RU2046181C1 - Method for development of oil deposits nonuniform about reservoir properties in different zones - Google Patents

Abstract

FIELD: oil-well drilling. SUBSTANCE: drilling out deposits according to design well grid, geophysical, hydrodynamic, and laboratory investigations, hydrocarbon sampling in mode of depleted stratum energy, followed by pumping displacing agent in zones of poor penetrability. Pumping displacing agent in is carried out on decreasing stratum pressure by a value of initial oil displacement between zones of extraction and water bearing area. Wells with the highest rate of stratum pressure drop and the least hydroconductivity are developed for pumping displacing agent in. As stratum pressure is recovered over the deposit, additional wells with the least rate of stratum pressure recovery and the least hydroconductivity are developed for pumping displacing agent in. EFFECT: highly efficient development of wells. 2 dwg

Description

 The invention relates to the field of oil field development.

A known method of developing a zone-heterogeneous formation with selective effects on the poorly permeable part of the formation [1]
The disadvantages of the method: permeability values for carbonate deposits, determined in laboratory conditions by cores, according to geophysical and hydrodynamic studies, are very different from each other, the allocation of zones according to these conflicting data can lead to a random distribution of injection wells between zones of different permeabilities and, as a result, advanced production of oil reserves confined to zones of increased permeability of reservoirs; the location of injection wells is possible in an area with active hydrodynamic communication with the aquifer, which will cause additional costs for water injection.

Closest to the technical nature of the proposed is a development method that involves the selection of hydrocarbons in the mode of depletion of reservoir energy, followed by injection of a displacing agent. The latter is carried out after reducing the reservoir pressure by 10-20% below hydrostatic pressure or to the pressure of miscible displacement. The injection is carried out until the pressure is restored to hydrostatic and maintained at this level [2]
The main disadvantage of this method is that the development of wells for injection is carried out without taking into account the zonal heterogeneity of carbonate deposits, where zones of good permeability are contoured by small-sized zones of low permeability. The random location of injection wells between zones of different permeability leads to the advance development of oil reserves confined to zones of increased permeability.

 The purpose of the invention is to increase the oil recovery coefficient by increasing the coverage of the reservoir by water flooding.

 This goal is achieved by a method including drilling a reservoir according to the design grid of wells, conducting geophysical, hydrodynamic and laboratory studies, selecting hydrocarbons in the mode of depletion of reservoir energy and subsequent injection of a displacing agent into zones of low permeability.

 New is the fact that the injection of the displacing agent is carried out after reducing the reservoir pressure to the value of the initial pressure gradient between the selection zones and the aquifer. Wells are mastered for injection of the displacing agent, which have the highest rate of reservoir pressure drop and the lowest hydraulic conductivity on the deposits. As the reservoir pressure is restored through the reservoir, additional wells with the lowest rate of reservoir pressure recovery and the lowest hydraulic conductivity are being developed for injection of the displacing agent.

 In FIG. 1 shows a map of the conductivity of the experimental plot (zone I of good conductivity and zone II, III of weak conductivity); in FIG. 2 isobar map of the prototype before the flooding; in FIG. 3 the same, after 3 years of injecting water into a zone of good conductivity; in FIG. 4 the same, after 10 years of water injection; in FIG. 5 payment card isobar according to the proposed method after 3 years of pumping water into zone III; in FIG. 6 the same, after the development of injection into zone II; in FIG. 7 the same, after the development of water injection into zone I.

The method is as follows. The deposit is drilled according to the design grid of wells, after which geophysical, hydrodynamic and laboratory studies are carried out. Based on these studies, a map of hydroconductivity is built. The selection of oil is carried out by all wells at the same P _zab in the depletion mode until the reservoir pressure decreases by the value of the initial pressure gradient between the selection zones and the aquifer. This establishes a hydrodynamic connection between the oil and aquifer zones of the reservoir.

