Multistage hydraulic fracturing.

This work considers one of the most important issues in the development of oil fields - oil production efficiency. The importance of this issue is related to the fact that for many oil producing countries (e.g. oil fields in Western Siberia, Russia) most of conventional oil reserves are already involved in production and are represented by oil fields at a late stage of development that are characterized by a sharp decrease in productivity. Almost all remaining oil reserves are represented by oil fields that cannot be developped economically with conventional technologies. As an illustration, new fields of Western Siberia are characterised by the formations with extremely low permeability. Economically reasonable development of this kind of oil reserves can be provided only by means of modern unconventional techniques. One of the most efficient and, therefore, widely used solutions for this problem is hydraulic fracturing. By means of this technology the production well inflow can be significantly increased. During hydraulic fracturing, a liquid (gel) is injected into the well at a pressure higher than the fracture pressure. With further injection of fluid into the formation, a highly permeable fracture is created, the created fracture is then propped open by the proppant. Further, the fluid flow first occurs from the formation into the fracture, similar to radial, and then linear fluid flow in the fracture to the well. The fracture created by means of hydraulic fracturing, unlike other stimulation methods, significantly increases the drainage area by increasing the drainage radius related now to the length of the fracture and provides a linear inflow to the well. From the other hand, unconventional status of a high persentage of oil reserves in the world is related also with remote location of oil bearing formations. Drilling horisontal wells in many cases solves this problem and at the same time leads to the increase of production efficiency due to decrease of the number of wells required for a certain oil production. Due to mentioned facts, the majority of newly drilled wells (in particular in Western Siberia) are represented by Horisontal wells with Multistage hydraulic fracturing. In this regard, the discussion of this kind of well completion is highly relevant.