№1 January 2012Table of contents Issue Archive
№1 January 2012Table of contents Issue Archive
№ 7 (July - August 2011)
Etienne Bourdelet, head of Shtokman Development AG (SDAG) Drilling Directorate and Anatoliy Verkienko, drilling engineer, discuss how drilling will be performed within the scope of the Shtokman project.
By Etienne Bourdelet. Anatoliy Verkienko
Production drilling at the Shtokman field during Phase I includes several stages, envisaging working at three drilling locations in the range of four kilometers (16 wells initially, with more wells to be drilled later on). Each well will take 100 days to drill, including time for unexpected technical problems and weather.
The Shtokman gas condensate field consists of four productive formations; however, Phase I development envisages developing only two gas formations, J0 and J1, which lie atop each other. At the same time, each separate well will allow extracting gas from only one formation. Once the FID is made, the subsea group must install the subsea templates on a seabed before the work starts. So, after the FID is made in mid-December, as is planned, drilling will begin around July 2014.
Average J1 vertical well depth will amount to about 2,200 meters; at the same time, the average measured depth of wells to this formation will amount to about 3,388 meters. The Shtokman field’s reservoirs have a very good productivity, so the wells will be slightly bigger than usual. They are in the top category regarding their productivity and size; there are probably no more than 50 such wells worldwide. The wells are designed to produce gas for 50 years with minimal intervention.
In the drilling areas, two semi-submersible drilling platforms will be operating at the three drilling centers. Each drilling unit will operate for approximately two years; out of these, of which they will work in parallel for about a year. Due to the climate in the region, the working area of the rig will be closed and heated to temperatures above freezing. The platforms have been specifically designed to have frame reinforcement (armor plating) in the case of collisions with blocks of ice (rated ice cover – no more than 40 percent).
One of the main special features of offshore drilling is the mobility of the rig caused by waves on the sea surface. Generally, the rig remains in operation with vertical motion in the range of 1 to 4 meters, and 10-50 meters, or 2-3 degrees of lateral motion. To allow this, the marine riser has a flexible connection with the seafloor marine equipment and a heave compensator at the drilling unit.
First, drilling of the vertical section is performed; then, the trajectory gradually increases inclination and enters the productive formation at an angle of practically 80 degrees for the J0 wells, with drilling of a sub-horizontal section (about 88 degrees) for J1 wells. This is achieved by using special drilling and navigation equipment.
Drilling mud – the “blood” of a well – will force the operation of a hydraulic downhole motor, which will rotate a drilling bit (rolling bit or a PDC bit), and will also bring the cuttings to the surface. The downhole equipment has a number of sensors which measure hole trajectory inclination, its drift direction, downhole weight on bit and vibrations, formation density, natural gamma ray level, etc. All that information is sent back to the surface using mud pulse – this technology for measuring various parameters and sending them over a distance is called telemetry. The downhole tools create pressure waves by opening and closing a device, and pressure sensors let us read them so we know what is happening down there. This technology has already been proven in use for about 20 years.
In addition to hydraulic downhole motors brought into operation by the drilling mud, there is a technology called “rotary steerable drilling”. Using this technology, we can control and aim the drilling tools in the direction planned from the surface; at the same time, rotation of the tool does not stop, while trajectory changes take place automatically. This is a challenge in itself, and it is also affected by the fact that the Shtokman field is located at a high latitude, so the magnetic field is weaker and navigation there requires the use of special technologies. But we can make the well go the direction we want. Geological conditions in the region are relatively easy, which is to our advantage.
Use of complex computerized equipment requires special personnel training; therefore, we need to have more electronics specialists and fewer electricians on board. Electric power will be generated on board the rig using diesel engines.
Gas will not be used for this purpose. As far as environmental protection is concerned, it should be noted that reserves in the Shtokman field are mainly dry gas; the field has very little liquid hydrocarbons (condensate). Consequently, massive pollution, like an oil spill, is impossible. Still, the Barents Sea, being an Arctic area, is much more sensitive to pollution, so we know we will have to be more careful than in other places. Compared to other regions of the world, we will bring much more waste to the shore for treatment. The cuttings from the well are disposed overboard in most offshore operations worldwide. In case of Shtokman, except for the first two sections, the cuttings generated will be brought back to shore for treatment.
At the very end of development, when the field becomes depleted, in accordance with the existing requirements of the Russian legislation, the wells must be abandoned by installing a number of cement plugs and mechanical caps. Abandoning the wells will require large expenditures, but in the end the place itself will not be a danger to navigation and so on. Of course, we cannot know how the legislation will change, but every year it tends to demand more all over the world. Yet, even now, we have technical possibility to return the sea bottom practically to the original state and we will do it.
Shtokman gas-condensate field
is located in the central part of the Russian sector of the Barents Sea 550 km away from Kola Peninsula. By the explored reserves of natural gas Shtokman is now one of the largest fields in the world. Phase One of Shtokman field will be developed with annual production of 23.7 bn m3 of gas per year by Shtokman Development AG, a company created in February 2008, a joint project of three leading world companies Gazprom (51%), Total S.A. (25%) and Statoil ASA (24%).