A further technology in enhanced oil recovery is the drilling of multilateral wells, increasing the coverage area within strata. The first operational dual-bore well on the Yamal Peninsual, with horizontal wells running to a length of 1,000 metres, was constructed at the Novoportovskoye field.
A further technology aimed at increasing strata coverage involves the construction of a so-called “Fishbone” well — a horizontal well with multiple offshoots or branches. This construction allows significantly greater coverage of oil-saturated sections of strata in comparison with traditional horizontal wells while, at the same time, involving less extensive drilling works than are required in creating a multistage well. The fishbone construction allows each of the branches (“laterals”) to be directed at separate reservoirs, without having to encroach on adjacent strata containing either water or gas. This method of well construction is currently being actively embedded at the Vostochno-Messoyakhskoye field.
Multi-stage fracking
With the development of horizontal drilling, multi-stage fracking technology, involving the direct creation of fissures throughout several sections of a well, has become widely used. Today this tends to be used in conjunction with other technologies in enhanced oil recovery, although it is being constantly improved.
In developing complex low-permeability reservoirs the inadequacy of standard multi-stage fracking has become obvious insofar as each newly-fracked zone has to be kept separate from the preceding one by a metal or composite ball. The diameter of these balls is reduced from zone to zone, with the result that the way these wells are constructed makes more than 10 fracking operations impossible. New spaced-perforation technology has no such limitations.
Multi-stage fracking through spaced perforation involves multi-use compacted “cushions”-packers which expand under pressure to isolate those areas in which fracking has been completed. Once complete, the cushion deflates to its normal size and the equipment is transported to the next port.
Development of the Bazhenov formation
The drilling of horizontal wells with multi-stage fracking is the key technology in drilling for shale oil — including in production at the Bazhenov formation, which is very similar in terms of oil occurrence. The most recent insights into the geological structure of the Bazhenov formation suggest there are two key formations: an oil source bed, containing kerogenic shale (polymeric organic matter, which appears in such formations as shale oil) and interstratified beds containing light oil. The latter, moreover, comprises some 30 percent of the total depth of the formation. Such complex composition demands specific multi-stage fracking technologies, of which “рlug & perf” is one.
LLC Bryanskneftekhimprom is the first company in Russia to implement full-cycle technological solutions used throughout the global oil and gas industry in developing reserves at the Palyanovsky block, part of the Krasnoleninskoye field in the Khanty-Mansiysk Autonomous Okrug. This has involved, in particular, horizontal well sections being reinforced with flexible cement, meaning the fissures created can be relied upon to be kept apart, followed by multi-stage fracking involving the high-speed injection of process mud. The combination of good isolation and high-speed injection in fracking makes possible the formation of a concentrated network of fractures throughout the entire length of the horizontal section, thereby increasing the volume of hydrocarbons made available in development.