CN104089823A - Method for determining effective rock stress coefficient based on pore compression experiment - Google Patents
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Abstract
The invention discloses a method for determining an effective rock stress coefficient based on a pore compression experiment. The method comprises the following steps: selecting cores with similar physical properties in the same direction of the same rock, vacuumizing saturated fluid, gradually increasing triaxial confining pressure under the condition that the pore pressure is maintained to be room pressure, measuring the volume of fluid discharged from pores in the pressurization process, determining the rock pore compression coefficient, fitting a fitting function between the effective stress and the pore compression coefficient, measuring a pore pressure constant value of the saturated core and the pore pressure value after the confining pressure is increased, determining core pore volume reduction, and finally determining the effective rock stress coefficient value according to a calculation formula of the effective stress born by a rock matrix and the rock pore compression coefficient. The method is applied to low-permeability and ultralow-permeability reservoir stress research, the testing equipment is simple, the principle is clear, and the method is simple and accurate in measurement result.
Description
Technical field
The invention belongs to oil drilling technical field, relate to definite method of rock mechanics coefficient, relate in particular to a kind of method of determining rock effective stress coefficient based on hole compression experiment.
Background technology
In the fields such as all kinds of engineering designs, construction, mining, petroleum drilling, the definite of rock mechanics parameters is the important evidence of formulating drilling well, completion and oil and gas development and working measure.Especially in field of oil drilling, sandstone oil reservoir reservoir porous rock effective stress coefficient definite even more important, it directly affects the reasonable prediction of the effective stress that porous medium rock skeleton bears.The reasonable of rock mechanics parameters determined the design that finally affects oil field overall plan, and then affects 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 determining the effective stress that porous medium rock skeleton bears.In the last hundred years, numerous researchers have proposed computing method and the experimental formula of multiple definite porous medium rock effective stress coefficient.Nineteen twenty-eight, Hoffman gets simply by effective stress coefficient the factor of porosity of making porous medium in paper; 1954, Skempton and Bishop proposed the computing formula of the effective stress relevant with degree of consolidation; Nineteen fifty-seven, the effective stress coefficient that Geertsma proposes has been considered the difference between solid material and porous medium and has explained by the compressibility coefficient of skeleton particle and porous medium; 1969, Suklje proposed to consider the computing formula of the compressibility coefficient of skeleton particle material, porous medium and the effective stress of factor of porosity impact.2000, more domestic scholars, by effective stress is studied, proposed the body effective stress of porous medium and the concept of structure effective stress, had provided on this basis the computing formula of calculating double Effective Stresses; 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, the computing method of the elastic modulus parameter according to triaxial stress rock core in " big envelope ", " without big envelope " situation, the computing formula of 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 of applying this formula calculating porous medium rock need to adopt the method for iteration to calculate, computation process more complicated.
In the prior art, by the relation of Warpinski model description permeability and confined pressure and interior pressure, the computing formula of deriving effective stress coefficient is
coefficient a in formula
ican obtain by maximum likelihood function method the Fitting Calculation.First application maximum likelihood function method is determined needs the effective stress coefficient of porous medium according to definite conversion coefficient, permeability to be changed, then 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 quickly and accurately effective stress coefficient is the problem that numerous experimenters are 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 determining quickly and accurately the effective stress coefficient of sandstone oil reservoir reservoir porous rock.
Summary of the invention
The problem existing for solving prior art, the invention provides a kind of method of determining rock effective stress coefficient based on hole compression experiment, is 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 (can be both reservoir fluid, also can be the Experimental Flowing Object of the stable in properties of indoor configuration) determine and the method for sandstone oil reservoir reservoir porous rock effective stress coefficient realize the accurate measurement to rock effective stress coefficient under certain reservoir fluid pressure.The method can be in conjunction with the experimental facilities in existing permeation fluid mechanics field, overcomes 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 fast, accurately measure.
