CN107327298A - A kind of gas cut degree evaluation method based on well head spillway discharge - Google Patents
A kind of gas cut degree evaluation method based on well head spillway discharge Download PDFInfo
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- CN107327298A CN107327298A CN201710544230.8A CN201710544230A CN107327298A CN 107327298 A CN107327298 A CN 107327298A CN 201710544230 A CN201710544230 A CN 201710544230A CN 107327298 A CN107327298 A CN 107327298A
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- E—FIXED CONSTRUCTIONS
- E21—EARTH DRILLING; MINING
- E21B—EARTH DRILLING, e.g. DEEP DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- E21B47/00—Survey of boreholes or wells
- E21B47/10—Locating fluid leaks, intrusions or movements
Abstract
A kind of gas cut degree evaluation method based on well head spillway discharge, using gas liquid two-phase flow rule inside kill-job parameter and pit shaft, the quantitative relationship for realizing spillway discharge and casing pressure shut-in is described, and institute's result of calculation can objectively respond the risk class of gas cut degree.The present invention mainly for solve standing state gas cut degree can not effectively be differentiated the problem of, in the case that a kind of known well head spillway discharge Monitoring Data is provided, with reference to the gas cut degree method of the parameters such as kill-job technique and casing pressure peak value, the deficiency in conventional art is overcome, can be supported the use with various field well kick detecting devices.
Description
Technical field
The present invention relates to a kind of gas cut degree evaluation method based on well head spillway discharge, belong to deepwater drilling risk assessment
Technical field.
Background technology
During deepwater drilling, due to uncertain factors such as geology, weathers, cause drilling risk larger, often occur
The problems such as gas cut, well kick.Gas cut is very harmful to drillng operation, once it is out of hand, gas blowout accident is may result in, to platform people
Member's safety and the marine eco-environment cause great threat.After gas cut generation, early monitoring and gas cut degree to gas cut
Risk assessment works significant for later stage well control.At present, the assessment for gas cut degree depends on live work
Make the micro-judgment of personnel, with very big subjectivity, the validity of well control measure has a negative impact to the later stage.In Well Killing Process
In, if the kill-job time is too late, easily trigger well kick even gas blowout accident, if well killing fluid density is excessive, and easily fracturing stratum, make
Into leakage, while the selection liquid of kill-job discharge capacity produces influence to bottom pressure.The selection of kill-job parameter is largely dependent upon
Effective judgement of gas cut degree.At present, on the early monitoring of gas cut, domestic and foreign scholars expand substantial amounts of research, have developed
It is a series of in well head, the monitoring method in water proof pipeline section and shaft bottom, wherein well head spillway discharge monitoring method is obtained in marine drilling
Good application.Therefore, it is necessary to set up a kind of gas cut degree risk assessment side of the real-time monitoring based on well head spillway discharge
Method, so as to reduce kill-job operating risk.
The content of the invention
In view of the shortcomings of the prior art, the present invention provides a kind of gas cut degree evaluation method based on well head spillway discharge.This
Invention is supervised mainly for solving the problem of standing state can not effectively differentiate to gas cut degree there is provided a kind of known well head spillway discharge
In the case of surveying data, with reference to the gas cut degree method of the parameters such as kill-job technique and casing pressure peak value, overcome in conventional art
Deficiency, can be supported the use with various field well kick detecting devices.
