Research Prospect of Risk Assessment Technology of ...psc.tamu.edu/files/symposia/2008/symposium-program... · Because normal risk assessment methods are only suitable for steady

中国石油大学（北京）

油油气气安安全全工工程程技技术术研研究究中中心心

DONG Yao FAN Jian-chun

Research Prospect of Risk Assessment

Technology of Exploration Drilling in

High Sulfur Gas Field



Problems of Exploration Drilling in High-sulfur Gas Field

Problems of Exploration Drilling in High-sulfur Gas Field

1.high and steep structure prevails2.hard lithology, strong abrasiveness and bad drillability 3.easy to collapse 4. narrow safety window and severe loss circulationFormation dip 30-60

Sand-shale + thin-shaleEasy to collapse

Fault, crack, cava development

5.Several pressure systems coexist6.bad well conditions 7.long open hole, small clearance, much leakage, difficult to cement

—— extremely high risk



strata structure

shaft integritytimetime--varyingvarying

condition

well structure

formation fluid

formation pressure

strata structureuncertainuncertain

Drilling system of high sulfur gas wells is Drilling system of high sulfur gas wells is a strong timea strong time--varying and uncertain systemvarying and uncertain system

High m

easure adjusting frequency

Features of Exploration Drilling in High-sulfur Gas Field

Features of Exploration Drilling in High-sulfur Gas Field



Research StatusResearch Status

Because normal risk assessment methods are only suitable for steady state systems, it is of great difficulty to real-timely master the safety status of the drilling system to further guide drilling operation.

The main technical contents of risk assessment method aiming at offshore drilling platform in China are as follows:



1

Using preliminary hazard analysis (PHA) to systematically identify various risk sources in the drilling operations.

3

Analyzing the safety control mode of drilling operation and bringing forward corresponding measures and suggestions according to the key points of risk

2

Simulating and calculating the influence scopes of various accidents, using emergency model to analyze the key points of risk of operating personnel under various accident conditions



Schlumberger dynamic risk Schlumberger dynamic risk management of drillingmanagement of drilling

Fault top

Elastic coefficient

Drillable profile

Pore pressure profile

Stress profile

Stress direction

Geological data

Drilling data

Logging data

Data correction

Stratum model

Operation analysis and forecast

Risk forecast & countermeasu re of drilling

Drilling and geological liability scheme

Drilling Risk Profile

Risk countermeas ures in the next day

Task and liability in 24hr

Data check & analysis

Plan matche s reality

Rede sign

No

Accident report

Liability report

Reality reflection

Recent impleme ntation report

General rig &Geological condition

Drilling Team

Damage

No damage

Yes



Risk Assessment Method of Drilling ProcessRisk Assessment Method of Drilling Process

Index to be assessed of drilling parameters

Drilling parameter Drilling fluid density Hydraulic parameter

Bit pressure

speed

displacement

Standpipe pressure

Bit pressure drop

Annular pressure drop

Impact force

Jet velocity

Bit hydraulic horsepow

er

Hydraulic horsepow

er

Lifting velocity



SSelection of risk assessment methodelection of risk assessment method

Because the drilling parameter system has the features of multiple purposes, multiple index and the coexistence of certainty and uncertainty, the set pair analysis theory can be applied to the risk assessment of drilling parameter system.



Brief Introduction of the Set Pair Analysis TheoryBrief Introduction of the Set Pair Analysis Theory

The formula of the set pair analysis theory μ=a+bi+cj

a, b and c respectively represents the identical degree, the neutral degree and the opposite degree. i and j are respectively the mark symbol or corresponding coefficient of the neutral degree and the opposite degree.



Set pair

Set Pair Analysis

Actual dataRisk grading standard

Countermeasure

Determination of quantitative index

Calculation of connection degree of each of the index to each of the risk grades

Determination of the weight of the index

Calculation of the total connection degree

Determination of the risk grade

Delphi m

ethod



Mathematical modelMathematical model

(1) If the smaller the index value S is, the safer the system is, when the risk assessment index is in the 1st grade (I)

μi1= 1 x∈[0, Si(1)]

1+ x∈[Si(1),S i(2)]

-1 x∈[Si(2), +∞]



(2) When the risk assessment index is in the 2nd grade (II)

μi2= 1 x∈[Si(1),S i(2)]

1+ x∈[Si(2),S i(3)]

-1 x∈[Si(3), +∞]

