RU2085723C1 - Method for development of oil deposit made up of nonuniform reservoirs - Google Patents

Abstract

FIELD: oil production industry. SUBSTANCE: this relates to increasing oil recovery coefficient due to more uniform displacement of oil by agent. According to method, horizontal wells are drilled in productive thickness of oil bed so that distance from flooding source to horizontal well at its each point is inversely proportional to oil reserve in given zone and directly proportional to conductivity of oil beds. In case of multiple-bed deposit or large thickness, horizontal well is driven in the form of several loops, and aforesaid relationship is maintained in each loop. EFFECT: high efficiency. 1 dwg

Description

 The invention relates to the development of oil fields having in their section heterogeneous reservoirs.

A known method of developing an oil field by drilling horizontal and vertical wells [1]
The disadvantage of this method is the low coefficient of oil recovery in heterogeneous reservoirs due to uneven displacement.

The closest in technical essence to the proposed is a method of developing an oil field, according to which a multilayer oil field is drilled with vertical and horizontal wells with the opening of all layers [2]
A significant drawback of this method is that under conditions of an inhomogeneous reservoir, uneven production of formations by area and thickness occurs due to the difference in the filtration rates and the distances from the waterflood source to the horizontal wells of production wells. This leads to 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.

 The goal is achieved by the described method of developing an oil field represented by heterogeneous reservoirs, including drilling it with a system of injection and production wells with vertical and horizontal shafts.

 What's new is that horizontal wellbores in the reservoir are positioned so that the distance from the injection well to the horizontal wellbore at each point is inversely proportional to the oil reserves in this zone and directly proportional to the conductivity of the reservoirs, and when developing a multi-layer or large thickness of the reservoir a horizontal well is carried out in the form of several turns with the indicated pattern in each turn.

 The drawing shows a diagram of one of the options for placing horizontal and vertical injection and production wells according to the proposed method.

 The method is carried out in the following sequence.

 The field, represented by heterogeneous reservoirs, is drilled by vertical wells, which in the development system will mainly be used as injection wells along a 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 the study of vertical wells, the distribution over the area of formation thickness, permeability and porosity is determined. Then, design injection and production wells are placed so that during the development of the oil field the displacement front fits evenly to the horizontal trunks of the production wells. To do this, in the design well placement scheme, isolines of equal production in the strata are first drawn so that the distance from the waterflood source to this line at each point is inversely proportional to the oil reserves and directly proportional to the conductivity in each stratum. Then, in the diagram near this line, trajectories of the horizontal part of production wells in each formation are drawn on both sides, forming a spiral curve. Depending on the thickness of the formation, there may be an incomplete turn or several turns in each formation. At the same time, they maintain a certain distance between the trunks of adjacent horizontal wells in the same formations so that premature flooding of horizontal wells from each other does not occur. This distance is calculated using hydrodynamic models or taken according to field tests and, as a rule, it is 50-100 m. Stagnant zones are determined on hydrodynamic models and vertical production wells are placed in these areas.

 The deposit is drilled according to the developed design well placement scheme. Injection wells are injected, producing for production, including horizontal ones. Oil is displaced by the injected displacing agent. Horizontal wells due to the fact that they are located at a distance directly proportional to the conductivity of the reservoirs and inversely proportional to the reserves, provide uniform displacement over the entire area.

 The injected water from the injection well, displacing oil, moves towards the horizontal producing well. The rate of advancement depends on the conductivity of the formation and the oil reserves concentrated in this zone. Due to the heterogeneity of the collector, its conductivity and reserves are different in different directions. Therefore, uneven displacement occurs. But according to the proposed method, the distance from the waterflooding source to each point of the horizontal wellbore is set directly proportional to the conductivity and inversely proportional to the reserves, which leads to equalization of the approach time of the water front in all directions. That is, there occurs a simultaneous approach of the displacing fluid to the horizontal wellbore at all points. Due to this, premature flooding of part of the opened interval in highly conductive zones to the development of oil reserves is eliminated. Uniform crowding occurs with maximum coverage. In addition, the presence of a partial or full turn, or several turns of the shafts in each layer ensures uniform production across the thickness of the production facility. Oil is displaced uniformly throughout the entire volume of the reservoir, the volume of associated displacing fluid produced is reduced, and, as a result, oil recovery is increased.

