Drilling platform

The drilling platform

DRILLING PLATFORM (EN: drilling platform; DE: Bohrplattform, Bohrinsel; FR: echafaudage de forage; ES: plataforma de sondeo; RU: буровая платформа) is the installation for the drilling within the water areas, with the purpose of exploration or operation of the mineral resources under the bottom of the sea.

The drilling platforms are mostly non-self-propelled, the acceptable speed of their towing is 4-6 knots (during the roughness of the sea of up to 3 points, with the magnitude of the wind of 4-5 points). In the working position, on the point of the drilling, the drilling platforms withstand the joint action of the roughness of the sea with the height of the waves of up to 15 metres, and of the wind with the speed of up to 45 metres per second. The operating mass of the floating drilling platforms (with the technological reserves of 1700-3000 tonnes) reaches 11000-18000 tonnes, the autonomy of the work according to the ship and technological reserves is 30-90 days. The power of the energetical installations within the drilling platform is 4-12 megawatts. Depending on the structure and purpose, they distinguish the self-lifting, semi-submersible, submersible, and stationary drilling platforms, and drilling ships. There are most distributed the self-lifting (47% of the total quantity, 1981), and semi-submersible (33%) drilling platforms.

They use the self-lifting (see the Figure # 1) floating drilling platforms for the drilling mostly in case of the depth of the sea of 30-106 metres. They represent by themselves the water-displacing three-legs or four-legs pontoon with the industrial equipment, which is raised above the surface of the sea with the help of the lifting-locking mechanisms onto the height of 9-15 metres. During the towing, the pontoon with the raised legs is floating; at the point of the drilling, the legs are lowered. Within the modern self-lifting floating drilling platforms, the speed of the lifting (lowering) of the pontoon amounts to 0.005-0.08 metres per second, while the speed of the legs amounts to 0.007-0.01 metres per second; the total lifting ability of the mechanisms is up to 10 thousand tonnes. According to the method of the lifting, they distinguish the lifting mechanisms with the walking action (mostly pneumatic and hydraulic), and with the continuous action (electromechanical). The structure of the legs ensures the possibility for the installation of the drilling platforms onto the ground with the load-carrying ability of at least 1400 kilopascals, with the maximal deepening of these legs into the soil of up to 15 metres. The legs have the square, prismatic, and spherical shape, are equipped with the toothed rack along the entire length, and are terminated with the shoe.

The floating drilling platforms of the semi-submersible type

They use the floating drilling platforms of the semi-submersible type for the drilling of the boreholes mostly in case of the depth of the sea of 100-300 metres, and these platforms represent by themselves the pontoon with the industrial equipment, which is raised above the surface of the sea (at the height of up to 15 metres) with the help of 4 or more stabilizing columns, which base themselves onto the underwater hulls (2 or more). They transport the drilling platforms to the point of the drilling on the lower hulls with the draught of 4-6 metres. The floating drilling platform submerges itself for 18-20 metres by the method of the intake of the water ballast into the lower hull. For the retention of the semi-submersible drilling platforms, there is used the eight-point anchoring system, which is ensuring the limitation of the movement of the installation from the mouth of the borehole of at most 4% of the depth of the sea.

They use the submersible drilling platforms for the drilling of the exploratory or operating boreholes for petroleum and gas at the depth of the sea of up to 30 metres. These platforms represent by themselves the pontoon with the industrial equipment, which is raised above the surface of the sea with the help of the columns of the square or cylindrical shape, the lower ends of which base themselves onto the water-displacing pontoon or shoe, where the ballast tanks are situated. The submersible floating drilling platform stands onto the ground (with the load-carrying ability of at least 600 kilopascals) as the result of the filling of the ballast tanks within the water-displacing pontoon with water.

They use the stationary marine drilling platforms for the drilling and operating of the cluster of the boreholes for petroleum and gas in case of the depth of the sea of up to 320 metres. From one platform, they drill up to 60 obliquely directed boreholes. The stationary drilling platforms represent by themselves the structure in the form of the prism or of the four-sided pyramid, which rises above the level of the sea (for 16-25 metres), and which bases itself onto the bottom with the help of the piles, which are driven into the bottom (the framed drilling platforms), or with the help of the foundation shoes (the gravitational drilling platforms). The above-water part comprises the place, onto which there is placed the energetic, drilling, and technological equipment, the dwelling block with the helicopter pad, and other equipment with the total mass of up to 15 thousand tonnes. They construct the base block of the framed drilling platforms in the form of the tubular metal grating, which comprises 4-12 columns with the diameter of 1-2.4 metres. They fixate the block with the help of the piles, which are driven into the bottom, or which are fixated into the boreholes by the concrete. The gravitational platforms are constructed wholly of the reinforced concrete, or as the combined type (the legs are made of metal, the shoes are made of the reinforced concrete), and are retained at the expense of the mass of the built structure. The bases of the gravitational drilling platform comprise 1-4 columns with the diameter of 5-10 metres.

The stationary drilling platforms are purposed for the long-duration (at least 25 years) work at the open sea, and they are presented with the high requirements for the ensuring of the existences for the servicing personnel, for the increased fire and explosion safety, for the protection against corrosion, for the measures on the protection of the environment (see the "Marine drilling" article), and so on. The distinctive peculiarity of the stationary drilling platforms is the permanent dynamism, that is for each productive field there is developed its own design for the providing of the platform with the energetic, drilling, and operating equipment, while there determine the structure of the platform the conditions within the region of the drilling, the depth of the drilling, the yield and the quantity of the boreholes, the quantity of the machine tools for the drilling.

The stationary drilling platforms