CN104089823B - A kind of method based on hole compression experiment determination rock effective stress coefficient - Google Patents
A kind of method based on hole compression experiment determination rock effective stress coefficient Download PDFInfo
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Abstract
The invention discloses a kind of method based on hole compression experiment determination rock effective stress coefficient, the same direction of same rock is chosen the close rock core of physical property, vacuumize saturated fluid, when maintaining pore pressure and being room pressure, increase by three axle confined pressures gradually, measure the fluid volume that pressure process mesoporosity is discharged, determine pore space compressibility of rock, the fitting function of matching effective stress and pore compressibility, measure the pore pressure steady state value of saturated core and the Pore Pressure force value after increasing confined pressure, determine rock pore volume decrease, the effective stress of bearing according to rock skeleton and the computing formula of pore space compressibility of rock, finally determine rock effective stress coefficient value.Method of the present invention, is applicable to the research of hyposmosis, super-low permeability reservoir stress, and testing apparatus is simple, and clear principle, method is succinct, measurement result is accurate.
Description
Technical field
The invention belongs to oil drilling technical field, relate to the defining method of rock mechanics coefficient, particularly relate to a kind of method based on hole compression experiment determination rock effective stress coefficient.
Background technology
In the fields such as all kinds of engineering design, construction, mining, petroleum drilling, the determination of rock mechanics parameters is the important evidence formulating drilling well, completion and oil and gas development and working measure.Especially, in field of oil drilling, the determination of sandstone oil reservoir reservoir porous rock effective stress coefficient is even more important, and it directly affects the reasonable prediction of the effective stress that porous medium rock skeleton bears.Rock mechanics parameters rationally determine the design finally affecting oil field overall plan, and then affect the yield in oil field.
Porous medium rock effective stress coefficient is the important computations parameter in rock-soil mechanics, permeation fluid mechanics field, is used for the effective stress determining that porous medium rock skeleton bears.In the last hundred years, numerous researcher proposes multiple computing method and the experimental formula of determining porous medium rock effective stress coefficient.Nineteen twenty-eight, effective stress coefficient is taken as the factor of porosity of porous medium simply by Hoffman in paper; 1954, Skempton with Bishop proposed the computing formula of the effective stress relevant with degree of consolidation; Nineteen fifty-seven, the effective stress coefficient that Geertsma proposes is considered the difference between solid material and porous medium and is stated by the compressibility coefficient of skeleton particle and porous medium; 1969, Suklje proposed the computing formula of the effective stress of compressibility coefficient and the factor of porosity impact considering skeleton particle material, porous medium.2000, more domestic scholars, by studying effective stress, proposed the body effective stress of porous medium and the concept of structure effective stress, gave the computing formula calculating double Effective Stresses on this basis; Separately there are some scholars by introducing the computing formula of multinomial rock mechanics parameters derivation effective stress coefficient; Also have some scholars according to Warpinski model, application maximum likelihood function method defines efficacy coefficient.
In the prior art, according to the computing method of the elastic modulus parameter of triaxial stress rock core in " big envelope ", " without big envelope " situation, the computing formula deriving porous medium effective stress coefficient is
in formula, K
frthe bulk modulus of-rock skeleton, unit is Mpa
-1; K
sthe bulk modulus of-solid material, unit is Mpa
-1; The effective stress coefficient of η-porous medium rock.The effective stress coefficient applying this formulae discovery porous medium rock needs to adopt the method for iteration to calculate, computation process more complicated.
In the prior art, describe the relation of permeability and confined pressure and interior pressure with Warpinski model, the computing formula deriving effective stress coefficient is
coefficient a in formula
ican obtain by maximum likelihood function method the Fitting Calculation.The effective stress coefficient of application maximum likelihood function method determination porous medium, first needs the conversion coefficient according to determining to change permeability, then the permeability after matching conversion, and computational accuracy is poor.
