conductor pile interaction.pdf

7/29/2019 Conductor pile interaction.pdf

1/8

sOCIETY OF PETROLEUM ENGINEERS OF AIME6200lforthentral Expressway =R SPE 3490Dallas, Texas 75206

THIS IS A PREPRINT --- SmJECT TO CORRECTION

Of fshore Pl atf ormConductor Pi pe I nteracti onBy

T. H. Yang and G. W. Cooper, Continental Oil Co.

This pa?er was p~epared for the 46th Annual Fall Meeting of the Society of Petroleum Engineersof AIME, to be held in New Orleans, La., oct. 3- 6, 1971. Permission to copy is restricted to anabstract of not more than 300 words. Illustrations may not be copied. The abstract should containconspicuous acknowledgment of where and by whom the paper is presented. Publication elsewhere afterpublication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL isusually granted upon request to the Editor of the appropriate journal provided agreement to giveproper credit is made.

Discussion of this paper is invited. Three copies of any discussion should be sent to theSociety of Petroleum Engineers office. Such ~iscussion may be presented at the above meeting and,with the paper, may be consideredfor publication in one of the two SPE magazines.

ABSTRACT cOffshore platform-conductorpipe inter-

action is investigated and th~ conductors in the role of transmitti;,~L[-zontal l~~ds

Reese and Matlock [3, 4, 5, 6], Bouwkamp [7],Cooper .~],.:~.lumbergand Strader [9], Freuden-thal &l Gaj~z [10], Kqrsan and Koehler [11],and McClella~ et al [121, It is apparentfromxhe -fcmegoingstudie& that no specific


2/8

2 OFFSHORE PLATFORM-CONDconductors to act as piling must be under-stood in the course of structural design.Therefore, an investigation was undertakento study the nature of the structure-conduc-tor interaction, and to evaluate the conduc-tors in the role of transmitting horizontalloads into the soil.

DESCRIPTION OF STRUCTURJZA representative six-pile platform,

located in the Eugene Island area off theLouisiana Coast, was analyzed for thisinvestigation. Figures 1 and 2 show,respectively, a complete elevation and abrief plan of the structure.

A prefabricated six-pile jacket withbracing plans at the elevations (+) 1O-O,(-) 25-0, (-) 61-0, (-) 98-0, (-) 136-0,and (-) 176-0 was erected in a water depthof 176 feet. A 72-foot by 80-foot deck wassupported by six piles which had been driventhrough the vertical members of the jacket.The deck was seated high enough above thewater surface to provide an adequate clear-ance from the exposure to the design waves.The deck legs and the jacket were thenspliced at (+) 15-6 level.

Twelve conductor pipes were requiredfor the twelve production wells drilled onthis platform. These conductors were in-stalled on site through conductor guidesset at (+) 10-0, (-) 25-0, (-) 98-0, and(-) 176-0 levels.

@DESIGN CtiSIDERATIONS-

ORPIPE INTERACTION SPE-3490were attached at the tips ofthese simulated piles.

Case 2: The setup was the same as des-cribed in Case 1 except thepiles were treated as fixed-endat a distance equivalent to thelength of dummy pile below themud line.

Case 3: Well conductors were consideredas structural elements. Withproper end connection codes incomputer program, these pipeswere connected to the platformin such a way that they wereallowed to carry only lateralshear forces and would contri-bute strength to the wholestructure. Piles as well asconductors below the mud linewere simulated with dummy mem-bers in which translational androtational springs were attachedat their tips.

Case 4: The same setup of Case 3 wasused with the exception that thepiles and conductors were fixedat a distance equivalent tothe length of simulated membersbelow the mud line.

f- .- calculation of spring con-stants was based on Rease andMatlock work [3] and the lengthsof simulated memberswere deter-

#!i&Ptobe 375 inches, 261 in-


3/8

mentioned previously. The wave directions~~ ~~a~~.ip-Figure 2 ~re;A. Wave impinging on the platform

from east,B. Wave impinging on the platform from

east southeast in the directionperpendicular to the diagonal ofthe platform,

c. Wave impinging on the platformfrom south southeast along thediagonal of the platform, and

