RU2034137C1 - Method for development of paraffin crude oil pools - Google Patents

Abstract

FIELD: oil producing industry. SUBSTANCE: water is injected through injection wells drilled vertically down to pool roof, horizontally in pool roof, and again vertically with entrance into pool. Minimal length of horizontal part of injection well ensuring heating of injected water up to temperature not less than temperature of paraffin precipitation is determined by formula given in invention description. EFFECT: reduced expenditures for construction of injection wells with prevention of paraffin precipitation from oil when nonheated water is injected in injection well. 3 dwg

Description

 The invention relates to the oil industry, in particular to a method for developing oil fields saturated with paraffin.

 There is a method of developing oil fields, which consists in injecting heated water into the reservoir [1] The disadvantages of this method are the need to create a system for maintaining reservoir pressure (RPM) and reservoir temperature (PPT) in the field, which is associated with the organization of a complex energy economy. With the implementation of such a system, the cost of extracted oil sharply increases due to an increase in energy costs.

 There is a method of developing deposits of paraffin oils, which cold water is injected into the reservoir with a flow rate that compensates for oil extraction by production wells and maintaining reservoir pressure [2] However, with this method, the reservoir temperature is lowered in the bottomhole formation zone, which is in the reservoir of oil saturated with paraffin , leads to the precipitation of dissolved paraffin from the oil inside the reservoir, an increase in the permeability heterogeneity of the porous medium, and a sharp decrease in oil production with increasing water cut ty of extracted products.

There is also a known development method involving heating water in a well. When moving along the barrel of the injection well to the bottom, it is heated by the deep heat of the Earth to a temperature not lower than the temperature of paraffin deposition from the oils. The length of the path of movement of the injected water and its flow rate is determined depending on the properties and temperatures of the rocks. With this in mind, conduct an inclined injection well at an angle to the vertical, providing the necessary length of the path of water passage [3]
In this method, as shown by the calculations, in order to obtain the temperature of the injected water at the bottom of the injection well equal to or higher than the reservoir temperature, it is necessary to have a significantly greater length of the inclined injection well compared to the vertical. This leads to an increase in the cost of drilling the deviated well.

 The aim of the invention is to reduce the cost of building injection wells, while maintaining the prevention of precipitation of dissolved paraffin from the oil when unheated water is pumped into the injection well.

ln

, (1) где L длина горизонтального участка скважины, м;
β- показатель теплопередачи, 1/м;
θ_o- температура нейтрального слоя Земли, приведенная к устью скважины, ^оС;
Г_N планетарный геотермальный градиент Земли, ^оС/м;
Н глубина кровли залежи нефти, м;
t_з.в. температура воды на входе в горизонтальный участок, ^оС;
t_о температура нагнетаемой воды, ^оС.The goal is achieved by the fact that in the method for developing a paraffin oil deposit, including water injection through injection wells and oil extraction through production wells, water is injected through injection wells drilled vertically to the top of the deposit, horizontally along the roof of the deposit and again vertically with the entrance to the reservoir, the minimum length of the horizontal part of the injection well, providing heating of the water injected into the reservoir to a temperature not less than the temperature of paraffin deposition, is determined by the formula:
L

ln

, (1) where L is the length of the horizontal section of the well, m;
β - heat transfer rate, 1 / m;
θ _o - temperature of the neutral layer of the Earth, reduced to the wellhead, ^C;
Г _N planetary geothermal gradient of the Earth, ^o C / m;
N depth of the roof of the oil deposits, m;
t _z.v. water temperature at the entrance to the horizontal section, ^о С;
t _{about the} temperature of the injected water, ^about C.

 The proposed method is as follows.

 To develop a reservoir of oil saturated with paraffin, according to the proposed method, a grid for placement of injection wells is selected. The formation pressure and the temperature of the formation, the temperature of oil saturation with paraffin (the temperature of paraffin deposition), the geothermal temperature gradient and the thermal properties of rocks at different depths are determined.

 Unheated water injected into the oil reservoir when passing from the wellhead to the end of the vertical well and then to the bottom of the well through its horizontal section is heated as a result of heat exchange with the rocks surrounding the well and should enter the face, into the formation with a temperature not lower than the temperature of paraffin deposition. The degree of water heating along its path from the wellhead to the bottom of the well depends on the thermophysical properties of the rocks, the temperature of the injected water at the wellhead, the geothermal gradient of the Earth, and the length of the horizontal section of the injection well.

