RU2544931C1 - Carbonaceous oil deposit development method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: in a carbonaceous oil deposit development method that includes drilling of horizontal wells with a core sampling from the productive formation, performance of core laboratory tests, acid treatment and multiple hydraulic fracturing of the formation in these wells, according to the invention the core is sampled at different sections along the whole length of the horizontal shaft. The sampled core is subjected to the laboratory tests to determine the fracturing pressure, at that the sections are identified along the shaft where the minimum fracturing pressure P_min, MPa, and the maximum fracturing pressure P_max, MPa is required. Each section is treated by acid; at that the acid concentration for each section is set as identical. During the acid treatment each treated section of the formation is isolated temporarily by packers from the remaining part of the well. Then multiple proppant hydraulic fracturing of the formation is made under pressure that does not exceed P_max. At that at the sections, where P_max is required the acid treatment is performed in a volume of Q_max, m³/m, at the sections where P_min is required the acid treatment is performed in a volume not exceeding 10% of the maximum value. At the remaining sections the volume of the injected acid is defined proportionally to the obtained fracturing pressure in compliance with the following ratio: $${\text{Q}}_{\text{n}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{n}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}},$$

where Q_n is the specific volume per meter of the thickness, which is required for the injection to the n^th section of the formation along the horizontal shaft, m³/m, P_n is the required fracturing pressure at the n^th section of the formation along the horizontal shaft, MPa.

EFFECT: improved sweep efficiency and increased oil recovery of the oil deposit.

1 dwg

Description

The invention relates to the oil industry and may find application in the development of low-permeability heterogeneous carbonate oil deposits.

A known method of hydraulic fracturing of a carbonate formation, including perforation of the walls of the well in the required interval of the well with channels with a depth of at least the length of the stress concentration zone in the rocks from the well bore, descent of the tubing string with a packer into the well, sealing the annulus with a packer above the perforation interval, filling the well process fluid for 0.2-0.4 wellbore volume. The gelled fracturing fluid is injected into the well in equal portions in 3-5 cycles with the injection of acid portions of 0.7-0.75 volumes of the gelled fracturing volume after them; at the end of the last cycle, salable oil or fresh water is pumped in a half times the volume of the pipe string with subsequent exposure of 1-2 hours, remove the reaction products of the acid with the rock, remove the packers and remove it from the pipe string from the well (RF patent 2455478, class E21 B43 / 267, E21 B43 / 27, publ. 10.07.2012).

The disadvantage of this method is its low efficiency when carried out in a heterogeneous formation, especially containing low permeability sections. Accordingly, the oil recovery of the known method is low.

The closest in technical essence to the proposed method is a method of hydraulic fracturing of a carbonate formation, including perforation of the walls of the well in the required interval of the well with channels of depth not less than the length of the stress concentration zone in the rocks from the well bore, descent of the tubing string with a packer into the well, sealing the annulus the space of the packer above the perforation interval, conducting hydraulic fracturing by injecting a gel-like fracturing fluid into the well pami and acid. Hydraulic fracturing of the carbonate formation is carried out sequentially in several stages, moreover, at the first stage, a gel-like fracture fluid is pumped in a volume of at least 6 m ³ , at the second stage, a gel-like fracture fluid is injected in a mixture with a proppant, and metal spheres with a fractional composition 12 are used as proppant / 18, or 16/20, or 20/40 mesh, made of magnesium metal, and the proppant is injected in batches with a gradual increase in its concentration in a mixture with a gel at the third stage, pumping liquid is pumped - industrial water in an amount equal to the internal volume of the tubing string lowered into the well; at the fourth stage, hydrochloric acid is pumped in a volume of at least 0.6-0.7 of the total volume of the prepared gel-like liquid rupture, at the fifth stage pumping liquid is pumped - industrial water in an amount equal to the internal volume of the tubing string lowered into the well, plus 0.2 m ³ (RF patent No. 2509883, cl. E 21 B 43/267, E21 B43 / 27, publ. 03/20/2014 - prototype).

The disadvantage of this method is the low coefficient of coverage and low oil recovery in the development of a heterogeneous reservoir. Carrying out proppant hydraulic fracturing technology at the beginning leads to hydraulic fracturing along a section of the formation that requires less hydraulic fracturing pressure and is characterized by better reservoir properties. Subsequent injection of acid leads not only to a reaction with magnesium, but also to the rock itself, which further increases the permeability of this area. As a result, lower permeability areas remain undeveloped.