 The initial threshold shear pressure of oil is understood to mean the pressure drop at which fluid can be transferred from the water part of the reservoir to the oil bearing when the structural and mechanical properties of reservoir oil are manifested, the value of which depends on the initial gradient of the shear pressure, determined by the dependence obtained on the basis of experimental work. During the operation of wells, blocks of isobars are constructed quarterly, with the help of which zones with a weak backwater of the marginal region are established, the boundaries and sizes of zones with low reservoir properties, dead-ends are specified. In these zones, a sharp decrease in reservoir pressure occurs with relatively small fluid withdrawals.

 Wells are being mastered for injection of the displacing agent, which have the highest rate of reservoir pressure drop in the deposits and the smallest hydraulic conductivity dispersed over the area if possible. In this case, oil is displaced from low-permeable and with low backwater of the aquifer to highly permeable elevated parts of the reservoir. Higher pressures are created in the poorly permeable zone than in the well-permeable zone, which leads to the equalization of the coefficient of formation coverage by filtration in these different areas and, consequently, to an increase in the oil recovery coefficient in the whole reservoir. Studies show that in this case, the oil recovery coefficient is increased by 13% compared with the prototype. The reservoir pressure is restored in the reservoir, the intensity of which varies in different zones. At the stage of reservoir pressure restoration, zones isolated from injection wells, lenses, and dead-end zones are established on isobar maps. In these zones, the pressure recovery rate is the smallest or negative. As the reservoir pressure is restored, additional wells are mastered under water injection with the lowest rate of reservoir pressure recovery and the lowest hydraulic conductivity. This leads to an additional increase in reservoir coverage by water flooding and an increase in oil recovery coefficient.

 PRI me R. The carbonate deposit was drilled along a square grid with a well spacing of 200 m. 18 wells were drilled. The permeability of the reservoir (K) varies from 0.020 to 0.579 D and an average of 0.196 D.

The zone of increased permeability of reservoirs (more than 0.300 D) occupies the northwestern and central part of the site (Fig. 1). A decrease in permeability is noted in a southeast direction. The average permeability of these zones is 0.100 D. The effective oil-saturated thickness of the formation varies from 2.8 to 10 m on average 6.4 m, a decrease in thickness is observed in the eastern and southeastern parts of the site. The viscosity of oil for all wells is the same, therefore, we construct a map of conductivity (Fig. 1) of the reservoir (kR), which shows that 3 zones are distinguished in the reservoir. The conductivity of these zones is very different from each other. The balance reserves of the zones are respectively: according to IQ _b 1156 thousand tons, according to II Q _b = 300 thousand tons, according to III Q _b 900 thousand tons.

In the initial stage, the selection of oil was carried out in natural mode, the operation mode of the selected zones was determined. In this case, the mode of deposits was close to elastic. According to the displacement characteristics (Kopytov’s method), the final oil recovery coefficients were determined, which by zones are respectively: 12, 7, 8%
To create a hydrodynamic connection, the reservoir pressure was reduced by a threshold ΔР _from 18 kg / cm ² in the low-permeability zone, the average permeability of which was 0.1 D.

L (1) где G(Т_плР_пл) начальный градиент давления при пластовых значениях температуры (Т_пл) и давления (Р_пл), кгс/м²; L безразмерный коэффициент, равный для исследуемых объектов разработки 0,43; θ (Т_плР_пл) предельное динамические напряжение сдвига пластовой нефти при пластовых значениях температуры и давления, дин/м²; m пористость коллектора; К проницаемость коллектора
θ(T_плP_пл)=

0,33

+

-0,0516

+0,0408

0,0028

Г $\genfrac{}{}{0ex}{}{\text{2}}{\text{a}}$ +Г_м+Г

0,04

0,252 дин/см² (2)
где А содержание асфальтенов, 10,8 мас. С содержание смол, 24,4 мас. Г_а содержание азота, м³/м³ 3,93; Г_м содержание метана, м³/м³ 5,68; Г_э содержание этана, м³/м³ 4,15; L расстояние между скважинами 200 м.The threshold pressure value is determined by multiplying the initial oil shear pressure gradient by the distance between the oil circuit and the first producing wells according to the dependence (Devlikamov VB and other Anomalous Oils. M. Nedra, 1975, p. 167):
ΔP _c = G (T _pl P _pl ) · L = 0.71 · α · θ (T _pl P _pl )

