RU2490428C1 - Oil deposit development method - Google Patents

Abstract

FIELD: oil and gas industry.

SUBSTANCE: during oil deposit development air is pumped through injection wells and oil is extracted through producing wells. Bed shaliness and sintering temperature for clay is predetermined; then in-place permeability is defined after clay sintering; a radius of borehole environment with varied permeability is calculated where balancing of injection pressure with formation pressure takes place. Borehole environment of the injection well is treated thermally by air pumping and arrangement of dry burning in the borehole environment and sintering of clays till the calculated radius is reached in the area treated thermally. At that air pumping is stopped periodically and water is pumped in order to cool and crack sintered clay. Thereafter pumping of a working agent is started.

EFFECT: improvement of oil recovery factor for the oil deposit with low-permeability reservoir.

1 ex, 3 dwg

Description

The invention relates to the oil industry and may find application in the development of oil deposits.

A known method of developing a highly viscous oil field, including the injection of an oxidizing agent, the organization of in-situ combustion, the selection of oil and the injection of a polymer non-combustible water-soluble material (RF Patent No. 2429346, publ. September 20, 2011).

The known method is applicable only to deposits with high permeability of the reservoir.

Closest to the proposed invention in technical essence is a method of developing deposits of highly viscous oil or bitumen, according to which air is pumped into the formation, dry in situ combustion is initiated, followed by air and water injection and wet in situ combustion. A reagent is introduced into the injected water, during thermolysis of which an insoluble precipitate and oxygen are formed on the combustion front. As a reagent, potassium permanganate is used in an amount of 55-60 g / l of water or calcium nitrate in an amount of 1000-1100 g / l of water. Oxygen released during thermolysis intensifies the combustion process. The choice of chemicals depends on the temperature at the combustion front, which depends mainly on the fuel concentration of 1 m ^{3 of} rock and the physicochemical properties of oil and rock (RF Patent No. 1630375, publ. 03/27/1995 - prototype).

The disadvantage of this method is the low oil recovery deposits. This drawback is especially noticeable when developing a reservoir with a low permeability formation, the reservoir of which is close in properties to a non-reservoir.

The proposed invention solves the problem of increasing oil recovery of an oil reservoir with a low permeability reservoir.

The problem is solved in that in the method of developing an oil deposit, including air injection through injection wells and oil extraction through production wells, according to the invention, the clay content of the formation and sintering temperature of clays are preliminarily determined, the permeability of the formation after sintering of clays is determined, the radius of the near-wellbore zone with altered permeability is calculated where the injection pressure is equalized with reservoir pressure, heat treatment of the near-wellbore zone of the injection well is carried out by injection into air with the organization of dry combustion in the near-wellbore zone and sintering of clays until the heat-treated zone of the calculated radius is reached, the air injection is periodically stopped and a rim of water is pumped in to cool and crack the sintered clay, and then proceed to pump the working agent.

SUMMARY OF THE INVENTION

The development of an oil reservoir with a reservoir, the permeability of which is close to zero, presents certain difficulties due to the difficulty of injecting a working agent into the reservoir, which is most often water. Even a significant increase in pressure and the use of stimulation technologies such as hydraulic fracturing, does not lead to the desired result. The presence of clays in the reservoir during flooding leads to swelling of clays, an even greater decrease in permeability, and makes development almost impossible. There are practically no real ways to develop such deposits, and well-known technical solutions for waterflooding or in-situ burning do not allow developing a deposit with high oil recovery. The proposed invention solves the problem of increasing oil recovery deposits with low permeability reservoir. The problem is solved as follows.

During the development of an oil deposit, air is pumped through injection wells and oil is taken through production wells. Clay clay and sintering temperature of clays are preliminarily determined. Determine the permeability of the formation after sintering clays. The radius of the near-wellbore zone with a changed permeability is calculated, as well as the radius at which the injection pressure and reservoir pressure are equalized. Heat treatment of the near-borehole zone of the injection well is carried out by air injection with the organization of dry combustion and sintering of clays until the heat-treated zone reaches the calculated radius. Periodically stop the injection of air and pump a rim of water to cool and crack sintered clay. After that, they proceed to the download of the working agent. After heat treatment, clay permeability increases. During heat treatment, clay is fired and converted into porous stone. Periodic water cooling contributes to the phased creation layer by layer of sintered clay stone and increase the permeability of the collector.

