CN104949899B - A kind of assay method of Polymer Used For Oil Displacement effective viscosity in porous media - Google Patents

Abstract

The invention discloses a method for measuring the effective viscosity of a polymer for oil displacement in a porous medium, which is characterized in that it consists of the following steps: a) prepare a polymer solution for oil displacement; b pass the relationship curve between shear stress and shear rate , get the consistency coefficient H and flow index n of the polymer solution by regression; c fill the sand pipe model, and measure the permeability k and porosity of the sand pipe model d Polymer solution floods the sand-fill pipe; e Subsequent water flooding: measure the hydraulic permeability k _f and residual resistance coefficient F _RR after polymer flooding; f corrects the Blake-kozeny equation, and finally obtains the effective viscosity calculation formula as formula ( 5) or formula (6): or g. Consistency coefficient H, flow index n, permeability k, hydraulic permeability k _f after polymer flooding, porosity Or the residual resistance coefficient F _{RR is} substituted into the above formula to calculate the effective viscosity.

Description

A method for measuring the effective viscosity of polymers used for oil displacement in porous media

technical field

The invention belongs to the technical field of measuring the viscosity of a polymer used for oil displacement in oilfield tertiary oil recovery, and in particular relates to a method for measuring and calculating the effective viscosity of a polymer used for oil displacement in a porous medium.

Background technique

At present, polymer flooding has become an important means to increase and stabilize production in the old oilfields in eastern China. Most of the displacement agents used in polymer flooding are acrylamide copolymers, such as partially hydrolyzed polyacrylamide, cationic polyacrylamide, hydrophobic Associative polyacrylamide, etc. It is generally believed that the main mechanism of polymer flooding is to reduce the mobility of the water phase, improve the water-oil mobility ratio, and then increase the sweep coefficient to achieve the purpose of enhancing the recovery factor. There are usually two ways to reduce the mobility of the water phase: increase the viscosity of the water phase and reduce the permeability of the water phase (Zhang Peng, Wang Yefei, Zhang Jian et al., Several Influencing Factors of Hydrophobic Association Polyacrylamide Displacement Ability, Oilfield Chemistry, 2010, Volume 72, Issue 4, pages 462-468). Therefore, the viscosity of the polymer solution is one of the important indicators to measure the performance of the displacement agent. It should be noted that the viscosity of the water phase mentioned here is not the apparent viscosity, but the effective viscosity of the polymer solution when it percolates in the porous medium. This viscosity not only includes the viscosity factor of the polymer solution in the porous medium, but also Elasticity is included. Therefore, the effective viscosity of the polymer more truly reflects the viscosity of the polymer when it flows in the porous medium, and it is more valuable for the design and implementation of the mine plan (Cheng Jiecheng, Flow characteristics of BP16 solution in porous media, Daqing Petroleum Geology and Development, Volume 8, Issue 2, 1989, pages 47-52).

At present, there are two main formulas for calculating the effective viscosity, formula (7) is one of them, μ _ef is the effective viscosity; ΔP is the displacement pressure difference of the polymer solution; L is the length of the sand packing pipe; v _D is the polymer solution The seepage velocity; K _f is the water flushing permeability after the polymer solution passes through.

The calculation of effective viscosity using formula (7) takes into account the effect of polymer retention in porous media on viscosity, but the formula does not reflect the non-Newtonian fluid properties of polymer solutions.

Another calculation formula for calculating the effective viscosity is the Blake-kozeny equation, see formula (8). In this formula, H is the consistency coefficient, n is the flow index, and k and φ are the permeability and porosity of the rock, respectively. Although this calculation method takes into account the non-Newtonian fluid properties of polymers, it does not take into account the impact of polymer retention in pores on permeability and porosity.

In the calculation of effective viscosity, it is necessary to take into account the non-Newtonian hydrodynamic properties of the polymer solution, and also reflect the influence of the polymer on the permeability and porosity after the polymer flows through the porous medium, so that the calculated effective viscosity can be closer to reality Condition.

Contents of the invention

In order to solve the above-mentioned technical problems, the object of the present invention is to provide a method for measuring and calculating the effective viscosity of polymers for oil displacement in porous media, which comprehensively considers the non-Newtonian hydrodynamic properties of polymers and the impact of polymer retention in porous media. Establish an effective calculation method for viscosity determination.

