CN110552695A - Rapid evaluation method for offshore oil reservoir polymer flooding feasibility under different oil prices - Google Patents

Abstract

The invention relates to a method for rapidly evaluating the feasibility of polymer flooding in offshore oil reservoirs under different oil prices. Standard comparison, if the standard is met, it will go to the next step, otherwise it is not feasible; 2: Determine the economic limit value of enhanced oil recovery R1 under the oil price to be evaluated through the economic limit value template of polymer flooding in offshore oil reservoirs under different oil prices; 3: Based on the EOR value templates of polymer flooding under different oil mobility of reservoirs, the EOR value R2 corresponding to the oil mobility Ω of the reservoir to be evaluated is determined. 4: If R2≥R1, the offshore oil reservoir is Polymer flooding is initially feasible, and vice versa. Using the invention to evaluate the feasibility of polymer flooding in offshore oil reservoirs, considering the influence of oil price, permeability and crude oil viscosity combination, etc., is more realistic and more accurate, avoids the risk of potential oil reservoirs being missed by single index judgment The rapid evaluation of reservoir flooding feasibility provides great support.

Description

A rapid evaluation method for the feasibility of polymer flooding in offshore oil reservoirs under different oil prices

technical field

The invention relates to a rapid evaluation method for the feasibility of polymer flooding in offshore oil reservoirs under different oil prices, and belongs to the technical field of chemical flooding enhanced oil recovery for oilfield development.

Background technique

At present, polymer flooding has become an important means of enhancing oil recovery in offshore oilfields. However, when evaluating the resource potential of polymer flooding in offshore reservoirs or quickly evaluating the feasibility of polymer flooding in an offshore reservoir, this is often not given. The specific polymer flooding scheme of the oil reservoir, but the key parameters of the reservoir (such as the depth of the reservoir, the salinity of the formation water, the temperature of the reservoir, the permeability, the viscosity of the underground crude oil, etc.) The parameters related to polymer flooding in the Technical Specification for Yield Method Screening SY/T6575-2016 are compared and roughly judged one by one, so as to judge whether the reservoir is suitable for polymer flooding and whether it is feasible. However, this method has the following problems: first, the influence of different oil prices on the selection of relevant indicators is not considered, resulting in inability to make detailed decisions under different oil prices; secondly, the selection and determination of a single indicator will ignore the combination of different parameters and indicators or the impact of complementary advantages and disadvantages, resulting in many Potential reservoirs were missed or misjudged.

Therefore, there is no method in the prior art that is relatively fast, considers comprehensive parameters, and can quickly evaluate the feasibility of polymer flooding in reservoirs under different oil prices. The traditional method has the problems of time-consuming and labor-intensive, omission of judgment and misjudgment, and failure to consider the impact of different oil prices.

SUMMARY OF THE INVENTION

In view of the above problems, the purpose of the present invention is to provide a rapid evaluation method for the feasibility of polymer flooding in offshore oil reservoirs under different oil prices, which can quickly determine the feasibility of polymer flooding in offshore oil reservoirs under different oil prices.

For achieving the above object, the present invention mainly comprises the following steps:

Step 1): Compare formation water salinity, formation water divalent ion content, reservoir temperature, oil layer lithology, and permeability coefficient of variation with industry standards, and enter step 2) if the conditions are met, otherwise the reservoir polymer is indicated drive is basically infeasible;

Step 2): Establish a template for the economic limit value of polymer flooding for enhanced oil recovery under different oil prices in offshore reservoirs. According to the oil price required for evaluation and the incremental operating cost of a single well, the oil price and the incremental operating cost of a single well are determined through the template. The economic limit R1 of polymer flooding enhanced oil recovery in offshore reservoirs;

Step 3): Establish a polymer flooding enhanced oil recovery value template under different oil mobility of reservoirs (that is, the ratio of different reservoir permeability and different formation crude oil viscosity), and calculate the reservoir oil flow of the reservoir to be evaluated Ω, and find the enhanced oil recovery value R2 corresponding to the oil mobility Ω of the reservoir through the template determined in this step.

Step 4): Compare the EOR value R2 corresponding to the oil mobility of the reservoir in step 3) with the EOR economic limit value R1 determined in step 2), if R2>R1, it proves that the Polymer flooding in offshore oil reservoirs is initially feasible and can be further studied; on the contrary, if R2<R1, it can be preliminarily judged to be infeasible.

