CN102495935A - Determination method for risk of storage medium leakage of underground natural gas storage reservoir - Google Patents

Abstract

The invention provides a determination method for risk of storage medium leakage of an underground natural gas storage reservoir. The method is used for determining the risk of storage medium leakage of the underground natural gas storage reservoir based on a fuzzy fault tree so as to judge the possibility of leakage failure of the underground natural gas storage reservoir. In the method, the fault tree for the storage medium leakage from a salt cavern underground natural gas storage reservoir to the outside atmospheric environment is established, the probability of basic event causing the storage medium leakage to the outside atmospheric environment is determined by a historical data statistical method and an established engineering evaluation model, influence of various risk factors on the probability of basic event is introduced into the calculation of the probability of basic event in the form of correction factors, and simultaneously, according to the principle of controlling the leakage mode by a main event, and the fault tree logic, the determination methods for the risk of small-leakage mode, big-leakage mode and cracking mode storage medium leakage of the salt cavern underground natural gas storage reservoirs are established.

Description

The assay method of a kind of underground natural gas storage storage medium risk of leakage

Technical field

The present invention relates to the assay method of a kind of underground natural gas storage storage medium risk of leakage, particularly a kind of based on the assay method of fault tree to cave type underground natural gas storage storage medium risk of leakage.

Background technology

Present China is many salt caves of planning construction type underground natural gas storage, the transfering natural gas from the west to the east one line matching construction Jintan gas storage in the construction, and existing 5 old chambeies get into to annotate fells and transports the row order section, will reach the scale in 62 single chambeies during " 12 "; Transfering natural gas from the west to the east tafelberg, matching construction Henan, two wires, Hubei cloud answer project such as salt hole air reserved storeroom also will during " 12 ", build.How to adopt an effective measure; Reduce of the influence of various hazard factor, avoid the underground natural gas storage accident to take place, effectively underground gas storage is carried out preventive maintenance underground gas storage safety; Accomplish to control in advance in advance, become the major issue that China gas storage supvr faces.

Salt cave type underground natural gas storage is one of present main in the world rock gas storing mode and means, in the emergency peak regulation of rock gas, can play a key effect.Yet; Possibly receive the harmful effect of hazard factor such as burn into equipment failure, erosion, hydrate generation, mechanical damage, disaster, maloperation, rock salt creep in the operational process of underground natural gas storage; Cause gas storage stability and safe reliability to reduce; Even cause catastrophic accident, leak, dissolve chamber inefficacy and reservoir area subsidence etc. like gas.According to statistics: underground natural gas storage, salt cave has taken place repeatedly in the operation phase, and safety and environment have been produced huge devastating impact; Accident pattern comprises that mainly leakage and injectivity and productivity descend two types, and wherein leakage accident accounting example is maximum.Therefore, the safety problem of underground natural gas storage can not be ignored.

How to adopt an effective measure, reduce of the influence of various hazard factor, avoid the underground natural gas storage accident to take place, effectively underground gas storage is carried out preventive maintenance, accomplish to control in advance in advance, become the major issue that the gas storage supvr faces underground gas storage safety.Underground natural gas storage, salt cave risk assessment technology is the effective technology means that address this problem; Its objective is and systematically discern the salt cave risk factors of underground natural gas storage operation phase; Estimation risk factors possibility size and severity of consequence that personnel, property or environment are had a negative impact, and underground natural gas storage, definite salt cave risk level are controlled risk taking targetedly; Its safety and steady operation is guaranteed in the generation of preventing accident.Report seldom that about the research of salt cave underground natural gas storage risk assessment the underground natural gas storage risk assessment of salt cave does not still have according to complying with both at home and abroad.The underground natural gas storage risk assessment of salt cave is the result of comprehensive underground natural gas storage failure probability and consequences analysis, confirms the process of its risk level.The assay method of underground natural gas storage, salt cave risk of leakage is one of key point of setting up underground natural gas storage, salt cave risk assessment technology, and is significant for the leakage accident generation of prevention gas storage and lifting China underground natural gas storage safety management level.Therefore, the assay method of studying effective underground natural gas storage risk of leakage is particularly urgently with important.

Summary of the invention

The present invention aims to provide the assay method of a kind of salt cave type underground natural gas storage storage medium risk of leakage; Be used to judge that the leakage failure possibility takes place in the underground natural gas storage; For the type underground natural gas storage risk assessment of salt cave provides the failure probability data; The present invention can solve the problem of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave, for prevention underground natural gas storage, salt cave leakage accident provides technological means, thereby guarantees the safety and steady operation of underground natural gas storage, salt cave.

The assay method of a kind of underground natural gas storage storage medium risk of leakage is measured underground gas storage storage medium risk of leakage based on the method for fuzzy fault tree.

Concrete technical scheme is realized by following steps:

The assay method of a kind of underground natural gas storage storage medium risk of leakage comprises the steps:

A obtains the data information of underground natural gas storage, salt to be evaluated cave;

B is based on the data information of underground natural gas storage, said salt cave, and identification causes the risk factors that storage medium leaks;

C sets up fault tree to leak into the atmosphere incident as top event, confirm secondary incident, elementary event and cause the cut set of top event successively;

D confirms the relation of said elementary event and said risk factors;

E calculates said risk factors and causes the elementary event probability of happening that is associated based on the data information and the engineering judgment model of underground natural gas storage, said salt cave;

F confirms that said risk factors cause the different probability distribution that mold leakage takes place to atmosphere of revealing;

G confirms that according to the said top event cut set that causes said causing causes the main event that leaks into the generation of atmosphere incident in the top event cut set;

H reveals probability distribution according to said elementary event probability of happening and said risk factors, confirms the probability of happening and the said probability of happening that causes the cut set of top event of said main event;

I calculates the probability of happening of said secondary incident under the said top event according to the probability of happening and the said fault tree of said main event;

J calculates the probability of happening of said top event under the said different leakage pattern according to the said probability of happening that goes on foot fault tree and said secondary incident.

