CN102587888A - Method for determining migration velocity of displacement front in CO2 miscible displacement physical simulation - Google Patents

Abstract

The invention discloses a method for determining the migration velocity of a displacement front in CO2 miscible displacement physical simulation, belonging to the detection field of oil pool physical simulation. The method for determining the migration velocity of a displacement front in CO2 miscible displacement physical simulation comprises the following steps of: firstly, determining the oil saturation distribution in different positions in a porous medium by use of the imaging technology; obtaining the oil saturate change curve in a sand filling model in the imaging view field; then, determining the characteristic moment point passing through the imaging view field of the displacement front; and finally, obtaining the migration velocity of the displacement front by use of an analysis method. The method can determine the migration velocity of the displacement front in the CO2 miscible displacement process and accurately obtain the flowing law of CO2 in the oil-containing porous medium so as to provide analysis basis for the nondestructive detection in the CO2 miscible displacement physical simulation process.

Description

A kind of definite CO 2The method of displacing front migration velocity in the miscible displacement of reservoir physical analogy

Technical field

The present invention relates to a kind of definite CO ₂The method of displacing front migration velocity in the miscible displacement of reservoir physical analogy belongs to the reservoir physical simulation detection range.

Background technology

With CO ₂Inject oil reservoir and not only can improve oil recovery factor, produce huge economic benefit, and can realize CO ₂Geology is buried, and solves CO ₂The environmental problem that reduces discharging, therefore, this method should be to solve human development and enhancement of environment this contradicts an effective way of problem.Pass through CO ₂The technology of driving can further improve the 10%-15% of oil recovery on the basis of routine techniques, therefore further further investigation utilizes CO ₂The relevant issues that improve the oil recovery factor technology are very necessary.Yet adopt the normal experiment method; Can only regard the actual formation model as one " black box "; Only through monitoring injection, the flow of extraction and the situation that pressure is analyzed the displacement of reservoir oil; This experimental technique can not accurately be grasped occurrence status and the migration process of fluid in porous media, obviously has certain limitation.

Summary of the invention

In order to overcome the problem that exists in the above-mentioned prior art, the present invention provides a kind of definite CO ₂The method of displacing front migration velocity in the miscible displacement of reservoir physical analogy.This method utilizes technology such as magnetic resonance imaging (MRI) or CT imaging to CO ₂Flowing law in the oil-containing porous media is held accurately, and through to saturation data analysis that imaging technique obtains, can confirm CO ₂Displacing front migration velocity in the miscible displacement of reservoir process.

Technical scheme of the present invention is: a kind of definite CO ₂The method of displacing front migration velocity comprises following concrete steps in the miscible displacement of reservoir physical analogy:

(1) obtains in the imaging visual field oil saturation change curve in the sandpack column

All lamella signal strength values in a certain moment in the displacement process are superimposed, and the whole three-dimensional oil-containing of filling model in the visual field that obtains forming images is distributed in the two-dimensional projection image perpendicular to the displacement direction, this projected image and CO ₂Do not inject the ratio of the projected image of initial time, be the saturation distribution of projected image, it is averaged in the projection plane of the imaging visual field, oil saturation change curve in the sandpack column in the visual field that obtains to form images;

(2) confirm nine the characteristic moment point of displacing front through the imaging visual field

Through oil saturation change curve in the sandpack column in the imaging visual field is analyzed; Find with displacing front through corresponding nine the obvious characteristics moment point of imaging visual field process: characteristic moment point O moment corresponding is that the mixed phase of displacing front drives head and arrives the lower end, the visual field of forming images, and characteristic moment point A is CO ₂Leading edge begins to get into imaging lower end, the visual field, and characteristic moment point B is that the displacing front afterbody gets into imaging lower end, the visual field fully, and characteristic moment point C is that the mixed phase of displacing front drives upper end, the head arrival imaging visual field, and characteristic moment point D is CO ₂Leading edge begins to arrive upper end, the imaging visual field; Characteristic moment point E is that the displacing front afterbody is broken through upper end, the imaging visual field fully; Characteristic moment point F is that the displacing front afterbody is broken through whole glass sand filling model fully, and characteristic moment point G is that secondary moves back saturated end, and characteristic moment point H is that displacement test finishes;

