Method For Reassessment Of Fixed Offshore Platforms
Field of the Invention
5 [OOOI] The present invention relates generally to a
method for reassessing fixed offshore platforms, more
particularly to a reassessment method of fixed offshore
platforms where one or more critical parameters including
pile data and soil data are not available.
10
Background of the Invention
[0002] An offshore platform, or an oil platform is a
large structure that is used to drill wells for
15 extracting and processing oil and natural gas. A fixed
offshore platform may be fixed to the ocean floor to
perform the required exploration and production
operations (E&P Operations). The fixed offshore platform
generally comprises well head, living quarter, water
20 injection and flare jackets that are involved in the E&P
Operations of the offshore platforms.
[0003] The fixed offshore platform structure are designed
and installed as per the provisions of Design Standards
25 prevailing at the time of installation of jackets.
[0004] Some of the structural codes/standards which
provide guidelines for re-assessment of structural
adequacy of existing fixed offshore platforms are
30 mentioned below:
API RP 2A-WSD Recommended Practice for Planning,
Design and Constructing Fixed Offshore Platforms -
Working Stress Design-2lst Edition;
DNV-RP-C205 Recommended Practice on "Environmental
Conditions and Environmental Loads" April 2007;
DNV-0s-C101 OFFSHORE STANDARD Design Of Offshore
Steel Structures, General (LRFD Method), April 2011;
5 American Institute of Steel Construction (AISC).
API Recommended Practice 2SIM, Structural Integrity
Management of Fixed Offshore Structures
API Recommended Practice 2GE0, Geotechnical and
Foundation Design Considerations
10 API Recommended Practice 2MET, Derivation of
Metocean Design and Operation Conditions
[0005] The re-assessment of fixed offshore platforms is
carried out by analyzing soil-pile-structure which
15 requires data such as structural drawings of piles as
originally built, jacket and soil reports of old
platform.
[0006] At numerous instances, data records of the
20 originally-built information of pile structure, and soil
information at the time of installation of the
substantially old platforms are not available. Thus, the
reassessment of these platforms becomes a challenging
task. In some scenarios, pile data of the old platforms
25 is present, however soil data and related records are
missing and vice-versa. In such cases, the reassessment
of the aged fixed platforms becomes difficult. Alternate
guidelines, alternate standards or codes are also not
available for reference, to carry out any structural
30 analysis in the absence of soil data or pile data or
both. Therefore, the reassessment and subsequent
recertification of old structures of fixed offshore
platforms is not possible in such cases. In the absence
of recertification, the statutory bodies might deny
approval for life extension of operation in these
offshore oil well platforms. This gives rise to the
scenarios of building new offshore structures for
5 extracting and processing oil and natural gas. However,
installing and commissioning new offshore structure to
continue production of oil and gas, amounts to huge
capital expenditure (CAPEX).
10 [0007] In light of the above, there is a need for a
method to provide reassessment of fixed offshore platform
to assess the remaining service life of existing fixed
offshore structures in the scenarios of missing data
records of originally-built offshore platform. Further,
15 there is a need for a method to provide reassessment of
fixed offshore platform in absence of soil data, pile
drawings, structural drawings of the fixed platform.
Summary of the Invention
20
[0008] A method for reassessment of one or more fixed
offshore platforms is provided.
[0009] In one embodiment of the present invention the
25 method comprises the steps of: accumulating performance
data of a first fixed offshore platform, the performance
data corresponding to one or more parameters; selecting
at least one parameter from the one or more parameters;
identifying if the performance data corresponding to the
30 selected parameter for the offshore platform is available
or missing; evaluating a second offshore platform based
on the selected parameter to obtain data pertaining to
the second offshore platform, the second offshore
platform being located at a vicinity of the first
offshore platform; performing interpolation of the data
pertaining to the second offshore platform to determine
the interpolated performance data; performing analysis of
5 at least one of: the available performance data or the
interpolated performance data for reassessing the first
offshore platform and thereby determining remaining
service life of the first offshore platform.
