**2.5 The analysis of external and internal factors and threats for safety of sea platforms**

The analysis of threats for off-shore oil and gas production platforms is the first stage of the accidents' risks analysis for the specified objects and provides estimation of their safety level [1, 2]. The threat for SP is the probabilistic characteristic defining a possibility of the impact of affecting factors of specific type, intensity and duration in response to some dangerous (extreme) event that can take place both in the territory of the object and in the external environment. Therefore, the analysis of threats for SP has to be preceded by assessment of dangerous events which can initiate impact of the affecting factors on platforms.

The secondary dangers occur and provoke secondary affecting factors when some object's process modules – SP parts are damaged. The possibility of initiation of these secondary threats will be defined by vulnerability of an object in relation to the primary threats. Thus, the analysis of threats has to be made in an agreement with assessment of vulnerability of the SP parts in relation to the affecting factors acting on them.

The danger to SP is defined by the pattern of random events or processes (*Th*): extreme external natural and technogenic impact, wrong personnel actions and operating conditions of the object technical systems having the potential which can lead to accident. Examples of such events are: seismic activity, extreme wave or ice loads (external dangers), loss of the oil tank containment or of fatigue damages accumulation (internal dangers). The danger of an extreme event is a random variable which, in the simplest case, can be characterized by the probability of occurrence of an event *P Th* ð Þ during a certain period (1 year) or the during the platform's operational lifetime (**Figure 7**).

Threats for SP are characterized by impacts on an object of the affecting factors of dangerous events. The threat is also a random event (process) *H*, which

#### **Figure 7.**

*Presentation of accident occurrence and development as a complex event. (a) Probabilities of the elementary events are described with the help of point estimations, and (b) probabilities of the elementary events are described with the help of probabilistic determination.*

Broadly speaking, the offshore oil and gas facilities can be classified by the following signs: structural materials; design features; methods of fixing to a bottom; ice resistance indications; and functional features. The design features of offshore oil and gas facilities incorporate the following types: stationary platforms; submersible and semi-submersible platforms; pendulum constructions; tension structures; platforms of SPAR type (with the underwater cylindrical foundation); access brid-

**Utility Fixed to the bottom Floating Islands**

Integrated With anchor mooring

Dynamic positionable Outlined Non-

outlined

The Russian continental shelf area exceeds 6 million sq. km that takes about 25% of a shelf zone of all the World Ocean. The Arctic and Far East shelf areas are the

With respect to environmental, bathymetric, engineering-geological, seismic and other conditions, the shelf of Russia is different from others due to a number of

• severe ice conditions (large drifting ice fields, ice ridges, floating ice

• high level of seismicity (on the Far East shelf); and

• analyze the Russian and foreign regulating documents;

different stages of their life cycle;

• difficult engineering and geological conditions.

• shallow waters (depths less than 100 m) leading to significant increase in

In designing platforms for the Russian shelf, as a rule, it is necessary to consider

When developing scientifically grounded methodology of design of gravitationtype platforms for use on Russia shelf, i.e., design providing the required reliability and safety level and, as much as possible, based on the lessons learned by the international and Russian specialists in design, construction and operation of plat-

• set up an integral approach to platforms reliability and safety assurance at

• select correct existing and develop new methods of definition of environment

When selecting this or that type of platform jack design along with environmental conditions, it is necessary to take into account the impact of the field development general scheme, production method and hydrocarbons transportation technology as well as terms of platform fabrication and transportation on site.

a combination of at least three factors from listed above. This is unlike world

Ice-resistant constructions can be grouped as follows (**Table 1**).

ges and pier sites; and dams and unpaved sites.

**2.4 Russian shelf specific conditions**

Pile supported

*Probability, Combinatorics and Control*

areas of the greatest interest.

