RU2067165C1 - Method for development of oil deposit - Google Patents

Abstract

FIELD: oil production. SUBSTANCE: oil deposit is exposed by pattern of producing and injection wells. When triangular uniform well pattern is employed, enlarged ten-slot area members are formed. Mine wells are located uniformly over the perimeter, and one in the center of triangle. Injection wells are located in the triangle corners. The remaining seven wells are equipped as producing. Heat carrier is injected and production is withdrawn by cycles in three stages. At the first stage, heat carrier is injected into injection wells and in three, every other, of the six producing wells. At the second stage, heat carrier is also injected, and in producing wells injection is replaced by withdrawal of product and vice versa. At the third stage, heat carrier is injected through injection wells, and product is withdrawn through the central producing well. The other producing wells are stopped. Cycles of heating stimulation are repeated until full completion of formation stimulation. Then, injected into injection wells is nonheated water and withdrawal is accomplished from all producing wells. EFFECT: higher efficiency. 4 dwg, 2 tbl

Description

 1. The invention relates to the oil industry to methods for developing deposits of highly viscous oils based on the injection of coolant into the reservoir.

 The essence of existing field development technologies with the injection of coolant into the reservoir is that a productive object is opened with a grid of producing (DS) and injection (NS) wells with the formation of areal or linear heat exposure systems.

In scientific and geological foundations, the use of triangular, square and linear well placement schemes has been proposed for the development of oil fields. To influence the reservoirs with water, a coolant or other agent, arealic 5, 7, 9, or more inverted elements or one, two or more in-line layout patterns of production and injection wells are usually formed [1, 2]
One of the most common technologies for thermal stimulation of a formation is based on the principle of creating a “thermal rim” of a given final size. This method was more cost-effective in comparison with the method of continuous injection of the coolant until the end of the development of the object of influence.

The disadvantage of this method is that it is usually used in unidirectional oil displacement from injection wells to production ones. This leads to the fact that, depending on the layout of the wells and the nature of the heterogeneity of the development object, areas are formed that are not covered by the displacement or the so-called "oil pillars". Practice shows that the oil reserves of such "pillars" in some cases are commensurate with the reserves of the areas covered by crowding. In addition, due to the low speeds of movement of the heat front, producing wells are forced to work for a long time in adverse "cold" conditions. Improve the way, i.e. It is possible to achieve increased formation coverage by stimulation and to intensify the operation of production wells by applying a combined treatment of the formation with a coolant through a system of injection and production wells. At the same time, coolant is injected into injection wells, while steam and thermal treatments of the bottom-hole zone (PTOS) are carried out in production wells. An example of such a technology is described in [3]
Modifications of the “thermal rims” method include those technologies in which, in order to increase the heat utilization coefficient, the coolant is not continuously injected, but cyclically with cold water being injected between the cycles. A method of developing oil fields using the specified technology is described in [4]
The authors of this application for an invention propose a method for developing oil fields with coolants, which combines the best qualities of the technology of "thermal rims", combined stimulation of the formation through a system of injection and production wells, cyclic treatment of the formation with coolant and unheated water.

 The authors could not detect the existence of close analogues, therefore, the development method [6] was adopted as the prototype as the closest in terms of the complex of technological solutions to the claimed technology.

 The purpose of the invention is the creation of an effective method for the extraction of viscous oil, which provides: high coverage of the object of development by thermal exposure; intensification of oil production and increase in final oil recovery; a significant reduction in investment in the construction of steam injection wells of special designs.

