RU2024740C1 - Method for development of heterogeneous multilayer oil field - Google Patents

Abstract

FIELD: development of oil fields. SUBSTANCE: first, oil field is drilled with vertical wells by employing wide well spacing pattern. Then, producing wells are drilled for each layer with horizontal well bores. Beginning and end of horizontal wellbore are located at the same distance from the source of displacing agent. Wellbore length of the producing well in producing level is established proportional to oil reserves and inversely proportional to their productivity. Length of well bore in horizontal producing wells in coupling rows is set not in excess of 70% of distance to well pattern. EFFECT: higher efficiency. 2 dwg

Description

 The invention relates to the development of oil fields represented by heterogeneous multilayer reservoirs.

 A known method of developing an oil field by drilling horizontal and vertical wells [1]. The disadvantage of this method is the low oil recovery coefficient of multilayer deposits due to the small coverage of the reservoirs by drainage along the thickness of the development object.

 The closest in technical essence to the proposed one is a method of developing an oil field by drilling horizontal and vertical wells [2]. According to this method, a multilayer oil field is drilled by vertical and horizontal wells with the opening of all formations, the longest part of the horizontal wellbore being located in more productive reservoirs. A significant drawback of this method is that in the conditions of a heterogeneous multilayer field, uneven production of formations with different reservoir characteristics occurs. The opening of more productive formations with the longest horizontal trunk length will lead to the premature development of the latter, the extraction of large amounts of water and, as a result, to low oil recovery.

 The aim of the invention is to increase the coefficient of oil recovery due to a more uniform displacement of oil by the agent.

 This is achieved by a method including drilling a field with a system of wells with vertical and horizontal shafts, with the opening of all layers of a multilayer field. What is new is that initially the field is drilled with wells with vertical shafts along a sparse relative to the design grid, then production wells with horizontal shafts are drilled in each formation, while the beginning and end of the horizontal well are placed at the same distance from the source of the displacing agent, and the length of the well of the producing well in the reservoir it is set directly proportional to oil reserves and inversely proportional to their productivity, and the length of the barrel in horizontal production their wells in rows of lock is set no more than 70% of the distance of the grid project.

 In FIG. 1 shows a layout of horizontal and vertical injection and production wells by the proposed method; figure 2 is a section along aa in figure 1.

 The method is carried out in the following sequence. A multilayer field, represented by heterogeneous reservoirs, is drilled by vertical wells along a rarefied grid two or more times less than the design one. The drilling grid depends on the size of the field and its geological structure. If the field has significant dimensions and the parameters of the layers do not change both in the section and in area, then the original vertical wells are drilled along a more sparse grid. Drilling the initial vertical wells allows us to clarify the geological structure of the field and to outline the placement of horizontal wells. According to a study of these wells, the number of formations, their productivity and reserves are determined. Explore the marginal region and the energy characteristics of the layers. According to the results obtained, the necessary type of impact on oil reservoirs is determined (natural regime, maintenance of reservoir pressure, oil displacement by agents). Then drill production wells with a horizontal wellbore equidistant from the source of impact. The term "equidistant" means the equality of the distances of the beginning and end of the horizontal well of the producing wells of the corresponding rows (orbits) to the source of the displacing agent.

 When developing a field in natural mode, horizontal shafts should be parallel to the oil-water contact. When agents are pumped into wells, the trunks of the I, II ... rows, respectively (orbits with an areal flooding system) should have equal distances from the sources of impact. With this arrangement, the geometric heterogeneity created by horizontal trunks will not lead to additional uneven displacement of oil by the agent.

 To reduce oil losses in the tightening zones, horizontal wells are placed with the longest possible shafts. Tightening zones are formed in the region of the flux-dividing parts of the deposit area (for example, in a three-row placement system, the central row will be a tightening zone). The term "maximum possible length of the wellbore" means the maximum length of the horizontal wellbore, at which the agent does not break into a working well from the nearest neighboring wells that have been shut down from service due to flooding. This length depends on the geological and physical characteristics of reservoirs and saturating fluids, the type of displacing agent, it is determined by modeling the reservoir system.

·

, где К - проницаемость пласта;
h - толщина пласта;
μ- вязкость пластового флюида;
ΔР - перепад давления между пластом и забоем скважины;
R_k - радиус контура питания;
r_c - радиус скважины.As you know, with a radial flow of fluid to the bottom of the well, the main pressure drop falls on the bottomhole formation zone. This can be clearly demonstrated by analyzing the formula of the influx of Dupia:
q _n =

·

where K is the permeability of the reservoir;
h is the thickness of the reservoir;
μ is the viscosity of the reservoir fluid;
ΔР - pressure difference between the reservoir and the bottom of the well;
R _k is the radius of the power circuit;
r _c is the radius of the well.

