RU2455471C1 - System of solid low-productive zonary-heterogeneous oil formation development - Google Patents

Abstract

FIELD: oil and gas production.

SUBSTANCE: development system includes productive multi-hole ring holes with main vertical bore and side bores the horizontal areas of which in productive formation are directed symmetrically in radial directions in relation to the main bore, and vertical injection wells located by even square five-spot pattern of water flooding. According to the invention in the centre of the square there is a ring productive well, and in the four corners of the square - vertical injection wells. The distance between neighbouring productive wells is taken larger than the average size of the zone of permeability chaotic changing. The horizontal areas of side bores of adjacent ring holes are symmetrically turned relatively one another.

EFFECT: increase of production rate of zonary-heterogeneous formations regarding permeability, reduction of drill works and well operation cost.

1 tbl, 2 dwg

Description

The invention relates to the oil industry, in particular to the field of development and exploitation of oil fields by multilateral horizontal wells.

One of the most effective ways to increase well productivity is to lay horizontal sidetracks in low-productivity or idle wells. To reduce the number of wells during field development and reduce the cost of their construction, the method of multi-hole drilling is used [1, pp.21-24]. The essence of the method lies in the fact that from the main wellbore, after its attachment, sidetracks are drilled. The number of sidetracks and their location depends on the geological features of the formation and its physical characteristics.

In [2], data are presented on the operation of horizontally branched wells with three or more shafts. Horizontal-branched boreholes had a complex spatial architecture associated with the spatial location of oil-saturated zones in the reservoir. Horizontal trunks were divorced in both vertical and horizontal planes relative to the main vertical trunk. In [2] it is noted that the use of multilateral wells allowed to increase oil production rates by an average of 2.2 times. The presented results on the operation of multilateral wells with horizontal branching indicate that the increase in current oil production is practically independent of the number of additional sidetracks and is on average 2.2 times compared with the production rate of a single-well horizontal well. When operating a multilateral well with horizontal branching, the production rate of the well is determined by the production rate of one wellbore with the least filtration resistance. This is the trunk that crosses highly permeable formation zones along its length. Contribution to the total production rate of other wellbores will be insignificant. Consequently, the development of the reservoir area drained by a multilateral well will be uneven.

Of the well-known technical solutions, the closest and at the same time being the basic one is a multi-wellbore device for fan-like interval production of productive formations [3]. An oil field with a heterogeneous permeability reservoir is drilled with a rare grid of wells. Each production well has a main wellbore and a system of sidetracks with a horizontal fan radially symmetric direction in the interval of the reservoir. This design of a multilateral well allows for fan-based interval production of productive formations. Sequential interval production of a part of a productive formation drained by a multilateral well fan, with the repetition of cycles, allows to increase the waterflood coverage of unproductive zone-heterogeneous permeability formations.

The maximum possible production of oil reserves from zonal heterogeneous permeability formations with a system of multi-hole fan wells depends on the layout of production and injection wells, on the distance between adjacent production and injection wells and on the location of the side shafts of fan wells relative to each other.

The aim of the proposed development system is to increase the oil recovery of zonal heterogeneous permeability layers, reducing the cost of drilling and the cost of operating wells.

This goal is achieved by the fact that an oil field with a zone-heterogeneous permeability formation is drilled with a rare grid of fan-made production and vertical injection wells. Each fan producing well has a main vertical wellbore and a system of sidetracks, the horizontal sections of which in the reservoir are directed symmetrically in radial directions relative to the main vertical wellbore. When developing a field with hard-to-recover reserves with a constant number of production and injection wells, the maximum flow rate is achieved with a five-point scheme of areal flooding. A fan producing well is located in the center of the square, and vertical injection wells are located in the four corners of the square. Each injection well serves four production wells. For each production well, the front of the displacing water approaches symmetrically from four different sides. The difference from the standard five-point layout of wells is that production wells are multilateral wells with a symmetrical arrangement of horizontal lateral shafts.

The layout of production wells is determined by the average size of the zones that make up the zonal-heterogeneous formation and between which there is a random variation in permeability values. The step of spatial chaotic variability of permeability strongly affects the amount of recoverable oil reserves and is the most important parameter of the model of a zone-heterogeneous oil permeability and discontinuity. In addition to zonal permeability heterogeneity, a zonal heterogeneous reservoir has chaotic discontinuity, i.e. chaotic spread of zones of the non-collector of zero permeability [4, p. 322-323].