For achieving the above object, the technical solution used in the present invention is: a kind of method of determining rock effective stress coefficient based on hole compression experiment, and it comprises the following steps according to sequencing:
(1) in the same direction of same rock, choose rock core, and measure the physical-property parameter of rock core;
Rock core be shaped as right cylinder, the physical property of the rock core of choosing is similar, needs the basic physical-property parameter of measuring 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 in the situation that maintaining pore pressure and being constant pressure, increase gradually by three axle confined pressures, measure the fluid volume that reduces to discharge due to volume of voids in pressure process, determine pore space compressibility of rock C
p;
Utilize vacuum system to vacuumize saturated processing to rock core, first rock core is vacuumized to processing, remove the assorted gas of core sample piece inside, then under vacuum state, add the fluid of certain specification to soak, allow rock core fully absorb, in order to accelerate absorption rate, in immersion process, rock core and fluid are applied to certain external pressure, and its external pressure is determined with compactness extent according to rock core is loose.
Described fluid is normal saline solution.The three axle confined pressures that rock core is applied are larger, and the volume of voids of rock core reduces more, thereby the fluid volume of discharging is also larger.
(3) computing formula of the effective stress of bearing according to rock skeleton, in the time that pore pressure is constant pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, arrange pore space compressibility of rock C under the different confined pressures of determining in step (2)
pdata, determine rock core effective stress σ
effwith pore space compressibility of rock C
pfitting function;
In the time that pore pressure is constant pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, the confined pressure of rock core is the overlying stress of rock.
(4) utilize the pore pressure steady state value P that leaves and takes a saturated core for subsequent use in overburden porosity proving installation measuring process (2)
cwith the pore pressure value P increasing after confined pressure
c-add;
(5) determine that according to the increment of the rock core pore pressure of measuring in step (4) rock skeleton compresses the decrease Δ V of rear rock pore volume
add;
(6) computing formula of the effective stress of bearing according to rock skeleton, supposes different effective stress coefficient η
i, corresponding different effective stress σ
eff-i, then determine pore space compressibility of rock C according to the fitting function of step (3)
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) decrease of rock pore volume in comparison step (5) and step (7), determines the error delta between the two
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) be provided with efficacy coefficient iterative increment Δ η, carry out i=i+1 and η
i+1=η
i+ Δ η operation, wherein i=(0,1,2 ... n);
(10) repeating step (6)-(9), δ is worked as in judgement
i+1× δ
i< 0, i=(0,1,2 ... n), stop calculating, determine that rock effective stress coefficient is η
n.
The present invention is by the contrast rock close with lithology physical property, the rock signature of test porous medium rock, 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 close oil reservoir rock of mechanical property, the pore compressibility effective stress suffered with it of rock is 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 of choosing is at least two.
In above-mentioned arbitrary scheme, preferably, in described step (1), the physical property of the rock core of choosing is close, and described physical-property parameter comprises permeability and factor of porosity.
In above-mentioned arbitrary scheme, 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 when Δ V-confined pressure changes, framework deformation is discharged, cm
3;
Δ P-confined pressure variable quantity, MPa.
In above-mentioned arbitrary scheme, preferably, in described step (2), the number of times that three axle confined pressures increase is at least three times.
In above-mentioned arbitrary scheme, 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 arbitrary scheme, 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 arbitrary scheme 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 arbitrary scheme, preferably, the pore pressure steady state value of described saturated core and the measuring method that increases the pore pressure value after confined pressure be, saturated core is put into core holding unit, opens constant pressure pump, will in rock core and pipeline, be full of fluid; First valve downstream is closed, then upstream valve is closed, the pore pressure steady state value of measuring saturated core is P
c; Open confined pressure pump, increase the confined pressure of saturated core, after corresponding pore pressure rising is stable, measuring the pore pressure value increasing after 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 arbitrary scheme, 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 sealing between V-valve downstream and upstream valve, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
In the time 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 arbitrary scheme preferably, the volume of voids V that the cumulative volume sealing between described valve downstream and upstream valve is rock core
pand the volume V of pipeline between valve downstream and upstream valve
dsum.