The invention for the case of drilling a deposit on a uniform triangular grid is to implement the following chain of technological solutions and technological methods:
1) form enlarged 10-point areal elements of the thermal effect "large triangles" with nine evenly spaced around the perimeter and one well in the center of a large triangle (figure 1);
2) injection wells are located at the vertices of the large triangle, the remaining seven wells are producing;
3) the development of the element is carried out by the method of thermal cycling, in which the coolant is pumped and the products are selected in cycles;
4) each cycle of stimulation is carried out in three stages. At the first stage, the coolant is pumped into the injection wells and at the same time in three (through one) of six production wells located on the sides of the triangle (Fig. 2), the production is taken from the remaining four production wells; the second stage repeats the first, except that the production wells located on the sides of the triangle are changed by the functions of transferring them from the injection mode to the selection mode and vice versa; at the third stage, the coolant is injected only through injection wells, production is taken from the central producer, and the remaining wells are stopped;
5) the cycles of heat exposure are repeated 3 to 5 times until the completion of the injection into the reservoir of the estimated amount of coolant;
6) switch to the mode of pushing the heat rim from the periphery to the center of the triangle by pumping unheated water into the injection wells and selecting products from all production wells.

 All of the listed stages of the technology implementation contain elements of novelty and therefore relate to essential features.

 Consider in more detail the order of the method and the significance of each operation in the process.

1. Determination of the required amount of coolant
As in any other technology, the total amount of coolant Q _p necessary for the effective heating of the exposure element (in our case, the "big triangle") is preliminarily calculated. The calculation procedure is described in [1, p. 736] and [4, p. 26]
2. Distribution of coolant pumped into the reservoir through injection and production wells
In the “big triangle” scheme, the total amount of coolant Q _p is introduced into the formation through both injection and production wells. In this case, the condition is satisfied:
ΣQ _ns + ΣQ _ds = Q _p ,
where ΣQ _{ns is the} amount of coolant introduced into the formation through injection wells,
ΣQ _{ds is the} amount of coolant introduced into the formation through production wells.

From FIG. 2 4 it follows that the following distribution of volume Q _{p is} most natural:
ΣQ _ds = _2/3 Q _p ,
ΣQ _ns = 1/3 Q _p ,
those. the coolant is distributed in proportion to the areas "served" by production and injection wells. Mining wells located at the vertices of a regular hexagon "serve" the internal area, which is 2/3 of the area of the entire element. For injection wells, 1/3 of the element’s area remains.

3. Determining the amount of heat introduced into the reservoir through a separate well
From FIG. 2 4 it follows that each injection well, located at the top of the triangle, acts on the development element only in the sector with an angle of 60 ^o . Therefore, only one sixth of the coolant pumped into the injection well is spent on heating this development element. For condition ΣQ _ns = 1/3 1/3 Q _p Q _p to upload into each of the coolant injection wells in a volume of 2/3 _ns Q Q _p.

Similarly, for production wells located on the sides of the triangle, the service sector of the element is 180 ^° and only half of the volume of coolant pumped into these wells is spent on heating the element. Therefore, to satisfy the condition _x = ΣQ 2/3 2/3 Q _p Q _p to upload into each of the coolant extracting wells in a volume Q _x Q _p 2/3.

Thus, the ratio of injection volumes into injection and producing wells is:
Q _ns 3 Q _ds ,
i.e., it is necessary to pump coolant 3 times more into injection wells than into production ones.

4. The choice of the number of cycles and volumes of coolant injection in cycles
The number of cycles "n" in the thermocyclic process is provided within 3 5 cycles.

Choosing n determines the injection volumes in cycles:
Q $\genfrac{}{}{0ex}{}{\text{w}}{\text{ns}}$ = 2/3 _n × Q _p and Q $\genfrac{}{}{0ex}{}{\text{w}}{\text{ds}}$ = 2/9 _n × Q _p
5. Organization of thermocyclic process mode
Each individual exposure cycle consists of three stages.

The duration of the cycle in time is determined by setting the rate of injection of the coolant into a separate well q
t _c = Q $\genfrac{}{}{0ex}{}{\text{w}}{\text{ns}}$ / q
The duration of the stage is:
t _e 1/3 x tz
At the first stage (during t _e ), the coolant is pumped into injection wells and three production (through one) in the amount of Q _e 2/9 _n x Q _p for each well, production is carried out through the remaining four wells.