Preferably, underground natural gas storage, the salt cave information material in the described steps A comprises salt cave underground gas storage library information, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor, maintenance and/or maintenance history data.

Preferably, underground natural gas storage, the salt cave information in the described steps A comprises gas storage title, gas storage type evaluation salt cave well numbering, salt cave well designed life and salt cave well active time.

Preferably, the storage medium characterisitic parameter in the described steps A comprises the Dynamic Viscosity of storage medium type, gas constant, rock gas molecular weight, rock gas relative density and rock gas.

Preferably, the salt cave well geometric shape parameters in the described steps A comprises salt cave volume, storage capacity, work tolerance, cushion steam amount and tubing string size.

Preferably, the operational factor in the described steps A comprises the maximum operating pressure of well head, the minimum operating pressure of well head, salt cave maximum design pressure, salt cave minimal design pressure, salt cave temperature, injecting gas temperature and peak performance.

Preferably, maintenance in the described steps A and/or maintenance history comprise the incident of leakage that has taken place, the salt cave unstability incident and the maintenance history that have taken place.

Preferably, the risk factors among the said step B classify as that burn into erosion, equipment failure, operation are relevant, six types of mechanical damage and natural forces.

Preferably, leak through the well head facility among the described step C and be said secondary incident through the underground ground that leaks into.

Preferably, the said leakage through the well head facility comprises that emergency shut-in valve leaks, well head leakage below well head leakage, packer leakage, tubing leak and the tubing hanger above the tubing hanger.

Preferably, said through undergroundly leaking into that ground comprises that packer leaks, leak path to ground, leakages of salt cave top board, cap rock leakage, casing leak, leaking and pass through the leakage of surface string cement mantle through the production casing cement mantle.

Preferably, elementary event described in the step C is emergency shut-in valve leakage, well head leakage below well head leakage, packer leakage, tubing leak, the tubing hanger above the tubing hanger, the leak path to ground, the leakage of salt cave top board, cap rock leakage, casing leak, leaks and leak through the surface string cement mantle through the production casing cement mantle.

Preferably; The cut set that causes top event described in the step C comprises 6 cut sets; Being followed successively by cut set 1 leaks for emergency shut-in valve; Cut set 2 is that well head leaks above the tubing hanger, and cut set 3 be that well head leaks below packer leakage, tubing leak and the tubing hanger, and cut set 4 leaks and the cap rock leakage for leak path, salt cave top board to ground; Cut set 5 is packer leakage, casing leak, leaks and leak through the surface string cement mantle through the production casing cement mantle, and cut set 6 is for leaking through the production casing cement mantle and leaking through the surface string cement mantle.

Preferably, the model of engineering judgment described in the step e comprises that erosion CALCULATION OF FAILURE PROBABILITY model, casing corrosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause casing leak and salt cave top board leakage probability computation model and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model.

Preferably, said erosion CALCULATION OF FAILURE PROBABILITY model is suc as formula shown in (1)

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\×\mathrm{ratio}=2.572\×{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\×\mathrm{ratio}$

(1)

E wherein _kBe erosion rate (inferior/year) that W is that sand flow velocity (Kg/day) V is that flow rate (m/s) D is pipe diameter (mm), S _kBe geometric shape parameters, Pf _ErosionThe probability (inferior/year) that causes equipment failure for erosion; T is equipment wall thickness (mm); Ratio is that gas storage accounts for the year ratio with throughput rate operation in maximum day.

Preferably, said casing corrosion CALCULATION OF FAILURE PROBABILITY model is based on the theoretical corrosion default of confirming of stress-strength interference and increases the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, shown in (2).

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}}<0}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{STTS}\right)\mathrm{dP}$

(2)

This model adopts Monte Carlo method to calculate, wherein, f (d, L, t, D, SMTS P) is variable d, L, t, D, SMTS, the joint probability density function of P, D is the cover external diameter of pipe, d is the thickness of etch pit; T is a wall thickness; L is the effective length of wall thickness loss; P is effectively interior the pressure, and SMTS is the tensile strength of material, LSF _BurstBe limit state function, it is that operating pressure explosion takes place when surpassing the burst pressure of prediction that corrosion default increases the ultimate limit state cause the explosion of residue tube wall, and limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF _burst＝P _burst-P _op

(3)

When LSF＞0; LSF=0 and LSF＜0 is represented safety, the limit and failure state respectively;

$P_{\mathrm{burst}}=\stackrel{\&OverBar;}{P_{\mathrm{burst}}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]$

(4)

$\stackrel{\&OverBar;}{S_f}=\mathrm{SMTS}$

(5)

$M={[1+\frac{{0.8\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000120653660000011.png"\; state="\{\{state\}\}">L</figure-callout>}}^2}{\mathrm{Dt}}]}^{1/2}$

(6)

P wherein _BurstBe prediction inefficacy stress,

Be flow stress, M is the Folia coefficient; A is the area of metal loss

A ₀Be original area (L * t);

P _OpIn effectively clean, press; At first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as the pipe internal pressure, and subtract each other with the pipe external pressure, take absolute value; During conservative, at last two values are relatively got effectively clean interior pressure that maximal value is born as production casing.