In above-mentioned arbitrary scheme preferably, in described step (6), effective stress coefficient η
ivariation range be 0-1.
In above-mentioned arbitrary scheme preferably, in described step (9), effective stress coefficient iterative increment Δ η=0.001.
In above-mentioned arbitrary scheme, 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, ultra-low penetration 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, realizes the research of the stress sensitive degree to rock.The testing apparatus that the method requires is simple, and test philosophy is clear, wherein, in the situation that lacking reservoir fluid parameter, can adopt the test fluid flow of the stable in properties of indoor laboratory configuration.Compared with the method for calculating effective stress coefficient with existing experiment, technical scheme of the present invention is more convenient, quick.The present invention, under the true pressure condition of simulating oil deposit reservoir, utilizes the effective stress coefficient of the testing of equipment estimation porous medium rock of conventionally test rock permeability, and its method of testing is succinct, accurate.
Brief description of the drawings
Fig. 1 is according to a kind of process chart of determining the method for rock effective stress coefficient based on hole compression experiment of the present invention;
Fig. 2 is according to a kind of schematic diagram of determining the overburden porosity proving installation of the method for rock effective stress coefficient based on hole compression experiment 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 further to understand summary of the invention of the present invention, elaborate the present invention below in conjunction with specific embodiment.
Embodiment mono-:
As shown in Figure 1, a kind of method of determining rock effective stress coefficient based on hole compression experiment, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, in the same direction of rock, choose 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
| Rock core numbering | Length (cm) | Diameter (cm) | Permeability (mD) | Gas is surveyed factor of 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 are vacuumized, then immerse saturated fluid in normal saline solution, in the situation that maintaining pore pressure and being constant pressure, rock core YWT-B1 is increased to three axle confined pressures gradually, measure the volume of the normal saline solution that reduces to discharge due to volume of voids 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 when Δ V-confined pressure changes, 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.
In the time that pore pressure is constant 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 of determining in arrangement step (2)
p, and then the effective stress σ of definite rock core YWT-B1
effwith pore compressibility C
pbetween relation, as shown in Table 2.
Table two: the relation between effective stress and the pore compressibility of rock core YWT-B1
| 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, application linear fit obtains the pore compressibility of rock core YWT-B1 and the relation function of effective stress is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) utilize overburden porosity proving installation to measure the pore pressure steady state value P of rock core YWT-B2
cwith the pore pressure value P increasing 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, will in rock core YWT-B2 and pipeline, be full of normal saline solution, the confined pressure value stabilization of rock core YWT-B2 is at 17.24MPa; First valve downstream 4 is closed, then upstream valve 5 is closed, between valve downstream 4 and upstream valve 5, the cumulative volume of sealing 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, increase the confined pressure of rock core YWT-B2 to 17.93MPa, after corresponding pore pressure rising is stable, measure the pore pressure value P increasing after confined pressure
c-addfor 14.01MPa.Upstream pressure sensor 7 and downstream pressure sensor 6 are respectively used to respond to the force value of 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 sealing between V-valve downstream and upstream valve, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
The decrease of determining 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, 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) decrease of the volume of voids of rock core YWT-B2 in comparison step (5) and step (7), determines the error delta between the two
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n).
(9) be provided with efficacy coefficient iterative increment Δ η=0.001, effective stress coefficient initial value η
0=0, utilize Matlab programming software, carry out i=i+1 and η
i+1=η
i+ Δ η operation, wherein i=(0,1,2 ... n).
(10) repeating step (6)-(9), δ is worked as in judgement
i+1× δ
i< 0, i=(0,1,2 ... n), stopping calculating, is under 15.15MPa in effective stress, determines the effective stress coefficient η of rock core YWT-B2
nbe 0.201.