D. Wave impinging on the platformfrom south.

The foundation conditions at the sitewhere the platform was erected might be classi-fied by t-hemajor soii s~ra~a as foiiows:-.--

Stratum I, between the mud line and 54feet below, contained very soft-to-firmgray clay.Stratum II, from 54 to 163 feet belowmud line, contained firm-to-very stiffgray clay.Stratum III, from 163 to 318 feet belowmud line, contained dense-to-very graysilt. w

Stratum IV, from 318 to 410 feet anddeeper, contained very stiff clay.Sets of soil resistance-pile deflection

with similar end-conditions first. It isthen followed by the comparison of the resultsfor the structure with different end condi-tions.

Basically, there are three axis systems,i.e., overall axis system, member axis system,and oblique axis system, which may be used bycomputer program FRAN in performing structuralanalysis. These systems are interrelatedand may be transformed from one system to theother system, or vice versa. Discussion ofthis investigation is litiitedto the use ofoverall axis system and oblique axis system.

Tables 1 through 4 show the summary ofshear components and vector shears on thepiles at the mud line for all cases and load-ing conditions investigated. The loadingconditions A, B, C, and D in each case study-----.--...2. l.-......-..l:,-a-.++n..e rCULL==~UUU LU tl!=WaVG ULL=LLLUA,Oii,8, ,and D respectively. The values provided inthese tables are the resultant shears inthe overall axis system. In the analyses ofCases 1 and 2, the wave forces impinging onthe conductors were hand-calculated andwere applied at the corresponding conductorguides on each bracing levels. For Cases 3and 4, the wave forces on the conductorswere generated by the computer. It iS ob-vious from these tables that the resultantshear components for Cases 1 and 2 aregenerally greater than that of Cases 3 and 4.Since the maximum difference is within 2 per-cent, it is deemed that this tolerance isacceptable and the comparison of the resultsmay be justified in the analysis of such acomplicated structure.


4/8

4 OFFSHORE PLATFORM-CONDin Case 3 but is greater in Case 4. It isalso noted that the conductors carry muchmore shear in both components in Case 3 thanthat in Case 4. This is primarily due tothe difference in the nature of a semi-rigidconnection from the characteristics of arigid connection at the supports. As aresult, one would expect a greater deflectionQf the structure at the mud line for Case 3.With a larger deflection at the mud lineand the fact that the piles are much stifferthan the conductors, it is apparent thatthe conductors with semi-fixed connectionwill carry greater shear than the conduc-tors with fixed-end connection.

In the analysis of the foundation,the piles may be treated as batter orvertical piling depending on the designersphilosophy. Generally, the analysis maybe simplified if the piies are consideredas vertically embedded and are subjectedto axial force, lateral shear and bendingmoment simultaneously at the mud line wherethe lateral shear is normal to the piles.For this puspose, the resultants givenin Tables 1 through 4 are transformed fromoverall axis system to oblique axis system,and the shear components are combined intovector shears which are perpendicular topiling elements. The resultant shear vec-tors are shown in Figures 3 and 4.

In Figure 3, the vector shears oneach individual pile at the mud line areshown for all loading conditions for thestructure with semi-fixed supports, i.e.,for Cases 1 and 3. - ----- 1.-.-..4.-.+.-4J.lle V=CLUL S1lCCXLJ-=LLA=

rOR PIPE INTERACTION SPE-3490presented, the following conclusions may bemade:

1.

2.

3.

4.

The conductor pipes will transmitsignificant horizontal loads intothe foundation media and the selec-tion of end-conditions for supportsaffects the results considerably.For semi-fixed supports, the twelveconductors cause a reduction oftotal lateral shear on individualpiles between 34.7% to 41.0%.For fixed supports, the same numberof conductors cause a reduction oftotal horizontal shear on indivi-dual piles between 20.4% to 26.9%.It is therefore concluded that thenegligence of conductors in therole of transmitting the horizontall--a- ..