Design Gravity based

*Ice resistant oil and gas utilities.*

**Table 1.**

hummocks, etc.);

wave loadings;

forms, it is necessary to:

loads;

**82**

features:

practice.

can take place in case of occurrence of a dangerous event and be characterized by conditional probability *P H*ð Þ j*Th* . For the abovenamed dangers, the events listed below will act as threats:

• in earthquake case, the seismic wave will reach the site where object is located; and

technogenic nature hazards which are resulting in extreme external impacts on the platform. Depending on the location of danger source (i.e., location of the place where the initiating event starts) outside or inside the platform boundaries, it should be taken into account the external and internal threats damaging and affect-

Internal threats for SP are initiated by dangerous process potential of the

• mass and composition of chemically dangerous substances W which are on the

Among internal threats to SP are operational loads on parts and components of oil and gas production facility (OGPF), impact of harsh chemical environment, control system failures, etc. The considerable segment of internal threats range for OGPF is caused by human factor action (mistakes at a design stage, construction

The probabilistic approaches usually are used for description of the initiating events and affecting factors [1–4]. The necessity to use the probabilistic methods is determined by lack of knowledge about comprehensive system "SP—the environment," on the one hand, and by stochastic nature of the processes occurring in a system and environment and by high uncertainty inherent to the examined system (uncertainty of system parameters, materials strength characteristics, external loads, etc. and also the uncertainty explained by limited knowledge of an object) on

The threats (affecting factors) H(t) influencing SP (**Figure 8a**), in general, should be considered not only as the separate and determined processes (a) but also as random events (**Figure 8b**) and *stochastic processes* (**Figure 8c**). This is due to the fact that during analysis of the platforms' vulnerability relative to the prevailing threats, an essential role is played by damages' accumulation and fatigue mechanism of ultimate limit states reaching. Such approach necessitates review threats as dynamic task taking into account history of operational loads and dynamic and cyclic impacts of the affecting factors (external loads, influence of extreme

and operation of the platform, including violation of regulations, etc.). Among external threats are affecting factors resulting from natural and technogenic events (processes) happening outside SP boundaries. Seismic impacts, hurricane, technogenic accident on the neighboring object, collision with the sea vessel, extreme weather conditions, etc. are between initiating events of the external type. Besides mentioned above, external threats include the events connected with interruptions in work of energy, telecommunication and transportation infrastructures which lead to breakdown of technological processes, damage of platform's control and supply systems and terrorist attacks which also can be

ing factors. Risks *R*ð Þ*τ* used in expressions (1)–(9) depend on them.

*Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States…*

*DOI: http://dx.doi.org/10.5772/intechopen.88894*

• amount of the reserved on the object energy *E*.

classified as an external threat to the platform.

temperatures, harsh environment, etc.).

*Presentation of the threat as a random process.*

following [1–3]:

the other hand.

**Figure 8.**

**85**

platform; and

• loss of the oil tank containment will cause the oil leak.

Vulnerability of SP to threat of this type is defined as the conditional probability in case of the affecting factor's impact on an object when the latter one will get a certain damage rate *P DS* ð Þ *<sup>k</sup>*j *H* , where *k* is an object damage rate.

If it is required to get more accurate description of danger of an extreme event, it should not be characterized by the point estimation of probability of occurrence of a dangerous event *P Th* ð Þ but by the distribution curve of danger intensity *pTh*ð Þ *Ω* or integral distribution function *PTh*ð Þ *Ω* presented in **Figure 7** (where *Ω* characterizes dangerous event intensity). In particular, the seismic hazard can be characterized by distribution of probabilities of potential earthquake intensity degree, while threat from loss of tank containment can be characterized by the distribution of probability of the effective opening area. At the same time, threats will be characterized by family of the conditional distribution functions *pH*∣*Th*ð Þ *w* corresponding to different intensity *Ω* of a dangerous event. Then the dangers of an earthquake and loss of containment mentioned above will correspond to the threats described by family of probabilistic distributions of amplitudes of vibration accelerations of soil on site of platform location at different earthquake magnitudes and family of probabilistic distributions of volume of leaked oil for different diameters of effective openings.

Vulnerability of an object relative to impact of the affecting factor with intensity *w* will be characterized by the vulnerability curve *V* ¼ *P DS* ð Þ j*W* ¼ *w* , which defines the conditional probability of sustained damage of level *DS* with the proviso that a random value intensity *W*takes a certain value (*W* ¼ *w*).

