After a long period of development and production, due to casing deformation or damage, underground falling object accident is difficult to deal with. As well as underground water cone or gas cone and other factors. Some oil and water Wells can not maintain normal production, resulting in the annual decline of crude oil and natural gas production. Which seriously threatens the normal production of oil fields.
In order to reduce the comprehensive cost of drilling, especially to effectively utilize the existing borehole and give full play to the potential of old borehole. Domestic oil fields have strengthened the research and application of sidetracking technology of small borehole with window. After several years of continuous development, this technology has been gradually mature and perfect.
Window side drilling technology is a new technology and process that utilizes the old well borehole to redevelop the reservoir and to make full use of some of the original production and transport equipment of the old well to give full play to the production potential of the original well, thus prolonging the service life of the old well and improving the crude oil production. At the same time, the old well borehole can be used to greatly reduce the construction cost and shorten the construction period. Improve comprehensive economic benefits. Therefore, the secondary development of oil and gas resources in old Wells by side drilling with Windows has a broad application prospect.
As there are many differences in reservoir depth, reservoir physical properties, geological characteristics and casing procedures in each oilfield. A lot of research work needs to be done on how to effectively utilize casing window sidetracking technology. And improve reservoir development effect. Which mainly includes the selection and matching of drilling equipment. Well trajectory design, monitoring and control, selection of drilling fluid and completion fluid and on-site treatment and maintenance. Completion and cementing, logging and perforating, etc., to form a set of side drilling technology suitable for each oilfield.
The lateral drilling technology is mainly using in the following well conditions. Poor downhole technical condition (casing deformation or damage, downhole object fall). No oil is producing from an oil well or a low-producing well. Old well oil reservoir channeling or high water cut. Adjust well pattern to excavate remaining oil and increase recoverable reserves; Deepen old Wells to develop or explore deep reservoirs.
Optimal design of window position
The selection of sidetracking location is related to the casing integrity of the original well, the formation lithology. The longitudinal distribution of oil and water layer, the tool inclination ability, the way of window opening and the geological design. The general principle of selecting the sidetrack position is to make use of the long old hole as much as possible. Shorten the drilling cycle, save the drilling cost, ensure the safety of drilling construction. Extend the effective life of the well and improve the production of the well. It can be summarizing as follows:
(1) The sidetracking position should be as deep as possible. The casing should be intact above the sidetracking position without deformation, fracture, or leakage. The window should be in a well section with good cementing quality and small inclination. And avoid the casing collar for 2 to 3m.
(2) If the section milling mode is using to open the window. The formation is stable and drillable within at least 20m of the sidetracking position. So as to facilitate shoulder construction and new hole drilling, and not easy to return to the old hole.
(3)In other words. The sidetracking position should be selecting in sandstone or non-expansive mudstone formation as far as possible. And it is best to avoid the expansive shale and rock salt well section, and avoid the flooding area of old Wells. Sidetracking position should avoid perforating well section as far as possible to ensure the safety of window opening and drilling.
(4) For the oil well with serious sand production, channeling and casing fracture after perforating. The side drilling effect should be considering comprehensively when the location of the window is selecting. Generally, the window opening position should be more than 30m away from the perforating well section.
(5) Comparing well history and logging data. The position of window should meet the requirements of comprehensive parameters such as azimuth, horizontal displacement, deviation point and borehole curvature.