In the step 1), the comparison process of formation water salinity, formation water divalent ion content, reservoir temperature, oil layer lithology, permeability coefficient of variation and industry standards is as follows:

①The salinity of formation water should be less than 60000mg/L, otherwise the polymer flooding of the reservoir is basically unfeasible;

②The total amount of divalent ions (Ca ²⁺ and Mg ²⁺ ) in formation water should be less than 300mg/L, otherwise polymer flooding in the reservoir is basically unfeasible;

③ The reservoir temperature must be less than 85℃, otherwise the polymer flooding of the reservoir is basically unfeasible;

④The lithology of the reservoir is clastic rock or carbonate rock, otherwise the polymer flooding of the reservoir is basically unfeasible;

⑤ The variation coefficient of reservoir permeability is 0.5-0.85, otherwise polymer flooding in this reservoir is basically unfeasible.

If any of the above ①-⑤ is not satisfied, the polymer flooding of the reservoir can be judged as basically infeasible.

In the step 2): establishing a polymer flooding enhanced oil recovery economic limit value template for offshore oil reservoirs under different oil prices, and according to the oil price required for evaluation, the template is used to determine the polymer flooding enhanced oil recovery in offshore oil reservoirs under this oil price economic limit. The specific process is as follows:

①Establish the economic evaluation model of polymer flooding in offshore oilfields. Specific steps are as follows:

a. The economic evaluation of polymer flooding is carried out using the financial net present value method, and the cash outflow includes investment, production cost and tax. Then the formula for calculating the net present value of polymer flooding is:

Among them, NPV is the net present value, yuan; i is the calculation time (i=1, 2, ...), years; Q _oi is the annual oil increase, square; Q _pi is the annual injection volume, _t ; ic is the expectation Yield, %; P _o is the price of crude oil, yuan/m3; α is the crude oil commodity rate, %; Is is the incremental _cost of single well investment, yuan/well; n is the number of injection wells, well; C _m is the increase in Mass production cost, yuan/square; P _p is the polymer price, yuan/t; R is the comprehensive tax rate, %; R _s is the resource tax rate, %.

b. Let NPV=0, according to the formula of net present value, the expression of economic enhanced oil recovery of polymer flooding can be obtained:

Among them, _Roe is the value of economic enhanced oil recovery, %; _ro is the ratio of annual oil increase to total oil increase, %; N is the produced geological reserves, square.

c. If the expected internal rate of return is 12%, and the development data of polymer flooding reservoirs in Bohai Oilfield and the investment and cost of polymer flooding are substituted into formula (2), the limit internal rate of return of polymer flooding in offshore oilfields can be obtained EOR expression under EOR is shown in Eq. (3).

Roe = _300.16 /(0.1783P _o -125.48) (3)

②According to formula (3), make the economic limit enhanced oil recovery chart of polymer flooding under different oil prices, as shown in Figure 2.

③ Set the oil price to be evaluated and the incremental operating cost of a single well, and compare the economic limit enhanced oil recovery chart to determine the economic limit enhanced oil recovery R1 under the oil price to be evaluated and the incremental operating cost of a single well.

In the step 3), the polymer flooding enhanced oil recovery value template and its specific numerical value acquisition process under different oil reservoir mobility (that is, the ratio of different reservoir permeability to different formation crude oil viscosity) are as follows:

①According to the current implementation of polymer flooding in Bohai Oilfield, a typical one-injection-one-production directional well reservoir numerical model is established, as shown in Figure 3.

②Fixing parameters such as injection-production well spacing, displacement fluid viscosity, polymer injection timing, injection speed, and injection age, only the combination of permeability and underground crude oil viscosity changes (permeability (1500mD ~ 12000mD) and underground crude oil viscosity) are studied. (The variation range of 150mPa·s～1200mPa·s) is divided into 8 equal parts), when different combinations are investigated by numerical simulation, the enhanced oil recovery value of typical model polymer flooding relative to water flooding is shown in Figure 4.

3. the formation permeability in accompanying drawing 4 is divided by formation crude oil viscosity, obtains reservoir oil reservoir oil mobility, and accompanying drawing 4 is further transformed into vertical well polymer flooding enhanced oil recovery under different oil reservoir reservoir oil mobility The value template, as shown in Figure 5.

④ Calculate the oil mobility of the oil reservoir, and obtain the corresponding enhanced oil recovery value R2 under the mobility with reference to Fig. 5 .

In the step 4), the R1 in the step 2) is compared with the R2 in the step 3). If R2>R1, it proves that the polymer flooding of the offshore oil reservoir is preliminarily feasible, and further research can be done; on the contrary, if R2< R1, it can be preliminarily determined to be infeasible.

Description of drawings

Figure 1 is a diagram of a rapid evaluation method for the feasibility of polymer flooding in offshore oilfields under different oil prices;

Fig. 2 is the schematic diagram of the economic enhanced oil recovery chart (different single well incremental operating costs) of polymer flooding in the Bohai Oilfield of the present invention;

3 is a schematic diagram of a polymer flooding-injection-production model of a typical directional well in the Bohai Oilfield of the present invention;

Figure 4 is a schematic diagram of the enhanced oil recovery value of polymer flooding relative to water flooding under different viscosities and permeability of a typical model of the present invention;

Fig. 5 is a polymer flooding enhanced oil recovery value template of the present invention under different oil mobility of reservoirs.