In the table. Figure 1 shows the pressure drops between the bottom and the reservoir, calculated according to the Dupia formula with the following initial data:
μ = 3 MPa ˙ s; q _n = 100 m ³ / day;
k = 0.5 μm ² ; h = 5 m.

 As can be seen from the data in Table 1, the main pressure drop in the bottomhole zone is at a distance of 100-150 m (with a well grid of 500x500 m, this is 30% of the total distance between the wells). Thus, the maximum possible horizontal wellbore length is 70% of the total distance between the wells.

 Consider the implementation of the proposed method in the area with the designed development system for a 3-row flooding system.

) и по запасам (соответственно 1345,2376 и 1704 тыс.т.). Расстояние между проектными скважинами 500х500 м (скв. 1-13). На участке было пробурено 5 вертикальных скважин (1, 3, 7, 11, 13) через 1000 м по принципу от известного к неизвестному через одну скважину. В процессе бурения и пробной эксплуатации скважин были определены параметры пластов и насыщающих их флюидов, подсчитаны запасы нефти по каждому пласту. В соответствии с запроектированной системой разработки определяют длину горизонтального ствола скважин в стягивающей зоне. Скважины 6 и 8 в этой зоне бурят с длиной горизонтальной части 70% (как показали расчеты, для этих условий) от расстояния между скважинами проектной сетки, т.е. 350 м. По пластам в зависимости от запасов и продуктивности длины горизонтальных стволов составят по первому пласту 76 м, по второму 274 м и по пласту 3 вертикальный ствол (фиг.2).The productive interval consists of 4 layers, including one of them is a non-collector with a thickness of 15 m. The layers named 1, 2 and 3 differ in productivity (10.0, 5.0 and 15.0 respectively

) and reserves (respectively 1345.2376 and 1704 thousand tons). The distance between the project wells is 500x500 m (wells 1-13). Five vertical wells were drilled on the site (1, 3, 7, 11, 13) after 1000 m on a principle from known to unknown through one well. During the drilling and trial operation of the wells, the parameters of the reservoirs and the fluids saturating them were determined, and the oil reserves for each reservoir were calculated. In accordance with the designed development system, the length of the horizontal wellbore in the tightening zone is determined. Wells 6 and 8 in this zone are drilled with a horizontal part length of 70% (as shown by calculations for these conditions) from the distance between the wells of the design grid, i.e. 350 m. According to the strata, depending on the reserves and productivity, the length of horizontal trunks will be 76 m in the first stratum, 274 m in the second stratum and vertical trunk in stratum 3 (Fig. 2).

 The lengths of horizontal wells 1 of rows 4, 5, 9, 10 are set shorter by the amount of the undeveloped part by the horizontal trunk of the inner rows. Horizontal wells of the first rows (orbits) should not screen subsequent rows. Reducing the length of the wellbores of the first rows will also lead to a decrease in the likelihood of a water breakthrough and premature retirement of wells due to flooding. In our case, the lengths of the horizontal part of the wellbores of the 1st row are 150 m (500-350 m).

 To create a continuous displacement front, the development of injection wells for injection in the injection row is carried out through one.

=

=

=

, где q₁, q₂, q₃, q_Σ - годовая добыча нефти соответственно по пластам и объекту в целом;
Q₁, Q₂, Q₃, Q_Σ - извлекаемые запасы соответственно по пластам и в целом по объекту.Due to the fact that the length of the horizontal part of the trunk is distributed across the strata in direct proportion to the reserves and inversely proportional to their productivity, uniform development of reserves over the strata occurs. The condition for the uniformity of the rates of formation development is as follows:

=

=

=

, where q ₁ , q ₂ , q ₃ , q _Σ is the annual oil production in the reservoirs and the entire facility, respectively;
Q ₁ , Q ₂ , Q ₃ , Q _Σ - recoverable reserves, respectively, in the reservoirs and in the whole object.

 It is known that the annual oil production is equal to the product of the productivity coefficient, the magnitude of the depression per reservoir and the number of days of well operation.