10 [OOIO] The one or more parameters are set using one or
more available standards pertaining to design and safety
of the one or more offshore platforms. Further, the
performance data of the first fixed offshore platform is
accumulated by accessing historical data of the first
15 fixed offshore platform to retrieve the performance data
corresponding to the one or more parameters. The
performance data may also be accumulated by determining
the performance data based on the one or more parameter
20 [ O O I I ] The performance of the first offshore platform is
evaluated by analyzing ageing, fatigues, damages, and
repair occurred to the first offshore platform. The
performance parameters include soil, pile structure,
design structure etcetera that are predefined based on
25 one or more standards pertaining to design and safety of
the one or more offshore platforms. In one embodiment of
the present invention, the performance parameters include
but are not limited to pile characteristics, soil
characteristics, original structural designs and modified
30 structural designs of the one or more offshore platforms.
Further, the pile characteristics include pile
penetration data and thickness data of the original
design condition of the first offshore platform.
[0012] The soil data are collected for performing soil
analysis and thereby determining the performance data
corresponding to the soil characteristics for the first
5 offshore platform, the soil samples being collected / insitu
test being carried out at actual location or nearest
vicinity location of the first offshore platform.
[0013] The first platform is assessed for its original
10 design condition without having any post installation
modifications.
[0014] The method further comprises the steps of tagging
a label of "Pass" if it is identified that the first
15 offshore platform is in its original design conditions;
and a "FAIL" if it is identified that the first offshore
platform is not in its original design conditions. When
the first offshore platform is tagged with a label of
"FAIL" then it is reassessed by performing advance
20 mitigation processes.
Brief Description of the Accompanying Drawings
[0015] The present invention is described by way of
25 embodiments illustrated in the accompanying drawings
wherein:
[0016] FIGS. la and lb illustrate the method for reassessing
old platforms where pile data is available and
30 soil data is missing, in accordance with an embodiment of
the present invention;
[0017] FIG. lc is a table illustrating an example of soil
data, in accordance with an embodiment of the present
invention;
5 [0018] FIG. Id illustrates the derivation of axial
capacity of piles with the soil data as per Table 1 of
Fig. lc for the platform under test, in accordance with
an embodiment of the present invention;
10 [0019] FIG. 2a illustrates an example of soil data
interpolation to find out the missing data for location X
wherein data of two nearby locations A and B are
available, in accordance with an embodiment of the
present invention;
15
[0020] FIG. 2b illustrates an example of soil data
interpolation to find out missing data for location X
wherein data of nearby locations A and B are available,
in accordance with an embodiment of the present
20 invention;
[0021] FIGS. 2c, 2d, and 2e show tables for available
soil data of location A, available soil data of location
B, and interpolated soil data of location X respectively,
25 in accordance with an embodiment of the present
invention;
[0022] FIG. 3 illustrates the method for re-assessing
old platforms where soil data is available and pile data
30 is missing, in accordance with an embodiment of the
present invention;
[0023] FIG. 4 illustrates the method for re-assessing
old platforms where pile data and soil data are missing,
in accordance with an embodiment of the present
invention;
[0024] FIG. 5 illustrates the method for re-assessing old
platforms where structural drawings of the offshore
platform is missing, in accordance with an exemplary
embodiment of the present invention;
10
[0025] FIG. 6 is a table illustrating field results of
the re-assessment method with missing pile data, in
accordance with an exemplary embodiment of the present
invention.
15
Detailed description of the invention
[0026] A method for providing reassessment of fixed
offshore platform is disclosed. The invention provides
20 for a method of reassessment of a fixed offshore platform
to assess the remaining service life of the fixed
offshore structures in the scenarios of missing data
records, wherein the missing data is data related to
soil, pile, and structural drawings of originally-built
25 offshore fixed platform.
[0027] The following disclosure is provided in order to
enable a person having ordinary skill in the art to
practice the invention. Exemplary embodiments are
30 provided only for illustrative purposes and various
modifications will be readily apparent to persons skilled
in the art. The general principles defined herein may be
applied to other embodiments and applications without
departing from the spirit and scope of the invention.
Also, the terminology and phraseology used is for the
purpose of describing exemplary embodiments and should
not be considered limiting. Thus, the present invention
5 is to be accorded the widest scope encompassing numerous
alternatives, modifications and equivalents consistent
with the principles and features disclosed. For purpose
of clarity, details relating to technical material that
is known in the technical fields related to the invention
10 have not been described in detail so as not to
unnecessarily obscure the present invention.