Technical scheme is as follows：
A kind of gas cut degree evaluation method based on well head spillway discharge, including gas cut scale evaluation stage：
1) kill-job solves the pressure dependence in pit shaft after closing well；
2) after well killing fluid injects, the calculating of strata pressure is carried out, generally, fluid pressure is big in drill string during gas cut
It in annulus hydrostatic power, and can consider without gas in drill string, therefore strata pressure can be tried to achieve by following formula：
Pp=Psp+0.00981ρdD (II)
In formula (II), D --- well depth, m；ρd--- initial drilling fluid density, g/cm3；
3), it is necessary to which well killing fluid density and kill-job pump speed are calculated and selected, to well killing fluid density calculating public affairs during kill-job
Formula is as follows：
In formula (II), Psp--- Standpipe pressure during closing well, MPa；ρd1--- well killing fluid density, g/cm3；
During actual well drilled, to ensure drilling safety, it usually needs drilling fluid density is increased a bit, recommends increase
Value is determined on a case-by-case basis：
It is preferred that：The drilling fluid density of oil well is 0.05~0.10g/cm3, the drilling fluid density of gas well for 0.07~
0.15g/cm3；
It is preferred that：Oil well obtains drilling fluid density for 1.5~3.5MPa, and the drilling fluid density of gas well is 3.5~5.0MPa；
4) in kill-job, it is necessary to carry out kill-job pump speed selection, in kill-job cyclic process, generally pressed with low pump speed
Well, kill-job formula for displacement calculation is：
Q '=(1/3~1/2) Q (IV)
In formula (IV), Q ' --- kill-job discharge capacity, m3/s；Q --- normal discharge capacity, m during drilling well3/s；
5) after the completion of well killing fluid density and kill-job pump speed are calculated, the vertical pressure of kill-job is determined, including determine the vertical pressure of initial cycle
With end of a period circulating pressure：
1. initial cycle is vertical presses PTi：
PTi=Psp+Pc (V)
In formula (V), Pc--- kill-job circulating pressure, MPa；PTi--- the vertical pressure of initial cycle, MPa；
2. end of a period circulating pressure PTf：
In formula (VI), PTf--- end of a period circulating pressure, MPa；
6) after the completion of well killing fluid density and kill-job pump speed are calculated, in Well Killing Process, if shaft bottom gas cut amount is zero, two-phase
Equations for tow-phase flows when flow equation is with gas cut is similar, obtains kill-job model as follows：
Gas continuity equation：(quote：China Petroleum Univ.'s Master's thesis, Pang Hua, page 17)
Liquid continuity equation：
Gas-liquid two-phase mixed equation：
With reference to related subsidiary equation, the subsidiary equation includes：Drilling fluid viscosity, the property of natural gas, external environment temperature
The solution equation of degree, convection transfer rate and thermal source item, calculates in the case of different spillway discharges, is produced in Well Killing Process respectively
Casing pressure peak value, that is, try to achieve the relation of well head spillway discharge and casing pressure peak value, so as to differentiate gas cut degree and well control risk is commented
Valency.
The present invention also includes the conventional data input stage before the gas cut scale evaluation stage, adjusts rank in real time
Section, casing pressure and spillway discharge calculation stages, wherein the data input stage refer to from live Drilling Design scheme and well log
The middle relevant design parameter and sleeve parameters for extracting gas cut well；Drilling progress when the real-time adjusting stage refers to be occurred according to gas cut
And the parameter supplement that arrangement and method for construction is carried out, so as to be calculated according to kill-job model casing pressure and spillway discharge, finally according to casing pressure
And the real-time quantitative relation of well head spillway discharge, build under different well head spillway discharges, casing pressure peak computational and method for evaluating safety,
As the gas cut scale evaluation stage, the stage ensure that timely and effectively carries out accurate evaluation after gas cut generation to its risk.
According to currently preferred, the kill-job uses driller's method kill-job：First circulation week uses former circulation of drilling fluid
Discharge contaminated drilling fluid in well；After kill-job drilling fluid allocation is good, starts second circulation week, well killing fluid is pumped into well；
In the step 1) in, the pressure dependence in the pit shaft is tried to achieve according to U-tube principle, is:
Psp+Phi=Pp=Pa+Pha (I)
In formula (I), Psp--- Standpipe pressure during closing well, MPa；Phi--- liquid column hydrostatic pressure, MPa；Pp--- strata pressure, MPa；
Pa--- casing pressure shut-in, MPa；Pha--- two-phase mixture pressure in mineshaft annulus, MPa.Preferentially driller's method is used in the present invention
Kill-job is carried out, other well killing methods are still applicable, simply wellbore pressure relation solves mode and changed, and should make corresponding tune
Just, the gas cut degree evaluation principle proposed in the present invention is applied to all kill-job modes.
According to currently preferred, the step 6) differentiate gas cut degree and the method bag evaluated well control risk
Include：Maximum allowable casing pressure shut-in is determined, is comprised the following steps that：In above-mentioned Well Killing Process, bottom pressure and wellbore annulus pressure
Change with the injection of well killing fluid, casing pressure shut-in is also to change constantly.According to the requirement of well control technique in marine drilling handbook,
Closing well in the case of whatsoever, the maximum allowable casing pressure shut-in takes the minimum value in three below pressure parameter：
1. wellhead assembly rated operating pressure；Such as subsea blow out preventer；
2. the 80% of sleeve pipe weakness internal pressure strength；This parameter can be determined by sleeve pipe model；
3. stratum weakness (generally casing shoe at) fracture pressure allow casing pressure shut-in=
pLT-0.0098×ρ×HC, wherein pLTFor formation fracture pressure, HCFor stratum weakness depth.