Preferably; Said salt cave closure causes in casing leak and the salt cave top board leakage probability computation model; Comprise that with the closed relevant incident in salt cave casing leak and salt cave top board leak; Suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the probability that the Model Calculation salt cave closure shown in the formula (7) causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}$

(7)

Wherein F (x) leaks the salt cave closing capacity distribution function that takes place for causing casing leak and salt cave top board, and x fells and transports the salt cave closing capacity (%) that row causes for annotating.

Preferably, earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise in the described step e:

E1 confirms the relation of seismic amplitude and frequency according to the Gutenberg-Richter rule;

E2 confirms the relation of ground peak accelerator and seismic amplitude according to the Gutenberg-Richter rule;

E3 confirms the seismic frequency of said salt cave well area and the relation of ground peak accelerator based on the relation of said seismic amplitude and frequency and the relation of said ground peak accelerator and seismic amplitude;

E4 confirms that earthquake causes the said ground peak accelerator threshold value that well lost efficacy;

E5 is according to the seismic frequency of said salt cave well area and the relation and the said ground peak accelerator threshold value of ground peak accelerator, confirms the distance between tomography and the salt cave well and annually causes the relation between the frequency that salt cave well lost efficacy because of earthquake;

E6 confirms that according to causing relation and the distance between salt to be evaluated cave well and the tomography between the frequency that salt cave well lost efficacy because of earthquake said every year earthquake causes salt cave well failure probability.

Preferably, the said different leakage patterns in the step F comprise little leakage, gross leak and the three kinds of patterns of breaking, and wherein annotate to adopt 1% of pipe diameter and be little leakage, annotate to adopt 10% of pipe diameter and reveal for big, annotate adopt the pipe diameter 100% for breaking.

Preferably, the said risk factors in the step F cause shown in the elementary event probability of happening according to the form below 1 that is associated:

Leakage size

Corrosion

Erosion

Equipment failure

Operation is relevant

Mechanical damage

Natural force

Little leakage

93％

93％

70％

39％

35％

26％

Gross leak

6.9％

6.9％

29％

60％

64％

54％

Break

0.1％

0.1％

1.0％

1.0％

1.0％

20％

Every type of risk factors of table 1 cause the probability distribution of different leakage mode

Preferably, the main event described in the step G is meant the situation that generation takes place just to cause leaking for two or more said elementary events jointly, the elementary event of control leakage size size in the leak path.

Preferably, the probability of happening of main event described in the step H is meant, calculates the probability of happening of confirming the main event under the different leakage mode according to formula (8), and it is designated as the probability of happening of corresponding cut-set.

Pf _ij＝1-∏(1-Pf _jkA _ki)

(8)

Pf wherein _IjFor the leakage mode of main event j is the probability of happening of i;

Pf _JkBe the probability of happening of main event j under risk factors k influence;

A _IkFor risk factors k causes the probability that leakage mode i takes place;

I is a leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking;

J is the main event numbering; K is risk factors, from 1-6 represent respectively that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force.

Preferably, the probability of happening of secondary incident described in the step I is meant that the said probability of happening substitution formula (9) of the cut set of top event that causes among the H set by step calculates:

Pf _il＝1-∏(1-Pf _im)

(9)

Pf wherein _IlFor the leakage mode of secondary incident 1 is the probability of happening of i;

Pf _ImFor cut set is m and the leakage mode probability of happening when being i;

I is a leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking; 1 is secondary Case Number; M is the corresponding cut set numbering of secondary incident.

Preferably, under the different leakage mode, said top event probability of happening comprises following two kinds of situation according to logical diagram among the step C among the step J:

First kind be between the said secondary incident logical relation for and the door relation, the said top event of said different leakage mode is calculated by formula (10):

Pf _i＝∏Pf _il

(10)

Second kind be between the said secondary incident logical relation for or door relation, the said top event of said different leakage mode is calculated by formula (11):

Pf _i＝1-∏(1-Pf _il)

(11)

PF wherein _iFor salt cave well leaks into the probability of happening of the leakage mode i of atmosphere, i is a leakage mode, and 1 is secondary Case Number.

The present invention has set up the fault tree that underground natural gas storage, salt cave storage medium leaks into the ambient atmosphere environment; Adopt the engineering judgment model of historical data statistical method and foundation; Confirmed to cause that storage medium leaks into the elementary event probability of happening of ambient atmosphere environment; And the various risks factor is introduced in the elementary event probability calculation the influence of elementary event probability of happening with the form of correction factor; Control the principle and the fault tree logic of leakage mode simultaneously according to main event; The salt cave type underground natural gas storage storage medium of having set up little leakage, gross leak and fracture mode leaks into the method for calculating probability of ambient atmosphere environment, has solved one of key issue of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave.The present invention can predict that reasonably salt cave type underground natural gas storage storage medium leaks into the probability of ambient atmosphere environment according to actual design parameter and operating mode situation, can be gas storage safety management person prevention underground natural gas storage, the salt cave leakage accident of adopting an effective measure foundation is provided.

Description of drawings

Fig. 1 salt cave well storage medium leaks into the fault tree of ambient atmosphere environment.

The relation of Fig. 2 casing corrosion failure probability and working time.

The seimic salt of Fig. 3 cave well failure probability and salt cave well are to the distance of tomography.

Embodiment

Below in conjunction with embodiment the present invention is further described in detail, the embodiment that provides has been merely and has illustrated the present invention, rather than in order to limit scope of the present invention.

Step 1: the information material that obtains underground natural gas storage, salt to be evaluated cave

Information material comprises underground natural gas storage, salt cave basic document, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor and maintenance/maintenance history data, shown in table 2-table 6.