The object of the invention is a kind of measuring calculation method of polymer effective viscosity in porous media realized in this way, it is characterized in that being made up of following steps:

a. Preparation of polymer solution for oil displacement: According to the total salinity of injected water in the oil field, use distilled water and chloride salt to prepare simulated injection water, and then use simulated injected water to dissolve polymer for oil displacement to obtain polymer for oil displacement solution;

b. Determination of consistency coefficient and flow index: use a rheometer to measure the rheological curve of the polymer solution, obtain the relationship curve between shear stress and shear rate, and return the consistency coefficient H and flow index n of the polymer solution;

c. Filling the sand-filling pipe model: use quartz sand to fill the sand-filling pipe, the diameter of the sand-filling pipe is 2.5cm, and measure the permeability k and porosity of the sand-filling pipe model And get the permeability k and porosity The relational formula (1), where r is the pore radius, τ is the tortuosity:

d. Polymer solution to replace the sand filling pipe: set the displacement of the constant flow pump to 0.23ml/min, inject the polymer solution until the pressure is stable;

e. Subsequent water flooding: set the displacement of the constant flow pump to 0.23ml/min, inject simulated injection water, measure the hydraulic permeability k _f and residual resistance coefficient F _RR after polymer flooding, and assume that the pore radius r after polymer flooding and the tortuosity τ do not change, then the porosity after polymer flooding can be obtained The relationship between FRR and hydraulic permeability k _{f after polymer flooding is expressed in formula (2); the relationship between residual resistance coefficient FRR and permeability k and water measured permeability k f after} polymer flooding is expressed in formula (3):

f. Calculate the effective viscosity:

Correction equation: due to the retention property of polymer in the porous medium, the permeability and porosity decrease, so the hydraulic permeability k _f after polymer flooding is used instead of the permeability k of the porous medium, and the porosity after polymer flooding is used instead of original porosity Then, the revised Blake-kozeny equation is formula (4):

Substituting formula (2) and formula (3) into formula (4), the calculation formula of effective viscosity is finally obtained as formula (5) or formula (6):

or

Substitute into the calculation: then the consistency coefficient H, flow index n, permeability k, hydraulic permeability k _f after polymer flooding, porosity Or the residual resistance coefficient F _{RR is} substituted into formula (5) or formula (6) and the calculation result is the effective viscosity.

In the preparation of the polymer solution for oil flooding in the above step a: the chloride salt is composed of sodium chloride, calcium chloride and magnesium chloride.

In the above step c of filling the sand-filling pipe model: the particle size of the quartz sand is 80-100 mesh, and the length of the sand-filling pipe is 30-50 cm.

Beneficial effect:

The present invention is a method for measuring and calculating the effective viscosity of a polymer used for oil displacement in porous media, comprehensively considering the non-Newtonian hydrodynamic properties of the polymer and the reduction of the permeability and porosity caused by the retention of the polymer in the porous medium. The impact of the existing technology solves the problem that the effective viscosity of the polymer used for oil displacement in the porous medium and the calculation method cannot be accurately obtained.

Description of drawings

Fig. 1 is the flowchart of the inventive method;

Fig. 2 is the shear stress-rate curve figure that mass fraction is the polymer solution of 0.1% among the present invention;

Fig. 3 is a shear stress-rate curve diagram of a polymer solution with a mass fraction of 0.2% in the present invention.

detailed description

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

Example

A method for determining and calculating the effective viscosity of a polymer for oil displacement in porous media, as shown in Figure 1:

1. Use distilled water to prepare simulated injection water with a total salinity of 8625mg/L (calcium and magnesium ions 602mg/L). Dissolve 1097.71g of sodium chloride, 68.13g of calcium chloride, and 297.28g of magnesium chloride hexahydrate crystals sequentially in 100mL of distilled water. The simulated injection water was used to dissolve the acrylamide copolymer for oil displacement, and the polymer solutions with mass fractions of 0.1% and 0.2% were prepared respectively.

2. Use a HAAKE MARS III rheometer (rotor: PZ38) to measure the rheological curve of the polymer. Set the measurement temperature to 80°C, the shear rate to 0-800s ^-1 , and measure the relationship between the shear stress and the shear rate. The shear stress-rate curves of 0.1% and 0.2% polymer solutions are shown in Fig. 2 and Fig. 3. The consistency coefficient H and flow index n of the polymer solution obtained from the curve regression are shown in Table 1, respectively.