When developing a zone-heterogeneous monolithic oil reservoir with a system of producing fan wells with a uniform square grid of their placement, the maximum possible oil production is achieved when the horizontal sections of the sidetracks of adjacent wells are symmetrically deployed relative to each other.

It is the placement according to the uniform square five-point waterflooding pattern, in the center of the square of which there is a fan producing well, and in the four corners of the square there are vertical injection wells, with a distance between adjacent producing wells exceeding the average size of the zone of random permeability variability, and a symmetrical reversal of horizontal sections of the sidetracks relative to each other adjacent fan wells, is the essence of this invention.

Thus, the inventive system for the development of a monolithic unproductive zone-heterogeneous formation meets the criteria of the invention of "novelty." When studying other technical solutions in this technical field, the features that distinguish the claimed invention from the prototype were not identified and therefore they provide the claimed technical solution with the criterion of "significant differences".

The technical essence of the invention is illustrated by the layout of the fan producing and vertical injection wells of figure 1 and the location of the vertical and horizontal shafts of producing wells and vertical injection wells of figure 2.

Figure 1 shows the layout of the fan producing wells 1 and injection wells 2. The distances between adjacent rows of production and injection wells 2σ. The length of the perforated horizontally located sections of the trunks of fan wells L.

Figure 2 shows the location of the vertical (•) and horizontal (□) shafts of a fan producing well and a vertical injection well (○) depending on the angle (θ) of the horizontal section of the trunk.

When developing an oil field, fan producing and injection wells are operated continuously. The design of a multilateral well allows cyclic fan-based interval production of productive formations, the essence of which is as follows. They begin to make a selection of fluid from the last drilled horizontal wellbore, control the flow rate of the fluid, the pressure at the bottom and the water cut of the produced fluid. If during operation the fluid flow rate decreases, i.e. injection wells do not provide pressure recovery in the reservoir, or a sharp increase in water cut of produced products occurs, i.e. pumped water reached the wellbore, then the selection of fluid from the last horizontal wellbore is stopped (close the valve). The penultimate horizontal wellbore valve is opened, the inset of which is located below the last horizontal wellbore along the axis of the main wellbore, and fluid is sampled, controlling fluid flow rate, bottomhole pressure and water cut of produced fluid. Moreover, in the contour of the drainage interval of the last horizontal wellbore, from which fluid withdrawal was stopped, there is a gradual restoration of pressure and redistribution of saturations that tend to an equilibrium phase distribution in the pore space. In a similar manner, the following horizontal trunks are connected in series and the liquid is taken from them. At the final stage of the cycle of fan-interval interval operation of the well, the valve of the main vertical wellbore is opened and fluid is taken from the drainage circuit of the formation zone immediately adjacent to the main wellbore. During this period of time, the pressure and the equilibrium distribution of phases in the pore space of the formation are restored in the reservoir intervals previously previously drained by the laterally horizontal trunks of the formation. Next, close the valve of the vertical wellbore, open the valve of the last lateral wellbore (from which the operation of the well began) and select the fluid, controlling the flow rate of the fluid, pressure on the bottom and watering of the produced fluid. The entire cycle of fan-interval interval operation of a multilateral well is repeated in the same sequence. The fan well operation is stopped after the maximum possible development of oil reserves from the productive part of the formation drained by this well.

Sequential interval production of a part of a productive formation drained by a multilateral well, with the repetition of cycles, makes it possible to increase the waterflood coverage of unproductive zone-heterogeneous permeability formations, increase the uniformity of oil reserves production from them, and thereby ensure the maximum possible production of oil reserves.

An example of a system for developing a monolithic unproductive zone-heterogeneous oil reservoir

An oil reservoir located in Western Siberia is a monolithic layer of low productivity, high zonal heterogeneity and with a small effective oil-saturated thickness. The development of deposits by vertical wells is unprofitable.