 An example of a specific implementation.

 The implementation of this method, consider the example of the development of a field site, composed of two productive formations (see figure 1 and 2).

According to the results of research in the area of exploration wells drilled initial drilling vertical wells (NN _borehole. 1, 2, 3, 6, 7, 8, 11, 12 and 13) on the grid to 1200 x 1200 m.

 The thicknesses, porosity, permeability and oil saturation of the strata were determined in these wells. The physicochemical properties of oils were investigated. We built lithological maps of the strata and calculated their reserves. As you know, oil reserves and conductivity are directly proportional to the effective oil-saturated thickness of the formations, therefore, in calculating the determination of the distances from the source, waterflooding to the horizontal well, the ratio of conductivity to reserves was replaced simply by the average permeability of the formations.

 We found the meeting points of the displacement fronts in the zone between each two injection wells. In this example, the reservoir consists of two layers and therefore this is done for each layer. The desired point was determined by calculation.

где l $\genfrac{}{}{0ex}{}{\text{1}}{\text{1-6}}$ расстояние от скважины N 1 до точки встречи фронта между скважинами NN 1 и 6 по первому пласту;
Z_1-6 расстояние между скважинами NN 1 и 6;
K $\genfrac{}{}{0ex}{}{\text{1}}{\text{1}}$ средняя проницаемость первого пласта в зоне скважины N 1;
K $\genfrac{}{}{0ex}{}{\text{1}}{\text{6}}$ проницаемость первого пласта в зоне скважины N 6.

where l $\genfrac{}{}{0ex}{}{\text{one}}{\text{1-6}}$ the distance from the well N 1 to the point of frontal intersection between the wells NN 1 and 6 along the first formation;
Z _{1-6 the} distance between the wells NN 1 and 6;
K $\genfrac{}{}{0ex}{}{\text{one}}{\text{one}}$ the average permeability of the first layer in the zone of the well N 1;
K $\genfrac{}{}{0ex}{}{\text{one}}{\text{6}}$ the permeability of the first layer in the zone of the well N 6.

Having determined these points between each pair of injection wells, we constructed contour lines for meeting the displacement fronts for each formation (see drawing). In the drawing, the isolines along the upper layer are shown by a solid line and a dashed line along the lower layer. By conducting parallel curves along these contours at a distance of 25-50 m in the direction of the injection well, trajectories of horizontal wells in productive formations were constructed. In the considered example, around the injection well N 7, an irregularly shaped spiral curve was obtained in two turns. One turn in the upper layer and the second in the lower layer. Similarly received the trajectory of horizontal wells and near other injection wells (NN wells _. 1, 2, 3, 6, 8, 11, 12 and 13). In tightening stagnant zones placed additional production wells; depending on the shape of these zones, the wells can be either vertical or horizontal of various shapes. In the considered example, due to the small size of these zones, these are four vertical production wells (N wells _. 4, 5, 9, and 10). We drilled the placed production wells in accordance with the developed scheme and put them into operation. Injection wells were received for injection. When operating wells to a maximum water cut of produced products of 98%, the water flooding coefficient (K _s ) was 0.8; the coefficient of coverage by water flooding (K _ohm ) of 0.95 and with a displacement coefficient (K _in ) of 0.6 oil recovery was 45.6% compared to 38.4% according to the known method, according to which K _s = 0.8; K _OH = 0.8; K _in = 0.6. For the considered area with an average geological reserves per well of 850 thousand tons, an additional 61.2 thousand tons of oil will be produced.

Claims (1)

 A method of developing an oil field represented by heterogeneous reservoirs, comprising drilling a system of injection and production wells with vertical and horizontal shafts, characterized in that the horizontal well shafts in the reservoir are positioned so that the distance from the injection well to the horizontal well at each point is inversely proportional to the oil reserves in this zone and in direct proportion to the conductivity of the reservoirs, moreover, when developing a multilayer or more With the greatest thickness of the deposit, the horizontal wellbore is carried out in the form of several turns with the indicated pattern in each turn.

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