Underground natural gas storage, table 2 salt cave essential information

Numbering	Attribute	Unit	Parameter value
					1	The gas storage title	Text	Underground natural gas storage, salt cave, Jintan
2	The gas storage type	Text	Salt cave type
				2	The basic overview of gas storage	Text	At present at labour salt cave Jing5Kou
3	Estimate salt cave well numbering	Text	X1
				4	Salt cave well designed life	Year	50
5	Salt cave well active time	Year						4

Table 3X1 well storage medium characterisitic parameter

Numbering	Attribute	Unit	Parameter value
					1	Storage medium	Text	Rock gas
2	Gas constant	J/K.mol	8.314
				3	The rock gas molecular weight	kg/mol	0.023
4	The rock gas relative density	/	0.575
				5	The Dynamic Viscosity of rock gas	cp	0.000118

Table 4X1 well geometric shape parameters

Numbering	Attribute	Unit	Parameter value
					1	Salt cave volume	104m3	10.5
2	Storage capacity	104m3	1521

3	Work tolerance	104m3	787
				4	The cushion steam amount	104m3	734
5	Salt cave mean diameter	m	40
				6	Notes are adopted the sleeve pipe interior diameter	mm	159.4
7	The production casing overall diameter	mm	244.5
				8	The production casing wall thickness	mm	9.19
9	The surface string overall diameter	mm	339.7
				10	The surface string wall thickness	mm	9.65
11	Notes are adopted length of tube	m	940
				12	Well head internal flow diameter	mm	159.4
13	The well head wall thickness	mm	9.19
				14	Flow diameter in the emergency shut-in valve	mm	149.2
15	The emergency shut-in valve wall thickness	mm	31.75

Table 5X1 operational factor

Numbering	Attribute	Unit	Parameter value
					1	Maximum well head operating pressure	kPa	13.5
2	Minimum well head operating pressure	kPa	6.5
				3	Average wellhead pressure	kPa		10
4	Crude salt cave pressure	kPa	14
				5	Minimum salt cave pressure	kPa	7
6	Average salt cave pressure	kPa	10.5
				7	Salt cave temperature		53
8	The gas input temp	C	20
				9	Peak performance (MPR)	104m3/d	153
10	Average preformance (%MPR)		100％
				11	The atmosphere medial temperature	C	20
12	Annual days running	day	180
				13	The time that maximum day throughput rate moved in 1 year	day	14
14	Salt cave make rate in time under arms	％	0.38

Table 6X1 well servicing/maintenance history data

Numbering	Attribute	Unit	Parameter value
					1	The incident of leakage that has taken place	Inferior	0
2	The salt cave unstability incident that has taken place	Inferior	0
				3	Maintenance history	Text	Do not have

Step 2: identification causes the risk factors that salt cave well storage medium leaks into the ambient atmosphere environment

The risk factors that salt cave well leaks comprise that burn into erosion, equipment failure, operation are relevant, six types of mechanical damage and earthquakes.

Step 3: set up the fault tree that salt cave well storage medium leaks into the ambient atmosphere environment

Leaking into atmosphere with salt cave well is top event (seeing accompanying drawing 2), considers to identify 11 elementary events (table 7), 9 cut sets (table 8) through the leakage of well head facility with through the underground two kinds of situation in ground that leak into

Table 7 causes the elementary event that leaks into the generation of atmosphere top event

Numbering	Elementary event	Numbering	Elementary event
				X1	Emergency shut-in valve leaks	X7	Salt cave top board leaks
X2	Well head leaks above the tubing hanger	X8	Cap rock leaks
				X3	Packer leaks	X9	Casing leak
X4	Tubing leak	X10	Leak through the production casing cement mantle
				X5	Well head leaks below the tubing hanger	X11	Leak through the surface string cement mantle
X6	Leak path to ground

Table 8 causes the cut set that top event takes place

Step 4: the relation of confirming elementary event and various risks factor

In conjunction with industry experience, confirm the influence relation (table 9) of the described various risks factor of step 2 to the elementary event probability of happening.Show that to colluding incident possibly caused by corresponding risk factors in the table.

Table 9 various risks factor is to the influence relation of elementary event probability of happening

Step 5:, calculate the various risks factor and cause the elementary event probability of happening that is associated based on historical statistical data and engineering judgment model.

Adopt engineering judgment Model Calculation various risks factor to cause that the elementary event probability of happening process that is associated is following:

Erosion causes that the probability of happening of elementary event X1, X2, X4 and X5 calculates

Erosion is relevant with elementary event X1, X2, X4 and X5, and the erosion CALCULATION OF FAILURE PROBABILITY model (formula 1) in the available summary of the invention calculates,

Erosion CALCULATION OF FAILURE PROBABILITY model is suc as formula shown in 1

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\&times;\mathrm{ratio}=2.572\&times;{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\&times;\mathrm{ratio}$

(1)

E wherein _kBe erosion rate (inferior/year) that W is that sand flow velocity (Kg/day) V is that flow rate (m/s) D is pipe diameter (mm), S _kBe geometric shape parameters, Pf _ErosionThe probability (inferior/year) that causes equipment failure for erosion; T is equipment wall thickness (mm); Ratio is that gas storage accounts for the year ratio with throughput rate operation in maximum day.

Parameter and result of calculation are seen table 10, and flow rate is to obtain according to the medial temperature of correspondence and average calculation of pressure.

Table 10 erosion causes the probability of happening of elementary event X1, X2, X4 and X5

Corrosion causes that cover tube failure probability of happening calculates

Casing corrosion CALCULATION OF FAILURE PROBABILITY model is based on the theoretical corrosion default of confirming of stress-strength interference and increases the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, shown in (2).