[0028] The present invention would now be discussed in
context of embodiments as illustrated in the accompanying
15 drawings.
[0029] FIGS. la and lb illustrate the method for reassessing
old fixed offshore platforms when pile data is
available and soil data is missing, in accordance with an
20 embodiment of the present invention. In this method, the
structure of an old or aged offshore platform is assessed
to determine its remaining service life. The assessment
of the offshore platform facilitates in identifying the
problem that is causing weakness and fatigue to the
25 offshore platform. The fixed offshore platform structure
are generally designed and installed as per the
provisions of one or more off shore structural
codes/standards. Therefore the reassessment is also
carried out based on the guidelines and provisions of
30 various available standards.
[0030] At step 102, a first fixed offshore platform is
evaluated based on one or more parameters and performance
data is accumulated. The first fixed offshore platform is
the platform under test and it is an old fixed offshore
5 platform. The parameters are the performance parameters
that facilitate in evaluating performance of the first
fixed off shore platform by reviewing age of the platform,
fatigue present on the platform, various damages present
on the platform structures such as cracks, dents, holes
10 etcetera. For example, ageing of the offshore platform
may be reviewed by identifying any damages caused by
fatigue and corrosion. The review of strength and fatigue
of the platforms are required to assess the structural
integrity of the installation. The first platform, or the
15 platform under test is further examined to identify if
any repair of damages has been carried out. Further,
service history of the platform is also examined and
studied to accumulate historical data pertaining to
performance. Thus, one or more performance parameters of
20 the offshore platform is set, and based on the same, an
inspection plan is prepared for the platforms in order to
evaluate service life of the offshore platform beyond its
original design life.
25 [0031] In this embodiment of the present invention, the,
reassessment of the fixed platform is carried out when
soil data for the offshore platform to be assessed is not
available. Thus it is identified if the performance data
(i.e. soil data) corresponding to the selected
30 performance parameter (i-e. soil) is missing or available
for the first offshore platform. In the scenario of
missing performance data, at step 104, the area in the
vicinity of the offshore platform is examined to confirm
the existence of a second offshore fixed platform or any
boring location in vicinity. The efforts are made to find
suitability of soil using soil data of nearest platform
(i.e. the second offshore platform) to the first fixed
5 platform, and once that is identified, the second
platform is examined for assessment based on a selected
performance parameters such as soil.
[0032] At step 106, soil data of nearby platforms and/or
10 boring locations are collected from soil investigation
reports. The investigation of soil provides information
such as composition of soil, soil characteristics, how
efficiently the soil resists at the bottom of the ocean
bed due to the massive installation of the platform
15 structure etcetera. Various soil data is extracted on the
basis of the examination and analysis of the collected
soil reports. The soil data is further used in soil data
interpolation. Therefore at step 108, a check is
performed to confirm if the interpolation of the
20 extracted soil data is possible.
[0033] If interpolation of the extracted soil data is
possible, then interpolation is performed at step 110.
Else, soil samples are collected from another location in
25 the vicinity of the site and data is extracted from the
newly collected samples/in-situ test at step 112. The
newly collected samples are accordingly examined and
analyzed for obtaining soil data that can subsequently be
used for the soil data interpolation at step 110.
30
[0034] At step 114 a check is performed to confirm if the
platform under test is being assessed for its original
design condition without having any post installation
modifications. At step 116, the platform under test is
assessed and is tagged with a label of "FAIL", if it is
not passing original design condition and having any post
5 installation modification. For an output result occurring
as "FAIL", the step 112 is repeated and soil data are
collected from nearby location in the vicinity of the
platform. Thereafter, data is extracted from the newly
collected samples / in-situ tests and rest of the steps
10 are processed as described above.
[0035] At step 118 another check is performed to confirm
if the platform under test is being assessed for its
current design condition and is having any post
15 installation modifications. At step 120, the platform
under test is assessed and is tagged with a label of
"PASS", if it is being analyzed for current design and
post installation modifications.