We give some calculations of the proposed method. We make some assumptions. Let heating to temperature T ^* increase the permeability k by a factor of n, i.e. k ^* = nk. Let as a result of processing the permeability increased n times in the radius r ^* from the well (Fig. 1). Then we will write how well injectivity will change

$$Q_I=\frac{2\pi h{k}^{*}}{\mu B}\frac{(p_C-p^{*})}{\ln \left(\raisebox{1ex}{$r^{*}$}\!\left/ \!\raisebox{-1ex}{$r_C$}\right.\right)}(\mathrm{one})$$

$$Q_{II}=\frac{2\pi h{k}^{*}}{\mu B}\frac{(p^{*}-p_K)}{\ln \left(\raisebox{1ex}{$r_K$}\!\left/ \!\raisebox{-1ex}{$r^{*}$}\right.\right)}(2)$$

Formula (1) expresses the flow of the injected agent from the well in zone I (Fig. 1), which is determined by the cylindrical region r_C<r <r^*, where r_C - well radius. Formula (2) expresses the flow in zone II (figure 1) - a cylindrical region with r^*<r <r_K. In (1) and (2), the following notations were adopted: h is the reservoir thickness, B is the volumetric coefficient of the injected agent, μ is its viscosity, p_C - bottomhole pressure, p^* - pressure at a distance r^*, r_K - the distance at which the pressure is compared with the reservoir, p_K - reservoir pressure.

From the law of conservation of flow it follows that Q _I = Q _II , therefore, throttle response

$$Q=Q_I=Q_{II}=\frac{2\pi hk{k}^{*}}{\mu B}\left(\frac{p_C-p_K}{k^{*}\ln \left(\raisebox{1ex}{$r_K$}\!\left/ \!\raisebox{-1ex}{$r^{*}$}\right.\right)+k\ln \left(\raisebox{1ex}{$r^{*}$}\!\left/ \!\raisebox{-1ex}{$r_C$}\right.\right)}\right)$$

The dependence of the flow on the processing radius is shown in Fig.2. Here it was believed that r _K = 25 m is the distance at which the pressure is compared with the reservoir, and r _C = 0.2 m is the radius of the well.

The processing radius depends on the amount of oxidant injected. How much the permeability has increased depends on the temperature created, respectively, both on the amount of oxidant injected and on the rate of injection of the oxygen-containing mixture.

Concrete example

An oil reservoir is developed with the following characteristics: average depth - 2631 m, reservoir temperature 92 ° C, initial reservoir pressure 26.8 MPa, porosity 0.18%, permeability (core) 2.4 mD, average oil saturation 0.52, reservoir - clay cement, has a polymineral composition and is represented by kaolinite - from 31 to 49%, hydromica - from 14 to 34%, chlorite - from 23 to 35%, mixed-layer formations - from 5 to 13%, the volume of cement varies from 8 to 19%, oil viscosity 1.77 / 1.38 MPa * s, oil density at reservoir conditions: 0.818 g / cm ³ , oil density at surface conditions: 0.867 g / cm ³ , the average total thickness of the reservoir is 96.7 m, the average effective oil saturated thickness is 8.3 m, the reservoir is porous, the type of deposit is lithological, the oil-water contact (WOC) is not opened.

According to the results of core research, clayey clay and sintering temperature of clays are determined. Clay content is from 8 to 19%, the sintering temperature of clay is 150-600 ° C. Determine the permeability of the formation after sintering clays. The dependence of the increase in permeability on temperature is shown in Fig 3.

The radius of the near-wellbore zone with a changed permeability, which depends on the propagation of the heat front, and the radius at which the injection pressure is equalized with the reservoir pressure, are calculated. Heat treatment of the near-well zone of the injection well is carried out by air injection with the organization of dry combustion in the near-well zone according to the following regime: for 3 months - air injection at a rate of 24,000 nm ³ / day, after which within 2 weeks - water injection at a rate of 100 m ³ / day The cycle is repeated at least 4 times.

T.O. clay sintering is carried out until the heat-treated zone reaches a calculated radius of 26.3 m.