1 x∈[0, Si(1)]




(3)When the risk assessment index is in the 3rd grade (III)

μi3= 1 x∈[Si(2),S i(3)]

1+ x∈[Si(3),S i(4)]

1+ x∈[Si(1),S i(2)]

-1 x∈[-∞,S i(1)] or x∈[Si(4), +∞]




(4)When the risk assessment index is in the 4th grade (IV)

μi4= 1 x∈[Si(2),S i(3)]

1+ x∈[Si(3),S i(4)]

1+ x∈[Si(1),S i(2)]

-1 x∈[-∞,S i(1)] or x∈[Si(4), +∞]




(5) When the risk assessment index is in the 5th grade (V)

μi5= 1 x∈[Si(4),S i(5)]

1+ x∈[Si(3),S i(4)]

-1 x∈[-∞,S i(3)]




Nature Nature

The nature of the risk assessment of the drilling parameter system based on the set pair analysis theory is making the real- time monitoring data and the risk grading standard of each of the index compose a set pair, then the risk grade of the drilling parameter system can be obtained.



Index OptimizationIndex Optimization

The deviation value of the index monitoring value from the index optimal value which is suitable for formation pressure system can be regarded as the assessment index for the mathematical model.



Application Example Application Example

Supposing that the drilling fluid density in the first spud in section of a certain well is 1.14~1.16g/cm3, while the optimum drilling fluid density for this well section is 1.155 g/cm3, the speed in this section is 61~69r/min, while the optimum speed for this well section is 63 r/min.



And supposing the risk grading standard and the weight of the drilling fluid density and the speed for this first spun in section of this well are as follows:

under the condition of only considering the drilling fluid density and the speed, the results are as follows:



Risk grade Deviation value of drilling fluid density (g/cm3)

Deviation value of speed (r/min)

I safe 0.01 3

II

relatively safe

0.02 5

IIIgenerally safe

0.03 7

IV unsafe 0.04 9

Vextremely unsafe

0.05 11

Risk Grading Standard for Deviation Value of Drilling Parameter System Index



Monitoring Value of Drilling Parameter System Index

Index

Deviation value of the minimal design value of

drilling fluid density (g/cm3)

Deviation value of the maximum design value of

drilling fluid density (g/cm3)

Deviation limit of speed (r/min)

value 0.005 0.015 6



Weight of Risk Assessment Index of Weight of Risk Assessment Index of Drilling Parameter SystemDrilling Parameter System

Index Deviation limit of drilling fluid density

Deviation limit of speed

value 0.6 0.4



General Connection Degree of Every Risk General Connection Degree of Every Risk Grade of the Phenomena that the Grade of the Phenomena that the

Formation is fracturedFormation is fracturedConnection

degree I I I I I I I V V

μj 0.6 0 0.2 -0.8 -1

The risk grade of the phenomena that the formation is The risk grade of the phenomena that the formation is

fractured during the drilling process in this section is fractured during the drilling process in this section is

grade I.grade I.



General Connection Degree of Every Risk General Connection Degree of Every Risk Grade of the Phenomena that the Grade of the Phenomena that the

Formation Fluid Invades the ShaftFormation Fluid Invades the Shaft

Connection degree

I I I I I I I V V

μj -0.2 0.8 -0.6 -0.8 -1

The risk grade of the phenomena that the formation is The risk grade of the phenomena that the formation is

fractured during the drilling process in this section fractured during the drilling process in this section

is grade II.is grade II.



Difficulty Difficulty

The emphasis and the difficulty of The emphasis and the difficulty of assuring the correctness of the risk assuring the correctness of the risk assessment result is assuring the scientific assessment result is assuring the scientific and the accuracy of the index weight and and the accuracy of the index weight and the risk grading standard of every index.the risk grading standard of every index.



Conclusion Conclusion

The set pair analysis method can be The set pair analysis method can be applied to the risk assessment of drilling applied to the risk assessment of drilling process.process.

The assessment result can provide The assessment result can provide preference for realpreference for real--timely guiding drilling timely guiding drilling process. process.



The set pair analysis method is an The set pair analysis method is an effectively way to analyze uncertain effectively way to analyze uncertain multiplemultiple--objective decision making objective decision making problems.problems.



The end

Thank you!

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Research Prospect of Risk Assessment Technology of ...psc.tamu.edu/files/symposia/2008/symposium-program... · Because normal risk assessment methods are only suitable for steady