For sandstone oil reservoir reservoir porous rock, can utilize the experiment condition of existing mensuration core permeability, the mensuration of carrying out effective stress coefficient is quickly and accurately the problem that numerous experimenter is concerned about very much.The calculating assay method of existing effective stress coefficient, mostly be applicable to the research field of earth's surface rock-soil mechanics, the error that result of calculation may cause is larger, its computing formula is complicated and need to carry out a large amount of experiments and evaluation work, can not meet the needs of the effective stress coefficient determining sandstone oil reservoir reservoir porous rock quickly and accurately.
Summary of the invention
For solving prior art Problems existing, the invention provides a kind of method based on hole compression experiment determination rock effective stress coefficient, being particularly useful for determining sandstone oil reservoir reservoir porous rock effective stress coefficient.Its objective is: under the condition of certain reservoir fluid pressure, applicating fluid (both can be reservoir fluid, also can be the Experimental Flowing Object of the stable in properties of indoor configuration) determine the method for sandstone oil reservoir reservoir porous rock effective stress coefficient to realize the accurate measurement to rock effective stress coefficient under certain reservoir fluid pressure.The method in conjunction with the experimental facilities in existing permeation fluid mechanics field, can overcome the shortcoming that current effective stress coefficient experimental calculation method is loaded down with trivial details, complicated, error is larger, realize reservoir effective stress coefficient quick, accurately measure.
For achieving the above object, the technical solution used in the present invention is: a kind of method based on hole compression experiment determination rock effective stress coefficient, and it comprises the following steps according to sequencing:
(1) on the same direction of same rock, choose rock core, and measure the physical-property parameter of rock core;
The shape of rock core is right cylinder, and the physical property of the rock core chosen is similar, needs the basic physical-property parameter measured to comprise permeability, factor of porosity etc.
(2) by rock core vacuumizing saturated fluid, leave and take one of them saturated core for subsequent use, remaining saturated core is when maintaining pore pressure and being room pressure, increase by three axle confined pressures gradually, measure the fluid volume of discharging because volume of voids reduces in pressure process, determine pore space compressibility of rock C
p;
Vacuum system is utilized to vacuumize saturated process to rock core, first process is vacuumized to rock core, remove the assorted gas of core sample block inside, then the fluid adding certain specification under vacuum conditions soaks, rock core is allowed fully to absorb, in order to accelerate absorption rate, in immersion process, apply certain external pressure to rock core and fluid, its external pressure is loose and compactness extent and determining according to rock core.
Described fluid is normal saline solution.The three axle confined pressures applied rock core are larger, and the volume of voids of rock core reduces more, thus the fluid volume of discharging is also larger.
(3) computing formula of the effective stress of bearing according to rock skeleton, when pore pressure is room pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, pore space compressibility of rock C under the different confined pressures determined in arrangement step (2)
pdata, determine rock core effective stress σ
effwith pore space compressibility of rock C
pfitting function;
When pore pressure is room pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, the confined pressure of rock core and the overlying stress of rock.
(4) the pore pressure steady state value P leaving and taking a saturated core for subsequent use in overburden porosity proving installation measuring process (2) is utilized
cwith the Pore Pressure force value P increased after confined pressure
c-add;
(5) according to the decrease Δ V of rock pore volume after the increment determination rock skeleton compression of the rock core pore pressure measured in step (4)
add;
(6) computing formula of the effective stress of bearing according to rock skeleton, supposes different effective stress coefficient η
i, then corresponding different effective stress σ
eff-i, then according to the fitting function determination pore space compressibility of rock C of step (3)
pi, wherein i=(0,1,2 ... n);
(7) according to the computing formula of pore space compressibility of rock, different pore compressibility C is determined
pithe decrease Δ V of corresponding volume of voids
i, wherein i=(0,1,2 ... n);
(8) comparison step (5) and the decrease of rock pore volume in step (7), determine error delta therebetween
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) be provided with efficacy coefficient iterative increment Δ η, perform i=i+1 and η
i+1=η
i+ Δ η operates, wherein i=(0,1,2 ... n);
(10) repeat step (6)-(9), judge to work as δ
i+1× δ
i< 0, i=(0,1,2 ... n), then stop calculating, determine that rock effective stress coefficient is η
n.
