Borehole stability evaluation method for highly-deviated well

Abstract

The invention discloses a borehole stability evaluation method for a highly-deviated well. The borehole stability evaluation method includes steps of adopting interval transit time and density logging information to obtain formation pressure Pp, and determining the magnitude and direction of ground stress and formation rock strength parameters; converting the obtained ground stress into borehole stress of deviated well coordinates; determining the criterion of borehole instability judgment of the highly-deviated well; establishing a variation rule between borehole instability and deviation and azimuth angles thereof, and formulating borehole stability countermeasures of the highly-deviated well. In the borehole stability evaluation method, a set of complete and assorted mechanical evaluation methods combined with geology, well drilling, logging, core, laboratory tests and mechanics analysis methods takes shape, mechanical mechanism of borehole stability of the highly-deviated well can be evaluated, so that reliable basis is provided for determination of platform displacement optimization, borehole track optimization and a safe drilling fluid density window determination of the highly-deviated well.

Description

technical field [0001] The invention relates to the technical field of large-displacement and horizontal well drilling in oil and gas drilling, in particular to a method for evaluating wellbore stability under the condition of large well deviation. Background technique [0002] Extended-reach wells and horizontal well drilling methods are mainly used in the development of coastal oil and gas, offshore oil and gas and shale gas resources at home and abroad to improve the benefits of oil and gas exploration and development. [0003] However, extended-reach wells and horizontal wells often encounter the problem of wellbore instability when drilling under the condition of large well deviation, especially in deep wells in shale formations, where the problems of wellbore collapse and leakage are very prominent, resulting in complex drilling accidents and high timeliness. Downhole safety cannot be guaranteed, and drilling costs have risen sharply, seriously affecting the progress o...

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Problems solved by technology

[0004] Carrying out systematic, feasible, and accurate research on the mechanical mechanism of wellbore instability in highly deviated wells is of great significance to take reasonable countermeasures and ensure wellbore stability in highly deviated well drilling. Formation core collection and indoor strength measurement, establishment of in-situ stress and formation strength profiles using well logging data, formation pore pressure prediction, wellbore stress analysis of deviated wells, calculation models of collapse pressure and fracture pressure combined with wellbore trajectory, etc. A series of complicated problems make this problem face many practical difficulties in the specific application to field engineering

[0005] In 2008, during the drilling of highly deviated wells in the beach sea of ​​an eastern oilfield, 3 extended-reach wells successively suffered from serious borehole collapse and pipe sticking accidents, and a maximum of 5 filling sidetracking accidents occurred in a single well, and the drilling cycle of a single well increased by 1 times, the cumulative cost of loss of rotary steerable tools and cycle loss for a single well is more than 15 million yuan

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