The proposed invention solves the problem of increasing the coverage ratio and increasing oil recovery of oil deposits.

The problem is solved in that in a method for developing a carbonate oil reservoir, including drilling horizontal wells with coring in a producing formation, conducting laboratory tests of the core, acid treatment and multiple hydraulic fracturing in these wells, according to the invention, cores are taken in different areas along the entire length of the horizontal the trunk, laboratory tests are carried out on the selected core to determine the fracture pressure, while identifying areas along the trunk where minimal P _min , MPa, and maximum P _max , MPa, hydraulic fracturing pressure, the acid treatment of each section is preliminarily carried out, and the acid concentration for each section is set the same, during the acid treatment, each treated section of the formation is temporarily isolated by packers from the rest of the well, then multiple proppant hydraulic fracturing under pressure not exceeding P _max , and in areas where P _max is required, acid treatment is carried out in a volume of Q _max , m ³ / m, where P _min , acids are required new processing is carried out in a volume of not more than 10% of the maximum, i.e. Q _min = 0 ... 0.1 · Q _max , in the remaining sections the volume of injected acid is determined in proportion to the hydraulic fracture pressures according to the ratio:

, $${\text{Q}}_{\text{n}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{n}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}}$$

,

where Q _n is the specific acid volume per meter of thickness required for injection into the n-th section of the formation along the horizontal wellbore, m ³ / m,

P _n - the required fracturing pressure in the n-th section of the reservoir along the horizontal trunk, MPa.

SUMMARY OF THE INVENTION

The oil recovery of a low-permeability heterogeneous carbonate oil reservoir, which has permeability sections differing by an order of magnitude, and developed by horizontal wells, is significantly affected by the reservoir coverage coefficient. To increase it, acid treatments and hydraulic fracturing are widely used. However, the heterogeneity of the reservoir along the horizontal trunk leads to uneven production, because sections differ in permeability, required hydraulic fracture pressure, rock density, etc. The existing technical solutions do not fully allow under such conditions to conduct multiple hydraulic fracturing and acid treatment along the horizontal wellbore, while increasing the coverage factor and oil recovery. Low-permeability areas remain uninvolved, and high-permeability areas are developed and watered pretty quickly. The proposed invention solves the problem of increasing the coverage ratio and increasing oil recovery of oil deposits. The problem is solved as follows.

In FIG. 1 is a schematic illustration of a section of an oil reservoir, the reservoir of which is opened by a horizontal well with an acid treatment process. Designations: 1 - productive formation, 2 - horizontal well, 3 - horizontal wellbore, 4 - flexible pipes, 5 - filter, 6 - twin packers, I, II, III, IV - sections of formation 1 along horizontal well 3, characterized by the required pressure fracturing, h ₁ , h ₂ , h ₃ , h ₄ - average oil-saturated thickness of the corresponding sections I, II, III, IV.

The method is implemented as follows.

The oil reservoir section, the reservoir 1 of which is represented by the carbonate type of the reservoir and the purely oil zone, is opened with a horizontal well 2 with an open horizontal well 3 (Fig. 1). In the process of drilling from the reservoir 1, core samples are taken in different areas along the entire length of the horizontal trunk 3.

Next, laboratory tests are carried out on the selected core to determine the fracture pressure. Thus, sections along the trunk are identified where a minimum P _min , MPa, and a maximum P _max , MPa, fracturing pressure are required. For example, four sections of reservoir 1 were identified along the horizontal trunk 3 — I, II, III, IV with the corresponding average oil-saturated thicknesses h ₁ , h ₂ , h ₃ , h ₄ .

In areas where the maximum hydraulic fracturing pressure is required, acid treatment is designed and carried out, where the minimum hydraulic fracturing pressure is required, the acid treatment is carried out in a volume of not more than 10% of the maximum, i.e. Q _min = 0 ... 0.1 · Q _max . According to studies, the injection of acid into such areas in a volume greater than 10% of the maximum leads to uneven subsequent development of the reservoir and, accordingly, low oil recovery.

In the remaining sections, the volume of injected acid is determined in proportion to the fracture pressures obtained. Proportionality is a linear dependence, therefore, knowing P _min , P _max , Q _min , Q _max , we can write a system of equations of the form y = A · x + B:

(1) $$\begin{array}{l}{\text{Q}}_{\text{min}}=\text{A}\cdot {\text{P}}_{\text{min}}+\text{B}\\ {\text{Q}}_{\text{max}}=\text{A}\cdot {\text{P}}_{\text{max}}+\text{B}\end{array}$$

(one)

where A and B are the proportionality coefficients.