20 100361 At step 122, the platform under test is assessed
as "FAIL" if it is identified that the platform under
test is not being analyzed for current design and post
installation modifications. At step 124, advance analysis
and mitigation measures are performed so that the
25 platform under test can be accordingly assessed. The
advance analysis is a non-linear pushover analysis that
is carried out to assess the reserve strength ratio
available with the platform as per the recommended
practice. In a scenario when the offshore platform
30 structure does not pass the test of non-linear pushover
analysis, then other options are implemented such as load
reduction and strengthening of failing members and
examination and analysis of the joints.
[0037] In one or more embodiments of the present
invention, soil data includes but is not limited to
5 description of the type of soil, depth measurements of
occurrence below the seafloor and various engineering
properties of the soils such as strengths, density and
deformation behavior of the soils existing in the layers.
10 [0038] An example of soil data is presented in Table 1 of
Fig. lc, wherein PHI - angle of internal friction; Su =
undrained shear strength; flim = limiting shaft friction
resistance; qlim = limiting end bearing resistance; e50 =
strain at 50% failure stress; and k = modulus of subgrade
15 reaction.
[0039] According to the embodiments of the present
invention, the soil data as shown in Table 1 of Fig. lc
is used for creating a digital model of the soil which
20 can subsequently be used for carrying out the analysis of
the soil. It can also be used for the analysis of the
structure and foundation of the offshore platform. The
analysis is termed as interactive analysis of soil,
foundation and structure that is carried out using
25 suitable computer software including analysis software
for example, SESAMB, SACSB etc. Further, the load bearing
capacity that is used to determine the safety of
foundation against failure with respect to design loads,
is evaluated on the basis of the soil data. In an
30 exemplary embodiment of the present invention, the soil
data (of Table-1, Fig. lc) is used as inputs for
performing analysis using the analysis software SESAMB
and SACS@. The pattern and combinations of input data and
their formats may be different depending on the software
system used for the analysis.
5 [0040] Figure id shows the derived axial capacity of
piles with the soil data as per Table 1 for the platform
under test. The axial load bearing capacity of the
offshore platform against compression and tension load
being applied on the platform is assessed to determine
10 the factor of safety for the bearing capacity failure of
the foundation with respect to the imposed design axial
loads. The data mentioned in Table 1 is used to determine
soil resistance on the surface and at the bottom of the
pile foundation used for supporting the jacket platforms
15 by following the recommended practice such as the code of
practice from API (American Petroleum Institute). The
foundation capacity is primarily dependent on the
properties of soil at the site location in which it is
installed along with the geometry of the pile foundation.
2 0
[0041] Fig. 2a shows a linear interpolation for an
unknown value of a parameter at point X using the known
values of the same parameter at points A and B. for
25 example, if distance between A and B is 100 meter; value
of a parameter at A is 10.0; and value of same parameter
at B is 12.0, then rate of variation of parameter will be
as follows;
(12.0-10.0) /100=0.02 / meter ;
30 interpolated value of X for same parameter will be
(12-0.02) *30 =11.4
[0042] The Soil properties within an area in the offshore
typically shows both lateral and vertical variations
depending on the distance between two particular points
and the geological parameters of that area. In a
sedimentary deposit in the offshore, various natural
agents cause the deposition of soil in layers and these
5 layers generally extend horizontally within an area
varying in thickness. However, when the distance between
two locations is relatively high, the corresponding soil
layers between two locations vary in terms of soil type,
layer sequence, thickness, and various other properties.
10 However, such variations are generally not abrupt but
possess gradual variations. The gradual variations in
soil data helps in finding or identifying a missing data
between two locations by the process of interpolation.
The interpolation of soil parameters for a location is
15 therefore the values of the soil parameters based on the
values of the same parameters which are known at a nearby
distance from the particular location.
100431 Interpolation is possible between nearby locations
20 when the similarity exists for layers of soil with
respect to soil properties, sequence of their occurrence
(below the seafloor) and types of soil within
corresponding layers. When corresponding layers or soil
types do not match between nearby locations in terms of
25 soil layering, properties, sequence of their occurrence
(below the seafloor) and types of soil within the layers,
such interpolation is not possible.
100441 According to the embodiments of the present
30 invention, the method of soil data interpolation
comprises the following steps. The soil profiles of
various soil samples of a given area is identified
including distances between one or more location points
within the area, and characteristics of the soil samples.
