www.GustoMSC.com

Phase 2 ISO 19905-1 Benchmarking study

GustoMSC21 Oct 2010

Comparison for MSC CJ62 rig of ISO

versus SNAME for Clay and Sand site

Basic data

Jack-up:

MSC design CJ62 type drilling rig

Some numbers in the analyses:

17118 t elevated (survival) weight

Triangular shaped hull, spacing 62 m

3 truss legs, leg length 175.3 m, chord spacing 16 m, X-brace

Spudcan (traditional shape), 250 m^2

Pre-load capacity per leg 13680 t

Fixation systems 9500

BLM rack-pinion jacking system type C170 (54 pinions)

Chords tubular with racks

Basic data

Spudcan / penetration data:

Some numbers in the analyses:

Pre-load at seabed applied: 152.9 MN

Effective diameter B = 17.84 m

Maximum bottom area 250 m^2

Tip to maximum area = 1.60 m

Basic data

site conditions:Site description North Sea (dense) sand GoM (deep) clay

General

Water depth (LAT) 104.7 80

Airgap 25 20

SWL 2 2.5

Metocean

Hmax 28 22.0

Tass 15.8 16.0

Wind 45 50

Current 1.00 1.50

Soil Dense sand Soft clay

Basic data

Wave kinematics & wave period:Site description North Sea sand - fixity GoM (deep) clay - fixity

Dynamics

Intrinsic wave period / DAF 15.8 s / 1.25 16.0 s / 1.16

Apparent wave period / DAF 15.2 s / 1.28 15.0 s / 1.18

Applied in assessment 1.28 for ISO

1.25 for SNAME

1.16 for ISO & SNAME

Wave kinematics

Latitude or region 58.50 North Sea TRS (GoM)

Directional spreading factor 0.90 0.87

Kinematics reduction factor 0.80 0.77

Applied in assessment 0.86 on kinematics ISO

0.86 on wave height

SNAME

0.86 on kinematics

Basic data

soil conditions sand site:Site description North Sea (dense) sand

type - Medium dense (silica) sand

Internal friction angle [deg] 34

Effective subm weight ’ [kN/m3] 11

Steel-soil friction angle [deg] 29 = ( – 5)

Relative density Dr [%] 65

Poisson’s ratio [-] 0.2

Shear modulus G 23765* sqrt(Vswl/(101.3A)

D50/D90 particle size 0.095mm / 0.15mm

Basic data

Foundation data:Site description North Sea (dense) sand

Leg penetration estimate [m] 1.4

Spudcan contact diameter [m] / [%] 14.0 / 80%

Foundation fixity

Shear modulus G [MPa] 50 (soil data)

Applied G in fixity [Mpa] 46 MPa, based on recommendations

Rotational stiffness [MNm/rad] 53000

Capacity VHM - Standard sand, VL0 = 152.9 MN

Basic data

soil conditions clay site:Site description GoM (deep) clay - fixity

type - Very soft to stiff calcareous clay

Shear strength [kPa] See table

Shear modulus [MPa] See table

OCR [-] 1.0 – 1.4 (see table)

Poisson’s ratio [-] 0.5

Sensitivity ratio [-] 2.7

Basic data

Foundation data:

**) Tables in ISO to be added to include effects of poisson’s ratio > 0

Site description GoM (deep) clay - fixity

Leg penetration estimate [m] 45.6

Gross capacity [MN] 190 (pre-load = 153)

Backfill (after pre-loading) [MN] 8 (8 m)

Shear modulus for fixity

Shear modulus G [MPa] 43 (soil data) => G/su = 730

Applied G in fixity [Mpa] 34 MPa, limited to G/su ≤ 600 in line

with recommendations

Embedment factor [-] 2.2 **), ISO gives 2.4

Rotational stiffness [MNm/rad] 284000 MNm/rad, ISO = 310000

Yield surface (ISO, gross cap) V=190, H=20, M = 401, a = 0.99

Yield surface (SNAME, net cap) V = 153, H = 19.2, M = 428, a = 0.99

Summary of results – sand site

North Sea site sand - pinned sand – fixity

ISO SNAME % ISO SNAME %

Leg penetration [m] 1.40 1.35-1.43 0% - -

SDOF-DAF 1.54 1.47 15% 1.28 1.25 12%

External OTM [MNm] 3022 2796 8% 2640 2486 6%

Max/

Min V reaction [MN]