From the system of equations we find:

, (2) $$\text{A}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}$$

, (2)

(3) $$\text{B}={\text{Q}}_{\text{min}}-{\text{P}}_{\text{min}}\cdot \frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}$$

(3)

Thus, in the general case, if Q _n is the specific acid volume per meter of thickness required for injection into the n-th section of the formation along the horizontal well 3, m ³ / m, and P _n is the required fracture pressure in this n-th section , MPa, then the required acid volume can be determined from the ratio by substituting expressions (2) and (3) in the linear equation:

(4) $${\text{Q}}_{\text{n}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{n}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}}$$

(four)

According to studies, this approach allows you to effectively treat the bottom-hole zone of the formation with acid and align productivity along horizontal bore 3 for subsequent proppant fracturing. Also, acid treatment carried out with this approach reduces the difference in the required fracture pressure values.

The process of acid treatment is as follows: filter 5 is lowered into boreholes 3 on flexible pipes 4, and filter 5 is equipped with dual packers 6 at the front and rear. Filter 5 is lowered to the “toe” of barrel 3, i.e. packers 6 are packaged into section IV, acid is pumped in a volume of Q ₄ , squeezed with technical fluid, withstood the necessary time, packers are unpacked 6. Then filter 5 is moved to section III and the same operations are carried out. Similarly, the remaining sections are treated sequentially to the heel of the well. Moreover, the acid concentration for each plot is set the same. Temporary isolation of the treated section of the formation by packers 6 from the rest of the well prevents acid from entering other areas.

Then design and implement multiple proppant hydraulic fracturing under pressure not exceeding P _max according to any of the known technologies. Fracturing cracks are fixed with the proppant of some of the well-known brands.

Well 2 is put into operation. Development is carried out until the full economically viable production of oil deposits.

The result of the implementation of this method is to increase the coverage ratio and increase oil recovery of oil deposits.

An example of a specific implementation of the method

The oil reservoir section, the reservoir 1 of which is represented by Domanic deposits, the carbonate type of the reservoir and the purely oil zone, is opened with a horizontal well 2 with an open horizontal well 3 (Fig. 1) 400 m long. The oil zone thickness varies along the well within 8-15 m .

The reservoir lies at a depth of 1650 m, the permeability of the reservoir varies between 1-50 mD, averaging 8 mD, porosity 12%, initial reservoir pressure 16 MPa, oil viscosity under reservoir conditions 15 MPa · s.

In the process of drilling from the reservoir 1, core samples are taken in different areas along the entire length of the horizontal trunk 3.

Next, laboratory tests are carried out on the selected core to determine the fracture pressure. As a result, four sections of formation 1 were identified along the horizontal trunk 3 — I, II, III, IV. The average oil-saturated thickness of the sections are: h ₁ = 8 m, h ₂ = 12 m, h ₃ = 15 m, h ₄ = 11 m. The required fracturing pressures were: P ₁ = 33 MPa, P ₂ = 30 MPa, P ₃ = 26 MPa, P ₄ = 29 MPa.

Thus, P _min = P ₃ = 26 MPa, and P _max = P ₁ = 33 MPa.

In section I, where P _max is required, an acid treatment is designed and carried out, the volume and concentration of acid Q _{max are} calculated using one of the known methods. Accept for processing a solution of hydrochloric acid Hcl with a concentration of 16% and a specific volume per meter of formation thickness Q ₁ = Q _max = 2.0 m ³ / m. Taking into account the thickness of the reservoir of the first section, V ₁ = 2.0 · 8 = 16 m ^{3 is} obtained.

In section III, where P _min is required, a hydrochloric acid of the same concentration is designed and treated with a specific volume Q _max = 0.1 · Q _max = 0.1 · 2 = 0.2 m ³ / m. Given the thickness of the formation of the III plot receive V ₃ = 0.2 · 15 = 3 m ³ .

In sections II and IV, the volume of injected acid is determined in proportion to the hydraulic fracture pressures obtained and calculated by the formula (4).