H-1)+(t_у-θ_o +

exp(-β·H), (2) где t_у температура закачиваемой воды на устье нагнетательной скважины, ^оС;
θ_o- температура нейтрального слоя Земли, приведенная к устью скважины, ^оС;
β- показатель теплопередачи, 1/м;
Г_N планетарный геотермальный градиент Земли ^оС/м;
Н глубина кровли залежи нефти, м;
t_з.в. температура воды на входе в горизонтальный участок, ^оС.The heating of water in the vertical part of the wellbore is determined by the formula
t _{C. in} θ _o +

H-1) + (t _y -θ _o +

exp (-β · H), (2) where t is _the temperature of the injected water at the mouth of the injection well, ^о С;
θ _o - temperature of the neutral layer of the Earth, reduced to the wellhead, ^C;
β - heat transfer rate, 1 / m;
Г _N planetary geothermal gradient of the Earth ^about S / m;
N depth of the roof of the oil deposits, m;
t _z.v. water temperature at the entrance to the horizontal section, ^about C.

, (3) где λ_п средний коэффициент теплопроводности окружающих скважину горных пород, Вт/м˙^оС);
Q расход закачиваемой воды, м³/с;
С_рв. ˙ρ_в- объемная удельная теплоемкость закачиваемой воды, Дж/(кг˙^оС);
d_п средний коэффициент температуропроводности окружающих скважину горных пород, м²/с;
τ- время закачки воды, необходимое для создания оторочки, с;
d диаметр скважины на горизонтальном участке, м.The value of β is calculated by the formula:
β

, (3) where λ _{p is the} average coefficient of thermal conductivity of the rocks surrounding the well, W / m˙ ^о С);
Q flow rate of injected water, m ³ / s;
From the _rv. ˙ρ _в - volume specific heat of the injected water, J / (kg˙ ^о С);
d _{p the} average coefficient of thermal diffusivity of the rocks surrounding the well, m ² / s;
τ is the water injection time necessary to create the rim, s;
d borehole diameter in a horizontal section, m

(5)
По формуле (2) с учетом формул (3) (5) определяют температуру нагрева воды на вертикальном участке скважины t_з.в. В том случае, когда она окажется ниже температуры выпадения парафина, осуществляют ее дальнейший нагрев в горизонтальном участке скважины. Температуру нагрева воды на этом участке вычисляют по формуле, аналогичной формуле (2), с учетом того, что геотермический градиент в направлении горизонтали равен нулю, а температуру нейтрального слоя Земли θ₁ приводят к условиям залегания пласта на глубине Н по формуле:
θ₁=θ_o+ Г_N˙ Н (6)
Температуру на входе в горизонтальный участок берут равной t_з.в., а в конце участка принимают равной и выше пластовой температуры t_o, длину горизонтального участка обозначают L. С учетом принятых обозначений формула для нагрева воды геотермальным теплом на горизонтальном участке имеет вид:
t_o θ₁ + (t_з.в. -θ₁) ˙exp (β˙L) (7)
В этой формуле θ₁ определяют по формуле (6), β- по формуле (3), t_з.в. по формуле (2), t_о из условия выпадения парафина. Необходимую длину горизонтального участка нагнетательной скважины получают из соотношения (1)
L

ln

П р и м е р. Пласт, содержащий высокопарафинистую нефть, мощностью h 20 м, расположен на глубине Н 3800 м. Температура начала выпадения парафина в пласте t_o 60^оС. Средний коэффициент пористости пласта К_п 0,2. Необходимая закачка воды Q 3,5˙10^-3 м³/c. Удельная объемная теплоемкость нагнетаемой воды С_рв ˙ ρ_в= 4,2 ˙10⁶ Дж/(кг˙^oC).The value of the rim of the injected water V _in [m ³ ] is determined based on the thickness of the formation h [m] of the porosity coefficient K _p , the oil displacement coefficient K _n and the radius of the bottomhole formation zone r [m] according to the formula:
V _in K _n ˙K _n ˙π˙r ² ˙h (4)
Water injection time τ [c] is determined by the expression:
τ