The present invention is by the lithology physical property of contrast and test porous medium rock, rock that rock signature is close, and matching rock effective stress and pore space compressibility of rock curve, be coupled together experiment and calculating, finally determines the effective stress coefficient of rock.Its principle is: for the oil reservoir rock that mechanical property is close, the pore compressibility of rock and the effective stress suffered by it are similarity relation, pore space compressibility of rock under contrast different aperture pressure, calculate the size of corresponding effective stress, and finally define span or the occurrence of efficacy coefficient.
Preferably, in described step (1), the rock core quantity chosen is at least two.
In above-mentioned either a program preferably, in described step (1), the physical property of the rock core chosen is close, and described physical-property parameter comprises permeability and factor of porosity.
In above-mentioned either a program preferably, in described step (2), the computing formula of pore space compressibility of rock is
In formula, C
p-pore space compressibility of rock, MPa
-1;
V
p-rock pore volume, cm
3;
The pore fluid volume that during Δ V-confined pressure change, framework deformation is discharged, cm
3;
Δ P-confined pressure variable quantity, MPa.
In above-mentioned either a program preferably, in described step (2), the number of times that three axle confined pressures increase is at least three times.
In above-mentioned either a program preferably, in described step (3) and step (6), the computing formula of the effective stress that rock skeleton bears is σ=σ
eff+ η P,
In formula, the overlying stress of σ-porous medium rock, Mpa;
σ
effthe effective stress that-porous medium rock skeleton bears, Mpa;
The pore-fluid pressure of P-porous medium rock, Mpa;
The effective stress coefficient of η-porous medium rock.
In above-mentioned either a program preferably, in described step (3), the fitting function of rock core effective stress and pore space compressibility of rock is C
p=f (σ
eff).
In above-mentioned either a program preferably, in described step (4), overburden porosity proving installation comprises core holding unit, constant pressure pump, confined pressure pump, upstream valve, valve downstream, upstream pressure sensor, downstream pressure sensor, differential pressure pickup.
In above-mentioned either a program preferably, the measuring method of the pore pressure steady state value of described saturated core and the Pore Pressure force value after increasing confined pressure is saturated core is put into core holding unit, opens constant pressure pump, be full of fluid by rock core and pipeline; First closed by valve downstream, then closed by upstream valve, the pore pressure steady state value measuring saturated core is P
c; Open confined pressure pump, increase the confined pressure of saturated core, after corresponding pore pressure rising is stable, the Pore Pressure force value measured after increasing confined pressure is P
c-add.
First close valve downstream, make to be full of fluid in rock core and pipeline, being generally full of pressure, to be no more than the fluid of 50Mpa comparatively suitable, then close upstream valve, keeps the intrapore hydrodynamic pressure of rock core constant.
In above-mentioned either a program preferably, in described step (5), the computing formula of rock pore volume decrease is Δ V
add=V (P
c-add-P
c) C
l,
In formula, the cumulative volume that V-between valve downstream and upstream valve closes, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
When calculating rock pore volume decrease, by the closed at both ends of core holding unit, the compressibility coefficient of rock core inner fluid is known.
In above-mentioned either a program preferably, the cumulative volume closed between described valve downstream and upstream valve is the volume of voids V of rock core
pand the volume V of pipeline between valve downstream and upstream valve
dsum.
In above-mentioned either a program preferably, in described step (6), effective stress coefficient η
ivariation range be 0-1.
In above-mentioned either a program preferably, in described step (9), effective stress coefficient iterative increment Δ η=0.001.
In above-mentioned either a program preferably, described rock is sandstone oil reservoir reservoir porous rock.