м³/м, $${\text{<figure-callout id="2" label="Q" filenames="00000008.png" state="{{state}}">Q</figure-callout>}}_{\text{2}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{2}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}}=\frac{\text{0.2}-\text{2.0}}{\text{26}-\text{33}}\cdot \text{(thirty}-\text{26)}+\text{0.2}=\text{1,2}$$

m ³ / m

м³/м. $${\text{Q}}_{\text{four}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{four}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}}=\frac{\text{0.2}-\text{2.0}}{\text{26}-\text{33}}\cdot \text{(29}-\text{26)}+\text{0.2}=\text{1,0}$$

m ³ / m.

Given the thickness of the reservoir II and IV sections receive, respectively, V ₂ = 1.2 · 12 = 14.4 m ³ and V ₄ = 1.0 · 11 = 11 m ³ .

The process of acid treatment is as follows: filter 5 is lowered into bore 3 on flexible pipes 4, and the filter 5 is equipped with dual packers 6 in front and behind. Filter 5 is lowered to the “toe” of barrel 3, i.e. in section IV, packers are packaged 6. Special units are used for hydrochloric acid treatment of the bottom-hole zone of wells (for example, ЦА-320). The acid is pumped in a volume of V ₄ = 11 m ³ , pressed through with a technical fluid (oil). After the acid solution is pushed into the reservoir, the valves on the injection line are closed, the well is left for the reaction of the hydrochloric acid solution with the rock, and the pressure drop is monitored on the manometer.

Then packers 6 are unpacked, filter 5 is moved to section III and the same operations are carried out, acid is pumped in a volume of V ₃ = 3 m ³ . Similarly, the remaining sections of the formation with acid volumes V ₂ = 14.4 m ³ and V ₁ = 16 m ^{3 are} treated sequentially to the “heel” of the well. The bottomhole zone of the well is cleaned of reaction products by pistoning.

Design and implement multiple proppant hydraulic fracturing under pressure not exceeding P _max = 33 MPa. They also start from the last IV site and successively carry out hydraulic fracturing, ending with I site. Fracturing cracks are fixed with the proppant of some of the well-known brands (20/40 mesh).

Well 2 is put into operation. Development is carried out until the full economically viable production of oil deposits.

As a result of the development, which was limited by watering the production well from 2 to 98%, 135.6 thousand tons of oil were produced from the oil reservoir, the coverage coefficient was 0.673 units, the oil recovery coefficient (CIN) was 0.330 units. According to the prototype, ceteris paribus, 117.5 thousand tons of oil was produced, the coverage coefficient was 0.584 units, the oil recovery ratio (CIN) was 0.286 units. The increase in recovery factor by the proposed method is 0.044.

The proposed method allows to increase the oil recovery coefficient.

The application of the proposed method will solve the problem of increasing the coverage ratio and increasing oil recovery of oil deposits.

Claims (1)

A method for developing a carbonate oil reservoir, including drilling horizontal wells with core sampling in a productive formation, conducting core laboratory tests, acid treatment and multiple hydraulic fracturing in these wells, characterized in that the core is taken in different areas along the entire length of the horizontal well, in the selected core tests are carried out on the core to determine the fracture pressure, while identifying areas along the trunk where a minimum P _min , MPa, and a maximum P _{max are} required , MPa, hydraulic fracturing pressure, the acid treatment of each section is preliminarily carried out, and the acid concentration for each section is set the same, during the acid treatment, each treated section of the formation is temporarily isolated by packers from the rest of the well, then multiple proppant hydraulic fracturing of the formation is carried out under pressure, not exceeding P _max , and in areas where P _max is required, acid treatment is carried out in a volume of Q _max , m ³ / m, where P _min is required, acid treatment is carried out in no more than 10% of the maximum, i.e. Q _min = 0 ... 0.1 · Q _max , in the remaining sections the volume of injected acid is determined in proportion to the hydraulic fracture pressures, according to the ratio:
$${\text{Q}}_{\text{n}}=\frac{{\text{Q}}_{\text{min}}-{\text{Q}}_{\text{max}}}{{\text{P}}_{\text{min}}-{\text{P}}_{\text{max}}}\cdot {\text{(P}}_{\text{n}}-{\text{P}}_{\text{min}}\text{)}+{\text{Q}}_{\text{min}}$$

,
where Q _n is the specific acid volume per meter of thickness required for injection into the n-th section of the formation along the horizontal wellbore, m ³ / m,
P _n - the required fracturing pressure in the n-th section of the reservoir along the horizontal trunk, MPa.

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