Table 1 Consistency coefficient H and flow index n of polymer solutions at different mass fractions

Mass fraction of polymer solution Consistency coefficient H flow index n 0.1% 0.2115 0.5150 0.2% 0.3154 0.4794

3. Use 80-100 mesh quartz sand to fill 6 sand-filling pipes. The diameter of the sand-filling pipes is 2.5cm and the length is 30cm. The permeability and porosity of the sand-packed pipe model were determined using the method in the Recommended Practice for Polymer Evaluation for Enhanced Oil Recovery in the Petroleum and Natural Gas Industry Standard of the People's Republic of China (SY/T6576-2003). The permeability and porosity of the six sand-packed pipe models are shown in Table 2.

Table 2 Permeability k and porosity of the sand-filled pipe model

4. Use 0.1% and 0.2% polymer solution to flood 6 groups of sand-packing pipe models respectively. The experimental temperature is 80°C, and the displacement of the constant flow pump is set at 0.23ml/min. When the inlet pressure is stable, use the simulated water injection to replace the sand filling pipe model with the same displacement, record the inlet pressure when the inlet pressure no longer decreases, and calculate the hydraulic permeability k _f after polymer flooding by Darcy's formula. Equation (3) calculates the residual resistance coefficient F _RR .

6. Consistency coefficient H, flow index n, permeability k, hydraulic permeability k _f after polymer flooding, porosity Or the residual resistance coefficient F _{RR is} substituted into formula (5) or formula (6) to calculate the effective viscosity, and the results obtained are shown in Table 3.

or

Various data measured in the test in table 3

Claims (3)

1. the assay method of a kind of Polymer Used For Oil Displacement effective viscosity in porous media, it is characterised in that by following steps group Into：

A, Polymer Used For Oil Displacement solution preparation：The total salinity of water is injected according to Oil Field, distilled water and chlorate is used Simulated injection water is prepared, simulated injection water dissolving Polymer Used For Oil Displacement is reused and obtains Polymer Used For Oil Displacement solution；

B, measure consistency coefficient and flow stance index：Using the rheological curve of rheometer measurement polymer solution, shear stress is obtained With the relation curve of shear rate, the consistency coefficient H and flow stance index n of polymer solution are returned out；

C, filling sand-filling tube model：Fill out sand tube is loaded using quartz sand, a diameter of 2.5cm of fill out sand tube determines sand-filling tube model Permeability k and porosity

D, polymer solution displacement fill out sand tube：The discharge capacity of constant flow pump is set as 0.23ml/min, injection of polymer solution is until pressure Power is steady；

E, sequent water flooding：The discharge capacity of constant flow pump is set as 0.23ml/min, simulated injection water is injected, the water after poly- drive is determined and surveys and ooze Saturating rate k_fAnd residual resistance factor F_RR, the porosity after poly- drive is drawn by formula (2)Residual resistive system is drawn by formula (3) Number F_RR, formula (2) and formula (3) are as follows：

<mrow> <msub> <mi>F</mi> <mrow> <mi>R</mi> <mi>R</mi> </mrow> </msub> <mo>=</mo> <mfrac> <mi>k</mi> <msub> <mi>k</mi> <mi>f</mi> </msub> </mfrac> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> <mo>;</mo> </mrow>

F, calculating effective viscosity：Water after consistency coefficient H, flow stance index n, permeability k, poly- drive is surveyed into permeability k_f, porosityOr Residual resistance factor F_RRSubstitution formula (5) or formula (6) result of calculation are effective viscosity, and formula (5) or formula (6) are as follows：

Or

2. a kind of assay method of Polymer Used For Oil Displacement effective viscosity in porous media according to claim 1, it is special Levy and be in the preparation of step a Polymer Used For Oil Displacement solution：The chlorate is made up of sodium chloride, calcium chloride, magnesium chloride.

3. a kind of assay method of Polymer Used For Oil Displacement effective viscosity in porous media according to claim 1, it is special Levy and be in step c filling sand-filling tube models：The granularity of the quartz sand is 80-100 mesh, and back-up sand length of tube is 30-50cm.