Embodiment bis-:
As shown in Figure 1, a kind of method of determining rock effective stress coefficient based on hole compression experiment, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, in the same direction of rock, choose 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
| Rock core numbering | Length (cm) | Diameter (cm) | Permeability (mD) | Gas is surveyed factor of 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 immerse saturated fluid in normal saline solution, in the situation that maintaining pore pressure and being constant pressure, rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 are increased respectively to three axle confined pressures gradually, measure the volume of the normal saline solution that reduces to discharge due to volume of voids 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, in the time that pore pressure is constant pressure, the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effbe confined pressure separately, 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 of determining in arrangement step (2)
p, and then the effective stress σ of definite 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 effective stress and the pore compressibility of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
Under logarithmic coordinate, application linear fit obtains the pore compressibility of three rock cores and the relation function of effective stress is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) utilize overburden porosity proving installation to measure the pore pressure steady state value P of rock core YWT-B4
cwith the pore pressure value P increasing 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, will in rock core YWT-B4 and pipeline, be full of normal saline solution, the confined pressure value stabilization of rock core YWT-B4 is at 27.64MPa; First valve downstream 4 is closed, then upstream valve 5 is closed, between valve downstream 4 and upstream valve 5, the cumulative volume of sealing 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, increase the confined pressure of rock core YWT-B4 to 27.93MPa, after corresponding pore pressure rising is stable, measure the pore pressure value P increasing after 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, the decrease of determining 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, 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) decrease of the volume of voids of rock core YWT-B4 in comparison step (5) and step (7), determines the error delta between the two
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n).
(9) be provided with efficacy coefficient iterative increment Δ η=0.001, effective stress coefficient initial value η
0=0, utilize Matlab programming software, carry out i=i+1 and η
i+1=η
i+ Δ η operation, wherein i=(0,1,2 ... n).
(10) repeating step (6)-(9), δ is worked as in judgement
i+1× δ
i< 0, i=(0,1,2 ... n), stopping calculating, is under 19.11MPa in effective stress, determines the effective stress coefficient η of rock core YWT-B4
nbe 0.279.
Embodiment tri-:
As shown in Figure 1, a kind of method of determining rock effective stress coefficient based on hole compression experiment, it comprises the following steps according to sequencing:
(1) choose certain low permeability sandstone reservoir reservoir porous rock, in the same direction of rock, choose 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
| Rock core numbering | Length (cm) | Diameter (cm) | Permeability (mD) | Gas is surveyed factor of 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 immerse saturated fluid in normal saline solution, in the situation that maintaining pore pressure and being constant pressure, rock core YWT-B1, rock core YWT-B2, rock core YWT-B3 are increased respectively to three axle confined pressures gradually, measure the volume of the normal saline solution that reduces to discharge due to volume of voids 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, in the time that pore pressure is constant pressure, the effective stress σ of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
effbe confined pressure separately, 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 of determining in arrangement step (2)
p, and then the effective stress σ of definite 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 effective stress and the pore compressibility of rock core YWT-B1, rock core YWT-B2, rock core YWT-B3
Under logarithmic coordinate, application linear fit obtains the pore compressibility of three rock cores and the relation function of effective stress is C
p=1.787 × 10
-4-1.1403 × 10
-4× lg
10(σ
eff).
(4) utilize overburden porosity proving installation to measure the pore pressure steady state value P of rock core YWT-B4
cwith the pore pressure value P increasing 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, will in rock core YWT-B4 and pipeline, be full of normal saline solution, the confined pressure value stabilization of rock core YWT-B4 is at 17.24MPa; First valve downstream 4 is closed, then upstream valve 5 is closed, between valve downstream 4 and upstream valve 5, the cumulative volume of sealing 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, increase the confined pressure of rock core YWT-B4 to 17.93MPa, after corresponding pore pressure rising is stable, measure the pore pressure value P increasing after 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, the decrease of determining 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, 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 corresponding pore compressibility and the volume decrease of different effective stress coefficients of rock core YWT-B4.
Table seven: corresponding pore compressibility and the volume decrease of different effective stress coefficients of rock core YWT-B4
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 further define the occurrence of efficacy coefficient.
