Hanze F2A Gravity Base Structure - FoundOcean

Hanze F2A Gravity Base StructureUnderbase grouting for the 83.5m tall, 9,000 tonnesteel gravity base structure in the North SeaSubsea and offshore groutingfor the global energy construction industries

Underbase grouting for the steel foundationsof the largest field in the Dutch North SeaABOUT THE HANZE F2A FIELDHanze was the largest field to be developed in theDutch North Sea. The development is a steel-gravitybased production and storage platform. Hanze islocated in block F/2 in the Dutch sector, North Sea.The field has reserves exceeding 34 million barrelsof oil, as well as 40bcf of associated gas. The fieldcovers 4.5km² between 1,340 and 1,478m below sealevel.GRAVITY BASE STRUCTURE DESCRIPTIONThe foundation is of steel construction and gravitybase design. It contains 12 central oil storage cells,whilst the cells to the North and South ends of thestructure are used for ballast water. The void formedbetween the underside of the base and the seabedwas filled with a sodium silicate/cement grout inorder to ensure an even load distribution betweenthe structure and the seabed. The structural integrityof the platform was dependent on the correctplacement and retention of good quality grout inthe voids beneath the base.QUALITY CONTROLDuring mixing, the slurry density was monitoredby densitometers mounted on the mixer units. Theslurry density was also monitored at intervals using apressurised slurry density balance.One sample was taken during the grouting of eachcompartment. For each sample the slurry densitywas measured and recorded three 75 mm groutcubes were manufactured. Each cube was markedto identify the platform, compartment number, timeand date of casting and the specific gravity.The samples were cured underwater at the seabedtemperature of 8 o c ± 0.5 o c until removed for testing.All cubes were tested at age 28 days. Periodic bleedtests were also undertaken using graduated glassmeasuring cylinders. These were filled with 200ml ofgrout and a reading of the grout level was takenevery 30 minutes for the next four hours. The amountof bleed was calculated as a percentage of theoriginal grout volume, and was generally between3-6%.THE MIXING SYSTEMCompartment grouting was carried out in pairs,with two penetrations in the dividing cell wall topermit grout flow between the first and secondcompartment of each pair. One primary and onesecondary grout line was provided for each pairof compartments, together with two 8” outlet portslocated in the outer wall of the second compartment.Cement was stored in bulk pressurised silos anddelivered to a surge tank above the mixer. Waterwas delivered to the mixer from the vessel firemainpipework and measured into the mixing tank throughKey Project FactsOperatorVeba (now Petro-Canada)ContractorSMIT Maritime ContractorsRegionNetherlandsWater depth -43mTotal cement606.18 tonnesTotal sodium silicate 58,191 litresCrew size 8EquipmentGrout mixer and pumps2 x 100 t capacity silos3 x Sodium Silicate tanksWorkshop and LabUmbilical Winch and Hose3 x Grout Density probesGrout specification 0.175 MPa @ 28 daysCuring temperature 8 o cMobilisation port Rotterdam, NetherlandsInstallation vessell North Prince

The Hanze F2AGravity Base Structurein situ’a mechanical flowmeter. Water entered the mixerthrough a high pressure jet and cement througha rotary valve at a fixed rate. Sodium Silicate wasadded via a flow meter through the water jet in afixed proportion to the water flow rate. The groutwas transferred to a ten barrel capacity tank fromwhere it was drawn off by the pump and deliveredto the GBS via a flexible hose. The grout was mixedand pumped at a rate of between 40-45m 3 per hour.This rate was restricted by the water supply from thevessel.Grout pumping continued until the theoreticalvolume required to fill the void had been pumped,and good quality grout flow from the outlets hadbeen confirmed by ROV.THE ENGINEER’S PERSPECTIVEGrouting was proceeding well until contingencyprocedures had to be implemented to successfullyfill a number of the compartments.During filling compartments 101+140, 61+20 and71+30 it was reported by ROV that the grout wasleaking into the adjacent compartments 102,62 and 72, under the dividing cell walls. Thesecompartments were not designed to be grouted.Together with 112, these were intended for later useduring the de-ballasting and removal of the GBS atthe end of its life. However, due to this leakage, anadditional 50m3 of grout needed to be pumpedinto each of the leaking pairs to completely fill themand produce good returns from the grout outlet.No flow was detected by ROV from the groutoutlets during filling of compartments 91+130. Afterapproximately 114m3 of grout had been pumpedthe ROV reported that flow was actually comingfrom the outlet of 121+160 which had been grouted5 hours previously. Pumping was then transferredto the secondary grout line, and grouting wassuccessfully completed.During grouting via the line marked 100+92, theROV reported that compartments 110+122 wereactually being filled. The hoses had been incorrectlylabelled. We completed grouting this compartmentand moved to fill 100+92 via 110+122’s grout line.> Visit www.foundocean.com for more case studies

HEADQUARTERSListon ExchangeListon CourtMarlowBuckinghamshireSL7 1ERUnited KingdomT: +44 1628 567 000F: +44 1628 567 001UK OFFSHORE SERVICE BASEUnits 3-5 Telford Square Business ParkHoustoun Industrial EstateLivingstonWest LothianEH54 5PQScotlandT: +44 1506 440 330F: +44 1506 440 340INDIA#205-208 Rushabh ComplexDalia Industrial AreaPlot No. D8, Opp Fun RepublicAndheri (W)Mumbai 400053IndiaT: +91 2 22 673 2305F: +91 22 2673 2307MALAYSIADataran Hamodal, Block B, Level 2No.4, Jalan Bersatu 13/4Petaling JayaKuala LumpurSelangor Darul Ehsan, 46200MalaysiaT: +60 3 796 091 09F: +60 3 796 091 08CHINAHai Feng AsiaRm 1204, Block AHeychang GardenGuang An Men Wai Da JieBeijingChina 100055T: +86 10 6345 0922F: +86 10 6345 0923www.foundocean.comGeneral enquiries to info@foundocean.comTechnical enquiries to technical@foundocean.com