When making decision on what physical parameter of impact of dangerous process on an object to select for threat intensity evaluation, it is necessary to consider vulnerability of an object relative to action of different components of such impact: for example, in case of seismic impact on the platform, some parts of the equipment and structures are the most sensitive impact from soil vibration accelerations, while the another to vibration amplitudes.

Within that narrative, the accident initiation on SP can be considered as the complex event occurring in case of occurrence of simultaneous random events cascade (**Figure 7a** or **b**):


#### **2.6 Damaging and affecting factors**

SP operation is associated with production, storage and transportation of considerable volumes of dangerous materials, transformation of considerable volumes of energy, running of hazardous technological processes on the platform as well as with presence in areas of SPs' location of external sources of natural and

## *Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States… DOI: http://dx.doi.org/10.5772/intechopen.88894*

technogenic nature hazards which are resulting in extreme external impacts on the platform. Depending on the location of danger source (i.e., location of the place where the initiating event starts) outside or inside the platform boundaries, it should be taken into account the external and internal threats damaging and affecting factors. Risks *R*ð Þ*τ* used in expressions (1)–(9) depend on them.

Internal threats for SP are initiated by dangerous process potential of the following [1–3]:


Among internal threats to SP are operational loads on parts and components of oil and gas production facility (OGPF), impact of harsh chemical environment, control system failures, etc. The considerable segment of internal threats range for OGPF is caused by human factor action (mistakes at a design stage, construction and operation of the platform, including violation of regulations, etc.).

Among external threats are affecting factors resulting from natural and technogenic events (processes) happening outside SP boundaries. Seismic impacts, hurricane, technogenic accident on the neighboring object, collision with the sea vessel, extreme weather conditions, etc. are between initiating events of the external type. Besides mentioned above, external threats include the events connected with interruptions in work of energy, telecommunication and transportation infrastructures which lead to breakdown of technological processes, damage of platform's control and supply systems and terrorist attacks which also can be classified as an external threat to the platform.

The probabilistic approaches usually are used for description of the initiating events and affecting factors [1–4]. The necessity to use the probabilistic methods is determined by lack of knowledge about comprehensive system "SP—the environment," on the one hand, and by stochastic nature of the processes occurring in a system and environment and by high uncertainty inherent to the examined system (uncertainty of system parameters, materials strength characteristics, external loads, etc. and also the uncertainty explained by limited knowledge of an object) on the other hand.

The threats (affecting factors) H(t) influencing SP (**Figure 8a**), in general, should be considered not only as the separate and determined processes (a) but also as random events (**Figure 8b**) and *stochastic processes* (**Figure 8c**). This is due to the fact that during analysis of the platforms' vulnerability relative to the prevailing threats, an essential role is played by damages' accumulation and fatigue mechanism of ultimate limit states reaching. Such approach necessitates review threats as dynamic task taking into account history of operational loads and dynamic and cyclic impacts of the affecting factors (external loads, influence of extreme temperatures, harsh environment, etc.).

**Figure 8.** *Presentation of the threat as a random process.*

can take place in case of occurrence of a dangerous event and be characterized by conditional probability *P H*ð Þ j*Th* . For the abovenamed dangers, the events listed

• loss of the oil tank containment will cause the oil leak.

certain damage rate *P DS* ð Þ *<sup>k</sup>*j *H* , where *k* is an object damage rate.

random value intensity *W*takes a certain value (*W* ¼ *w*).

ations, while the another to vibration amplitudes.

initiating extreme event *V* ¼ *pV*∣*<sup>H</sup>*ð Þ *w* .