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}}<0}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{STTS}\right)\mathrm{dP}$

(2)

This model adopts Monte Carlo method to calculate, wherein, f (d, L, t, D, SMTS P) is variable d, L, t, D, SMTS, the joint probability density function of P, D is the cover external diameter of pipe, d is the thickness of etch pit; T is a wall thickness; L is the effective length of wall thickness loss; P is effectively interior the pressure, and SMTS is the tensile strength of material, LSF _BurstBe limit state function, it is that operating pressure explosion takes place when surpassing the burst pressure of prediction that corrosion default increases the ultimate limit state cause the explosion of residue tube wall, and limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF _burst＝P _burst-P _op

(3)

When LSF＞0; LSF=0 and LSF＜0 is represented safety, the limit and failure state respectively;

$P_{\mathrm{burst}}=\stackrel{\&OverBar;}{P_{\mathrm{burst}}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]$

(4)

$\stackrel{\&OverBar;}{S_f}=\mathrm{SMTS}$

(5)

$M={[1+\frac{{0.8\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="HDA0000120653660000011.png"\; state="\{\{state\}\}">L</figure-callout>}}^2}{\mathrm{Dt}}]}^{1/2}$

(6)

P wherein _BurstBe prediction inefficacy stress,

Be flow stress, M is the Folia coefficient; A is the area of metal loss A ₀Be original area (L * t);

P _OpIn effectively clean, press; At first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as the pipe internal pressure, and subtract each other with the pipe external pressure, take absolute value; During conservative, at last two values are relatively got effectively clean interior pressure that maximal value is born as production casing.

Corrode relevantly with elementary event X3, X4 and X9, the probability of happening of X3, X4 adopts historical statistical data, and elementary event X9 then adopts the casing corrosion CALCULATION OF FAILURE PROBABILITY Model Calculation in the said step e in the summary of the invention.Adopt DSMC; Consider that two kinds of corrosion rate 0.15mm/ and 0.24mm/ have calculated the Changing Pattern of casing corrosion failure probability with working time; See accompanying drawing 3, because this salt cave well active time is 4 years, the casing corrosion failure probability when then getting 4 years 2 * 10-7 time/year.

Salt cave closure causes that casing leak and salt cave top board leakage probability calculate

Salt cave closure causes casing leak and salt cave top board leakage probability computation model; Comprise that with the closed relevant incident in salt cave casing leak and salt cave top board leak; Suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the probability that the Model Calculation salt cave closure shown in the formula (7) causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}$

(7)

Wherein F (x) leaks the salt cave closing capacity distribution function that takes place for causing casing leak and salt cave top board, and x fells and transports the salt cave closing capacity (%) that row causes for annotating.

With table 5 under arms the salt cave make rate 0.38% in the time be updated to the formula in the step e 7 described in the summary of the invention,

Promptly get salt cave closure and cause that casing leak and salt cave top board leakage probability are 2.17 * 10-15 time/year.

Earthquake causes salt cave well CALCULATION OF FAILURE PROBABILITY

Earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise:

E1 confirms the relation of seismic amplitude and frequency according to the Gutenberg-Richter rule;

E2 confirms the relation of ground peak accelerator (PGA) and seismic amplitude according to the Gutenberg-Richter rule;

E3 confirms the seismic frequency of certain salt cave well area and the relation of ground peak accelerator (PGA) based on step 1 and the definite relation of step 2;

E4 confirms that earthquake causes the PGA threshold value that well lost efficacy;

E5 is according to the PGA threshold value of the relation and the step 4 of step 3, confirms the distance between tomography and the salt cave well and annually causes the relation between the frequency that salt cave well lost efficacy because of earthquake;

Relation that E5 confirms according to step 5 and the distance between salt to be evaluated cave well and the tomography confirm that earthquake causes salt cave well failure probability.

Cause the CALCULATION OF FAILURE PROBABILITY model of salt cave well according to earthquake in the said step e in the summary of the invention, confirmed the relation of distance between salt cave well failure probability and salt cave well and the tomography, see accompanying drawing 4.The X1 well spacing is 500Km from the distance of tomography among the embodiment, and promptly salt cave well failure probability is looked into figure and can be known to be 6 * 10-4 time/year.For during conservative, suppose that seismic events only causes that elementary event X1 and X9 take place, then remember elementary event X1 and X9 because of seimic probability of happening be 6 * 10-4 time/year.The various risks factor causes that the elementary event probability of happening that is associated sees table 11.

Table 11 various risks factor causes the elementary event probability of happening that is associated

Step 6: confirm that the various risks factor causes that different leakage mode leak into the probability distribution rule that atmosphere takes place

Leak the underground natural gas storage can be divided into little leakage, gross leak and the three kinds of patterns of breaking, and can define as follows for the underground natural gas storage leakage size: little leakage-notes are adopted 1% of pipe diameter; Gross leak-notes are adopted 10% of pipe diameter; Break-annotate to adopt and manage 100% of diameter.It is different that the various risks factor causes that different leakage mode are leaked the probability that takes place, and probability distribution can be calculated by the table 1 in the technical scheme.

The various risks factor causes that different leakage mode leak into the probability distribution that atmosphere takes place and calculate by the table 1 in the said step F in the summary of the invention, and wherein for the natural force factor, 1 of present embodiment is considered by earthquake.

Step 7: the main event of confirming control leakage mode in each cut set

Confirm in each cut set the main event of control leakage mode by the said step F in the summary of the invention, the result sees table 12.

