Houston-based company DeepVision, jointly owned by Baker Hughes and Transocean Sedco Forex, is in the forefront of deepwater drilling technology. Most of today’s offshore oil and gas production is at water depths of less than 300 metres. At these water depths, the largest reservoirs have already been discovered and the oil and gas industry is therefore focusing on new areas in deeper water, up to 3,000 metres, to make new discoveries.
Drillers are facing entirely new challenges. Some relate to the riser and the mud. The drilling riser connects the rig to the well being drilled. Drilling mud is used to control the well and to bring cuttings back to the surface. In ten times deeper waters, the length of the riser becomes ten times longer and the pressure of the mud inside the riser ten times greater. This increased mud pressure can easily fracture the well, if not managed properly. Deep Vision project manager is Geir Sjøberg. He explains Our solution to this problem is the dual gradient drilling concept. Instead of having a mud column connected all the way from the rig to the seabed, we have substituted the mud in the riser with sea water. This gives one pressure gradient from the surface down to the seabed, and another pressure gradient from the seabed down into the well. Sea water weighs less than drilling mud and the actual mud weight can be increased without increasing the overall pressure in the well. The drilled cuttings and mud will be brought up to the rig using a pump system located at the wellhead close to the seafloor, thus ensuring the necessary circulation in the well. Sjøberg comes from Transocean Sedco Forex, the worlds largest drilling contractor, which established DeepVision together with Baker Hughes. Two major oil companies BP and Chevron are also contributing actively to the development. Though oil and gas is currently being produced from a number of fields where the sea depths are far greater than 300 metres although not 3,000 metres so far new technology must be made available to reduce costs yet maintain an acceptable level of safety. Current drilling and production from deep waters use what Sjøberg regards as traditional technology.
New areas become economic
Says Sjøberg, We want to develop technology that will allow companies to explore for oil and gas in areas so far regarded as difficult or impossible. Through the use of new technology, we will reduce the costs of drilling in deep waters by around a third compared with existing technology, and will reduce the risk associated with deepwater drilling. The financial risk is far greater in deep water compared to more traditional depths. The economic penalties for delays, lost production or the breakdown of equipment become greater. Repairs and intervention in deep water are more expensive and take longer. The day rate for a deepwater rig could be in the region of $200,000. The oil companys own costs including service companies and logistics are in addition to this. The total costs can be around $350,000 per day. Sjøberg explains, Drilling one complex deepwater well can take more than 90 days. This can be reduced to around 60 days using DeepVisions technology. The savings are considerable. At the present day rates, the investment costs can be recovered in two to three years. This is without factoring in the effects of larger completions and potentially reduced number of wells for a given field development.
Drilling without interruption
How can the time taken to drill a well be reduced? Geir Sjøberg elaborates. Depending on the distance from the surface to the seabed, the mud weight in the well needs to be kept within certain limits in order not to collapse or fracture the well. Drill casings are set at different depths to make sure the well at each elevation is not exposed to mud weight outside the defined limits. For conventional deepwater drilling these casings have to be set fairly often, while with dual gradient drilling, the defined limits are further apart and fewer casings need to be set. Each time a casing is set, the diameter of the well is reduced. If you run into problems this may jeopardise your ability to reach the pay zone. Also, if the hole size through the reservoir is not sufficient, future potential production from the well will be limited. And this is where DeepVisions concept will be most effective. A larger well bore and longer sections can be drilled without having to stop to put in new casings. Drilling with fewer interruptions means savings in time and in costs.
Knowledgeable consultant
For DeepVision, it was important to establish a qualification and verification programme right from the beginning. The project is complex and the consequences of a wrong decision or sub-optimal design would be serious. Sjøberg outlines DNVs contribution: This has not been simply verification as the concept is often defined. For DeepVision, DNV became involved in the development work early on, and has also acted as a knowledgeable risk-management consultant. There was a need for tools and methodologies to manage the risks involved at all levels and phases of the project, and for the identification of critical factors and a focused verification process to optimise overall performance. It is important for Transocean to succeed in developing technology to drill in deep water. The company has a fleet of 178 rigs and ships. Many of the newest ones have been built for operating in deep water. This is where the new opportunities lie, says Geir Sjøberg. Transocean Sedco Forex is committed to working with the major oil companies to develop the necessary technology for finding and producing oil from increasingly deeper waters, and we are aware that our competitors have similar goals.