Project Description

Garraf oil field is located in the province of Thi Qar, approximately five kilometres north-west of Al-Refaei city and 85km north of the city of Nasiriya. The field is owned by PETRONAS Carigali Iraq Holding (PCIHBV, 45%), Japex (30%) and North Oil Company (25%).

Development works for the oil field started in early 2011. Initial production started in August 2013.

The onshore oil field was discovered in 1984 and contains oil in cretaceous reservoirs. The field is 17.5km long and 5.5km wide. It is estimated to hold 1.3 billion barrels of oil reserves. The current production capacity of the field is 35,000 barrels of oil per day (bopd). It is expected to increase to 230,000bopd by 2017.

GTL were appointed during Concept stage as Engineering Consultants which subsequently included FEED and detailed design. GTL also undertook preliminary pile testing and CAT II checking for structures.

GTL are now in discussions regarding plants future expansion.

Client Name
PETRONAS Carigali Iraq Holding
Weatherford Oil & Gas

Project Name
Weatherford Oil & Gas

Services Provided
Concept & FEED Design
Geotechnical interpretation & Consultancy
Modularisation study
Structural Design & CAT II check
Foundation Engineering
Design of specialist piles
Project Management

Thi Qar province, Iraq

£8, 900,000.00


Senior Management

  • Gavin Rixon – Project Director
  • Karsten Richter – Lead Geotechnical Engineer
  • Stephen Whitham– Geotechnical Engineer


Geotechnical Ground Conditions and Geo-hazard Identification

The project was classified as Geotechnical Category 2 in accordance with DMRB (Design Manual Roads and Bridges) Volume 4 Part 1 Section 1 HD22/08, Managing Geotechnical Risk, Chapter 3.

Geographically, the FCP site was situated within the regional fertile basin fed by the Euphrates River. The site lies along the fringes of the Garraf River to the east, a tributary of the Euphrates River. The notable features within the local area was the lake and road that formed on the crest of an embankment.

Geologically the site was considered young as the ground has been formed by secondary or tertiary geological processes; alluvial clays from the Euphrates River delta and wind-blown sand formations from the desert. Geological records showed the site to be situated within a stable tectonic plate therefore the ground has not been influenced by mountain building events. As a result there is limited thickness (geological memoirs suggest approximately 15 to 30m) of superficial (drift) deposits attributable to the sediment deposits from the adjacent river systems. Sandstone bedrock was recorded beneath superficial deposits of the local region.

The exploratory borehole logs recorded numerous layers of clays, which GTL considered to be of alluvial origin, differentiated by changes in colour, strength or variations in the relative proportion of sand. Minor layers at depth of silt were also recorded.

Garraf Development was assigned to Seismic Zone 1 and the ground conditions encountered were categorised for seismic design purposes as Soil Profile SD.

The facilities are assigned to occupancy category 2.

Preliminary Static Load Testing

The load test system was specifically designed and consisted of a robust computerised system specifically used for controlling and monitoring the load testing process. The system was capable of accommodating the various test schedules In addition to the electronic sensors, the equipment had two main components, a data logger and a load maintainer. With these, the significant controlling aspects of the test were performed and the resultant test data stored.

Geographically, the FCP site was situated within the regional fertile basin fed by the Euphrates River. The site lies along the fringes of the Garraf River to the east, a tributary of the Euphrates River. The notable features within the local area was the lake and road that formed on the crest of an embankment.

The control and application of the scheduled load, was carried out hydraulically under computer control, correcting the load applied every 2.5 seconds where necessary.

Using a unique system the microprocessor-based logger was programmed to regulate the required functions, to check the safe progress of the test and to control all the load changes required.

Helical Pile Design

Over 2500 piles were installed at various depths and diameters to accommodate a modular type construction.

The foundation pile design was undertaken as a limit state design, whereby a distinction was made in ultimate limit states (ULS) and serviceability limit states (SLS).

Limit states is related to design situations, which were classified in persistent, transient, accidental and seismic design situations.

In accordance with the superstructure operation states, accidental design situations noted and classified in the foundation pile design.

Structural Design Review

A review of the Structural Design and Analysis was undertaken by GTL to evaluate the load combinations, the resulting base shear for the structure, and the resultant forces at each support, as they apply to the design of the foundations. Only “in-place” load cases were evaluated under this review. GTL’s reviewer has written a ‘summary of understanding’ for each load case and applicable load combination under which questions or clarifications have been raised.

GTL’s reviewer has not undertaken any design of the structure. The following review is not meant to supersede the Design Engineer’s results, but is intended to provide clarity to all interested parties regarding the loads and interaction of loads and design results between the structure (under American Code) and the foundations (under British Standard Code). Recommendations, when made, are given for the purpose of;

1) Revising the calculation set to provide a clear understanding of the structural design.

2) Requesting the analysis be re-run with the recommended parameters to identify realistic reactions at the base/supports.


“On behalf of WFT I would like to thank GTL for their invaluable input into this project. I have found GTL to be both professional and knowledgeable all of which has added value to this project” – WFT Project Director

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