Brief description of the oil reservoir YUS ₂

Depth, m 2950 Effective formation thickness, m 7.6 Coefficient of porosity,% 16.8 Initial reservoir pressure, MPa 29.9 Formation temperature, ° C 81 Saturation Pressure, MPa 9.2 The density of oil in surface conditions, kg / m ³ 875 The density of water in surface conditions, kg / m ³ 1016 The density of oil in reservoir conditions, kg / m ³ 853 The density of water in reservoir conditions, kg / m ³ 996 Oil viscosity in reservoir conditions, MPa · s 3.66 The viscosity of water in reservoir conditions, MPa · s 0.38 Approved geological reserves, million tons 6.8 Approved recoverable reserves, million tons 1.3 Approved Oil Recovery Factor 0.19

The oil recovery coefficient was calculated according to the method developed by V.D. Lysenko [4]. The validity of the practical application of this technique is based on many years of experience in its application in designing the development of many oil fields and solving inverse problems in the history of the operation of wells, experimental sites, deposits and deposits.

The completeness of oil recovery from the reservoir is characterized by the oil recovery coefficient K _but , which can be represented as the product of three coefficients

The first coefficient K _c is called the grid coefficient, which takes into account the influence of the design grid of wells, the coverage of the development of the balance of geological oil reserves with the designed well system, the share of the reservoir, the step of the random change in reservoir properties and the area of formations per well. The grid coefficient is determined by the formula:

where w = 0.23 is the fraction of non-collector plots; 2σ = 600 m - the distance between the producing wells, d = 300 m - the average geometric size of the zonal chaotic permeability variability. For the given values of the parameters of the oil reservoir, the grid coefficient is K _s = 0.809.

The second coefficient K _in is called the coefficient of oil displacement by the injected water. It is determined in laboratory conditions on rock samples of the considered formations with a sufficiently large pumping of water. When the displacement of oil by water _in K ranges from 0.5 to 0.8. For the considered oil reservoir, it is K _in = 0,61.

The third coefficient K _s is called the water flooding coefficient or the utilization ratio of mobile oil reserves, which is determined by the formula:

- коэффициент заводнения за начальный безводный период,

конечный коэффициент заводнения; V² - показатель результирующей неравномерности вытеснения нефти в добывающую скважину; А - предельная расчетная доля вытесняющего агента в дебите жидкости добывающей скважине, которая определяется по формуле:Where

- water flooding rate for the initial anhydrous period,

final flooding rate; V ² - an indicator of the resulting uneven displacement of oil into the producing well; And - the maximum estimated proportion of the displacing agent in the fluid flow rate of the producing well, which is determined by the formula:

where A ₂ is the maximum maximum weight fraction of the displacing agent in the production rate of the liquid of the producing well; µ _about - the coefficient of difference in the physical properties of water and oil, which is determined by the formula:

- соотношение подвижностей воды и нефти;

- соотношение плотностей воды и нефти в пластовых условиях; µ_н и µ_в - вязкости нефти и воды в пластовых условиях; γ_н и γ_в - плотности нефти и воды в поверхностных условиях; в - коэффициент увеличения объема нефти в пластовых условиях.Where

- the ratio of the mobilities of water and oil;

- the ratio of the densities of water and oil in reservoir conditions; µ _n and µ _in - viscosity of oil and water in reservoir conditions; γ _n and γ _in - the density of oil and water in surface conditions; in - the coefficient of increase in oil volume in reservoir conditions.

; неравномерность стягивания фронта вытеснения к рассматриваемой добывающей скважине с разных сторон от разных нагнетательных скважин, которая зависит от зональной неоднородности нефтяных пластов по продуктивности и обозначается

; геометрическую неравномерность вытеснения нефти агентом, которая зависит от схемы взаимного расположения добывающих и нагнетательных скважин

.The non-uniformity of the displacement of oil by the agent into the producing well V ² takes into account the action of all the main factors: layer-by-layer heterogeneity in the permeability of oil reservoirs

; non-uniformity of compression of the displacement front to the considered production well from different sides from different injection wells, which depends on the zonal heterogeneity of oil reservoirs in productivity and is indicated

; geometric non-uniformity of oil displacement by the agent, which depends on the mutual arrangement of production and injection wells

.

The resulting rate of displacement unevenness is determined by the formula:

.

.