144.7/

-0.5

140.0/

5.2

3%

/NA

131.6/

12.4

127.5/

16.0

3%

/NA

Chord Pu [MN] 119 111.1 7% 102 94.2 8%

Utilisations:

Holding 1.01 0.90 12% 0.80 0.76 5%

Chord 0.98 1.09 -10% 0.83 0.92 -10%

Overturning stab 1.08 0.97 11% 0.85 0.79 8%

Pre-load (1.05) (1.02) 3% (0.96) (0.93) 3%

VH bearing 1.39 1.27 9% 1.16 1.05 10%

Sliding (50% variable load) Leg lift 3.7 NA 1.36(1b) 0.98(1b) 39%

Sliding (100% variable load) > 5 2.9 NA 1.10 0.88 25%

Summary of results – sand site

Effect of apparent wave period in DAF (with fixity = 1.28) is 6%

more inertia load, 1% more total external loading and 0.5%

more vertical soil reaction

Effect of H = 0.86*H (SNAME) iso on wave kinematics (ISO) is

7% on w/c load, 5% on total external loading and 2.5% on

vertical soil reaction

Increased UC’s in general due to increased external loading

(see above). Chord improved. VH bearing check worse.

Two variations to see effects:

ISO using the exact external loading as in the SNAME case

ISO using the = 0.80 (new formula)

Summary of results – sand site

North Sea site ISO load variations SNAME

ISO

= 0.86

SNAME

ext loads

= 0.80 SNAME

External OTM [MNm] 2640 2486 2432 2486

Utilisations:

Holding 0.80 0.75 0.72 0.76

Chord 0.83 0.78 0.76 0.92

Pre-load (0.96) (0.93) (0.92) (0.93)

VH bearing 1.16 1.08 1.06 1.05

Sliding (50% variable load) 1.36 1.07 (2a)

0.98 (1b)

1.04 (2a)

0.89 (1b)

0.98

Sliding (100% variable load) 1.10 1.05 (2a)

0.88 (1b)

1.00 (2a)

0.77 (1b)

0.88

Summary of results – clay site

SNAME external loading and ISO external loading is based

both on: k = 0.86 on wave kinematics (not Height) and DAF on

intrinsic period.

Effect of apparent wave period in DAF is 15% more inertia load,

1% more total external loading and 0.5% more vertical soil

reaction

Effect of H = 0.86*H (SNAME) iso on wave kinematics (ISO) is

3% on w/c load, 2% on total external loading and 1.5% on

vertical soil reaction

Summary of results – clay site

Gulf of Mexico site Deep clay SNAME rev 3 orig

ISO SNAME % SNAME

Leg penetration [m] 45 45 0% -

SDOF-DAF 1.158 1.162 -2% 1.162 -2%

External OTM [MNm] 2743 2749 -0.2% 2749 -0.2%

Max reaction [MN] 162.9 115.5 3%(net) 126.2 -7%(net)

Fixity [%] 31% 35% 12% 20% 50%

Chord Pu [MN] 78.1 75 7% 89.5 -15%

Utilisations:

Holding 0.62 0.61 1% 0.73 -12%

Chord 0.65 0.73 -10% 0.87 -25%

(Pre-load) (0.91)net (0.90) 1% (0.97) -6%

VH bearing 1.05 0.80 30% 0.93 +12%

Sliding 0.67 0.66 1% 0.70 -4%

Summary of observations

In general the assessment progresses very similar: Leg penetration agree quite well

External loading (except apparent/intrinsic discussion)

Fixity (if SNAME has deep clay method and embedment updated)

Response

Holding, overturning

The step 1a pre-load check agrees, but is hardly ever allowed (H/V ratio exceeded or when fixity included)

The step 1b sliding check agrees

The structural check of the chord provides some significant improvement in the results (upto 20% due to safety and buckling load)

Foundation checks were found to be governing (by far)