**2.6 Damaging and affecting factors**

cascade (**Figure 7a** or **b**):

and

**84**

• in earthquake case, the seismic wave will reach the site where object is located;

Vulnerability of SP to threat of this type is defined as the conditional probability in case of the affecting factor's impact on an object when the latter one will get a

If it is required to get more accurate description of danger of an extreme event, it should not be characterized by the point estimation of probability of occurrence of a dangerous event *P Th* ð Þ but by the distribution curve of danger intensity *pTh*ð Þ *Ω* or integral distribution function *PTh*ð Þ *Ω* presented in **Figure 7** (where *Ω* characterizes dangerous event intensity). In particular, the seismic hazard can be characterized by distribution of probabilities of potential earthquake intensity degree, while threat from loss of tank containment can be characterized by the distribution of probability of the effective opening area. At the same time, threats will be characterized by family of the conditional distribution functions *pH*∣*Th*ð Þ *w* corresponding to different intensity *Ω* of a dangerous event. Then the dangers of an earthquake and loss of containment mentioned above will correspond to the threats described by family of probabilistic distributions of amplitudes of vibration accelerations of soil on site of platform location at different earthquake magnitudes and family of probabilistic distributions of volume of leaked oil for different diameters of effective openings. Vulnerability of an object relative to impact of the affecting factor with intensity *w* will be characterized by the vulnerability curve *V* ¼ *P DS* ð Þ j*W* ¼ *w* , which defines the conditional probability of sustained damage of level *DS* with the proviso that a

When making decision on what physical parameter of impact of dangerous process on an object to select for threat intensity evaluation, it is necessary to consider vulnerability of an object relative to action of different components of such impact: for example, in case of seismic impact on the platform, some parts of the equipment and structures are the most sensitive impact from soil vibration acceler-

Within that narrative, the accident initiation on SP can be considered as the complex event occurring in case of occurrence of simultaneous random events

2. threat: impact of affecting factor of dangerous event on SP parts *H* ¼ *pH*∣*Th*ð Þ *w* ;

3.vulnerability: damage of SP's parts as a result of impact affecting factors of the

SP operation is associated with production, storage and transportation of considerable volumes of dangerous materials, transformation of considerable volumes of energy, running of hazardous technological processes on the platform as well as with presence in areas of SPs' location of external sources of natural and

1.danger: realization of the extreme initiating event *Th* ¼ *pTh*ð Þ *Ω* ;

below will act as threats:

*Probability, Combinatorics and Control*

and

In such problem formulation, the definition of threat for SP will be characterized by the random vector-process which is functional of a vector of internal and external force actions *Q t*ð Þ, temperature influences *T t*ð Þ, fields of dangerous substances concentration *c t*ð Þ, radiations *ψ*ð Þ*t* and information flows *I t*ð Þ.

$$\overline{H}(t) = F(\overline{Q}(t), T(t), \overline{c}(t), \overline{\varphi}(t), \overline{I}(t)) \tag{10}$$

Physical and chemical bases of the analysis of accidents occurrence and evolution conditions are defined both by work processes in technical SP systems, and by external impacts on these processes.

It is important to note that requirements to detailed level of this object threats' description are defined based on the used destruction mechanisms—external and internal types. The analysis of threats to SP has to be carried out in a manner to provide required data for further calculations of the following:


facility-based—2, domestic—3, regional—4, national (federal)—5, global (transboundary)—6, planetary—7) shall be included in the list of such objects. Then, radius-vector in space of *W, E, I* will become a quantitative index of

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi

where *W*, *E*, *I* is the hazard class of object for each of accidents classes (from 1 to 7). In the first case, the quantitative value of this hazard will vary from 1.73 to

The hazards related to external natural processes in the territory of OGPFs location are evaluated in another way and with use of other criteria (earthquakes intensity degree, force of winds, level of floods, extremeness of climatic tempera-

The equation (11) can be accepted as unified for different types of dangers:

In traditional formulation when performing analysis of threats to OGPD initiated by dangerous processes, the first stage of the analysis or problem solving is assessment of losses and risks relevant to accidents on OGPD objects. The solution of the inverse task making it possible to classify the threats to OGPD coming from known consequences of accident occurred on an (**Table 2**) is of

At the solution of such tasks, the intensity of threats is subdivided into the

Group U1: the threats causing hypothetical accidents which can occur at the options and scenarios of development which are not predicted in advance, with

, j j *Tn* ¼ *W* � *E* � *I* (11)

*W*<sup>2</sup> þ *E* 2 þ *I* 2

*Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States…*

*DOI: http://dx.doi.org/10.5772/intechopen.88894*

tures, depths of holes, mass of landslides, volume of rainfall, etc.)

q

j j *Th* ¼

*Areas of dangerous and safe states of the system.*

12.2; and in the second case, it varies from 1 to 343.

technogenic, natural and natural-technogenic.

dangers to OGPF

**Figure 9.**

interest.

