The GASTAU Project will run from the Caraguatatuba Gas Treatment Plant to Taubaté Custody Transfer Station and São José dos Campos Refinery, in São Paulo State, Brazil.

The 97 kilometre pipeline will transport natural gas produced from the Mexilhão field, located in the offshore Santos Basin. The first phase of the field’s development is expected to produce 15 million cubic metres per day (MMcm/d) of gas. The project is of strategic importance to Brazil, aiming at increasing natural gas supply to feed industrial, automobile fuel and domestic consumption in the cities São Paulo and Rio de Janeiro.

The offshore platform and facilities, offshore and onshore pipeline and compressor stations are under construction simultaneously with the final completion date of the whole project scheduled for December 2010.

Brazilian pipeline construction company GDK S.A is responsible for two contracts for the GASTAU Project.

GDK was awarded a 32 kilometre section of the API 5L X70 pipeline running between São José dos Campos Refinery and Taubaté station. The scope of work involves the design, engineering, construction, pigging and testing, drying, commissioning and start-up support for the pipeline.

The second contract involves the execution of seven special crossings of major rivers, dams and highways. Petrobras tendered the special crossings contract separately due to the complexity of works involved and high level of execution difficulty.

The two contracts are managed and performed by two independent GDK teams, and both involve unique challenges.

Challenges

The 32 kilometre section of pipeline runs through a highly developed region, with industrial plants, big cities of more than two million inhabitants, large farms and an impressive highway network built within the vicinity of the project. Some sections of the pipeline cross densely populated housing development areas, and require twelve road crossings over a distance of less than one kilometre. A total of 35 road and highway crossings are being performed with large boring machines.

In addition, the GASTAU Pipeline is parallel to and located on the same right-of-way as three operating trunklines. This requires special construction procedures to ensure safe conditions are maintained to those existing lines.

GDK says that each kilometre of the pipeline has varying environmental conditions. Route terrain profile and soil conditions are varied, ranging from swamps to hills, side slope sections, rock incidence and farm lands.

GDK says that a detailed study and survey was required to select the most appropriate method for the particular characteristic of each of the crossings required for the project.

In addition to the technical execution requirements, GDK has also defined an environmental plan, as a major part of the two contracts is located inside a Federal Permanent Environmental Preservation Area, with strict environment restrictions. Safety was also a primary concern.

The GASTAU Project requires development within a tight contract schedule. GDK took this into consideration, as well as heavy rains experienced in the region from September to February, when conducting technical studies to select the final pipeline construction methods to be used. To comply with all these requirements, GDK’s team is using innovative methods and special equipment – some of which have never before been used for onshore pipeline construction.

The special equipment includes:

CAT 320 hydraulic excavators on Kori amphibious floating tracks to allow ditch opening at the steep rivers banks and in swampy areas; and, Extra-long Doosan 24 tonne hydraulic excavators, on special ‘H’ configured floating pontoon sets, to open the ditch in the deeper river beds, reaching up to 15 metres.

Paraíba River crossing

GDK says that one of the most challenging jobs under the contract is the Paraíba River crossing.

The Paraíba River – the most important river in the region – is 420 metres wide and 25 metres deep with a deep ‘V’ channel and steep banks that do not allow conventional construction methods or directional drilling methods.

After an extensive technical study, GDK has decided to apply a combined onshore and offshore solution. This solution is to prepare a pipe length with a concrete jacket to run along the entire width of the river and bank and kept afloat using twin-buoys sets.

Following the correct positioning of the 420 metre string at the crossing, the pipe will be lowered to the riverbed by water-ballasting the buoys. After reaching its correct position in the riverbed, a post-trenching machine – applied only in offshore pipelines – will excavate the ditch below the pipe, burying it one metre in to riverbed, and stabilising the pipe section.

GDK says that the application of this solution can be credited to the combination of the company’s expertise in both onshore and offshore pipeline construction. GDK has previously performed several offshore pipeline construction contracts. While assembling large diameter pipelines in a sensitive area of the Guanabara Bay in Rio de Janeiro, GDK employed a similar method resulting in a very cost effective solution to the client, as well as limiting the environmental impact of the project. Construction continuing on schedule

Completion of all the seven major crossings is scheduled to be achieved early this year. By October 2009, five of the crossings were already complete and the overall work progress had reached above 70 per cent. The pipeline contract is expected to be complete by March 2010, in line with a special requirement stipulated by Petrobras.