The main event of control leakage mode in each cut set of table 12

Step 8: the main event of different leakage mode and the probability of happening of corresponding cut-set calculate

Probability of happening with the little leakage of main event X1-is calculated as example, calculates according to G of step described in the summary of the invention and table 12, calculates to show that the little leakage probability of happening of main event X1-is 9.7 * 10-3, and corresponding cut-set [X1]-little leakage probability of happening is 9.7 * 10-3.The probability of happening result of calculation of the different leakage mode of main event is seen table 13.

Pf _1X1＝1-(1-Pf _X12A ₂₁)(1-Pf _X13A ₃₁)(1-Pf _X15A ₅₁)(1-Pf _X16A ₆₁)

Pf _1X1＝1-(1-4.93×10 ^-8×0.93)(1-1.37×10 ^-2×0.7)(1-6.79×10 ^-6×0.35)(1-6×10 ^-4×0.26)＝9.7×10 ^-3

The probability of happening of the different leakage mode of table 13 main event

Step 9: the probability of happening that calculates the different leakage mode of secondary incident under the top event

Can confirm that according to accompanying drawing 2 fault trees the secondary incident under the top event is A1 and A2, the probability of happening substitution formula (9) of the cut set that the secondary incident among the step I is corresponding is calculated the probability of happening of the different leakage mode of secondary incident.Little leakage mode probability of happening with secondary incident A1 is an example explanation computation process (formula).Table 14 is the probability of happening result of the different leakage mode of secondary incident under the top event.

Pf _1A1＝1-(1-Pf _1[x1])(1-Pf _1[x2])(1-Pf _1[x5])

Pf _1A1＝1-(1-9.7×10 ^-3)(1-2.8×10 ^-3)(1-2.97×10 ^-1)＝3×10 ^-1

The probability of happening of the different leakage mode of table 14 time level incident

Step 10: the top event probability of happening that calculates different leakage mode

Secondary incident A1 and A2 relation are or door concerns, then with the probability of happening substitution formula (1) 1 of the different leakage mode of secondary incident under the top event of calculating among the step I, can calculate the top event probability of happening of different leakage mode, see table 15.

The probability of happening that leaks into atmosphere of the different leakage mode of table 15

A kind of salt provided by the invention cave type underground natural gas storage storage medium leaks into the method for calculating probability of ambient atmosphere environment, is primarily characterized in that 1) confirmed that salt cave type underground natural gas storage storage medium leaks into the probability calculation information needed data and concrete parameter of ambient atmosphere environment; 2) risk factors that salt cave well storage medium leaked into the ambient atmosphere environment classify as that burn into erosion, equipment failure, operation are relevant, six types of mechanical damage and natural forces; 3) set up and be applicable to that salt cave well storage medium leaks into the fault tree of ambient atmosphere environment; 4) confirmed the relation of elementary event and various risks factor; 5) set up the engineering judgment model of the elementary event probability of happening that is associated with the various risks factor, comprised that erosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause probability calculation model that casing leak and salt cave top board leak and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model; 6) confirmed that the various risks factor causes that different leakage mode (little leakage, gross leak and break) leak into the probability distribution that atmosphere takes place; 7) nethermost elementary event in the leak path is defined as main event; 8) form with correction factor is incorporated into the influence of various risks factor to the elementary event probability of happening in the probability of happening calculating of the main event under the different leakage mode; 9) probability of happening of main event under the different leakage mode is designated as the probability of happening of its corresponding cut-set; 10), finally form the method for calculating probability that underground natural gas storage, a kind of salt cave storage medium leaks into the ambient atmosphere environment based on above characteristic.

The invention solves one of key issue of CALCULATION OF FAILURE PROBABILITY in the underground natural gas storage risk assessment of salt cave; Can predict that reasonably underground natural gas storage, salt cave leaks into the probability of atmosphere according to actual design parameter and operating mode situation, can be gas storage safety management person prevention underground natural gas storage, the salt cave leakage accident of adopting an effective measure foundation is provided.

Claims (25)

1. the assay method of a underground natural gas storage storage medium risk of leakage is characterized in that, based on method underground gas storage storage medium risk of leakage is measured.

2. assay method according to claim 1 is characterized in that, comprises the steps:

A obtains the data information of underground natural gas storage, salt to be evaluated cave;

B is based on the data information of underground natural gas storage, said salt cave, and identification causes the risk factors that storage medium leaks;

C sets up fault tree to leak into the atmosphere incident as top event, confirm secondary incident, elementary event and cause the cut set of top event successively;

D confirms the relation of said elementary event and said risk factors;

E calculates said risk factors and causes the elementary event probability of happening that is associated based on the data information and the engineering judgment model of underground natural gas storage, said salt cave;

F confirms that said risk factors cause the different probability distribution that mold leakage takes place to atmosphere of revealing;

G confirms that according to the said top event cut set that causes said causing causes the main event that leaks into the generation of atmosphere incident in the top event cut set;

H reveals probability distribution according to said elementary event probability of happening and said risk factors, confirms the probability of happening and the said probability of happening that causes the cut set of top event of said main event;

I calculates the probability of happening of said secondary incident under the said top event according to the probability of happening and the said fault tree of said main event;

J calculates the probability of happening of said top event under the different leakage patterns according to the said probability of happening that goes on foot fault tree and said secondary incident.

3. assay method according to claim 2; It is characterized in that underground natural gas storage, the cave of salt described in steps A information material comprises salt cave underground gas storage library information, storage medium characterisitic parameter, salt cave well geometric shape parameters, operational factor, maintenance and/or maintenance history data.

4. assay method according to claim 3 is characterized in that, underground natural gas storage, the cave of salt described in steps A information comprises gas storage title, gas storage type evaluation salt cave well numbering, salt cave well designed life and salt cave well active time.