(3) the displacing front migration velocity is obtained in analysis

Guaranteeing to inject CO ₂Under the condition of constant flow, the curve linear Fitting Analysis between characteristic moment point B on the saturation curves and the characteristic moment point C is obtained the displacing front migration velocity.

The invention has the beneficial effects as follows: this definite CO ₂The method of displacing front migration velocity in the miscible displacement of reservoir physical analogy; At first utilize imaging technique to confirm that the oil saturation of diverse location in the porous media distributes; Oil saturation change curve in the sandpack column in the acquisition imaging visual field; Confirm the characteristic moment point of displacing front then, utilize analytical method to obtain the displacing front migration velocity at last through the MRI imaging visual field.This method can be confirmed CO in the sandpack column ₂Displacing front migration velocity in the miscible displacement of reservoir process is to CO ₂Flowing law in the oil-containing porous media is held accurately, is CO ₂The nondestructive testing of miscible displacement of reservoir physical analogy process provides the analysis foundation.

Description of drawings

Below in conjunction with accompanying drawing and embodiment the present invention is described further.

Fig. 1 is a kind of definite CO ₂The flow chart of the method for displacing front migration velocity in the miscible displacement of reservoir physical analogy.

Fig. 2 is that the mixed phase of displacing front drives head arrival imaging lower end, visual field characteristic moment point O moment corresponding sketch map.

Fig. 3 is CO ₂Leading edge begins to get into imaging lower end, visual field characteristic moment point A moment corresponding sketch map.

Fig. 4 is that the displacing front afterbody gets into imaging lower end, visual field characteristic moment point B moment corresponding sketch map fully.

Fig. 5 is that the mixed phase of displacing front drives upper end, head arrival imaging visual field characteristic moment point C moment corresponding sketch map.

Fig. 6 is CO ₂Leading edge begins to arrive upper end, imaging visual field characteristic moment point D moment corresponding sketch map.

Fig. 7 is that point is broken through upper end, imaging visual field characteristic moment point E moment corresponding sketch map fully for the displacing front afterbody.

Fig. 8 is an oil saturation change curve in the sandpack column in the imaging visual field.

Among the figure: 1, back-up sand, 2, the mixed phase district, 3, CO ₂Leading edge, 4, the imaging visual field; O, A, B, C, D, E, F, G, H, characteristic moment point.

The specific embodiment

Fig. 1 is a kind of definite CO ₂The flow chart of the method for displacing front migration velocity in the miscible displacement of reservoir physical analogy.Introduce the specific embodiment that this method is set up below:

(1) oil saturation of confirming diverse location in the porous media distributes

With the MRI technology is example, at first obtains piece image I _O0, in displacement process, obtain another width of cloth image I then _Oi, oil saturation is in so any little volume elements:

$S_{\mathrm{oi}}(x,y,z)=\frac{I_{\mathrm{oi}}(x,y,z)}{I_{o0}(x,y,z)}---\left(1\right)$

S in the formula _Oi(x, y z) are the oil saturation of arbitrary volume elements in the space, I _Oi(x, y z) are the signal strength signal intensity size of arbitrary volume elements in the displacement process, I _O0(x, y, the signal strength signal intensity size of arbitrary corpusculum unit when being initial saturated oils z).

(2) obtain in the imaging visual field oil saturation change curve in the sandpack column

All lamella signal strength values in a certain moment in the displacement process are superimposed, and the whole three-dimensional oil-containing of filling model in the visual field that can obtain forming images is distributed in the two-dimensional projection image perpendicular to the displacement direction, this projected image and initial time (CO ₂Inject) time the ratio of projected image, be the saturation distribution of projected image, it is averaged oil saturation change curve in the sandpack column in the visual field that can obtain to form images in the projection plane of the imaging visual field.