If the reservoir is a monolithic reservoir, then the formula for determining the indicator of displacement unevenness takes the form:

от разных нагнетательных скважин устанавливается с учетом зональной неоднородности нефтяных пластов по продуктивности

, числа воздействующих нагнетательных скважин n_н и определяется по формуле:Uneven contraction of the displacement front from different sides

from different injection wells is established taking into account the zonal heterogeneity of oil reservoirs by productivity

, the number of acting injection wells n _n and is determined by the formula:

определяется этими же формулами.which is applicable provided that the distance between the wells is equal to or greater than the step of chaotic variability. With a five-point arrangement of production and injection wells, when the displacement of the displacement front occurs on four sides of the four injection wells, n _n = 4. When using horizontal wells with a not very large horizontal length, the calculation of the value

determined by the same formulas.

, которая учитывает схему взаимного расположения добывающих и нагнетательных скважин, их вид (вертикальные они или горизонтальные), рассчитывается по формуле:The geometric unevenness of oil displacement by the agent

, which takes into account the mutual arrangement of production and injection wells, their type (vertical or horizontal), is calculated by the formula:

- соотношение длин самой длинной L_max и самой короткой L_min линий тока, соединяющих добывающую скважину с нагнетательной. В случае эксплуатации многозабойной веерной скважины при последовательном подключении только одного ствола геометрическая неравномерность вытеснения нефти агентом в процессе эксплуатации скважины изменяется.Where

- the ratio of the lengths of the longest L _max and the shortest L _min streamlines connecting the producing well with the injection. In the case of operation of a multi-hole fan well with only one trunk connected in series, the geometric unevenness of oil displacement by the agent during the operation of the well changes.

With a five-point layout of wells (Fig. 1), the displacement front is contracted from four sides of four injection wells, i.e. well grid cell is symmetrical. Cell element comprises a production well and ^{a _1/4} part of the injection well. At various points in time, either a vertical wellbore or one of the horizontal lateral shafts, located at an angle θ to the line connecting the producing wells, is operated (Fig. 2).

, самой длинной линии тока L_max=2·σ, а соотношение этих длин равноWhen you connect a vertical wellbore of the producing well (figure 2, a) the length of the shortest streamline

, the longest streamline L _max = 2 · σ, and the ratio of these lengths is

Accordingly, the geometric unevenness of oil displacement is

при подключении вертикального и горизонтальных стволов, расположенных под углом θ, приведены в таблице 1. Длина горизонтальных перфорированных участков

.The corresponding values of L _max , L _min , M and

when connecting vertical and horizontal trunks located at an angle θ, are shown in table 1. The length of the horizontal perforated sections

.

Table 1. Fig.4 θ L _min L _max M

but

2 σ 1,414 0.0812 b 0 ° σ 2,333σ 2,333 0.508 at 22.5 ° 0.60 · σ 2,333σ 3,888 1,432 g 45 ° 0.414σ 2,333σ 5,636 2,542

пo всем возможным вариантам составляет:Arithmetic mean

for all possible options is:

, определяемая по вычисленному значению

, равнаUneven contraction of the displacement front

determined by the calculated value

is equal to

The rate of displacement of oil by the agent is

the waterflood coefficient for the initial anhydrous period is

final flooding ratio is equal to

When the viscosity of oil and water in reservoir conditions μ _n = 3.66 mPa · s and μ _a = 0.38 mPas mobility ratio of oil and water is:

If the ratio of the densities of water and oil γ _∗ = 1.17, then the coefficient of difference in the physical properties of oil and water is equal to:

With a maximum water cut of the produced fluid A ₂ = 0.95, the maximum proportion of the displacing agent is:

The utilization ratio of mobile oil reserves is equal to:

Oil recovery coefficient is equal to

K _but = K _s · K _in · K _s = 0.809 · 0.61 · 0.4317 = 0.213.

использовалось среднее арифметическое значение геометрической неравномерности вытеснения нефти агентом

по всем возможным вариантам расположения горизонтальных участков стволов веерных скважин.The obtained value of K _but = 0.213 exceeds the approved oil recovery coefficient K _but = 0.19. This is due to the fact that in determining the uneven contraction of the displacement front

the arithmetic mean of the geometric non-uniformity of oil displacement by the agent was used

according to all possible options for the arrangement of horizontal sections of fan well shafts.

The potential effect of increasing oil recovery

With the selected design grid, which does not change during the development of the field, the grid coefficient K _c remains unchanged. Therefore, the reserve for increasing oil recovery is associated with the coefficient of oil displacement K _in and the coefficient of water flooding or the utilization of mobile oil reserves K _s . An increase in K coefficient _is possible with a change in the displacing agent. In the proposed technology, water is used as a displacing agent.