 At the second stage of the same duration, the coolant is pumped in the same volumes into injection wells and three other production wells with their transfer to the injection mode, production is carried out through the remaining four wells.

At the third stage (during t _e ) the heat carrier in the same amount is pumped into the well only into injection wells, production is taken from the central production well, the rest of the production wells are stopped.

6. Organization of the final stage of element development
After the injection of the required amount of coolant is completed, they switch to the known mode of pushing heat to production wells by injecting unheated water into the formation. The required amount of unheated water is usually determined from the condition that the total injection volume of the displacing agent is about 2 3 the pore volume of the element formation ([1] [4]).

 Unheated water is pumped through injection wells, production wells are transferred to the selection mode.

 We describe the significance of the essential features in achieving the objective of the invention.

1) The choice of the "big triangle" as a characteristic element of the development and placement of injection wells at the vertices of the element provides a transition to a grid of wells, in which the ratio of the number of producing wells to the number of injection wells increases significantly
N _add / N _naked

So, for example, if you do not go to the scheme of "big" triangles ", but stop on the scheme of inverted 7-point elements with an injection well in the center of the element, then the ratio of the number of producing wells to the number of injection wells would be
N _ext / N _ng 2
In the scheme of "large triangles" this ratio is 8, which means that in the whole reservoir the number of injection wells is reduced by more than two times in comparison with the scheme of 7-point elements.

 Thus, the proposed layout of wells leads to a significant reduction in capital costs for the construction of special injection wells (usually the cost of building an injection well is 1.5 2 times higher than the cost of the producing well).

 This achieves the economic aspect of the purpose of the invention.

 2) The organization of the heat-cyclic impact in the order as described above is designed to provide a high coverage of the development element both by thermal and hydrodynamic effects.

Firstly, if the coolant is injected only through injection wells, then the effect of high coverage of the element by thermal action cannot be obtained. Therefore, the idea arose of distributing the required amount of coolant Q _p into injection and production wells.

 It is also irrational to conduct simultaneous injection into injection and into all production wells located on the sides of the triangle, leaving only the central well in the selection mode. As directly seen from FIG. 2 4, in this case, the opposed flows from the wells would interfere with the development of the heating and displacement process.

 A solution was found that production wells can be used in the injection mode through one of three wells in the injection mode and three in the selection mode.

 However, if the injection process is conducted through injection and three (through one) production wells for a long time, then there is a danger of a quick breakthrough of the coolant into the nearest production wells, the uniformity of coverage by displacement over the area is violated.

 Therefore, a thermal cyclic process is proposed in which each of the coolant injection cycles is designed to ensure both uniformity of coverage of the element by heating and symmetry of the displacement flows.

 This is achieved by the fact that at the first stage of the cycle the directions of heat and fluid flows are formed towards the nearest producing wells and the center of the triangle. At the second stage, towards other producing wells and the center. As a result, there is an alignment of the fronts of heating and displacement relative to the line of production wells. At the third stage of the cycle, by stopping the production wells, the heat and the displacement front are pushed to the central well.

 The cycles are repeated until the completion of the introduction of the coolant into the development element.

Usually the value of Q _{p is} large and if it is calculated only for one cycle, then the stages of the cycles will be long, at each stage there will be breakthroughs of the displacing agent in the producing wells. Another reason is very important here. The multi-cycle process is associated with multiple changes in the formation of directions of heat and hydrodynamic flows, which, as proved in the scientific literature and in practice, has a beneficial effect on the increase in oil recovery.

 By the time the cycles are completed, a significant area of the element will already be under thermal influence: these are zones between injection wells and the closest producers, an extensive zone of the heat zone along the perimeter of the hexagon, and a zone of heat penetration to the center of the element (Fig. 3).

 The completion of the element’s thermal exposure is achieved by pushing the heat rim to the central well by pumping unheated water through the injection wells (Fig. 4).