The soil profiles for the nearby locations from available
soil reports and shallow geophysical survey reports (if
available) are also reviewed and analyzed. Thereafter the
5 soil profiles of the given area and the nearby area are
compared to identify if any similarities between both
areas exist. The comparison between the soil profiles is
performed on one or more parameters including (a) types
of soil in the layers below seafloor; (b) properties of
10 the soil in the individual layers; (c) thickness of the
individual soil layers; (d) sequence of soil layers and
soil types.
[0045] Further, when the comparison of the soil profiles
15 of the given area and the nearby area indicates that any
similarity exists between the locations with respect to
the soil conditions then following steps are performed
for soil data interpolation.
[0046] (i) conducting linear interpolation of layer depth
20 or layer thickness for the location (where soil data is
not available) based on relative distance of the location
(where soil data is not available) from the nearby
locations (where soil data are available).
(ii) conducting linear interpolation of
25 corresponding soil parameters for the location (where
soil data is not available) based on the soil properties
at the locations (where data are available) and relative
distance of the location (where soil data is not
available) from the nearby locations where soil data are
30 available.
(iii) compiling new soil parameters and soil
layering or soil description table.
(iv) using soil parameters derived in step (iii)
for generating basic data and/or load-movement data for
use as input to interactive analysis of the soil-pilestructure
and their characteristics.
5 (v) using the soil parameters for assessment of
load bearing capacity of piles or pile characteristics
for the platform.
[0047] Fig. 2b illustrates an example of soil data
10 interpolation to find out the missing data for location X
wherein data of two nearby locations A and B are
available, according to the embodiments of the present
invention.
15 100481 Figs. 2c, 2d, and 2e show tables for available
soil data of location A, available soil data of location
B, and interpolated soil data of location X respectively,
according to an exemplary embodiment of the present
invention.
20
[0049] FIG. 3 illustrates the re-assessment method for
re-assessing old platforms where soil data is available
and pile data is missing, in accordance with an
embodiment of the present invention. In this method, the
25 reassessment process is carried out for identifying
issues that affect the efficiency of the offshore
platform when no data pertaining to pile parameters is
available. The reassessment is done as per the guidelines
given in different offshore structural codes/standards so
30 that extension may be allowed to the service life of the
offshore platform that passes the reassessment analysis
test.
[0050] The factors which can affect the efficiency of
offshore platforms include ageing, fatigue, structural
damage of the platform such as cracks, dents, holes
etcetera. The pile parameters that are deduced from the
5 actual size of jacket legs, standard annular space
between the legs and piles of the platform etcetera. In
an exemplary embodiment of the present invention, as the
fabrication of the piles is done by using steel grade of
ASTM-A 36, hence the analysis of pile parameters is done
10 based on the parameters of ASTM-A 36 which is a low
carbon steel that exhibits good strength coupled with
formability. The minimum thickness of one or more piles
is assumed based on the historical data and past service
or in-place analysis of the platform with respect to the
15 original design conditions of the platform. The static
capacity versus penetration depth curve can be generated
and pile penetration depth can be calculated based on
estimated load at time of original design considering a
minimum factor of safety of 1.5 for 100 year storm
20 conditions.
[0051] At step 302, historical data of previously
evaluated platform under test is accumulated. The
accumulated data may be stored in a database including a
25 manual database or a computer database. The database may
be accessed by authorized users to access the data. The
historical data pertains to performance data and service
history of the platform under test. The historical data
may also include the data pertaining to the evaluation of
30 the offshore platform. At step 304, the design level
analysis is carried out for evaluating pile penetration
depth and pile thickness data. The original design
condition of the platform is studied to obtain the
original design data. For example, the piles design may
comprise tubular piles or the piles that have been driven
into the marine floor. Also the pile design may depend on
the environmental conditions of the location of the
5 offshore platform installation. One or more design value
of the original design data is selected, based on which
the design level analysis is carried out. The parameters
such as pile diameter, penetration depth and ultimate
bearing capacity of pile are studied to obtain original
10 design data. The available analysis tool such as SACS or
SESAM software is used to carry out the analysis and
assessment of the offshore platforms. In various
embodiment of the present invention, the analysis may be
carried out using computer processors.