(8) decrease of the volume of voids of rock core YWT-B4 in comparison step (5) and step (7), determines the error delta between the two
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) be provided with efficacy coefficient iterative increment Δ η=0.001, effective stress coefficient initial value η
0=0, utilize Matlab programming software, carry out i=i+1 and η
i+1=η
i+ Δ η operation, wherein i=(0,1,2 ... n);
(10) repeating step (6)-(9), δ is worked as in judgement
i+1× δ
i< 0, i=(0,1,2 ... n), stopping calculating, is under 15.15MPa in effective stress, determines the effective stress coefficient η of rock core YWT-B4
nbe 0.201.
Those skilled in the art are understood that, of the present inventionly a kind ofly determine that based on hole compression experiment the method for rock effective stress coefficient comprises the combination in any of summary of the invention and embodiment part and the shown each several part of accompanying drawing of the invention described above instructions, as space is limited and for making instructions concisely not have each scheme that these are constituted to describe one by one.Within the spirit and principles in the present invention all, any amendment of making, be equal to replacement, improvement etc., within all should being included in protection scope of the present invention.
Claims (10)
1. a method of determining rock effective stress coefficient based on hole compression experiment, it comprises the following steps according to sequencing:
(1) in 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 in the situation that maintaining pore pressure and being constant pressure, increase gradually by three axle confined pressures, measure the fluid volume that reduces to discharge due to volume of voids in pressure process, determine pore space compressibility of rock C
p;
(3) computing formula of the effective stress of bearing according to rock skeleton, in the time that pore pressure is constant pressure, the effective stress σ of rock core
efffor the confined pressure of rock core, arrange pore space compressibility of rock C under the different confined pressures of determining in step (2)
pdata, determine rock core effective stress σ
effwith pore space compressibility of rock C
pfitting function;
(4) utilize the pore pressure steady state value P that leaves and takes a saturated core for subsequent use in overburden porosity proving installation measuring process (2)
cwith the pore pressure value P increasing after confined pressure
c-add;
(5) determine that according to the increment of the rock core pore pressure of measuring in step (4) rock skeleton compresses the decrease Δ V of rear rock pore volume
add;
(6) computing formula of the effective stress of bearing according to rock skeleton, supposes different effective stress coefficient η
i, corresponding different effective stress σ
eff-i, then determine pore space compressibility of rock C according to the fitting function of step (3)
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) decrease of rock pore volume in comparison step (5) and step (7), determines the error delta between the two
i=Δ V
add-Δ V
i, wherein i=(0,1,2 ... n);
(9) be provided with efficacy coefficient iterative increment Δ η, carry out i=i+1 and η
i+1=η
i+ Δ η operation, wherein i=(0,1,2 ... n);
(10) repeating step (6)-(9), δ is worked as in judgement
i+1× δ
i< 0, i=(0,1,2 ... n), stop calculating, determine that rock effective stress coefficient is η
n.
2. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, is characterized in that: in described step (1), the rock core quantity of choosing is at least two.
3. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 2, is characterized in that: in described step (1), the physical property of the rock core of choosing is close, and described physical-property parameter comprises permeability and factor of porosity.
4. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, 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 when Δ V-confined pressure changes, framework deformation is discharged, cm
3;
Δ P-confined pressure variable quantity, MPa.
5. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 4, is characterized in that: in described step (2), the number of times that three axle confined pressures increase is at least three times.
6. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, 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. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 6, 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. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, 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. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, it is characterized in that: the measuring method of the pore pressure value after the pore pressure steady state value of described saturated core and increase confined pressure is, saturated core is put into core holding unit, open constant pressure pump, will in rock core and pipeline, be full of fluid; First valve downstream is closed, then upstream valve is closed, the pore pressure steady state value of measuring saturated core is P
c; Open confined pressure pump, increase the confined pressure of saturated core, after corresponding pore pressure rising is stable, measuring the pore pressure value increasing after confined pressure is P
c-add.
10. the method for determining rock effective stress coefficient based on hole compression experiment as claimed in claim 1, 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 sealing between V-valve downstream and upstream valve, m
3;
C
lthe compressibility coefficient of-rock core inner fluid.
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