This radius is calculated as follows:

The number of days of air injection is 4 * 90 = 360. The air injection rate is 24000 nm ³ / day, and under reservoir conditions 89.5 m ³ / day. The volume of injected air in reservoir conditions is 360 * 89.5 = 32239 m ³ . The number of days of water injection is 4 * 14 = 56. The rate of water injection is 100 m ³ / day. The volume of injected water in reservoir units is 56 * 100 = 5600 m ³ . Summary uploaded volume - Q _sums = 37839 m ^3. Porosity - m = 0.18. The volume of the rock covered by the impact is V _breed = Q _sum /m=37839/0.18=210217 m ³ . The bottom-hole zone is a cylinder, the volume of which is: m ³ . V _cyl = π * R ² * H. In this case, H = 96.7 m. Therefore

$$R=\sqrt{\frac{V_{P\mathrm{about}R\mathrm{about}ds}}{\pi \ast H}}=\sqrt{\frac{\left[m^3\right]}{\pi \ast \left[m\right]}}=\sqrt{\left[m^2\right]}=\left[m\right]=\sqrt{\frac{Q_{\mathrm{from}\mathrm{at}mm\mathrm{but}Rn\mathrm{about}e}/m}{\pi \ast H}}=\sqrt{\frac{210217}{303.7}}=26.3m.$$

In this case, we believe that the entire zone covered by the action of the pumped fluid is subjected to heat treatment (due to the processing sequence, which is determined by the radial propagation of the heat front). And in turn, the zone covered by thermal exposure is a zone with altered permeability. Also, in this case (in the near-wellbore zone), when calculating the area affected by the thermal effect, we neglect the thermal conductivity, since the heat distribution due to the transfer of matter dominates the radial thermal conductivity (thermal conductivity per year gives less than a meter).

Thus, the radius of the near-wellbore zone with altered permeability is 26.3 m.

The radius at which the injection pressure is equalized with reservoir pressure is obtained from the calculation of the supply circuit.

It should be noted that although "in any mathematical models, the propagation of disturbances caused by the application of depression or repression on the reservoir gives a continuous function of pressure rise or fall when moving away from the well in the horizontal plane to infinity", discarding the "tail" of the function, you can get the radius where the injection pressure will be close to the reservoir pressure.

We introduce a number of concepts: p _k = p (r, 0) - the initial condition, it is the reservoir pressure. p _c = p (r _c , t) is the boundary condition at the well, it is the bottomhole pressure, where r _c is the radius of the well, at is time. p _r = p _c p _k - value repression, γ = 1.781 - Euler's constant, χ - diffusivity coefficient reservoir to - the threshold pressure gradient. Find r (t) - the radius of the power circuit from the following equality:

$$r(t)=\frac{{\mathrm{<figure-callout\; id="0"\; label="p\; p\; g"\; filenames="00000008.png,00000009.png"\; state="\{\{state\}\}">p\; </figure-callout>}}_p}{g_{}}$$

Thus, due to the fact that p _p = 45 [MPa] -26.8 [MPa] = 18.2 [MPa], γ = 1.781, t = 421 days, r _c = 0.2 m, a typical value of g ₀ = 0.0475 [MPa / m], χ = 864000 [m ² / day].

$$\begin{array}{l}r(t)=\frac{MP\mathrm{but}}{\frac{\left[MP\mathrm{but}\right]}{\left[m\right]}\frac{\left[m\right]}{\left[m\right]}}=\left[m\right]=\frac{18.2}{{0.0475}^{*}\mathrm{<figure-callout\; id="2"\; label="ln"\; filenames="00000008.png"\; state="\{\{state\}\}">ln</figure-callout>}\frac{2\sqrt{864000\ast 421}}{1.781\ast 0.2}}=\frac{18.2}{0.0475\ast \ln \frac{38144}{0.3562}}\\ =\frac{18.2}{0.0475\ast \ln 107085}=\frac{18.2}{0.0475\ast 11.581}=\frac{18.2}{0.55}=33.1\left[m\right]\end{array}$$

As a result of the calculations, we obtain the radius at which the injection pressure is equalized with a reservoir pressure of 33.1 m.

Periodically, namely after three months of air injection, it stops pumping and a rim of water is pumped in a volume of 1400 m ³ to cool and crack sintered clay.

Go to the injection of the working agent (cold water) through injection wells and the selection of oil through production wells.

As a result, oil recovery increased from 0.151% (according to the prototype) to 0.441% (according to the proposed method)

The application of the proposed method will improve oil recovery deposits.

Claims (1)

A method of developing an oil deposit, including air injection through injection wells and oil extraction through production wells, characterized in that the clay content of the formation and sintering temperature of the clays are preliminarily determined, the permeability of the formation after sintering of clays is determined, the radius of the near-wellbore zone with altered permeability, at which alignment occurs, is calculated injection pressure with reservoir pressure, conduct heat treatment of the near-wellbore zone of the injection well by air injection with the organization of dry about burning in the near-wellbore zone and sintering the clay until the heat-treated zone reaches the calculated radius, periodically stop the air injection and pump a rim of water to cool and crack the sintered clay, and then proceed to pump the working agent.

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