The method of the porous medium of measure and calculation by experiment rock effective stress coefficient of the present invention, is applicable to hyposmosis, super-low permeability reservoir stress sensitive research field.Application effective stress coefficient can be determined, under the condition of true reservoir burden pressure, pore pressure, real fluid parameter, to realize the research of the stress sensitive degree to rock.The testing apparatus that the method requires is simple, and test philosophy is clear, wherein when lacking reservoir fluid parameter, and the test fluid flow of the stable in properties that indoor laboratory can be adopted to configure.With existing test calculate effective stress coefficient method compared with, technical scheme of the present invention is more convenient, quick.The present invention is under the true pressure condition of simulating oil deposit reservoir, and utilize the effective stress coefficient of the testing of equipment estimation porous medium rock of conventionally test rock permeability, its method of testing is succinct, accurate.
Accompanying drawing explanation
Fig. 1 is the process chart according to a kind of method based on hole compression experiment determination rock effective stress coefficient of the present invention;
Fig. 2 is the schematic diagram of the overburden porosity proving installation according to a kind of method based on hole compression experiment determination rock effective stress coefficient of the present invention.
Figure labeling description: 1-core holding unit, 2-constant pressure pump, 3-confined pressure pump, 4-valve downstream, 5-upstream valve, 6-downstream pressure sensor, 7-upstream pressure sensor, 8-differential pressure pickup.
Embodiment
In order to further understand summary of the invention of the present invention, elaborate the present invention below in conjunction with specific embodiment.
Embodiment one:
As shown in Figure 1, a kind of method based on hole compression experiment determination rock effective stress coefficient, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, the same direction of rock is chosen two close rock cores of physical property, and the basic physical properties parameter of testing rock core, as shown in Table 1.
Table one: the basic physical properties parameter of rock core
| Core numbers | Length (cm) | Diameter (cm) | Permeability (mD) | Gas gaging hole porosity (%) |
| YWT-B1 | 6.138 | 3.775 | 0.1252 | 12.471 |
| YWT-B2 | 6.162 | 3.772 | 0.1272 | 12.378 |
(2) rock core YWT-B1 and rock core YWT-B2 is vacuumized, then saturated fluid in normal saline solution is immersed, when maintaining pore pressure and being room pressure, three axle confined pressures are increased gradually to rock core YWT-B1, measure the volume of the normal saline solution of discharging because volume of voids reduces in pressure process, according to the computing formula of pore space compressibility of rock
determine the pore compressibility of rock core YWT-B1,
In formula, C
p-pore space compressibility of rock, MPa
-1;
V
p-rock pore volume, cm
3;
The pore fluid volume that during Δ V-confined pressure change, framework deformation is discharged, cm
3;
Δ P-confined pressure variable quantity, MPa.
(3) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, in formula,
The overlying stress of σ-porous medium rock, Mpa;
σ
effthe effective stress that-porous medium rock skeleton bears, Mpa;
The pore-fluid pressure of P-porous medium rock, Mpa;
The effective stress coefficient of η-porous medium rock.
When pore pressure is room pressure, the effective stress σ of rock core YWT-B1
efffor confined pressure, i.e. the burden pressure of rock core, the pore compressibility C of rock core YWT-B1 under the different confined pressures determined in arrangement step (2)
p, and then determine the effective stress σ of rock core YWT-B1
effwith pore compressibility C
pbetween relation, as shown in Table 2.
Table two: the relation between the effective stress of rock core YWT-B1 and pore compressibility
| Effective stress (MPa) | Pore compressibility (MPa -1) |
| 6.90 | 0.000084438 |
| 13.79 | 0.000049619 |
| 20.69 | 0.000029185 |
| 27.59 | 0.000014688 |
| 34.48 | 0.000003529 |
Under logarithmic coordinate, the relation function of pore compressibility and effective stress that application linear fit obtains rock core YWT-B1 is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) overburden porosity proving installation is utilized to measure the pore pressure steady state value P of rock core YWT-B2
cwith the Pore Pressure force value P increased after confined pressure
c-add.