According to currently preferred, after maximum allowable casing pressure shut-in is calculated, the step 6) differentiate gas cut degree simultaneously
The specific method that well control risk is evaluated is included：
(1) calculate the step 6 respectively) in maximum allowable casing pressure shut-in under the conditions of three kinds；Three kinds of conditions are
Refer to the step 6) in maximum allowable casing pressure shut-in 1. 2. 3. under the conditions of three kinds；
(2) assume that other risk factors are constant, according to step 6) casing pressure and the corresponding relation of spillway discharge between any two are asked, paint
Relation curve processed：Abscissa is spillway discharge, unit m3, ordinate is when carrying out kill-job under the spillway discharge, to be produced during well control
Raw casing pressure peak value, units MPa, different curve represents the spillway discharge pass corresponding with casing pressure peak value under different kill-job discharge capacities
System, kill-job discharge capacity unit is m3/min；
(3) it is divided into by maximum allowable casing pressure shut-in as qualifications on the relation curve that step (2) is drawn several
Individual different region, division methods are：
The intersection point of maximum allowable casing pressure shut-in and first relation curve is the first intersection point, and abscissa is less than the first intersection point
Region is a-quadrant,
The intersection point of maximum allowable casing pressure shut-in and the last item relation curve is the second intersection point, and abscissa is more than first and handed over
Point, the region less than the second intersection point are B regions；
The region that abscissa is more than the second intersection point is C regions；
(4) Risk interval is determined：
The a-quadrant represents gas cut degree security interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced set
Voltage crest value is not over MACP peak value, tastefully quiet operation process safety；
B regions relative risk is interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced casing pressure peak value has
MACP peak value may be exceeded, but can be controlled by the regulation of kill-job discharge capacity in safe range, therefore be
Relative risk is interval；
The C regions are extremely dangerous interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced casing pressure peak value
It is bound to exceed MACP peak value, and risk, now kill-job blowout probability can not be lowered by the control of kill-job discharge capacity
Height, therefore be extremely dangerous interval.
The technical advantage of the present invention
The experience for depending on field personnel instant invention overcomes traditional gas cut Well Killing Process risk degree is sentenced
It is disconnected, there is very big subjectivity, using gas liquid two-phase flow rule inside kill-job parameter and pit shaft, realize spillway discharge with
The quantitative relationship description of casing pressure shut-in, institute's result of calculation can objectively respond the risk class of gas cut degree, compensate for deep water brill
Well field is when gas cut is found to the blank in terms of the assessment of gas cut degree, and the control to gas cut is significant.
Brief description of the drawings
Fig. 1 is the structured flowchart of the gas cut degree evaluation method of the present invention based on well head spillway discharge.
During Fig. 2 is the specific embodiment of the invention 1, by the measured data of South Sea XX-X wells, well is calculated using the present invention
The real-time quantitative relation of mouth spillway discharge and casing pressure peak value, the gas cut degree and well control risk drawn with reference to maximum allowable casing pressure shut-in
Schematic diagram, abscissa is well head spillway discharge volume, and ordinate is real-time corresponding shaft sleeve voltage crest value.
Embodiment
The embodiment of the inventive method is elaborated with specific embodiment below in conjunction with the accompanying drawings, but not limited to this.
