day, the initial ratio of emulsifier and water is taken 1: 2. The calculated amount of emulsifier and saline water, for example 2 m³ emulsifier and 4 m³ saline water with a density of 1120 kg / m³. The emulsion is mixed using a pump unit, for 30 minutes until a homogeneous composition is obtained in a volume of 6 m³.

Then the resulting emulsion is pumped into the well. Injection pressure increased and stabilized at 8.8 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content relative to the emulsifier with a ratio of 1: 4. For this, 1.2 m ^{3 of} emulsifier and 4.8 m ^{3 of} mineralized water are pumped into the tank by a pumping unit. Everything is mixed up. The resulting emulsion is pumped into the well. Injection pressure increased to 9.7 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content of up to 1:10. To do this, 0.5 m ^{3 of} emulsifier and 5.5 m ^{3 of} mineralized water are pumped into the measured capacity by the pumping unit. Injection pressure increased to 11.5 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content of up to 1:20. For this, 0.3 m ^{3 of} emulsifier and 5.7 m ^{3 of} mineralized water are pumped into the measured capacity by the pumping unit. Injection pressure increased to 13.2 MPa. The pressure increase does not exceed 1.2 times, so the next portion of the emulsion composition is prepared with an increased water content up to 1:40. An emulsion is prepared in the AC, for this 0.15 m ^{3 of} emulsifier and 5.85 m ^{3 of} mineralized water are pumped into the tank by a pumping unit. The injection pressure increased to 14.5 MPa and amounted to 0.97 of the permissible pressure value. The emulsion composition is stopped. After injection of the emulsion system, water is injected into the formation in a volume of 5-10 m ³ + tubing volume.

This approach to the implementation of the method is due to the feature of invert (hydrophobic) emulsions to significantly increase the viscosity and aggregative stability with increasing water content. A change in the water content in the emulsion, starting with lower values corresponding to an emulsion having a lower viscosity, and hence greater penetrating ability (mobility), to higher water contents in an emulsion having a higher viscosity, allows oil-saturated formations to be more widely involved in development and increase formation coverage by impact.

With a uniform distribution of the emulsion system in the formation, a more complete coverage of the formation occurs (without language formation) and the efficiency of oil displacement increases. Correctly selected ratio of emulsifier and water depending on the injectivity of the well improves the rheological properties of the emulsion system and facilitates the injection process, as well as increases the stability of the emulsion in reservoir conditions. Monitoring the injection pressure during the implementation of the method allows you to save the reservoir properties of the reservoir. Due to the above advantages of the method, there is an increase in the coverage of the formation by the impact compared to the prototype 2.4-10.1 times.

The present invention solves the problem of increasing the coverage of the formation due to a more uniform distribution of the emulsion over the formation, increasing the aggregate stability of the invert emulsion and improving the rheological properties of the injected emulsion due to the correctly selected ratio of emulsifier and water in accordance with the injectivity of the formation, preserving the reservoir properties of the formation due to control injection pressures, which are achieved by a method of treating a heterogeneous permeability of an oil reservoir by injection invert s emulsions obtained by mixing an emulsifier and an aqueous solution in a certain ratio.

Claims (1)

A method of treating a heterogeneous permeability of an oil reservoir by injection of an invert emulsion obtained by mixing an emulsifier and an aqueous solution in a certain proportion, characterized in that they use an emulsifier consisting of ethoxylated alkyl phenol AF ₉ -6 and oleic acid in a ratio of 2: 1, as well as a benzene-containing fraction, moreover, the total concentration of ethoxylated alkyl phenol AF ₉ -6 and oleic acid in the emulsifier is 15-39%, the rest is a benzene-containing fraction, I use as an aqueous solution t of saline water, before the injection of the emulsion, the permissible injection pressure and injectivity of the well are determined, when the injectivity of the well is below 250 m ³ / day, the emulsifier is mixed before injection with mineralized water in a volume ratio of 2: 1, and when the injectivity is above 250 m ³ / day - in the ratio 1: 2, while the injection in both cases is controlled by pressure, with an increase in injection pressure 1.1-1.2 times from the initial pressure, double the volume ratio of saline water in the emulsion to a ratio of 1: 4, with a further increase in pressure of 1, 1-1.2 times the ratio it is increased to 1:10 and then subsequently doubled to 1:40, while the injection pressure should not exceed 0.95 of the permissible pressure value.