5. assay method according to claim 3 is characterized in that, the characterisitic parameter of storage medium described in the steps A comprises the Dynamic Viscosity of storage medium type, gas constant, rock gas molecular weight, rock gas relative density and rock gas.

6. assay method according to claim 3 is characterized in that, the cave of salt described in steps A well geometric shape parameters comprises salt cave volume, storage capacity, work tolerance, cushion steam amount and tubing string size.

7. assay method according to claim 3; It is characterized in that operational factor described in the steps A comprises the maximum operating pressure of well head, the minimum operating pressure of well head, salt cave maximum design pressure, salt cave minimal design pressure, salt cave temperature, injecting gas temperature and peak performance.

8. assay method according to claim 3 is characterized in that, maintenance and/or maintenance history comprise the incident of leakage that has taken place, the salt cave unstability incident and the maintenance history that have taken place described in the steps A.

9. assay method according to claim 2 is characterized in that, risk factors described in the step B classify as that burn into erosion, equipment failure, operation are relevant, six types of mechanical damage and natural forces.

10. assay method according to claim 2 is characterized in that, leaks through the well head facility described in the step C and is said secondary incident through the underground ground that leaks into.

11. assay method according to claim 10 is characterized in that, the said leakage through the well head facility comprises that emergency shut-in valve leaks, well head leakage below well head leakage, packer leakage, tubing leak and the tubing hanger above the tubing hanger.

12. assay method according to claim 10; It is characterized in that, said through undergroundly leaking into that ground comprises that packer leaks, leak path to ground, leakages of salt cave top board, cap rock leakage, casing leak, leaking and pass through the leakage of surface string cement mantle through the production casing cement mantle.

13. assay method according to claim 2; It is characterized in that elementary event described in the step C is emergency shut-in valve leakage, well head leakage below well head leakage, packer leakage, tubing leak, the tubing hanger above the tubing hanger, the leak path to ground, the leakage of salt cave top board, cap rock leakage, casing leak, leaks and leak through the surface string cement mantle through the production casing cement mantle.

14. assay method according to claim 2; It is characterized in that; The cut set that causes top event described in the step C comprises 6 cut sets, is followed successively by cut set 1 and leaks for emergency shut-in valve, and cut set 2 is that well head leaks above the tubing hanger; Cut set 3 is that well head leaks below packer leakage, tubing leak and the tubing hanger; Cut set 4 leaks for leak path, salt cave top board to ground and cap rock leaks, and cut set 5 is packer leakage, casing leak, leaks and leak through the surface string cement mantle through the production casing cement mantle, and cut set 6 is for leaking through the production casing cement mantle and leaking through the surface string cement mantle.

15. assay method according to claim 2; It is characterized in that the model of engineering judgment described in the step e comprises that erosion CALCULATION OF FAILURE PROBABILITY model, casing corrosion CALCULATION OF FAILURE PROBABILITY model, salt cave closure cause casing leak and salt cave top board leakage probability computation model and earthquake to salt cave well CALCULATION OF FAILURE PROBABILITY model.

16. assay method according to claim 15 is characterized in that, said erosion CALCULATION OF FAILURE PROBABILITY model is suc as formula shown in (1):

${\mathrm{Pf}}_{\mathrm{erosion}}=\frac{E_k}{t}\&times;\mathrm{ratio}=2.572\&times;{10}^{-3}(S_{k}W{\left(\frac{V}{D}\right)}^2/t)\&times;\mathrm{ratio}$

(1)

E wherein _kBe erosion rate (inferior/year) that W is sand flow velocity (Kg/day), V is flow rate (m/s), and D is pipe diameter (mm), S _kBe geometric shape parameters, Pf _ErosionThe probability (inferior/year) that causes equipment failure for erosion; T is equipment wall thickness (mm); Ratio is that gas storage accounts for the year ratio with throughput rate operation in maximum day.

17. assay method according to claim 15 is characterized in that, said casing corrosion CALCULATION OF FAILURE PROBABILITY model is based on the theoretical corrosion default of confirming of stress-strength interference and increases the CALCULATION OF FAILURE PROBABILITY model that causes the explosion of residue tube wall, shown in (2):

${\mathrm{Pf}}_{\mathrm{burst}}=\underset{{\mathrm{LSF}}_{\mathrm{burst}}<0}{\&Integral;}...\&Integral;f(d,L,t,D,\mathrm{SMTS},P)\mathrm{dddLdtdDd}\left(\mathrm{STTS}\right)\mathrm{dP}$

(2)

This model adopts Monte Carlo method to calculate, wherein, f (d, L, t, D, SMTS P) is variable d, L, t, D, SMTS, the joint probability density function of P, D is the cover external diameter of pipe, d is the thickness of etch pit; T is a wall thickness; L is the effective length of wall thickness loss; P is effectively interior the pressure, and SMTS is the tensile strength of material, LSF _BurstBe limit state function, it is that operating pressure explosion takes place when surpassing the burst pressure of prediction that corrosion default increases the ultimate limit state cause the explosion of residue tube wall, and limit state function is suc as formula shown in (3), (4), (5) and (6):

LSF _burst＝P _burst-P _op(3)

When LSF＞0; LSF=0 and LSF＜0 is represented safety, the limit and failure state respectively;

$P_{\mathrm{burst}}=\stackrel{\&OverBar;}{P_{\mathrm{burst}}}\&times;\left(\frac{2t}{D}\right)\&times;\left[\frac{1-\left(\frac{A}{A_0}\right)}{1-\frac{A}{A_0}\left(M^{-1}\right)}\right]$

(4)

$\stackrel{\&OverBar;}{S_f}=\mathrm{SMTS}$

(5)

$M={[1+\frac{{0.8L}^2}{\mathrm{Dt}}]}^{1/2}$

(6)

P wherein _BurstBe prediction inefficacy stress,

Be flow stress, M is the Folia coefficient; A is the area of metal loss

A ₀Be original area (L * t);

P _OpIn effectively clean, press; At first according to the maximum operating pressure value of air reservoir and minimum operating pressure value respectively as the pipe internal pressure, and subtract each other with the pipe external pressure, take absolute value; During conservative, at last two values are relatively got effectively clean interior pressure that maximal value is born as production casing.

