Gazprom Neft Continues Applying High-Tech Drilling Methods

Gazprom Neft has successfully applied the Underbalanced Drilling Technology that gives opportunity to produce oil when the well is still being drilled. The use of this technology at the Archinskoe field operated by Gazpromneft-Vostok helped open 15 extra oil-bearing fractures, which is seven times more than with traditional drilling methods. Production rate of the new well is 160 tons of oil per day; it is more than twice the average production rate of similar wells, so this extra oil fully pays for the cost of bringing in the complex high-tech services.


At the fields operated by Gazpromneft-Vostok, oil is produced from fractured carbonate reservoirs*. Under such conditions, the well productivity depends on how many natural fractures inside the rock are opened in the course of drilling. With the traditional drilling method, formation fluid pressure in the well is higher than in the reservoir, so drilling mud infiltrates into the fractures in the rocks and partially blocks the inflow of oil into the well. Besides, if drilling mud is absorbed by the rock, drilling becomes impossible: drilling mud runs out quickly, the geosteering equipment signal is lost, the drilling bit is overheated. For this reason, traditional wells only manage to open one or two natural fractures in the rock.

The drilling mud loss problem is now solved by the Underbalanced Drilling Technology. The essence of the technology is that drilling mud is injected into the well at a pressure equal to or a little less than the reservoir pressure, which prevents drilling mud absorption by the rock. Maintaining the required pressure balance is a complex technical operation, and it required to mobilize over 400 tons of equipment that was stored in Finland, UAE and Iraq.

Underbalanced drilling is more expensive than conventional drilling methods. But its other upside is that oil production can be started immediately as the well is still being drilled. When the new well was being drilled at the Archinskoe field, 450 tons of oil was produced which significantly improved economics of the drilling operation. The equipment used in this technology allows putting the well onstream within two days after completion – eight times quicker than usual.

After applying at the Archinskoe field, the technology will be tested in carbonate reservoirs of Gazprom Neft’s other assets: Gazpromneft-Vostok, Gazpromneft-Orenburg and the Eastern Siberia. Working with carbonate reservoirs is one of the nine areas of the Gazprom Neft Technology Strategy.

"Carbonate fractured reservoirs is a complicated kind of reserves, and it is obvious that their share in our portfolio will be increasing. This is why is it so important to identify and test technologies that improve efficiency of oil production from these reservoirs", – the Gazprom Neft First Deputy General Director Vadim Yakovlev said.

Reference

* Gazprom Neft has come up with a program for introducing new technologies to produce oil from carbonate and fractured reservoirs which contain over 40% of the Company’s recoverable reserves or almost 600 million tons of hydrocarbons. The largest assets with such reservoirs are the Eastern Section of the Orenburgskoe field, the Kuyumbinskoe and the Chonskoe fields in the Eastern Siberia, the Badra project in Iraq, and the Prirazlomnoye field in the Pechora Sea. In the global petroleum balance, carbonate reservoirs are playing an increasingly significant role, and most of the discoveries in the recent years are made in this type of reservoirs.

Due to their characteristics, carbonate reservoirs require high competencies and careful selection of development technologies by petroleum engineers to ensure that their reserves are developed and produced efficiently and economically. The new program prepared by the Gazprom Neft Science and Technology Center includes 12 technology projects in the areas of exploration, field development, well drilling and oil production.

Most of oil in Russia and the world is produced from clastic reservoirs. This type of reservoir rocks is composed of fragments of pre-existing minerals and rocks; it is well-studied and characterized by a high predictability of the main development and production performance parameters. Carbonate reservoirs, unlike clastic, are most commonly formed by the growth of marine organisms or accumulation of sediments in the sea water. It is not unusual that carbonate oil reservoirs used to be coral reefs.

As the formation of carbonate sediments went on, the sea water reacted with the minerals and significantly changed their original composition which led to a great variety of reservoir properties of carbonate rocks. These rocks can be fairly porous but the pores are not always connected with each other, so the reservoir is practically impermeable and does not let hydrocarbons flow to the well.

Quite often these reservoirs have another feature: a large number of cracks, which requires a special approach to their development. For instance, these cracks may become channels for gas or water that can break into the oil zone and have negative effect on the oil production process.

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