(5)
According to the formula (2), taking into account formulas (3) (5), the temperature of water heating in the vertical section of the well _t.s.v. In the event that it is below the temperature of paraffin deposition, carry out its further heating in a horizontal section of the well. The temperature of water heating in this section is calculated by a formula similar to formula (2), taking into account the fact that the geothermal gradient in the horizontal direction is zero, and the temperature of the Earth’s neutral layer θ ₁ leads to bedding conditions at depth H by the formula:
θ ₁ = θ _o + Г _N ˙ Н (6)
The temperature at the entrance to the horizontal section is taken equal to t _z.v. , and at the end of the plot they take equal to and above the reservoir temperature t _o , the length of the horizontal plot is designated L. Given the accepted designations, the formula for heating water with geothermal heat in the horizontal plot is:
t _o θ ₁ + (t _{h.p. -θ 1} ) ˙exp (β˙L) (7)
In this formula, θ ₁ is determined by the formula (6), β- by the formula (3), t _z.v. by the formula (2), t _о from the condition for the precipitation of paraffin. The required length of the horizontal section of the injection well is obtained from the relation (1)
L

ln

PRI me R. Formation containing oil vysokoparafinistyh capacity h 20 m, is located at a depth of 3800 n m. The onset temperature of wax deposition in the formation t _o ^about 60 C. The average formation porosity coefficient K _f 0.2. Necessary water injection Q 3,5˙10 ^-3 m ³ / s. Specific volume heat capacity C _{p in} the injection water _in ˙ ρ = 4,2 ˙10 ⁶ J / (kg˙ ^o C).

The water temperature at the mouth t _at 24 ^o C, the temperature of the neutral layer of the Earth at the mouth θ _o = 15 ^o C.

The geothermal coefficient Г _N 0.03 ^о С / m, the coefficient of thermal conductivity of the rock and thermal diffusivity are respectively λ _p = 1.6 W / (m ˙ K), a _p 8˙10 ^-7 m ² / s. The diameter of the casing string is d0.168 m. The radius of the bottomhole zone is 35 m, the coefficient of oil displacement by water K _n 0.175.

3,3·10⁶ c
По формуле (3) определяют показатель теплопередачи
β

2,3·10^-4 1/м
По полученным данным определяют нагрев нагнетаемой воды геотермальным теплом при движении ее в вертикальном стволе скважины по формуле (2):
t_з.в θ_o +

(β·H-1)+

t_у-θ_o +

exp(-β·H)=
15 +

(2,3·10^-4·3800-1)+

24-15 +

=56,5^°C×
×exp(-2,3·10^-4·3800)=56,5^°C
Нагрев на горизонтальном участке скважины определяют по формуле (7). Если задана температура t_o 60^оС, то длину горизонтального участка нагнетательной скважины определяют по формуле (1) с учетом формулы (6):
L

ln

ln

207 м.Using the formula (4), the required amount of water is determined to create a rim: V _in K _n ˙K _p ˙π˙r ² ˙h 0.75˙0.2˙3.14 x x35 ² ˙20 11.5˙10 ³ m ³
By the formula (5) determine the time of water injection to create a rim:
τ

3.3 · 10 ⁶ s
By the formula (3) determine the heat transfer rate
β

2.3 · 10 ^-4 1 / m
According to the data obtained, the heating of injected water by geothermal heat is determined when it moves in a vertical wellbore according to the formula (2):
t _{C. in} θ _o +

(β · H-1) +

t _y -θ _o +

exp (-β · H) =
15+

(2.3 · 10 ^-4 · 3800-1) +

24-15 +

= 56.5 ^° C ×
× exp (-2.3 · 10 ^-4 · 3800) = 56.5 ^° C
Heating in the horizontal section of the well is determined by the formula (7). If the temperature t _o 60 ^о С is set, then the length of the horizontal section of the injection well is determined by the formula (1) taking into account the formula (6):
L

ln

ln

207 m.

 Feasibility study of the method.

 According to the proposed method, the injected water is heated to the temperature of the beginning of paraffin precipitation by the geothermal heat of the Earth without preheating it on the surface. Used injection well shorter than the prototype and lower cost.

