The Qatar Shell GTL (Gas to Liquids) project got off to a good start on 14th February with the spudding of the first of two appraisal wells in Qatar's massive North Field.

This is the largest gas field in the world and Shell expects to produce 1.6 billion standard cubic feet of gas per day to use as feedstock in a world-class GTL plant. This will be built at Ras Laffan and is scheduled to begin production in 2007 using Shell Middle Distillates Synthesis (SMDS) technology.

The total cost of the project is estimated at US $5 billion 'Shell in the Middle East' went offshore to see the drilling operation first hand and to meet the men responsible for Shell's drilling operations in Qatar...

"Shell's programme to drill two appraisal wells in Qatar's North Field is another important step on the long road to Shell's development of Qatar's gas reserves and the construction of a second- generation GTL plant, using the Shell Middle Distillates Synthesis process at Ras Laffan here in Qatar," says Bart Lismont, Upstream Manager for Qatar Shell GTL.

"This project heralds the coming of age of GTL technology and a new way of monetising gas apart from using pipelines to deliver gas directly to end customers or converting it into LNG [Liquefied Natural Gas]. It also marks the return of Shell to Qatar, a country with a great potential for the development of new business.

"It is anticipated that the GTL plant will need a natural gas feedstock of around 1.6 billion standard cubic [scf] of gas per day. The purpose of the two appraisal wells is to evaluate the two blocks, H4 and H5, which Shell has been awarded in Qatar's massive North Field. The objective of drilling the two wells is primarily to confirm the gas composition, which affects the economics of the project and the eventual plant design.

"The second purpose is to establish the gas-water contact, which impacts on the volumes in place and allows us to assess the porosity and/or permeability of the formations in which the gas is found, which determines how much gas the well will flow."

Bart goes on to explain, "The two blocks which have been awarded to Shell are both 144 square kilometres in area and 50 kilometres offshore from Qatar in a water depth of between 30 and 40 metres.

"Production platforms will be built in 2006 or 2007 on the two locations and gas will be produced from 16 development wells and delivered by sub-sea pipeline to Ras Laffan and, ultimately, into the GTL plant.

"We spudded the first well, NFS1-1, in block H5 on Saint Valentine's Day [14th February]. The well has been designed to have a total depth of 10,000 feet and will be a vertical well.

"Shell will be using ENSCO to drill the two wells and was pleased to get the ENSCO 96 jack-up rig as it was the only rig available with experience of drilling in Qatar waters. The ENSCO 96 was also the best option from the commercial aspect and, most importantly for Shell, the rig has very high HSE [Health, Safety and Environment] standards, with an excellent record over the last four years of no LTIs [Lost Time Injuries].

"The well will be drilled in five sections. We have already drilled the 36-inch section down to 600 feet and laid a 30-inch conductor pipe. We are currently drilling the 26-inch section with a Roller Cone bit. This section will go to a depth of about 2,400 feet, into which we will lay a 20-inch casing. The remaining three sections are the 17.5-inch and 12.25-inch, with the final 8.5-inch section going into our target, which is the Khuff gas reservoir at 10,000 feet," concludes Bart.

Taking up the story, Thierry de Meyer, Drilling Manager at Qatar Shell GTL, says, "This will not be an easy well to drill as Shell has no recent experience in Qatar. Some of the formations through which we have to drill are fractured and this can cause total losses of drilling mud which can be both costly and time consuming. These fractures and the possibility of weak hole integrity can also lead to the total loss of a well.

"The top formations are mostly limestone, which is where we can expect the mud losses, then shale, where the drilling will be much harder and we face such problems as getting the complete bottom hole assembly [BHAs] stuck in the well bore.

"One of the main risks associated with drilling wells in the Khuff reservoir is the presence of H2S [hydrogen sulphide] gas. This is a highly toxic, odourless and colourless gas which can kill at concentrations in the air in excess of 100 ppm [parts per million]. We expect that the gas we find will have an H2S content in the two to five per cent range.

"The Khuff reservoir is made up of four layers, one on top of the other, and covers a horizontal area around 80 kilometres by 100 kilometres. Whereas the reservoir layers are relatively uncomplicated structurally, there is significant heterogeneity in terms of composition and permeability. The latter determines the quantities of gas the well will flow.

"Important composition parameters are the CGR [Condensate Gas Ratio] and the inert gas content.

"The CGR can range from 20 to 40 barrels of condensate per million scf of gas. Inert gases, such as H2S, carbon dioxide and nitrogen, can range from five to 15 per cent. These gases have no commercial value and whilst H2S is highly toxic, carbon dioxide and H2S are both highly corrosive.

"So in terms of the gas we want to find, it should have a low level of inert gases and a high level of valuable condensate, as it is the condensate which is the icing on the cake, being an important element for the commercial success of the project.

"Shell aims to bring new technology and added value to Qatar Petroleum's offshore operations. We hope to be able to do this by adopting the use of new technologies in our operations, including a novel well test method, which is new to the region but which has been successfully tested by Shell in other parts of its global operations.

"This new process will cut the well testing time in half, saving some 25 rig days and in excess of US $3 million per well, without compromising the standards or quality of the data accumulation. "In the testing process, the well will be drilled with a fluid which will not damage the integrity of the well bore and we will use a liner with external packers and ported collars, through which we will be able to test the well.

"In Qatar we were able to hit the ground running as we could recruit several key staff from Shell's Soroosh/Nowrooz operations in the Gulf. An important factor in using these people was that they brought with them regional experience and knowledge of the formations, as well as on-the-job experience of Shell's operating and management systems.

"We are also making good use of several of Shell's global organisations and various centres of excellence around the world. These include Shell Exploration & Production's Well Testing Team in Houston and Shell E&P's Solutions for Sub Surface Team in Rijswijk in Holland.

"We expect to take 70 days to drill the first well and will then spend 35 days carrying out testing and closing the well. We will then move the rig to drill the second well, hopefully some time in May.

"Analysis of the data from the first well will be evaluated over the following six months and, depending on the results, development of the wells will take place in early 2006," he concludes.