**87**

following groups:

If, on the contrary, the fatigue mechanism of destruction is used, the threat cannot be considered as a separate extreme event and has to be characterized by process of on-stream loading.

The quantitative description of development of accidents initiation on SP can be performed on the basis of fundamental mechanisms of disasters physics, chemistry and mechanics. At the same time, the stages of occurrence and development of emergencies can be characterized by various combinations of physical, chemical and the mechanical affecting and damaging factors.

Analysis of the majority of accidents of technogenic and natural-technogenic nature occurred on SP demonstrates that they are determined by three major dangerous factors according to equation (5):


If to take into account (**Figure 5**) the classification of accidents on critical infrastructure objects as well as parameters *W, E, I* mentioned above, then for classification of oil and gas production facility (OGPF), it is possible to set their critical states' limit areas (**Figure 9**). When talking about critical infrastructure objects, without no doubt, the off-shore oil- and gas production platforms (local—1, *Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States… DOI: http://dx.doi.org/10.5772/intechopen.88894*

**Figure 9.** *Areas of dangerous and safe states of the system.*

In such problem formulation, the definition of threat for SP will be

substances concentration *c t*ð Þ, radiations *ψ*ð Þ*t* and information flows *I t*ð Þ.

provide required data for further calculations of the following:

external impacts on these processes.

*Probability, Combinatorics and Control*

low-cycle fatigue);

dynamics); and

process of on-stream loading.

dynamics).

**86**

creep-rupture strength theory);

and the mechanical affecting and damaging factors.

• uncontrolled leak of dangerous substances *W*;

gerous factors according to equation (5):

characterized by the random vector-process which is functional of a vector of internal and external force actions *Q t*ð Þ, temperature influences *T t*ð Þ, fields of dangerous

Physical and chemical bases of the analysis of accidents occurrence and evolution conditions are defined both by work processes in technical SP systems, and by

It is important to note that requirements to detailed level of this object threats' description are defined based on the used destruction mechanisms—external and internal types. The analysis of threats to SP has to be carried out in a manner to

• stress, stiffness and withstandability (with use of material resistance methods);

• stress and cyclic life and life time (with use of methods of theory of high- and

• stress and life capability—life time (with use of methods of creep theory and

• dynamic strength and life time (with use of methods of crash and fracture

• crack growth resistance (with use of methods of linear and nonlinear fracture

If, on the contrary, the fatigue mechanism of destruction is used, the threat cannot be considered as a separate extreme event and has to be characterized by

The quantitative description of development of accidents initiation on SP can be performed on the basis of fundamental mechanisms of disasters physics, chemistry and mechanics. At the same time, the stages of occurrence and development of emergencies can be characterized by various combinations of physical, chemical

Analysis of the majority of accidents of technogenic and natural-technogenic nature occurred on SP demonstrates that they are determined by three major dan-

• uncontrolled hazardous energy *E* release (mechanical and thermal); and

If to take into account (**Figure 5**) the classification of accidents on critical infrastructure objects as well as parameters *W, E, I* mentioned above, then for classification of oil and gas production facility (OGPF), it is possible to set their critical states' limit areas (**Figure 9**). When talking about critical infrastructure objects, without no doubt, the off-shore oil- and gas production platforms (local—1,

• uncontrolled flows of diagnostic and controlled information of *I*.

*H t*ðÞ¼ *<sup>F</sup> Q t*ð Þ, *T t*ð Þ,*c t*ð Þ, *<sup>ψ</sup>*ð Þ*<sup>t</sup>* ,*I t*ð Þ (10)

facility-based—2, domestic—3, regional—4, national (federal)—5, global (transboundary)—6, planetary—7) shall be included in the list of such objects.