Embodiment 1,
A kind of gas cut degree evaluation method based on well head spillway discharge, including gas cut scale evaluation stage：
1) kill-job solves the pressure dependence in pit shaft after closing well；
2) after well killing fluid injects, the calculating of strata pressure is carried out, generally, fluid pressure is big in drill string during gas cut
It in annulus hydrostatic power, and can consider without gas in drill string, therefore strata pressure can be tried to achieve by following formula：
Pp=Psp+0.00981ρdD (II)
In formula (II), D --- well depth, m；ρd--- initial drilling fluid density, g/cm3；
3), it is necessary to which well killing fluid density and kill-job pump speed are calculated and selected, to well killing fluid density calculating public affairs during kill-job
Formula is as follows：
In formula (II), Psp--- Standpipe pressure during closing well, MPa；ρd1--- well killing fluid density, g/cm3；
During actual well drilled, to ensure drilling safety, it usually needs drilling fluid density is increased a bit, recommends increase
Value is determined on a case-by-case basis：
It is preferred that：The drilling fluid density of oil well is 0.05~0.10g/cm3, the drilling fluid density of gas well for 0.07~
0.15g/cm3；
It is preferred that：Oil well obtains drilling fluid density for 1.5~3.5MPa, and the drilling fluid density of gas well is 3.5~5.0MPa；
4) in kill-job, it is necessary to carry out kill-job pump speed selection, in kill-job cyclic process, generally pressed with low pump speed
Well, kill-job formula for displacement calculation is：
Q '=(1/3~1/2) Q (IV)
In formula (IV), Q ' --- kill-job discharge capacity, m3/s；Q --- normal discharge capacity, m during drilling well3/s；
5) after the completion of well killing fluid density and kill-job pump speed are calculated, the vertical pressure of kill-job is determined, including determine the vertical pressure of initial cycle
With end of a period circulating pressure：
1. initial cycle is vertical presses PTi：
PTi=Psp+Pc (V)
In formula (V), Pc--- kill-job circulating pressure, MPa；PTi--- the vertical pressure of initial cycle, MPa；
2. end of a period circulating pressure PTf：
In formula (VI), PTf--- end of a period circulating pressure, MPa；
6) after the completion of well killing fluid density and kill-job pump speed are calculated, in Well Killing Process, if shaft bottom gas cut amount is zero, two-phase
Equations for tow-phase flows when flow equation is with gas cut is similar, obtains kill-job model as follows：
Gas continuity equation：(quote：China Petroleum Univ.'s Master's thesis, Pang Hua, page 17)
Liquid continuity equation：
Gas-liquid two-phase mixed equation：
With reference to related subsidiary equation, the subsidiary equation includes：Drilling fluid viscosity, the property of natural gas, external environment temperature
The solution equation of degree, convection transfer rate and thermal source item, calculates in the case of different spillway discharges, is produced in Well Killing Process respectively
Casing pressure peak value, that is, try to achieve the relation of well head spillway discharge and casing pressure peak value, so as to differentiate gas cut degree and well control risk is commented
Valency.
The kill-job uses driller's method kill-job：First circulation week discharges contaminated drilling well in well with former circulation of drilling fluid
Liquid；After kill-job drilling fluid allocation is good, starts second circulation week, well killing fluid is pumped into well；
In the step 1) in, the pressure dependence in the pit shaft is tried to achieve according to U-tube principle, is:
Psp+Phi=Pp=Pa+Pha (I)
In formula (I), Psp--- Standpipe pressure during closing well, MPa；Phi--- liquid column hydrostatic pressure, MPa；Pp--- strata pressure, MPa；
Pa--- casing pressure shut-in, MPa；Pha--- two-phase mixture pressure in mineshaft annulus, MPa.
The step 6) differentiate gas cut degree and the method evaluated well control risk includes：Determine maximum allowable closing well
Casing pressure, is comprised the following steps that：In above-mentioned Well Killing Process, bottom pressure and wellbore annulus pressure become with the injection of well killing fluid
Change, casing pressure shut-in is also to change constantly.According to the requirement of well control technique in marine drilling handbook, whatsoever situation ShiShimonoseki
Well, the maximum allowable casing pressure shut-in takes the minimum value in three below pressure parameter：
1. wellhead assembly rated operating pressure；Such as subsea blow out preventer；
2. the 80% of sleeve pipe weakness internal pressure strength；This parameter can be determined by sleeve pipe model；
3. stratum weakness (generally casing shoe at) fracture pressure allow casing pressure shut-in=
pLT-0.0098×ρ×HC, wherein pLTFor formation fracture pressure, HCFor stratum weakness depth.