Under the conditions of joint operation of the layers of a multi-layer object, having accepted the depression and the number of days of well operation as the same in the layers and equal to 10 MPa and 340 days, respectively, the annual maximum selection for the layers and the whole object was calculated. Having determined the rates of oil selection by formations, the layer-by-layer heterogeneity of reservoir formation was calculated (Table 2). From the data of table 2 it can be seen that the geological unevenness of the production of formations along the section when opening the strata with a trunk without taking into account their lengths in the formations is V ² = 0.23 units. Formations will be produced at different rates, which will lead to a decrease in oil recovery. When drilling wells with a horizontal wellbore, their flow rates (productivity) increase and with an increase in the length of the horizontal wellbore the flow rate increases to a greater extent. Therefore, when drilling wells with a horizontal wellbore of various lengths, production rates in the formations are brought to such values at which the rates of formation production are equalized. This thereby reduces the unevenness of the development of reservoirs in the object as a whole. Drilling wells with a horizontal wellbore of varying lengths in formations allows you to "remove" geological unevenness. To save material, the non-productive layer is drilled with a vertical shaft.

 PRI me R. The implementation of this method, consider the example of the development of a field site, composed of three productive formations (Fig. 1, 2). According to the results of research of exploratory drilling wells, initially vertical wells (wells 1, 3, 7, 11, 13) will be drilled along a sparse grid in the area. The thickness, porosity, productivity and oil saturation of the strata are determined in these wells. Investigate the physico-chemical properties of oils. Build lithological maps of the layers and calculate their reserves. In accordance with the designed waterflooding system, the system is simulated and the maximum possible length of horizontal shafts is determined.

 The calculations performed on the two-dimensional model of two-phase filtration for these conditions showed that the maximum possible trunk length is 70% of the design grid (350 m). An increase in the length of the horizontal wellbore over 350 m at the final stage leads to a breakthrough of water from stopped wells.

 Calculation of balance reserves by the volumetric method showed that the area contains 5425 thousand tons of oil, including by layers: 1-1345, 2-2377, 3-1705 thousand tons

 The oil recovery coefficients were calculated and recoverable reserves were determined by formations (Table 2).

 Determined the pace of selection for strata. From data 2 it can be seen that when drilling without taking into account lengths, the selection rate for a highly permeable formation (3 layer) is 4.25 times higher than for the second, and 1.18 for the first layer.

 For uniform development, the pace of development of the second and first layers must be brought to the level of the third by drilling longer horizontal shafts in these layers.

 In this example, the rate of development of a more productive third layer is 13.6% when opening the latter with a vertical trunk. From the condition that the productivity of the wells increases in direct proportion to the length of the trunks, determine the required lengths for the formations (Table 2).

The calculation is carried out in the following sequence (reservoir 1):
-q _o = P ˙ Δ P ˙ 340 = 10 t / day MPa. 10 MPa 340 days = 34 thousand tons
-Q _o = Q _b K _nor = 1345 thousand tons x 0.22 = 296 thousand tons

=

= 11,5%
-

=

= 1,18
- l = -

= 76 м
При необходимости увеличения темпа разработки высокопроницаемого пласта по нему также бурится горизонтальный ствол, но условие

= const по пластам должно соблюдаться для равномерной выработки.- i _u =

=

= 11.5%
-

=

= 1.18
- l = -

= 76 m
If it is necessary to increase the rate of development of a highly permeable formation, a horizontal well is also drilled on it, but the condition

= const across the strata must be respected for uniform output.

 The results of comparative development indicators of the known and proposed methods are presented in table.3.

 From the above values it is seen that when applying the proposed method, the layer-by-layer heterogeneity decreased from 0.5 to 0.2 units, the waterflood coefficient of the drained volume increased from 0.74 to 0.87 units. In general, the oil recovery factor for the facility increased by 5%. The increase in recoverable reserves will be 271 thousand tons.

Claims (1)

 METHOD OF DEVELOPING AN INHOMOGENEOUS MULTI-PLASTED OIL DEPOSIT, which includes drilling a field with a system of wells with vertical and horizontal shafts with opening all the layers of a multilayer field, characterized in that initially the field is drilled with wells with vertical shafts along a sparse relative to the design grid, then they are drilled trunks, while the beginning and end of the horizontal trunk is placed at the same distance t displacing agent source, mining and length of the wellbore in the reservoir is set directly proportional to oil stocks and inversely proportional to their efficiency, the length of the barrel in the horizontal production wells in the rows of lock is set no more than 70% of the distance of the grid project.

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