Wellbore Stability Research Method Applicable to Pressure-Depleted Formation

Abstract

The invention discloses a sidewall stability research method suitable for a pressure-depleted formation. In the method, knowledge points of multiple disciplines, such as the underground rock mechanics, the borehole geophysics, the continuum mechanics, the elastic mechanics and the mathematical statistics, are integrated, the method starts with microscopic deformation conditions of rock skeleton particles obtained after the formation pressure is depleted till to the macroscopic acoustic response performance, characteristic parameter variation and the like of rocks, makes full use of partial data, such as rock skeleton density logging, shale content logging, actual measurement points of the formation pressure and collapse and fracture pressure and the formation core, obtained when the oilfield formation pressure is not depleted, and finally the collapse and fracture pressure of the pressure-depleted formation is determined, so that guidance and reference are provided for selection of the density of a drilling fluid for pressure-depleted formation drilling. The computing method is high in precision, and just a few of errors exist in fracture pressure prediction.

Description

technical field [0001] The invention relates to the research on the well wall stability of the pressure-depleted strata in oil and gas field drilling, in particular to a research method applicable to the well wall stability of the pressure-depleted stratum. Background technique [0002] After a period of exploitation in most oil and gas fields, formation energy will decline to varying degrees. According to the statistics of field drilling in pressure-depleted formations, accidents such as lost circulation and pipe sticking are very likely to occur in pressure-depleted well sections. For example, after more than 20 years of exploitation in the MD gas field in the Yinggehai Basin in the western South China Sea, the reservoir pressure coefficient has dropped to about 0.5. In order to meet the requirements of the production plan, more adjustment wells have been drilled since 2010. During the drilling of adjustment wells, the accidents such as lost circulation and pipe sticking ...

AI Technical Summary

Problems solved by technology

Although some domestic and foreign scholars have studied the changes in ground stress and collapse pressure of pressure-depleted formations, they are all based on mathematical calculation models obtained on the basis that rock characteristic parameters do not change. The model is relatively simple, but the prediction accuracy of the collapse and fracture pressure is low, and a set of specific methods for predicting the wellbore stability of pressure-depleted formations has not yet been formed, which has many limitations in field practical application

If the collapse and fracture pressure of pressure-depleted formations are not accurately predicted, but the safe mud density window in the early stage of oil and gas field development is used, it is very likely that accidents such as lost circulation and pipe sticking will occur due to inaccurate selection of drilling fluid density

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