(3) confirm nine the characteristic moment point of displacing front through the imaging visual field

Analyze through oil saturation change curve in the sandpack column in the visual field that Fig. 3 is formed images; Can find to pass through the imaging visual field (shown in Fig. 2-7 with displacing front; The imaging visual field is to be positioned at certain a part of pipeline section on the sandpack column pipe) corresponding nine the obvious characteristics moment point of process: characteristic moment point O moment corresponding is that the mixed phase of displacing front drives head arrival imaging lower end, the visual field, and characteristic moment point A is CO ₂Leading edge begins to get into imaging lower end, the visual field, and characteristic moment point B is that the displacing front afterbody gets into imaging lower end, the visual field fully, and characteristic moment point C is that the mixed phase of displacing front drives upper end, the head arrival imaging visual field, and characteristic moment point D is CO ₂Leading edge begins to arrive upper end, the imaging visual field; Characteristic moment point E is that the displacing front afterbody is broken through upper end, the imaging visual field fully; Characteristic moment point F is that the displacing front afterbody is broken through whole glass sand filling model fully, and characteristic moment point G is that secondary moves back saturated end, and characteristic moment point H is that displacement test finishes.Thereby can displacement process be divided into eight processes and analyze:

1. OA section: along with CO ₂The injection oil saturation descends, because the inhomogeneities that plug shape mixed phase drives the leading edge head, decline curve is exponential trend, and downward gradient increases gradually;

2. AB section: along with CO ₂Inject oil saturation and continue to descend, same because plug shape CO ₂The inhomogeneities of leading edge head, decline curve is exponential trend, and downward gradient increases gradually;

3. BC section: oil saturation continues to descend, and overall distribution of pores is more even because glass sand is filled the model porous media, CO in the displacement process ₂With oily mixed phase, do not have serious fingering and channelling phenomenon to take place, thereby displacement process remain a constant speed basically, the full curve of oil-containing is exponential trend and descends;

4. CD section: break through imaging top, visual field process for mixed phase drives leading edge, because mixed phase drives the inhomogeneities of leading edge head, decline curve is exponential trend;

5. DE section: be CO ₂Leading edge breaks through imaging top, visual field process, because CO ₂The inhomogeneities of leading edge head, decline curve is exponential trend;

6. EF section: after oil saturation was reduced to a certain value, under constant displacement velocity condition, mixed phase drove the primary recovery rate of leading edge basically near remaining oil saturation, follow-up CO ₂Little to improving the recovery ratio effect;

7. FG section: be " secondary moves back saturated " process of oil in the porous media, oil saturation further descends;

8. GH section: after final oil saturation is reduced to a certain value, follow-up CO ₂Little to improving the recovery ratio effect, " secondary moves back saturation history " end be described after.

(4) the displacing front migration velocity is obtained in analysis

Analysis through to BC section on the saturation curves is visible, is guaranteeing to inject CO ₂Under the condition of constant flow, though a part of CO ₂Can be dissolved in the oil; And cause the displacing front distribution irregular because distribution of pores is inhomogeneous; But the displacing front propelling that in whole filling model, remains a constant speed basically in displacement process; And through to BC section linear relationship further linear fit analysis can obtain the displacing front migration velocity, detailed method is following:

Suppose in the displacement process in certain period that the oil content variable quantity is Δ V in the imaging visual field _o, and available following formula is represented:

ΔV _o＝AφΔh (2)

Wherein A is the cross-sectional area that glass sand is filled the model porous media, cm ²φ is a porosity, mark; Δ h is the displacement of displacing front, cm.

