CN106050196A - Method for determining good transfer-injection opportunity for early polymer injection of offshore heavy oil reservoir - Google Patents

Abstract

The invention discloses a method for determining the optimal timing of early polymer injection in offshore heavy oil reservoirs. The steps are as follows: (1) Obtaining the phase-permeability relationship between the two through the oil-water/oil-polymer phase permeability experiment of the core ; (2) Analyze the relationship between the mobility ratio and the water saturation through the formula of the mobility ratio, and judge the injection timing with M≤1; (3) Further analyze the water cut and the rate of change of the water cut and the reservoir water saturation (4) By comparison, it is found that the peak value of the water content change rate is consistent with the water saturation of M=1. That is, the timing of early polymer injection transfer is determined by the peak value of water cut change rate. This method is based on theoretical basis to guide the injection timing of polymer flooding, and can quickly and accurately determine the optimal timing of injection in offshore heavy oil reservoirs.

Description

A method for determining the optimal timing of early polymer injection in offshore heavy oil reservoirs

technical field

The invention belongs to the technical field of petroleum processing, and in particular relates to a method for determining a better timing for early polymer injection in offshore heavy oil reservoirs.

Background technique

Polymer flooding technology has matured in my country's onshore oilfields. After continuous technical research, it was applied to the polymer flooding development of offshore heavy oil reservoirs in 2007. However, due to the influence of the life of the offshore platform, it is imperative to speed up the development efficiency (Zhang Xiansong, Sun Fujie, Feng Guozhi, etc. Research and field test on the influencing factors of polymer flooding in heavy oil fields in Bohai Sea[J]. China Offshore Oil and Gas, 2007,19 (1):30-34).

Academician Zhou Shouwei proposed a new model of offshore oil reservoir development: blurring the boundaries of primary, secondary, and tertiary oil recovery, and through technological innovation and innovative technology integration, the oil field can quickly reach peak production and high-speed production in the early stage of production, and maintain strong productivity. Therefore, early injection is the core content of developing new models. For the polymer flooding development of heavy oil reservoirs, there should be a relatively optimal polymer injection timing, which can further increase the recovery rate and obtain the most ideal recovery rate compared with high water-cut polymer injection. After continuous research on physical model experiments and numerical simulations, it is concluded that polymer flooding in heavy oil reservoirs has the best effect of polymer injection under the condition of reservoir water cut of 0% or lower, and this result is also widely recognized by industry scholars. The water cut of the reservoir is 0%, that is, no water is produced in the production and development of the reservoir. This time period is a very wide time range. Moreover, the indoor research is also an experimental research for a certain block, which has certain limitations, and cannot guide other oil reservoirs of different types, nor can it quickly determine the timing of re-injection. Therefore, there is a need for a means to judge the best timing of transfer injection in the development of offshore oil reservoirs.

Contents of the invention

The purpose of the present invention is to provide a method for determining the optimal timing of polymer flooding in the early stage of polymer flooding development in offshore oil reservoirs. The method can quickly and accurately judge the optimal timing of polymer flooding in reservoirs. The actual development of physical flooding production provides transfer guidance.

In order to achieve the above-mentioned technical purpose, the present invention proposes such a judging method for judging the optimal timing of early polymer injection in heavy oil reservoirs. The method includes the following steps:

Step 1. Obtain the oil-water relative permeability curve through the indoor relative permeability experiment;

Step 2, using the mobility ratio formula for the oil-water phase permeability curve, analyzing the relationship between the water saturation and the mobility ratio M;

Step 3, using the oil-water phase permeability curve data, through the shunt flow equation, to obtain the relationship between water content and water saturation;

Step 4, deriving the water content fw, obtaining df _w /dt, and obtaining the relationship between the water content change rate and the water saturation;

Step 5, through data analysis, the best timing for polymer injection in the early stage of polymer flooding can be judged by the change rate of water cut.

Further, in the step 1, the oil-water/oil-accumulation relative permeability curve is obtained by taking a short core of φ25×80mm on site, degassing crude oil on the ground, and injecting water into the formation. Under the condition of formation temperature, the “unsteady State method" to measure the relative permeability curve.

Further, through the analysis of the data map obtained in step 2, it is obtained that the optimal injection timing range of polymer flooding is M≤1. In step 2, when the mobility ratio M=1, it is isoviscosity displacement, which is generally understood as "near-piston" displacement, and the displacement efficiency is better; when M<1, it is the high-viscosity fluid that displaces the low-viscosity fluid , the displacement efficiency is good; when M>1, low viscosity displaces high viscosity, that is, the most common "fingering phenomenon" occurs, the displacement efficiency decreases, and the sweep efficiency decreases accordingly.

Further, in said step 2, according to the mobility ratio formula,

$\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; \&CenterDot;</span>\frac{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}$

Calculate and analyze the relationship between water saturation and mobility ratio M.

Further, in the step 3, using the shunt equation

${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}}$

Converting the relative permeability relationship to component flow yields the water cut versus water saturation relationship.

Further, in the step 5, the water saturation about the mobility ratio is compared with the water saturation of the rate of change of the water content, and it is found that the maximum value of the rate of change of the water content is the value of M=1; The size can be used to judge the best timing of polymer injection in the early stage of polymer flooding.

The polymer flooding technology is to control the oil-water displacement front, expand the sweep efficiency, and improve the displacement efficiency; when the rate of water cut change reaches the fastest, it indicates that the injected water breaks through the reservoir. Channels are formed, and after the oil-water mobility ratio M>1, M rises very rapidly, which is not conducive to the fluidity control function of the polymer. Therefore, the timing of re-injection should be judged by the rate of change of moisture content.