 The method thus ensures that the coefficient of coverage of the development element by thermal exposure is increased to almost unity or taking into account the heterogeneity of the collectors of the object 0.85 to 0.95. Note that the coefficient of hydrodynamic and thermal coverage for inverted areal elements of development (5-, 7-, 9-point) usually does not exceed 0.7 0.75.

 High heat exposure directly leads to an increase in oil recovery coefficient, since with an increase in heat coverage, the hydrodynamic coverage can only increase.

 3) The proposed development method also provides for the intensification of oil production.

 In the process of thermocyclic impact, production wells alternately operate either in the coolant injection mode or in the selection mode. Therefore, in each cycle there is a deep heat treatment of the bottom-hole zones of the wells. We get an analogue of the so-called PTOS (steam cyclic treatment of wells), which, as you know, are mainly used for the intensification of oil production.

 From the above it follows that the development method fully ensures the achievement of the objectives of the invention.

 II. The development method proposed in paragraph I can be organized in such a way that in each of the cycles, the coolant is injected into the wells (both injection and production) not continuously, but in the alternation mode with portions of unheated water, by analogy with the method proposed in prototype.

 As justified in the prototype, the alternation of the injection of coolant with unheated water can reduce heat loss in the surrounding rocks, and, as a result, reduce the total coolant flow, and in heterogeneous formations, this injection method also contributes to an increase in the degree of oil recovery from the formation as a whole.

 The proposed method is designed for testing and further industrial implementation at the Gremikhinsky deposit in Udmurtia.

 The field is drilled along a uniformly triangular grid with distances between wells 173 x 173 m with the formation of 244 inverted 7-point elements of heat exposure, of which 109 "large triangles" can be made. The heat carrier is generated by steam generators of the UPG 60/160 type.

 The statement of this example is based on the real characteristics and the development system of the oil reservoir of reservoir A 4 of the Bashkir layer of the Gremikhinsky field.

 The example shows two options for the development of reservoir A 4 deposits: the first - according to the prototype technology for the scheme of 7-point inverted elements of the cyclic coolant and cold water injection and the second according to the new scheme of "big triangles", i.e. on the subject of the alleged invention are given in table.1.

 Calculation of technological indicators of reservoir development was carried out according to the VNII methodology modified at VNIPItermneft [1], taking into account a multilayer heterogeneous section. The calculation indices for the prototype and new technology are given in Table 2.

 The calculations (Table 2) give a clear idea of the significant advantage of the proposed technology of the "Big Triangle" over the prototype. So, with an equal number of drilled wells, the required number of injection wells is reduced by 55% or 2.2 times (109 against 244). The stock of producing wells increases by 21.5% and, as a result, the rate of annual oil production increases by 60% and its total recovery by 31.4%. Additional oil production per 1 injection well increases 2.2 times.

 The final oil recovery coefficient according to the proposed technology in absolute figures increases by 6.5% and in relative by 15.9% TTT1 TTT2 LYY2

Claims (1)

 A method of developing an oil field, including opening a reservoir with a grid of production and injection wells and cyclic pumping coolant and unheated water through injection wells and selecting products from production wells, characterized in that when using a uniform triangular grid of wells, enlarged ten-point areal elements of development with nine uniformly wells located along the perimeter and one in the center of the triangle, and injection wells have about the vertices of the triangle, and the remaining seven wells are equipped as production wells, while the coolant is injected and the products are taken in cycles, each of which is carried out in three stages: at the first stage, the calculated amount of coolant is pumped into injection wells and at the same time three through one of six producing wells wells located on the sides of the triangle, production is taken from the remaining four wells, on the second, coolant is pumped in the same way as on the first, and in production wells located one hundred of the triangle, change the injection mode to the selection mode and vice versa, in the third stage, the coolant is pumped only through the injection wells, and the production is taken from the central production well, and the rest of the production wells are stopped, and the heat treatment cycles are repeated three to five times until the supply is completed in formation of the estimated amount of coolant, after which they switch to the mode of promoting the heat rim by injecting unheated water into injection wells, and the selection of products removed from all producing wells.

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