As shown in Figure 2, rock core YWT-B2 is put into core holding unit 1, open constant pressure pump 2, be full of normal saline solution by rock core YWT-B2 and pipeline, the confined pressure value stabilization of rock core YWT-B2 is at 17.24MPa; First closed by valve downstream 4, then closed by upstream valve 5, the cumulative volume closed between valve downstream 4 and upstream valve 5 is 20.062ml, after pore pressure is stable, measures the pore pressure steady state value P of rock core YWT-B2
cfor 13.81MPa; Open confined pressure pump 3, the confined pressure increasing rock core YWT-B2, to 17.93MPa, after corresponding pore pressure rising is stable, measures the Pore Pressure force value P after increasing confined pressure
c-addfor 14.01MPa.Upstream pressure sensor 7 and downstream pressure sensor 6 are respectively used to the force value responding to fluid in upstream line and downstream line, and differential pressure pickup 8 is for responding to the pressure differential of fluid between upstream line and downstream line.
(5) by the closed at both ends of core holding unit, the compressibility coefficient of known normal saline solution is 4.511 × 10
-4mPa
-1, according to the computing formula Δ V of rock pore volume decrease
add=V (P
c-add-P
c) C
l, in formula,
The cumulative volume that V-between valve downstream and upstream valve closes, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
Determine that the decrease of rock core YWT-B2 volume of voids is 1.803 × 10
-3mL.
(6) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, supposes different effective stress coefficient η
i, then corresponding different effective stress σ
eff-i, then according to the fitting function C of step (3)
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff) determine the pore compressibility C of rock core YWT-B2
pi, wherein i=(0,1,2 ... n).
(7) according to the computing formula of pore space compressibility of rock
determine different pore compressibility C
pithe decrease Δ V of corresponding volume of voids
i, wherein i=(0,1,2 ... n).
(8) comparison step (5) and the decrease of the volume of voids of rock core YWT-B2 in step (7), determine error delta therebetween
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n).
(9) efficacy coefficient iterative increment Δ η=0.001 is provided with, effective stress coefficient initial value η
0=0, utilize Matlab programming software, perform i=i+1 and η
i+1=η
i+ Δ η operates, wherein i=(0,1,2 ... n).
(10) repeat step (6)-(9), judge to work as δ
i+1× δ
i< 0, i=(0,1,2 ... n), then stop calculating, under effective stress is 15.15MPa, determine the effective stress coefficient η of rock core YWT-B2
nbe 0.201.
Embodiment two:
As shown in Figure 1, a kind of method based on hole compression experiment determination rock effective stress coefficient, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, the same direction of rock is chosen four close rock cores of physical property, and the basic physical properties parameter of testing rock core, as shown in Table 3.
Table three: the basic physical properties parameter of rock core
| Core numbers | Length (cm) | Diameter (cm) | Permeability (mD) | Gas gaging hole porosity (%) |
| YWT-B1 | 6.138 | 3.775 | 0.1252 | 12.471 |
| YWT-B2 | 6.176 | 3.772 | 0.1797 | 11.347 |
| YWT-B3 | 6.180 | 3.770 | 0.1133 | 12.257 |
| YWT-B4 | 6.162 | 3.772 | 0.1272 | 12.378 |
(2) by four rock core vacuumizings in step (1), then saturated fluid in normal saline solution is immersed, when maintaining pore pressure and being room pressure, three axle confined pressures are increased respectively gradually to rock core YWT-B1, rock core YWT-B2, rock core YWT-B3, measure the volume of the normal saline solution of discharging because volume of voids reduces in pressure process, according to the computing formula of pore space compressibility of rock
determine the pore compressibility of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3.
(3) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, when pore pressure is room pressure, the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effbe respective confined pressure, i.e. the burden pressure of rock core, the pore compressibility C of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 under the different confined pressures determined in arrangement step (2)
p, and then determine the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effwith pore compressibility C
pbetween relation, as shown in Table 4.
Table four: the relation between the effective stress of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 and pore compressibility
Under logarithmic coordinate, the relation function of pore compressibility and effective stress that application linear fit obtains three rock cores is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) overburden porosity proving installation is utilized to measure the pore pressure steady state value P of rock core YWT-B4
cwith the Pore Pressure force value P increased after confined pressure
c-add.