Beneficial effects of the present invention: the method provided by the present invention for determining the optimum transfer timing of polymer flooding in offshore heavy oil reservoirs can be relatively simple and fast, and can accurately obtain the range of transfer timings for polymer flooding in heavy oil reservoirs, which is The actual development of heavy oil polymer flooding production provides guidance for transfer injection.

Description of drawings

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Fig. 1 is the oil-water relative permeability curve diagram under the reservoir condition;

Fig. 2 is the curve diagram of water content and water content change rate with respect to water saturation;

Fig. 3 is the relationship diagram of the variation of the mobility ratio with respect to the water saturation;

Fig. 4 is a judgment limit diagram of the optimal reinjection timing under specific reservoir conditions.

detailed description

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

As shown in Figures 1 to 4, it is an embodiment of the present invention, a method for judging the optimal timing of early polymer injection in heavy oil reservoirs, and the method includes the following steps:

(1) First prepare the relevant experimental procedures and experimental materials, ① core: on-site coring φ25×80mm; ② crude oil: surface degassed crude oil viscosity 122.8mPa·s; ③ injection water: formation simulated mixed water injection. The oil/water relative permeability curve is measured according to the "unsteady state method" of the national industry standard, as shown in Figure 1.

(2) Utilize formula 2 mobility ratio to oil-water relative permeability curve, analyze the relationship between mobility ratio M and water saturation, see Fig. 2;

(3) Using the shunt equation of formula 1 to convert the relative permeability relationship into component flow rate, and obtain the relationship between water cut and water saturation;

(4) Deriving the water content f _w to obtain df _w /dt, and obtaining the relationship between the water content change rate and the water saturation, as shown in Figure 3.

(5) It is mentioned in reservoir physics that when the mobility ratio of the displacing phase to the displacing phase is M≤1, it is beneficial to the displacing effect; The viscosity of the displacement phase is beneficial to control the mobility ratio and improve the sweep efficiency.

(6) Through the analysis of the data diagram obtained in (3)(5), see Fig. 4, it is found that the water saturation at M=1 is 0.175 and the same as the water saturation when the rate of increase of the water content reaches the maximum value. Since the mobility ratio is not easy to obtain in practical applications, it is judged by the water content and the rate of change of the water content, that is, when the rate of increase of the water content reaches the maximum value, it is the best timing for injection.

The method provided by the present invention for polymer flooding at the early stage of polymer flooding in offshore heavy oil reservoirs can simply and quickly obtain the timing of polymer flooding in offshore heavy oil reservoirs, and can provide transfer injection for the actual development of heavy oil polymer flooding production. guide.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the present invention. within the scope of protection.

Claims (7)

1. A method for judging the optimal timing of early polymer injection in heavy oil reservoirs, characterized in that the method comprises the following steps: Step 1. Obtain the oil-water relative permeability curve through the indoor relative permeability experiment; Step 2, using the mobility ratio formula for the oil-water phase permeability curve, analyzing the relationship between the water saturation and the mobility ratio M; Step 3, using the oil-water phase permeability curve data, through the shunt flow equation, to obtain the relationship between water content and water saturation; Step 4, deriving the water content fw, obtaining dfw/dt, and obtaining the relationship between the water content change rate and the water saturation; Step 5, through data analysis, the best timing for polymer injection in the early stage of polymer flooding can be judged by the change rate of water cut. 2. A method for judging the optimal timing of early polymer injection in heavy oil reservoirs according to claim 1, characterized in that, in said step 1, the relative permeability curve of oil-water/oil-accumulation is obtained by on-site coring φ25 The short core of ×80mm, as well as on-site ground degassed crude oil and formation water injection, under the condition of formation temperature, use the "unsteady state method" to measure the relative permeability curve. 3. the method for judging the optimal injection timing of early polymer injection in a kind of heavy oil reservoir according to claim 1, characterized in that, by analyzing the data map obtained in step 2, the optimal injection timing range for polymer flooding is M≤1. 4. A method for judging the optimal timing of early polymer injection in heavy oil reservoirs according to claim 3, characterized in that, in step 2, when the mobility ratio M=1, it is isoviscosity displacement, which is commonly understood It is a "near-piston" displacement, and the displacement efficiency is better; when M<1, the high-viscosity fluid displaces the low-viscosity fluid, and the displacement efficiency is good; when M>1, the low-viscosity fluid displaces the high-viscosity fluid, that is, The most common "fingering phenomenon" occurs, the displacement efficiency decreases, and the sweep efficiency decreases accordingly. 5. The method for judging the optimal timing of early polymer injection in a heavy oil reservoir according to claim 1, characterized in that, in step 2, according to the mobility ratio formula, $\mathrm{<span\; class="notranslate">\; m</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; S</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; .</span>\frac{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; o</span>}}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}}$ Calculate and analyze the relationship between water saturation and mobility ratio M. 6. The method for judging the optimal timing of early polymer injection in heavy oil reservoirs according to claim 1, characterized in that, in step 3, the flow distribution equation is used ${\mathrm{<span\; class="notranslate">\; f</span>}}_{\mathrm{<span\; class="notranslate">\; w</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; m</span>}}}$ Converting the relative permeability relationship to component flow yields the water cut versus water saturation relationship. 7. The method for judging the optimal timing of early polymer injection in a heavy oil reservoir according to claim 1, characterized in that, in step 5, the water saturation of the water saturation of the mobility ratio and the water cut rate of change are calculated. It is found that the maximum change rate of water cut is the value of M=1, which shows that the change rate of water cut is related to the mobility ratio, and before the maximum rate is the best time to control the flow ratio; that is Judging the optimal timing of polymer injection in the early stage of polymer flooding by the change rate of water cut.