After maximum allowable casing pressure shut-in is calculated, the step 6) differentiate gas cut degree and well control risk is evaluated
Specific method include：
(1) calculate the step 6 respectively) in maximum allowable casing pressure shut-in under the conditions of three kinds；Three kinds of conditions are
Refer to the step 6) in maximum allowable casing pressure shut-in 1. 2. 3. under the conditions of three kinds；
(2) assume that other risk factors are constant, according to step 6) casing pressure and the corresponding relation of spillway discharge between any two are asked, paint
Relation curve processed：Abscissa is spillway discharge, unit m3, ordinate is when carrying out kill-job under the spillway discharge, to be produced during well control
Raw casing pressure peak value, units MPa, different curve represents the spillway discharge pass corresponding with casing pressure peak value under different kill-job discharge capacities
System, kill-job discharge capacity unit is m3/min；
(3) it is divided into by maximum allowable casing pressure shut-in as qualifications on the relation curve that step (2) is drawn several
Individual different region, division methods are：
The intersection point of maximum allowable casing pressure shut-in and first relation curve is the first intersection point, and abscissa is less than the first intersection point
Region is a-quadrant,
The intersection point of maximum allowable casing pressure shut-in and the last item relation curve is the second intersection point, and abscissa is more than first and handed over
Point, the region less than the second intersection point are B regions；
The region that abscissa is more than the second intersection point is C regions；
(4) Risk interval is determined：
The a-quadrant represents gas cut degree security interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced set
Voltage crest value is not over MACP peak value, tastefully quiet operation process safety；
B regions relative risk is interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced casing pressure peak value has
MACP peak value may be exceeded, but can be controlled by the regulation of kill-job discharge capacity in safe range, therefore be
Relative risk is interval；
The C regions are extremely dangerous interval；When carrying out kill-job i.e. in the range of the spillway discharge, produced casing pressure peak value
It is bound to exceed MACP peak value, and risk, now kill-job blowout probability can not be lowered by the control of kill-job discharge capacity
Height, therefore be extremely dangerous interval.
In the present embodiment 1, by the measured data of South Sea XX-X wells, well head spillway discharge and casing pressure are calculated using the present invention
The real-time quantitative relation of peak value, the gas cut degree drawn with reference to maximum allowable casing pressure shut-in and well control risk schematic diagram, abscissa
For well head spillway discharge volume, ordinate is real-time corresponding shaft sleeve voltage crest value.
The South Sea XX-X well relevant parameters of table 1
Sleeve pipe and its parameter used in the well of this example 1 is as shown in table 2：
The sleeve parameters of table 2
In this analysis, bore drill bit when meeting gas cut and reached at the oil reservoir of shaft bottom, now the formation fracture of shaft bottom sand layers
Pressure is 1.59g/cm3；Stratum 2800m weakness sandstone fracture pressure is 1.48g/cm3；The nominal operation pressure of subsea blow out preventer
Power is 103MPa, much larger than downhole formation pressure；Sleeve pipe weakness is that its internal pressure strength is at the 2800m of protective casing
34.61MPa, therefore the maximum pressure allowed is its 80%, i.e. 27.69MPa.
Solve maximum allowable casing pressure shut-in：
Device rated operating pressure (preventer) is 103MPa；
Locate the 80% of internal pressure strength：27.69MPa：
Stratum 2800m weakness fracture pressure allows casing pressure shut-in=pLT-0.0098×ρ×HC=(1.48-1.14) ×
0.00981 × 2800=9.33MPa；Oil breakdown pressure allows casing pressure shut-in value=(1.59-1.14) × 0.0098 × 3630
=16MPa.
Therefore, maximum allowable shut-in casing pressure 9.33MPa, is minimum value in above-mentioned three：
At the same time, it is (safety, relative risk is extremely dangerous) three ranks risk grade classification；Result of calculation is such as
Shown in Fig. 2.As shown in Figure 2, it is less than 0.8m in spillway discharge3When, it is gas cut degree level of security, now carries out well control, risk journey
Degree is low；It is more than 0.8m in spillway discharge3Less than 4.83m3When, it is gas cut degree relative risk region, now carries out kill-job and answer emphasis to note
The selection for kill-job parameter of anticipating simultaneously carries out the preparation adjusted in good time；It is more than 4.83m in spillway discharge3When, it is that gas cut degree is extremely dangerous
Rank, now carries out well control degree of risk height, answers direct closing well to observe.Therefore, the example well should be adopted to gas cut as early as possible
Take measure, it is ensured that reach 4.83m in spillway discharge3Kill-job and well control are carried out before.