As shown in Figure 2, rock core YWT-B4 is put into core holding unit 1, open constant pressure pump 2, be full of normal saline solution by rock core YWT-B4 and pipeline, the confined pressure value stabilization of rock core YWT-B4 is at 27.64MPa; First closed by valve downstream 4, then closed by upstream valve 5, the cumulative volume closed between valve downstream 4 and upstream valve 5 is 20.062ml, after pore pressure is stable, measures the pore pressure steady state value P of rock core YWT-B4
cfor 22.34MPa; Open confined pressure pump 3, the confined pressure increasing rock core YWT-B4, to 27.93MPa, after corresponding pore pressure rising is stable, measures the Pore Pressure force value P after increasing confined pressure
c-addfor 22.45MPa.
(5) by the closed at both ends of core holding unit, the compressibility coefficient of known normal saline solution is 4.511 × 10
-4mPa
-1, according to the computing formula Δ V of rock pore volume decrease
add=V (P
c-add-P
c) C
l, determine that the decrease of rock core YWT-B4 volume of voids is 0.9917 × 10
-3mL.
(6) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, supposes different effective stress coefficient η
i, then corresponding different effective stress σ
eff-i, then according to the fitting function C of step (3)
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff) determine the pore compressibility C of rock core YWT-B4
pi, wherein i=(0,1,2 ... n).
(7) according to the computing formula of pore space compressibility of rock
determine different pore compressibility C
pithe decrease Δ V of corresponding volume of voids
i, wherein i=(0,1,2 ... n).
(8) comparison step (5) and the decrease of the volume of voids of rock core YWT-B4 in step (7), determine error delta therebetween
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n).
(9) efficacy coefficient iterative increment Δ η=0.001 is provided with, effective stress coefficient initial value η
0=0, utilize Matlab programming software, perform i=i+1 and η
i+1=η
i+ Δ η operates, wherein i=(0,1,2 ... n).
(10) repeat step (6)-(9), judge to work as δ
i+1× δ
i< 0, i=(0,1,2 ... n), then stop calculating, under effective stress is 19.11MPa, determine the effective stress coefficient η of rock core YWT-B4
nbe 0.279.
Embodiment three:
As shown in Figure 1, a kind of method based on hole compression experiment determination rock effective stress coefficient, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, the same direction of rock is chosen four close rock cores of physical property, and the basic physical properties parameter of testing rock core, as shown in Table 5.
Table five: the basic physical properties parameter of rock core
| Core numbers | Length (cm) | Diameter (cm) | Permeability (mD) | Gas gaging hole porosity (%) |
| YWT-B1 | 6.138 | 3.775 | 0.1252 | 12.471 |
| YWT-B2 | 6.176 | 3.772 | 0.1797 | 11.347 |
| YWT-B3 | 6.180 | 3.770 | 0.1133 | 12.257 |
| YWT-B4 | 6.162 | 3.772 | 0.1272 | 12.378 |
(2) by four rock core vacuumizings in step (1), then saturated fluid in normal saline solution is immersed, when maintaining pore pressure and being room pressure, three axle confined pressures are increased respectively gradually to rock core YWT-B1, rock core YWT-B2, rock core YWT-B3, measure the volume of the normal saline solution of discharging because volume of voids reduces in pressure process, according to the computing formula of pore space compressibility of rock
determine the pore compressibility of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3.
(3) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, when pore pressure is room pressure, the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effbe respective confined pressure, i.e. the burden pressure of rock core, the pore compressibility C of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 under the different confined pressures determined in arrangement step (2)
p, and then determine the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effwith pore compressibility C
pbetween relation, as shown in Table 6.
Table six: the relation between the effective stress of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 and pore compressibility
Under logarithmic coordinate, the relation function of pore compressibility and effective stress that application linear fit obtains three rock cores is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) overburden porosity proving installation is utilized to measure the pore pressure steady state value P of rock core YWT-B4
cwith the Pore Pressure force value P increased after confined pressure
c-add.