The potential effect of increasing the oil recovery coefficient is associated with an increase in the utilization rate of mobile oil reserves K _s . This coefficient depends on the zonal heterogeneity of the permeability of the oil reservoir, characterized by different filtration rates and, accordingly, the rate of oil displacement from various intervals of the reservoir section drained by the well. The fraction of non-reservoir sites in the total reservoir area is w = 0.23, and the remaining fraction of 0.77 represents reservoir zones with different permeabilities. The proposed technology of fan-wise interval production of productive formations takes into account the dynamics of the process of non-simultaneous flooding of reservoir zones with different chaotic permeability. This makes it possible to involve low-permeability formation zones into the filtration process, i.e. to cover flooding all moving oil reserves. The coefficient of use of mobile oil reserves To _s → 1. The oil recovery coefficient in this case will be equal to

K _but = K _s · K _in · K _s = 0.809 · 0.61 · 1 = 0.493,

those. increases by 2.5 times compared with the approved oil recovery coefficient.

All productive formations to one degree or another have geological heterogeneity. Permeability zonal chaotic reservoir heterogeneity leads to the displacement of oil from highly permeable zones. As a result, channels of low filtration resistance are formed, through which the displacing water reaches the producing wells, which leads to their rapid flooding. At the same time, significant oil reserves remain in low-permeability zones. Known methods of influencing the reservoir with the aim of increasing the coverage of the formation by water flooding are ineffective.

The physical nature of the proposed technical solution consists in the simultaneous manifestation of two processes:

1) non-stationary cyclic flooding of intervals of a section of a formation drained by a fan well in order to create periodic non-stationary pressure drops in these intervals between high-permeability and low-permeability zones of the reservoir;

2) sequential switching of fan well shafts leads to a change in the direction of the filtration flows.

Known hydrodynamic methods for enhancing oil recovery: unsteady cyclic water flooding and changing the direction of filtration flows include stopping groups of production and injection wells, as well as transferring the water injection line. Unlike well-known methods, the design of fan wells during their operation does not involve stopping production and injection wells during these processes. The implementation of these processes is achieved by sequential switching of the wells of production wells.

Economic justification

Analysis of accumulated drilling experience shows that the cost of 1 m of drilling a horizontally branched part of the trunk is 30-40% higher than the cost of drilling 1 m of a vertical well. The cost of construction of branched horizontal wells is 1.6 times higher than the cost of construction of vertical wells, the flow rates of branched horizontal wells are on average 5.3 times higher than vertical. Specific capital investments per 1 m of oil extracted from branched horizontal wells are 2.2 times less than for neighboring vertical wells [1, p.23].

Drilling branched horizontal wells is more expensive than drilling vertical wells, but increasing the productivity of branched horizontal wells and increasing oil recovery are so significant that economic efficiency significantly exceeds the initial cost of building branched horizontal wells.

Sources of information taken into account

1. Features of oil and gas production from horizontal wells. / Ed. G.P. Zozuli. - M.: Publishing Center "Academy", 2009. - 176 p.

2. Zagidullin R.G. Construction and operation of multilateral wells in OAO TATNEFT / R.G. Zagidullin, R.Kh. Fatkullin, I.G. Yusupov, etc. // Oil industry. - 2007. - No. 7. - S. 36-38.

3. Patent for utility model RU No. 98046. Published on September 27th, 2010. The device of a multilateral well for fan-wise interval production of productive formations / Ivanova Yu.V., Ivanov V.A.

4. Lysenko V.D. Oil Field Development: Theory and Practice. - M .: Nedra, 1996 .-- 367 p.

Claims (1)

A development system for a monolithic unproductive zone-heterogeneous oil reservoir, containing producing multi-hole fan wells with a main vertical wellbore and sidetracks, the horizontal sections of which in the productive stratum are directed symmetrically in radial directions relative to the main wellbore, and vertical injection wells located according to a uniform square five-point waterflooding pattern , characterized in that in the center of the square there is a fan producing well, and in four square crystals are arranged vertical injection wells; the distance between neighboring producing wells is greater than the average size of the zone of random permeability variability; horizontal sections of the sidetracks of adjacent fan wells located symmetrically deployed relative to each other.

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