The foundation (bearing) check level 2 needs some careful as it deviates from SNAME and adversely affects the outcome upto some 30 % in a step 2a/2b assessment (step 2c or step 3 has not been assessed) in terms of: The way to apply the material coefficient (on yield surface versus on capacity vector)

Excluding side resistance (a slice of the VHM surface)

Gross capacity versus net capacity (deep clay)

The foundation sliding for windward legs in SNAME is a pure step 1b check only, in ISO it is also the (relevant) VH bearing check, but here excludes side resistance

Chord strength

In general the chord strength check is similar, except: the material coefficient for axial loading is 1.10 (compared to 1.15 (1/0.85) for SNAME)

thechord axial strength Pn is based on a formula for Fy > 450 Mpa which gives more capacity

Discussion points

External loading:Wind load is identical

Wave/current loading affected by:

Application of kinematics reduction factor (method and value)

Inertia loading affected by use of apparent wave period i.s.o. intrinsic

Application of kin red fact directly on wave kinematics is the right way. Allowance to reduce the wave height underestimates OTM slightly. Both methods are presently allowed in both ISO and SNAME

ISO defines formula to calculate appropriate kin red fact for each rig&site specific case. The underlying method is in principle what is allowed to do (time domain simulation of wave/current loading in an irregular sea) in SNAME and ISO. The result may both be below and in excess of 0.86

In the present assessment cases using the appropriate kin red factor (0.80 NS and 0.77 GoM) in combination with DAFapparent leads to a reduction of external load:2.5% for NS

2508/2685 =>7% for GoM

Discussion points

The foundation (bearing) check level 2

Governing the assessment results upto step 2b assessment

Is more conservative than SNAME due to: The way to apply the material coefficient (on yield surface versus on capacity vector)

Excluding side resistance (a slice of the VHM surface)

Gross capacity versus net capacity (deep clay)

In the present (basic) cases the VH bearing check found was more conservative by:3% for sand (North Sea with same external loading)

30% for clay (GoM)

The pre-load check (net capacity) is in agreement, but inappropriate because of fixity in the calculations

The foundation sliding for windward legs in SNAME is a pure step 1b check only, in ISO it is also the (relevant) VH bearing check, but here excludes side resistance. Including the VH step 2a is relevant but should side resistance be included?

Sand check - comparison

0

2

4

6

8

10

12

14

16

18

20

0 20 40 60 80 100 120 140 160 180

VH & sliding comparison ISO - SNAMESAND - shallow penetration

ISO - factored yield

ISO - unfactored

Factored storm reactions [MN]

240 deg - leg 2

210 deg - leg 2

210 deg - leg 3

180 deg - leg 1

Sliding line (step 1b)

SNAME - unfactored

SNAME - allowed loads

Clay check - comparison

0.0

5.0

10.0

15.0

20.0

25.0

0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0

VH & sliding comparisonISO - SNAME

CLAY deep penetration

ISO - unfactored

ISO - Factored VH yield surface

Step 1b Sliding check for windward legs

SNAME - yield unfact

SNAME - allowed loads

SNAME - sliding step 1b

vector loads

vector yield

Panel 4 update HamburgThe foundation (bearing) check level 2 with the proposed

Panel 4 change as of 19th October 2010:

For sand, with fixity, the UC was 1.16. Using the new definition and

m = 1.075 i.s.o. 1.10 for partial contact, we arrive at UC = 1.11

It agrees properly with SNAME results UC = 1.05, the difference

being load.

It is shown by the UC calculated using the exact SNAME loading F

= 7.59, V = 127.5 => UC = 1.05 (SNAME = 1.05)

Panel 4 Hamburg updateThe foundation (bearing) check level 2 with the proposed

Panel 4 change as of 19th October 2010:

For clay, with fixity, the UC was 1.05. Using the new definition and

m = 1.10 i.s.o. 1.15 for full contact, we arrive at UC = 0.93. SNAME

= 0.80

0.0

5.0

10.0

15.0

20.0

25.0

0.0 50.0 100.0 150.0 200.0

VH slice of VHM surface for M=0

unfactored gross capacity yield surface

Factored VH yield surface, gross capacity by 1.15vector loads

vector yield

Step 1b Sliding check for windward legs

Oct update of factored yield surface, factor 1.10 on net capacity