Detailed ways

In order to make the purposes, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments These are some embodiments of the present invention, but not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

Example 1:

As shown in FIG. 1 , the present invention provides a rapid evaluation method for the feasibility of polymer flooding in offshore oil reservoirs under different oil prices. Through the chart provided by the method, combined with oil prices and reservoir parameters, it is possible to quickly obtain whether the offshore oil reservoir is suitable for Carry out polymer flooding, including the following steps:

1. Collect the basic information of the oil reservoir, compare the formation water salinity, formation water divalent ion content, reservoir temperature, oil layer lithology, and permeability variation coefficient with the industry standard, and go to step 2 if the conditions are met. Otherwise, the polymer flooding of the reservoir is basically unfeasible.

When this step is implemented, in terms of specific judgment criteria, as long as one index does not meet the requirements of the industry standard, it can be preliminarily judged that polymer flooding in the offshore oil reservoir is basically infeasible. For example, the salinity of formation water in this reservoir is 10000mg/L, the total content of divalent ions such as Ca ²⁺ and Mg ²⁺ in formation water is 180mg/L, the reservoir temperature is 66°C, and the lithology of the reservoir is sandstone (clastic rock) A), the permeability coefficient of variation is 0.6, the formation permeability is 5700mD, and the formation crude oil viscosity is 300mPa·s. Combined with the industry standard "Technical Specifications for Oilfield Enhanced Oil Recovery Methods Screening SY/T6575-2016", it is found that the salinity of formation water, the content of divalent ions in formation water, the reservoir temperature, the lithology of the oil layer, and the coefficient of variation of permeability are all consistent with Standard requirements, so you can go to step 2. If the total content of divalent ions such as formation water Ca ²⁺ and Mg ²⁺ in the reservoir is 1200mg/L, or the individual indicators such as reservoir temperature 96°C do not meet the above industry standards, the reservoir polymer is directly considered Drive is not possible.

2. Combined with the oil price used in the evaluation and the incremental operation cost of a single well, determine the economic limit of the polymer flooding in the offshore oil field to enhance the oil recovery value R1.

If the oil price used in the feasibility evaluation is 30$/bbl, 50$/bbl, and the incremental investment of a single well is 6 million yuan/well, then according to Figure 2, it can be obtained that the economic limit enhanced oil recovery values are 3.2 and 3.2 respectively. 1.3 percentage points.

3. Calculate the oil mobility Ω of the reservoir, and obtain the corresponding enhanced oil recovery value under this mobility with reference to Figure 5 .

In this step, the calculation method of the oil mobility of the oil reservoir is: oil mobility of the reservoir reservoir=reservoir permeability÷subsurface oil viscosity, the unit is mD/mPa·s. According to the assumed reservoir parameters mentioned in step 1, the reservoir oil mobility Ω=5700mD÷300mPa·s=19mD/mPa·s.

Further, referring to Fig. 5, it can be obtained that when the oil mobility of the reservoir is 19 mD/mPa·s, the enhanced oil recovery value of the polymer flooding in the offshore oil reservoir is 9 percentage points.

4. Compare the EOR value R2 corresponding to the oil mobility of the reservoir in step 3 with the EOR economic limit value R1 determined in step 2. If R2>R1, it proves that the offshore oil reservoir has aggregated The material flooding is preliminarily feasible, and further research can be done; on the contrary, if R2<R1, it can be preliminarily judged to be infeasible.

By comparison, it is found that the 9 percentage points obtained in step 3 are significantly higher than the 3.2 and 1.3 percentage points obtained in step 2. Therefore, when polymer flooding is performed in this offshore oil reservoir, if the incremental investment of a single well is 6 million yuan/well, then Whether the oil price is 30$/bbl or 50$/bbl, it can be determined that the polymer flooding of the offshore reservoir is feasible.