In addition, oil saturation S _oDefinition be:

$S_o=\frac{V_o}{V_p}---\left(3\right)$

V wherein _oFor glass sand in the FOV is filled the oil content in the model porous media, cm ³V _pFor glass sand in the imaging visual field is filled the voids volume of model porous media, cm ³

V _pCan further express with following formula:

V _p＝ALφ (4)

Wherein L is imaging visual field height, cm.

According to formula (2)-(4), can obtain average fltting speed

expression formula of displacing front:

$\stackrel{\‾}{v}=\frac{\mathrm{\Δh}}{\mathrm{\Δt}}=\frac{{\mathrm{\ΔS}}_o}{\mathrm{\Δt}}L---\left(5\right)$

Δ S wherein _oBe the variable quantity of oil saturation in the imaging visual field in the displacement process, mark; Δ t is the displacement process time variation amount, min.

in the formula (5) can obtain through the linear fit to BC section on the saturation curves, and then can be in the hope of the average fltting speed of displacing front.Because mixed phase drives in the process, a large amount of CO ₂With oil dissolving mixed phase, this speed is much smaller than CO ₂Injection rate.In addition; Can obtain displacing front and migrate to model pipe from imaging lower end, the visual field and export the used time through analyzing saturation curves BF section; According to known migration velocity, can obtain migration distance, this filling mold segment pipe range of this distance and reality is approaching basically; Thereby, further utilize the reliability of saturation curves analysis and solution displacement velocity method more than the proof.

Different characteristic when Fig. 2-7 passes through the imaging visual field for displacing front constantly.Corresponding with the obvious characteristics moment point on the oil saturation change curve in the sandpack column in the imaging visual field among Fig. 8.

Fig. 8 is oil saturation change curve in the sandpack column in the imaging visual field.Through oil saturation change curve in the sandpack column in the imaging visual field among the figure is analyzed; Can find to pass through the imaging visual field (shown in Fig. 2-7, the imaging visual field is to be positioned at certain a part of pipeline section on the sandpack column pipe) corresponding nine the obvious characteristics moment point of process with displacing front.

Claims (1)

1. definite CO ₂The method of displacing front migration velocity in the miscible displacement of reservoir physical analogy is characterized in that: comprise following concrete steps:

(1) obtains in the imaging visual field oil saturation change curve in the sandpack column

All lamella signal strength values in a certain moment in the displacement process are superimposed, and the whole three-dimensional oil-containing of filling model in the visual field that obtains forming images is distributed in the two-dimensional projection image perpendicular to the displacement direction, this projected image and CO ₂Do not inject the ratio of the projected image of initial time, be the saturation distribution of projected image, it is averaged in the projection plane of the imaging visual field, oil saturation change curve in the sandpack column in the visual field that obtains to form images;

(2) confirm nine the characteristic moment point of displacing front through the imaging visual field

Through oil saturation change curve in the sandpack column in the imaging visual field is analyzed; Find with displacing front through corresponding nine the obvious characteristics moment point of imaging visual field process: characteristic moment point O moment corresponding is that the mixed phase of displacing front drives head and arrives the lower end, the visual field of forming images, and characteristic moment point A is CO ₂Leading edge begins to get into imaging lower end, the visual field, and characteristic moment point B is that the displacing front afterbody gets into imaging lower end, the visual field fully, and characteristic moment point C is that the mixed phase of displacing front drives upper end, the head arrival imaging visual field, and characteristic moment point D is CO ₂Leading edge begins to arrive upper end, the imaging visual field; Characteristic moment point E is that the displacing front afterbody is broken through upper end, the imaging visual field fully; Characteristic moment point F is that the displacing front afterbody is broken through whole glass sand filling model fully, and characteristic moment point G is that secondary moves back saturated end, and characteristic moment point H is that displacement test finishes;

(3) the displacing front migration velocity is obtained in analysis

Guaranteeing to inject CO ₂Under the condition of constant flow, the curve linear Fitting Analysis between characteristic moment point B on the saturation curves and the characteristic moment point C is obtained the displacing front migration velocity.

Images