L (1) where G (T _pl R _pl ) the initial pressure gradient at reservoir values of temperature (T _pl ) and pressure (R _pl ), kgf / m ² ; L dimensionless coefficient equal to 0.43 for the studied development objects; θ (T _pl R _pl ) ultimate dynamic shear stress of reservoir oil at reservoir values of temperature and pressure, dyne / m ² ; m porosity of the reservoir; Collector permeability
θ (T _pl P _pl ) =

0.33

+

-0.0516

+0.0408

0.0028

G $\genfrac{}{}{0ex}{}{\text{2}}{\text{a}}$ + G _m + G

0.04

0.252 dyne / cm ² (2)
where And the content of asphaltenes, 10.8 wt. With resin content, 24.4 wt. F _and the nitrogen content, m ³ / m ³ 3.93; G _{m the} content of methane, m ³ / m ³ 5,68; G _e the ethane content, m ³ / m ³ 4.15; L the distance between the wells is 200 m.

The threshold value of the pressure drop ΔP _{s was} determined by the formula (1), which for the weakly permeable zone was 18.5 kg / cm ² .

We measured reservoir pressure by quarters over the entire drilled fund, and constructed isobar maps for these dates. Wells (zones) with the highest rate of reservoir pressure drop were determined using isobar maps. In the elastic regime, such zones are the well region. N 10, located in the zone of sooy hydroconductivity and the area of the well N 4, located in the zone of good conductivity. After reducing the reservoir pressure by ΔР _from 18 kg / cm ^2, well No. 10, which has the highest rate of reservoir pressure drop and is located in the zone of weak hydroconductivity, was mastered by injection of the displacing agent (Fig. 5). This caused an increase in reservoir pressure in the weakly conductive zone III and in some wells located in zone I of good conductivity. In zone II of weak conductivity in the region of well N 11 and in the region of well N 4 located in zone I, the pressure continued to decrease. Well N 11 was mastered for water injection with the highest rate of reservoir pressure drop located in the zone of weak conductivity (Fig. 6). At the same time, there was an increase in reservoir pressure throughout the reservoir, but the intensity of the rate of pressure recovery in the region of well No. 4 was the lowest in the reservoir. As the production of waterlogged wells in the reservoir, the rate of reservoir pressure restoration in this zone decreased. Therefore, they mastered under injection of water from two wells N 3 and 4 with the same intensity of reservoir pressure recovery, well N 4 with lower conductivity in this zone (Fig. 7). At the same time, reservoir pressure was equalized throughout the zone.

Thus, the choice of a well for injection of an agent according to the proposed method ensures the development of all sections of the reservoir under water pressure, and the rate of selection of reserves of various zones is determined. At the same time, the oil recovery coefficient in the zones reaches the values, respectively: 25, 20, 21%
The economic effect of the application of the proposed method consists of additional oil production (ΔQ _n ) from II and III zones, which according to the prototype would be developed under elastic conditions with a final oil recovery coefficient of 7.8%, respectively. Then the additional oil production will be:
Q _n Q _b ^II (0.20 0.07) + Q _b ^III (0.21 0.08) 156 thousand tons

Claims (1)

 METHOD FOR THE DEVELOPMENT OF ZONOALLY HOMOGENEOUS OIL COLLECTOR PROPERTIES OF OIL DEPOSITS, including drilling wells with wells, extraction of hydrocarbons in the mode of depletion of reservoir energy with simultaneous control of reservoir pressure and permeability, and subsequent injection of the displacing agent into zones with low permeability, which differs in oil penetration, which is different in that they are carried out until the reservoir pressure is reduced by the value of the initial oil shear pressure between the selection zones and the aquifer, while under pressure Wells that use reservoir pressure and permeability control have the highest rate of pressure drop and lowest hydraulic conductivity, and as reservoir pressure recovers from the reservoir under injection pressure, additional wells are used with the lowest rate of reservoir pressure recovery and the lowest hydraulic conductivity.

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