As shown in Figure 2, rock core YWT-B4 is put into core holding unit 1, open constant pressure pump 2, be full of normal saline solution by rock core YWT-B4 and pipeline, the confined pressure value stabilization of rock core YWT-B4 is at 17.24MPa; First closed by valve downstream 4, then closed by upstream valve 5, the cumulative volume closed between valve downstream 4 and upstream valve 5 is 20.062ml, after pore pressure is stable, measures the pore pressure steady state value P of rock core YWT-B4
cfor 13.81MPa; Open confined pressure pump 3, the confined pressure increasing rock core YWT-B4, to 17.93MPa, after corresponding pore pressure rising is stable, measures the Pore Pressure force value P after increasing confined pressure
c-addfor 14.01MPa.
(5) by the closed at both ends of core holding unit, the compressibility coefficient of known normal saline solution is 4.511 × 10
-4mPa
-1, according to the computing formula Δ V of rock pore volume decrease
add=V (P
c-add-P
c) C
l, determine that the decrease of rock core YWT-B4 volume of voids is 1.803 × 10
-3mL.
(6) the computing formula σ=σ of the effective stress of bearing according to rock skeleton
eff+ η P, supposes different effective stress coefficient η
i, its variation range is 0-1, then corresponding different effective stress σ
eff-i, then according to the fitting function C of step (3)
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff) determine the pore compressibility C of rock core YWT-B4
pi, wherein i=(0,1,2 ... n).
(7) according to the computing formula of pore space compressibility of rock
determine different pore compressibility C
pithe decrease Δ V of corresponding volume of voids
i, wherein i=(0,1,2 ... n), table seven is the pore compressibility and volume decrease that the different effective stress coefficients of rock core YWT-B4 are corresponding.
Table seven: the pore compressibility that the different effective stress coefficients of rock core YWT-B4 are corresponding and volume decrease
According to test result, when confined pressure is increased to 17.93MPa by 17.24MPa, volume of voids decrease is 1.803 × 10
-3mL, as shown in Table 7, the span of effective stress coefficient is between 0.2-0.3, need define the occurrence of efficacy coefficient further.
(8) comparison step (5) and the decrease of the volume of voids of rock core YWT-B4 in step (7), determine error delta therebetween
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) efficacy coefficient iterative increment Δ η=0.001 is provided with, effective stress coefficient initial value η
0=0, utilize Matlab programming software, perform i=i+1 and η
i+1=η
i+ Δ η operates, wherein i=(0,1,2 ... n);
(10) repeat step (6)-(9), judge to work as δ
i+1× δ
i< 0, i=(0,1,2 ... n), then stop calculating, under effective stress is 15.15MPa, determine the effective stress coefficient η of rock core YWT-B4
nbe 0.201.
Those skilled in the art are understood that, a kind of method based on hole compression experiment determination rock effective stress coefficient of the present invention comprises the summary of the invention of the invention described above instructions and the combination in any of embodiment part and each several part shown by accompanying drawing, as space is limited and not have each scheme of these combination formations to describe one by one for making instructions simple and clear.Within the spirit and principles in the present invention all, any amendment made, equivalent replacement, improvement etc., all should be included within protection scope of the present invention.