Claims (4)
1. a kind of gas cut degree evaluation method based on well head spillway discharge, it is characterised in that the evaluation method includes gas cut degree
Evaluation stage：
1) kill-job solves the pressure dependence in pit shaft after closing well；
2) after well killing fluid injects, the calculating of strata pressure is carried out,
Pp=Psp+0.00981ρdD (II)
In formula (II), D --- well depth, m；ρd--- initial drilling fluid density, g/cm3；
3) it is as follows to well killing fluid density calculation formula：
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In formula (II), Psp--- Standpipe pressure during closing well, MPa；ρd1--- well killing fluid density, g/cm3；
4) in kill-job, kill-job pump speed selection is carried out, kill-job formula for displacement calculation is：
Q '=(1/3~1/2) Q (IV)
In formula (IV), Q ' --- kill-job discharge capacity, m3/s；Q --- normal discharge capacity, m during drilling well3/s；
5) the vertical pressure of kill-job is determined, including determines the vertical pressure of initial cycle and end of a period circulating pressure：
1. initial cycle is vertical presses PTi：
PTi=Psp+Pc (V)
In formula (V), Pc--- kill-job circulating pressure, MPa；PTi--- the vertical pressure of initial cycle, MPa；
2. end of a period circulating pressure PTf：
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6) in Well Killing Process, if shaft bottom gas cut amount is zero, kill-job model is obtained as follows：
Gas continuity equation：
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With reference to related subsidiary equation, the subsidiary equation includes：Drilling fluid viscosity, the property of natural gas, ambient temperature is right
The solution equation of the coefficient of heat transfer and thermal source is flowed, is calculated respectively in the case of different spillway discharges, the casing pressure produced in Well Killing Process
Peak value, that is, try to achieve the relation of well head spillway discharge and casing pressure peak value, so as to differentiate gas cut degree and well control risk is evaluated.
2. a kind of gas cut degree evaluation method based on well head spillway discharge according to claim 1, it is characterised in that described
Kill-job uses driller's method kill-job：First circulation week discharges contaminated drilling fluid in well with former circulation of drilling fluid；Treat that kill-job is bored
After well liquid is configured, start second circulation week, well killing fluid is pumped into well；
In the step 1) in, the pressure dependence in the pit shaft is tried to achieve according to U-tube principle, is:
Psp+Phi=Pp=Pa+Pha (I)
In formula (I), Psp--- Standpipe pressure during closing well, MPa；Phi--- liquid column hydrostatic pressure, MPa；Pp--- strata pressure, MPa；Pa——
Casing pressure shut-in, MPa；Pha--- two-phase mixture pressure in mineshaft annulus, MPa.
3. a kind of gas cut degree evaluation method based on well head spillway discharge according to claim 1, it is characterised in that described
Step 6) differentiate gas cut degree and the method evaluated well control risk includes：Maximum allowable casing pressure shut-in is determined, specific step
It is rapid as follows：Maximum allowable casing pressure shut-in takes the minimum value in three below pressure parameter：
1. wellhead assembly rated operating pressure；
2. the 80% of sleeve pipe weakness internal pressure strength；
3. weakness fracture pressure in stratum allows casing pressure shut-in=pLT-0.0098×ρ×HC, wherein pLTFor formation fracture pressure,
HCFor stratum weakness depth.
4. a kind of gas cut degree evaluation method based on well head spillway discharge according to claim 3, it is characterised in that in meter
Calculate after maximum allowable casing pressure shut-in, the step 6) differentiate gas cut degree and the specific method bag evaluated well control risk
Include：
(1) calculate the step 6 respectively) in maximum allowable casing pressure shut-in under the conditions of three kinds；
(2) assume that other risk factors are constant, according to step 6) casing pressure and the corresponding relation of spillway discharge between any two are asked, draw and close
It is curve：Abscissa is spillway discharge, unit m3, ordinate is when carrying out kill-job under the spillway discharge, to be produced during well control
Casing pressure peak value, units MPa, different curve represents spillway discharge and casing pressure peak value corresponding relation under different kill-job discharge capacities, pressure
Well discharge capacity unit is m3/min；
(3) by maximum allowable casing pressure shut-in as qualifications, be divided on the relation curve that step (2) is drawn it is several not
With region, division methods are：
The intersection point of maximum allowable casing pressure shut-in and first relation curve is the first intersection point, and abscissa is less than the region of the first intersection point
For a-quadrant,
The intersection point of maximum allowable casing pressure shut-in and the last item relation curve is the second intersection point, and abscissa is more than the first intersection point, small
In the region of the second intersection point be B regions；
The region that abscissa is more than the second intersection point is C regions；
(4) Risk interval is determined：
The a-quadrant represents gas cut degree security interval；
B regions relative risk is interval；
The C regions are extremely dangerous interval.
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