15
[0052] At step 304, the current design condition of
the platform is studied to obtain the current design
parameters and data. The current design parameters and
data may include the data pertaining to design of post
20 installation and modification of the platform. Further
the current design parameters and data may also include
data pertaining to any damages that occurred to the
platform after its installation and during its past
service period.
2 5
[0053] The result of the analysis conducted at step 304
and step 306 is then checked to verify at step 308 if the
platform under test has passed the analysis test. At step
312, the platform under test is assessed and is tagged
30 with a label of "PASS" if it is verified that the current
design parameters of the platform under test has passed
the analysis test for the selected value (given value) of
the original design condition. However, the platform
under test is assessed and is tagged with a label of
"FAIL" if it is verified that the current design
parameters of the platform under test has not passed the
analysis test for the selected value (given value) of the
5 original design condition. Subsequently, at step 310,
advanced analysis and mitigation measures are performed
to assess the platform under test.
[0054] The advance analysis is the nonlinear pushover
10 structural analysis performed to determine the ultimate
strength of a platform using nonlinear pushover
structural analysis software, which applies an
incrementally increasing lateral load to the platform
model until collapse is predicted. The lateral pushover
15 load is representative of the loads acting on the
platform at the instance of collapse. Further, the
mitigation measures is the process which include
modifications or operational procedures that reduce
loads, increase capacities, or reduce environmental load
20 acting on the structure.
[0055] FIG. 4 illustrates the re-assessment method for
re-assessing old fixed offshore platforms where pile data
and soil data are missing, in accordance with an
25 embodiment of the present invention. Any fixed platform
may be evaluated at random intervals to obtain
performance data and service efficiency of the platform
under test. At step 402 the historical data of previously
evaluated platform is accumulated so that the pile data
30 of the platform under test may be extracted from the
accumulated historical data. At step 404, soil data is
extracted from the soil data collected from the vicinity
of the platform under test. In various embodiments of the
present invention, the soil data are collected from the
vicinity area whenever the soil data of the platform
under test is not available. The soil samples / in-situ
tests provide the soil data that can be used for the soil
5 data interpolation.
[0056] If soil data interpolation is possible with the
extracted soil data then further assessment is performed
based on the interpolated soil data at step 406. However,
10 if the interpolation of the soil data is not possible
then at step 410, new soil data are collected from a
location which is as near as possible to the platform
under test. The new soil samples / in situ tests are used
to extract new data and accordingly another data
15 interpolation is carried out for the reassessment of the
platform under test.
[0057] In the above mentioned scenario, the pile data is
missing and is not available to be used for the
reassessment of the platform under test. Therefore the
pile data is extracted by using other means such as
analyzing the original pile design data. At step 410, the
design level analysis is carried out for evaluating pile
penetration data and thickness data of the original
design condition of the platform. The study of the
original design condition of the platform provides one or
more design values and data wherein one of the one or
more values or data may be given as a reference to carry
out the reassessment method. Thus a reference data is
30 selected and the design level analysis is carried out
based on the selected data.
[0058] At step 412, the current design condition of the
platform is analyzed to obtain the current design
parameters and data that includes data pertaining to
design of post installation and modification of the
5 platform, data pertaining to any damages that occurred to
the platform after its installation and during its past
service period, etcetera.
[0059] The selected referenced data of the original
10 design condition and the current design parameters may be
compared to verify at step 414 if the platform under test
has passed the analysis test. At step 416, the platform
under test is assessed and is tagged with a label of
"PASS", if it is verified that the current design
15 parameters of the platform under test has passed the
analysis test for the selected value (reference value) of
the original design condition. However, the platform
under test is assessed and is tagged with a label of
"FAIL", if it is verified that the current design
20 parameters of the platform under test has not passed the
analysis test for the selected value (reference value) of
the original design condition. This indicates that an
advance assessment method is needed in these cases.
Therefore, at step 418, advanced analysis and mitigation
25 measures are performed for the reassessment of the
platform under test.