18. assay method according to claim 15; It is characterized in that; Said salt cave closure causes in casing leak and the salt cave top board leakage probability computation model; Comprise that with the closed relevant incident in salt cave casing leak and salt cave top board leak, suppose that salt cave closure causes the probability equalization that casing leak and salt cave top board leak, and sets up the probability that the Model Calculation salt cave closure shown in the formula (7) causes casing leak and salt cave top board to leak:

$F\left(x\right)=\frac{1}{0.018\&times;\sqrt{2\mathrm{\&pi;}}}{\&Integral;}_{-\&infin;}^x{e}^{(-\frac{1}{2}{\left(\frac{x-0.145}{0.018}\right)}^2)}\mathrm{dx}$

(7)

Wherein F (x) leaks the salt cave closing capacity distribution function that takes place for causing casing leak and salt cave top board, and x fells and transports the salt cave closing capacity (%) that row causes for annotating.

19. assay method according to claim 15 is characterized in that, earthquake causes that salt cave well CALCULATION OF FAILURE PROBABILITY model concrete steps comprise in the described step e:

E1 confirms the relation of seismic amplitude and frequency according to the Gutenberg-Richter rule;

E2 confirms the relation of ground peak accelerator and seismic amplitude according to the Gutenberg-Richter rule;

E3 confirms the seismic frequency of said salt cave well area and the relation of ground peak accelerator based on the relation of said seismic amplitude and frequency and the relation of said ground peak accelerator and seismic amplitude;

E4 confirms that earthquake causes the said ground peak accelerator threshold value that well lost efficacy;

E5 is according to the seismic frequency of said salt cave well area and the relation and the said ground peak accelerator threshold value of ground peak accelerator, confirms the distance between tomography and the salt cave well and annually causes the relation between the frequency that salt cave well lost efficacy because of earthquake;

E6 confirms that according to causing relation and the distance between salt to be evaluated cave well and the tomography between the frequency that salt cave well lost efficacy because of earthquake said every year earthquake causes salt cave well failure probability.

20. assay method according to claim 2; It is characterized in that the said different leakage patterns in the step F comprise little leakage, gross leak and the three kinds of patterns of breaking, wherein annotating and adopting 1% of pipe diameter is little leakage; Notes are adopted 10% of pipe diameter and are revealed for big, annotate adopt the pipe diameter 100% for breaking.

21. assay method according to claim 2 is characterized in that, the said risk factors in the step F cause shown in the elementary event probability of happening according to the form below 1 that is associated:

Leakage size Corrosion Erosion Equipment failure Operation is relevant Mechanical damage Natural force Little leakage 93％ 93％ 70％ 39％ 35％ 26％ Gross leak 6.9％ 6.9％ 29％ 60％ 64％ 54％ Break 0.1％ 0.1％ 1.0％ 1.0％ 1.0％ 20％

22. assay method according to claim 2; It is characterized in that; Main event described in the step G is meant the situation that generation takes place just to cause leaking for two or more said elementary events jointly, the elementary event of control leakage size size in the leak path.

23. assay method according to claim 2 is characterized in that, the probability of happening of main event described in the step H is meant, calculates the probability of happening of confirming the main event under the different leakage mode according to formula (8), and it is designated as the probability of happening of corresponding cut-set.

Pf _ij＝1-∏(1-Pf _jkA _ki)

(8)

Pf wherein _IjFor the leakage mode of main event j is the probability of happening of i;

Pf _JkBe the probability of happening of main event j under risk factors k influence;

A _IkFor risk factors k causes the probability that leakage mode i takes place;

I is a leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking;

J is the main event numbering; K is risk factors, from 1-6 represent respectively that burn into erosion, equipment failure, operation are relevant, mechanical damage and natural force.

24. assay method according to claim 2 is characterized in that, the probability of happening of secondary incident described in the step I is meant that the said probability of happening substitution formula (9) of the cut set of top event that causes among the H set by step calculates:

Pf _il＝1-∏(1-Pf _im)

(9)

Pf wherein _IlFor the leakage mode of secondary incident 1 is the probability of happening of i;

Pf _ImFor cut set is m and the leakage mode probability of happening when being i;

I is a leakage mode: 1 is little leakage, and 2 is gross leak, and 3 for breaking; 1 is secondary Case Number; M is the corresponding cut set numbering of secondary incident.

25. assay method according to claim 2 is characterized in that, under the different leakage mode, said top event probability of happening comprises following two kinds of situation according to logical diagram among the step C among the step J:

First kind be between the said secondary incident logical relation for and the door relation, the said top event of said different leakage mode is calculated by formula (10):

Pf _i＝∏Pf _il

(10)

Second kind be between the said secondary incident logical relation for or door relation, the said top event of said different leakage mode is calculated by formula (11):

Pf _i＝1-∏(1-Pf _il)

(11)

Pf wherein _iFor salt cave well leaks into the probability of happening of the leakage mode i of atmosphere, i is a leakage mode, and 1 is secondary Case Number.

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