Then, radius-vector in space of *W, E, I* will become a quantitative index of dangers to OGPF

$$|T\_h| = \sqrt{\overline{\mathcal{W}}^2 + \overline{E}^2 + \overline{I}^2}, |T\_n| = \overline{\mathcal{W}} \cdot \overline{E} \cdot \overline{I} \tag{11}$$

where *W*, *E*, *I* is the hazard class of object for each of accidents classes (from 1 to 7). In the first case, the quantitative value of this hazard will vary from 1.73 to 12.2; and in the second case, it varies from 1 to 343.

The hazards related to external natural processes in the territory of OGPFs location are evaluated in another way and with use of other criteria (earthquakes intensity degree, force of winds, level of floods, extremeness of climatic temperatures, depths of holes, mass of landslides, volume of rainfall, etc.)

The equation (11) can be accepted as unified for different types of dangers: technogenic, natural and natural-technogenic.

In traditional formulation when performing analysis of threats to OGPD initiated by dangerous processes, the first stage of the analysis or problem solving is assessment of losses and risks relevant to accidents on OGPD objects. The solution of the inverse task making it possible to classify the threats to OGPD coming from known consequences of accident occurred on an (**Table 2**) is of interest.

At the solution of such tasks, the intensity of threats is subdivided into the following groups:

Group U1: the threats causing hypothetical accidents which can occur at the options and scenarios of development which are not predicted in advance, with the greatest possible damages (total destruction of OGPD) and a large number of the victims.

◦ due to structural icing;

*DOI: http://dx.doi.org/10.5772/intechopen.88894*

◦ docking impact load; and

◦ helicopter impact load.

seismic magnitude of 7, 8 and 9.

presented in **Figure 10**.

taken into consideration.

**Figure 10.**

**89**

◦ waves *<sup>Р</sup>*wave and current *<sup>Р</sup>*curr loads;

◦ loads caused by sheet and hummocked ice *<sup>Р</sup>*ice;

*Hybrid Modeling of Offshore Platforms' Stress-Deformed and Limit States…*

The special loads are the seismic ones *Рseism* and those initiated by natural phenomena (structure base subsidence, additional dynamic loads due to impact of ice filed on the structure imbedded in ice); and ice load due to hummocked nature of ice fields (collision of the structure and iceberg). Seismic impacts are taken into account during design of stationary platforms constructed in different regions with

For definition of seismic loads, it is required to have data on seismological parameters of seismic zones: magnitudes, depths of earthquake sources, the epicentral distances, earthquakes frequency, seismicity of the site and spectral characteristics of seismic impacts depending on engineering-geological conditions on construction sites. Various types of loads on ice-resistant stationary platforms are schematically

When calculating the wind and wave loadings, it is expedient to accept load factor for one of loadings equal to 0.9, and for another equal to 1. This assumption is based on more realistic knowledge (from physical point of view) by reference to correlation between these processes. In the case of basic combination, the calculated values of short-term loadings (wind, wave and current) respectively refer to the reliability factor which is equal to 1. For special combinations, these loadings are calculated with factor 0.8, however, at the same time, as well as in the previous case, two possibilities of wind and wave impacts on ice-resistant structures are

*Symbolic diagram of application of external loads on ice-resistant stationary platforms: 1—derrick; 2—deck; 3—jack structure; and 4—bottom module. For loads, the following symbols are used: Рsw—gravity force; and*

*Рх, Ру—horizontal (shear) and vertical (transverse) reactions.*

◦ wind loads *<sup>Р</sup>*wind;

Group U2 group: the threats causing the beyond-design-basis accidents which are followed by permanent damages of the SP critical components with high level of damages and fatalities.

Group U3: the threats causing the design accidents followed by standard outperformance with predictable and acceptable consequences.

Group U4: the threats causing the SP operating mode accidents followed by deviations from normal operation conditions while OGPD is operating in standard mode.

Group U5: the threats when an object operates in standard mode.