Claims (14)
1., based on a method for hole compression experiment determination rock effective stress coefficient, it comprises the following steps according to sequencing:
(1) on the same direction of same rock, choose rock core, and measure the physical-property parameter of rock core;
(2) by rock core vacuumizing saturated fluid, leave and take one of them saturated core for subsequent use, remaining saturated core is when maintaining pore pressure and being room pressure, increase by three axle confined pressures gradually, measure the fluid volume of discharging because volume of voids reduces in pressure process, determine pore space compressibility of rock C
p;
(3) computing formula of the effective stress of bearing according to rock skeleton, when pore pressure is room pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, pore space compressibility of rock C under the different confined pressures determined in arrangement step (2)
pdata, determine rock core effective stress σ
effwith pore space compressibility of rock C
pfitting function;
(4) the pore pressure steady state value P leaving and taking a saturated core for subsequent use in overburden porosity proving installation measuring process (2) is utilized
cwith the Pore Pressure force value P increased after confined pressure
c-add;
(5) according to the decrease Δ V of rock pore volume after the increment determination rock skeleton compression of the rock core pore pressure measured in step (4)
add;
(6) computing formula of the effective stress of bearing according to rock skeleton, supposes different effective stress coefficient η
i, then corresponding different effective stress σ
eff-i, then according to the fitting function determination pore space compressibility of rock C of step (3)
pi, wherein i=(0,1,2 ... n);
(7) according to the computing formula of pore space compressibility of rock, different pore compressibility C is determined
pithe decrease Δ V of corresponding volume of voids
i, wherein i=(0,1,2 ... n);
(8) comparison step (5) and the decrease of rock pore volume in step (7), determine error delta therebetween
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) be provided with efficacy coefficient iterative increment Δ η, perform i=i+1 and η
i+1=η
i+ Δ η operates, wherein i=(0,1,2 ... n);
(10) repeat step (6)-(9), judge to work as δ
i+1× δ
i< 0, i=(0,1,2 ... n), then stop calculating, determine that rock effective stress coefficient is η
n.
2., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (1), the rock core quantity chosen is at least two.
3., as claimed in claim 2 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (1), the physical property of the rock core chosen is close, and described physical-property parameter comprises permeability and factor of porosity.
4., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (2), the computing formula of pore space compressibility of rock is
In formula, C
p-pore space compressibility of rock, MPa
-1;
V
p-rock pore volume, cm
3;
The pore fluid volume that during Δ V-confined pressure change, framework deformation is discharged, cm
3;
Δ P-confined pressure variable quantity, MPa.
5. as claimed in claim 4 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (2), the number of times that three axle confined pressures increase is at least three times.
6. as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (3) and step (6), the computing formula of the effective stress that rock skeleton bears is σ=σ
eff+ η P,
In formula, the overlying stress of σ-porous medium rock, Mpa;
σ
effthe effective stress that-porous medium rock skeleton bears, Mpa;
The pore-fluid pressure of P-porous medium rock, Mpa;
The effective stress coefficient of η-porous medium rock.
7., as claimed in claim 6 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (3), the fitting function of rock core effective stress and pore space compressibility of rock is C
p=f (σ
eff).
8. as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (4), overburden porosity proving installation comprises core holding unit, constant pressure pump, confined pressure pump, upstream valve, valve downstream, upstream pressure sensor, downstream pressure sensor, differential pressure pickup.
9. as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: the measuring method of the pore pressure steady state value of described saturated core and the Pore Pressure force value after increasing confined pressure is, saturated core is put into core holding unit, open constant pressure pump, be full of fluid by rock core and pipeline; First closed by valve downstream, then closed by upstream valve, the pore pressure steady state value measuring saturated core is P
c; Open confined pressure pump, increase the confined pressure of saturated core, after corresponding pore pressure rising is stable, the Pore Pressure force value measured after increasing confined pressure is P
c-add.
10., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, it is characterized in that: in described step (5), the computing formula of rock pore volume decrease is Δ V
add=V (P
c-add-P
c) C
l,
In formula, the cumulative volume that V-between valve downstream and upstream valve closes, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
11., as claimed in claim 10 based on the method for hole compression experiment determination rock effective stress coefficient, is characterized in that: the cumulative volume closed between described valve downstream and upstream valve is the volume of voids V of rock core
pand the volume V of pipeline between valve downstream and upstream valve
dsum.
12., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, is characterized in that: in described step (6), effective stress coefficient η
ivariation range be 0-1.
13., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, is characterized in that: in described step (9), effective stress coefficient iterative increment Δ η=0.001.
14., as claimed in claim 1 based on the method for hole compression experiment determination rock effective stress coefficient, is characterized in that: described rock is sandstone oil reservoir reservoir porous rock.
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| CN113536218B (en) * | 2021-07-13 | 2023-06-06 | 中国石油大学(北京) | Method and device for calculating rock pore volume compression coefficient |
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