[0060] F I G . 5 illustrates the re-assessment method for
re-assessing old platforms where structural drawings of
30 the offshore platform is missing, in accordance with an
exemplary embodiment of the present invention. At step
502 the historical data of previously evaluated platform
is accumulated so that the structural data pertaining to
structural drawings of the platform under test may be
extracted. The extracted structural data for the platform
under test is analyzed and another platform having
similar structure as that of the platform under test is
5 located. At step 504, a check is performed to verify if
another platform having similar design structure exists.
If a similar platform is available, then at step 506 the
assessment is performed based on the available standards.
10 [0061] In one embodiment of the present invention, the
assessment of the similar platform is performed as per
the IEOT-LIFE-002 (Institute of Engineering and Ocean
Technology, ONGC) methodology.
15 [0062] However, if it is found that any platform similar
to the structure of the platform under test is not
available for obtaining the structural design, then at
step 508, original structural drawings are obtained from
the actual site of the platform under test. The original
20 drawings of the platform under test may subsequently be
used for the reassessment of the platform.
[0063] FIG. 6 is a table illustrating field results of
the re-assessment method with missing pile data, in
25 accordance with an exemplary embodiment of the present
invention. The field result shown in the table is the
outcome of the re-assessment method carried out for a
four-legged well offshore platform secured to sea bed by
four main piles and four skirt piles. The re-assessment
30 was carried out using the re-assessment method with pile
data missing (as described in Fig 3 ) , and also using the
traditional method with available actual pile details.
It was found that the results (factor of safety of piles,
utility ratios of piles, members and tubular joints of
the jacket structure) for both the methods used are close
to each other and therefore the percentage deviation of
5 the results of the two methods are very less. Thus the
methodologies as described in the embodiments of the
invention is effective for the assessment of the offshore
platforms.
10 [0064] While the exemplary embodiments of the present
invention are described and illustrated herein, it will
be appreciated that they are merely illustrative. It will
be understood by those skilled in the art that various
modifications in form and detail may be made therein
15 without departing from or offending the spirit and scope
of the invention as defined by the appended claims.
We claim:
1. A method for reassessment of one or more fixed
offshore platforms, the method comprising the steps
5 of:
accumulating performance data of a first fixed
offshore platform, wherein the performance data
corresponds to one or more parameters;
selecting at least one parameter from the one or more
parameters;
identifying if the performance data corresponding to
the selected parameter for the offshore platform
is available or missing;
evaluating a second offshore platform based on the
selected parameter to obtain data pertaining to
the second offshore platform, the second offshore
platform being located at a vicinity of the first
offshore platform;
performing interpolation of the data pertaining to
the second offshore platform to determine an
interpolated performance data;
performing analysis of at least one of: the available
performance data or the interpolated performance
data for reassessing the first offshore platform
and thereby determining remaining service life of
the first offshore platform.
2. The method as in claim 1, wherein the one or more
parameters are set using one or more available standards
30 pertaining to design and safety of the one or more
offshore platforms.
3 . The method as in claim 1, wherein the performance
data of the first fixed offshore platform is accumulated
by accessing historical data of the first fixed offshore
platform to retrieve the performance data corresponding
5 to the one or more parameters.
4. The method as in claim 1, wherein the performance
data of the first fixed offshore platform is accumulated
by determining the performance data based on the one or
10 more parameters.
5. The method as in claim 1, wherein the one or more
parameters include but are not limited to pile
characteristics, soil characteristics, original
15 structural designs and modified structural designs of the
one or more offshore platforms.
6. The method as in claim 5, wherein the pile
characteristics include pile penetration data and
20 thickness data of the original design condition of the
first offshore platform.
7. The method as in claim 6, wherein soil data are
collected for performing soil analysis and thereby
25 determining the performance data corresponding to the
soil characteristics for the first offshore platform, the
soil data being collected from location or nearest
vicinity location of the first offshore platform.
8. The method as in claim 1, wherein the first
platform is assessed for its original design condition
without having any post installation modifications.
5 9. The method as in claim 1, wherein the first
offshore platform is tagged as "Pass" if it is identified
that the first offshore platform is in its original
design conditions.
10 10. The method as in claim 1, wherein the first
offshore platform is tagged as "FAIL" if it is identified
that the first offshore platform is not in its original
design conditions.
15 11. The method as in claim 10, wherein the first
offshore platform with a "FAIL" tag is reassessed by
performing advance mitigation processes.