According to the prior art for the conditions of the method of Example (heating to 60 ° ^C) requires deviated well with an inclination relative to the vertical, equal to ^about 31, and length of 4300 m.

According to the proposed method, the water is heated in a well, consisting of vertical and horizontal sections with a total length:
L _D H + L 3800 + 207 4007 m
To implement the heating of injected water according to the proposed method requires a shorter well length than the prototype:
ΔL = L _n -L _g 4300 4007 293 m
To assess the economic effect, use the ratio of the cost of deviated and horizontal wells.

To determine the cost of an inclined well, use the formula:
σ _n = 0.4˙ σ _o ˙ (1 + 1.5˙ К), (8) where σ _n is the cost of 1 m of a deviated well;
σ _about - the cost of 1 m of a vertical well;
K coefficient taking into account the deviation of the deviated well from the vertical.

For a deviation of more than 1000 m (conditions under consideration) K 1.78, formula (9) takes the form:
σ _n 1.47˙σ _about (9)
According to SUSN reference data on the cost of a horizontal well, there is information for a well with a horizontal length of 250 m:
σ _g σ _о ˙ (1.3-1.5), (10) where σ _g is the cost of 1 m of a horizontal well.

In FIG. 1 shows a comparison of injection wells drilled by the proposed method with the horizontal portion and slanted (prototype), the motion of the injected water is achieved in which the same heating to 60 ^C. The water injection below this temperature is considered unacceptable. The calculations are performed by (1) injection for various intensities and at different temperatures on the mouth 5, 15, 24 ^C. The dashed line designated wells of length related to the prior art, the solid lines to the proposed method. As can be seen from the obtained data, the existing achievements in horizontal drilling, including domestic one with a horizontal section length of 1000 to 1500 m, fully ensure the construction of injection wells that satisfy the conditions of geothermal heating of the injected water to a given temperature, while similar wells for the prototype are technically difficult .

 It turns out a significant gain in the length of the well by the proposed method in comparison with the prototype, which is implemented in the form of an economic effect, calculated by the formula (11) and shown in figure 2.

 The magnitude of the effect refers only to one deposit and one experimental site, and the widespread distribution of the proposed method will lead to a significant increase.

 The proposed method creates a real opportunity to refuse to heat the injected water using, for example, PTB 10/160 installations, which leads to additional costs for the injection of heated water in the development section considered in the example.

. (12)
Приведенные данные указывают на то, что уменьшение длины наклонной скважины при использовании предлагаемого способа может превосходить всю длину скважины с горизонтальным участком.Referring to FIG. 3 values of reducing the relative length of the well when applying the proposed method were determined by the formula:
L

. (12)
The data indicate that the decrease in the length of the deviated well when using the proposed method can exceed the entire length of the well with a horizontal section.

Claims (1)

METHOD FOR DEVELOPING A PARAFFIN OIL DEPOSIT, including water injection through inclined injection wells and oil extraction through production wells, characterized in that the injection wells are drilled vertically to the deposit roof for water injection, then horizontally along the roof and again vertically to the bottom, with the minimum horizontal length parts of the injection well are selected from the condition that the water injected into the reservoir is heated to a temperature not less than the temperature of paraffin deposition and determined in accordance with expression

where L is the length of the horizontal section of the well, m;
β heat transfer index, 1 / m, determined from the formula

where λ _{p the} average coefficient of thermal conductivity of the rocks surrounding the well, W / m · s;
Q flow rate of injected water, m ³ / s;
C _pb · ρ _in volumetric specific heat of the injected water, J / kg · ^o C;
a _{p the} average coefficient of thermal diffusivity of the rocks surrounding the well, m ² / s;
τ water injection time required to create a rim, s;
d borehole diameter in a horizontal section, m;
q _o temperature of the neutral layer of the Earth, reduced to the wellhead, ^o C;
G _N planetary geothermal gradient of the Earth, ^o C / m;
H depth of the roof of the deposit, m;
t _{0 is the} temperature of the injected water, ^o С;
t _{s. in} the water temperature at the entrance to the horizontal section, ^o C, determined in accordance with the expression

where t is _the temperature of the injected water at the mouth of the injection well, ^o C.

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