In the specific implementation process of this example, the economic limit enhanced oil recovery charts under different oil prices and the incremental operation cost of offshore polymer flooding single wells are pre-made, and the oil-reservoir mobility charts for different oil reservoirs are pre-made. Offshore polymer flooding enhanced oil recovery chart, only need to implement steps 1, 2, and 3 when determining the feasibility of offshore polymer flooding. The screening and determination of a single index will lead to the risk of many potential reservoirs being missed or misjudged (for example, according to the conventional screening method, in this example, the viscosity of underground crude oil of 300 mPa s will be considered unsuitable for polymer flooding, but the conventional method Without considering the positive impact of high permeability, the reservoir oil mobility method proposed in the patent of the present invention combines the reservoir permeability with the viscosity of the underground crude oil, which effectively avoids this risk). Therefore, the reservoir crude oil mobility method combining reservoir permeability and underground crude oil viscosity is used to quickly judge the feasibility of polymer flooding in offshore oil reservoirs. This idea and method should be the first content to be protected in the present invention. In addition, different The enhanced oil recovery chart of the polymer flooding in the offshore oil reservoir under the oil mobility of the oil reservoir and the overall rapid evaluation method finally formed by the present invention should also be the key protection contents of the present invention.

The specific embodiments described above further describe the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention, and are not intended to limit the scope of the present invention. protected range. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. A method for rapidly evaluating the offshore reservoir polymer flooding feasibility under different oil prices is characterized by comprising the following steps:

Step 1): comparing the salinity of the formation water, the content of divalent ions of the formation water, the temperature of a reservoir, the lithology of an oil layer and the variation coefficient of permeability with the industrial standard, and entering a step 2) if the conditions are met, otherwise, indicating that the oil reservoir polymer flooding is basically infeasible;

Step 2): establishing an economic limit value template of polymer flooding enhanced recovery under different oil prices of the offshore oil reservoir, and determining an economic limit value R1 of polymer flooding enhanced recovery of the offshore oil reservoir under the oil prices and the single-well incremental operating cost through the template according to the oil prices required by evaluation and the single-well incremental operating cost;

Step 3): establishing a polymer flooding enhanced recovery rate value template under different oil reservoir crude oil mobility (namely, the ratio of different reservoir permeability to different formation crude oil viscosity), calculating the reservoir crude oil mobility omega of the oil reservoir to be evaluated, and finding an enhanced recovery rate value R2 corresponding to the reservoir crude oil mobility through the template determined in the step.

Step 4): comparing the enhanced recovery rate value R2 corresponding to the reservoir crude oil fluidity in the step 3) with the enhanced recovery economic limit value R1 determined in the step 2), and if R2 is more than or equal to R1, proving that the offshore oil reservoir polymer flooding is primarily feasible and can be further researched; conversely, if R2< R1, it may be preliminarily determined to be infeasible.

2. The method for rapidly evaluating the feasibility of offshore oil reservoir polymer flooding at different oil prices according to claim 1, characterized in that when compared with industry standards, the single indexes of formation water mineralization, formation water divalent ion content, reservoir temperature, reservoir lithology and permeability variation coefficient do not meet standard requirements, namely the oil reservoir polymer flooding is directly considered to be infeasible, but the single indexes do not include two indexes of reservoir permeability and underground crude oil viscosity.

3. The method for rapidly evaluating the feasibility of offshore reservoir polymer flooding at different oil prices according to claim 1, wherein two single indexes of reservoir permeability and underground crude oil viscosity need to be considered in combination during evaluation. In the rapid evaluation method, the reservoir permeability and the underground crude oil viscosity are combined in a mode of the crude oil mobility of the reservoir of the oil reservoir, and the crude oil mobility of the reservoir of the oil reservoir is used for judging. The method for calculating the crude oil fluidity of the oil reservoir comprises the following steps: reservoir crude oil mobility ═ reservoir permeability ÷ underground crude oil viscosity, in mD/mPa · s units.

4. The method for rapidly evaluating the feasibility of offshore oil reservoir polymer flooding at different oil prices according to claim 1, characterized in that a template of economic limit value of polymer flooding enhanced recovery at different oil prices of the offshore oil reservoir and a template of enhanced recovery value of polymer flooding at different reservoir crude oil fluidity (i.e. ratio of different reservoir permeability to different formation crude oil viscosity) are established, so as to facilitate comparison and query.

5. The method for rapidly evaluating the feasibility of offshore reservoir polymer flooding at different oil prices according to claim 1, characterized in that the evaluation of the feasibility of offshore reservoir polymer flooding at different crude oil prices and single well incremental operating expenses can be realized by the chart of claim 4.

6. The method for rapidly evaluating the feasibility of polymer flooding of offshore reservoirs at different oil prices according to claim 1, characterized in that the evaluation of the feasibility of polymer flooding of offshore reservoirs at different crude oil prices and at single-well incremental operating costs can be more rapidly and conveniently carried out by the plate of claim 4.

7. The method for rapidly evaluating the feasibility of the offshore reservoir polymer flooding at different oil prices according to claim 1, wherein the risk of missed selection or erroneous judgment of a plurality of potential reservoirs suitable for polymer flooding due to single index screening and judgment is effectively avoided when the feasibility of the offshore reservoir polymer flooding at different oil prices is rapidly evaluated.