5/8

.,.. . ----- --- .-. . ------ cSPE-54YU 1.H. YANG anclG. w. LUUY!3K J

REFERENCES1. Lee, G. C., Offshore Structures Past, Transactions, ASCE, Vol. 127, Part I,

Present, Future, and Design Considera- 1962.tions, Proceedings, Offshore Explora-tion Conference, 1968. 7. Bouwkamp, J. G., Concept of Tubular

Joint Design, Journal of the Structural2. Howe, R. J., Design of Offshore Division, Proceedings, ASCE, Vol. 90.

Drilling Structures, Transactions, No. ST2, 1964.ASME, August 1955.

8. Cooper, G. W., Hurricane Damage to3. Reese, L. C. and Matlock, H., Non- Offshore Structures-Materials and

Dimensional Solutions for Laterally EnvironmentLoaded Piles with Soil Modulus Assumed * Presented at 22nd AnnualPetroleum Mechanical Engineering Con-Proportional to Depth, Proceedings, ference, ASME, Philadelphia, SeptemberEighth Texas Conference on Soil Mechanics 1967.and Foundation Engineering, SpecialPublication No. 29, Bureau of Engineer- 9. Blumberg, R. and Strader, N. R.,ing Research, The University of Texas, Dynamic Analysis of Offshore Structures,AuStiil, 1356. P~e~~ints: Offshore Technology Con-

ference, 1969.4. Reese, L. C. and Matlock, H., Numerical

Analysis of Laterally Loaded Piles, 10. Freudenthal, A. M. and Gaither, W. C.,Second Structural Division Conference Design Criteria for Fixed Offshoreon Electronic Computation, ASCE, Structures, Preprints, OffshorePittsburgh, lYbU.--- T--L_-l 1a~~.ecllliu~~~y-~~ferer&~e,L3

5. Matlock, H. and Reese, L. C., Founda- 11. Karsan, 1. D. and Koehler, A. M., Designtion Analysis of Offshore Pile-Supported of Offshore Platforms Subject to Seis-Structures, Proceedings, Fifth Inter- mit Loadings, Proceedings, Offshorenational Conference, International Exploration Conference, 1969.Society of Soil Mechanics and Founda-tion Engineering, Paris, July 1961. 12. McClelland, B., Focht, J. A., and Emrich,

W. J., Problems in Design and Installa-6. Matlock, H. and Reese, L. C., Generalized tion of Offshore Piles, Journal of theSolution for Laterally Loaded Piles, Soil Mechanics and Foundations Division,

Proceedings, ASCE, Vol. 95, No. SM6, 1969.


6/8

Ty@~~ ~ - SUMMARY OF SHEARS AT iWu. LINE FOR CASE 2STUTNSHEAR IN KIPSLOADING SHEAR VECTORCONDITION X-COMPONENT Y-COMPONENT IN KIPS

A 2057, 00 2057.B 1720. -1129. 2057.c 1144. -1689. 2040.D o. -1978. 1978. A

NOTE : LOADING CONDITIONS A, B, C, AND DCORRESPONDING TO THE WAVE DIRECTIONSA, B, c, AND D.TABLE3 - smy OF SHEARS AT MUD LINE FOR CASE 3 STUDY

SHEAR (KIPS) - X COMPONENT SHEAR (KIPS) - Y COMPONENTLOAD I NGCONDITION ON ONTOTAL CONDUCTORS % TOTAL CONDUCTORS %

A 2048 429 21.0 0. 0. 0.B 1702 359 21.1 -1112 -241 21.6c 1132 240 21.2 -1663 -362 21.8


7/8

(+)59-8

I M-w--n- IA 1 I 1 11 1 I 1 (+)o~oA / 4I 111111! I I II+)6-0NJ WI ; ;

(-)25-o

W..-.l! ?

111111111 i /[11(-)61 -0

l~m~l II

I III

1 NA I I (-me -oiillili 1 Iiw/ w w1 I I IIll /I 1111111

?2

.


8/8

VECTCIR SHEARS IN KIFS

L

c3z0.

()0rcitzr-lw

vIECTOR SHEARS IN KIPS, = (.

E=Es==I=.

.~-~ !,=.., ,l

3,.2.

10El,,

I

,;I,1I

conductor pile interaction.pdf

Documents