Method and device for determining formation collapse pressure

Abstract

The invention provides a method and device for determining formation collapse pressure. The method comprises the steps that rock mass weak plane parameters of a target formation and mechanical property parameters of the target formation are obtained; according to the rock mass weak plane parameters and the mechanical property parameters, a collapse pressure calculation model of the target formation is established; an initial input value of the collapse pressure calculation model is determined according to the rock mass weak plane parameters; and the initial input value is input into the collapse pressure calculation model for iterative calculation to obtain a collapse pressure value of the target formation. The method and device fully consider the influence of a rock mass weak plane structure of the target formation on the failure law of a rock mass, can obtain the relatively accurate collapse pressure value, can truly reflect the failure law of rocks with the weak plane structure, areconducive to accurate adjustment of the density of drilling fluid in the drilling process, and reduce the risk of collapse of a lower-layer well wall.

Description

technical field [0001] The invention relates to the technical field of petroleum drilling, in particular to a method and a device for determining formation collapse pressure. Background technique [0002] Wellbore instability is a common problem in oil drilling. According to statistics, more than 90% of wellbore instability occurs in shale formations, of which about 2 / 3 are in fractured shale formations. In shale formations, there are often serious and complex situations such as a large number of collapsed blocks and frequent drilling fluid loss due to the instability of the wellbore wall. In regions with strong tectonic movements such as Yumen Oilfield, Qaidam Basin, Junggar Basin, and Tarim Basin in western China, as well as Beibu Gulf Basin in the western part of the South China Sea and Bohai Oilfield, etc., the drilling of deep fractured shale formations has encountered serious problems. The problem of well wall collapse caused many collapsed and lost blocks, which caus...

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Problems solved by technology

[0010] But the above criterion ignores the intermediate principal stress σ 2 For the influence of the analysis results, while the rock failure is assumed to depend only on σ 1 and σ 3 , so the above criteria are only applicable to the analysis of complete strata

For example, for fractured shale, which has weak plane structures such as bedding and fractures inside, the rock usually fails along the weak planes. The failure law of rocks with weak surface structure can not be timely and accurately adjusted the density of drilling fluid during drilling, which increases the risk of wellbore collapse in the lower formation

Once the drilling fluid density is too low, because the formation has been damaged, even if the drilling fluid density is increased later, the wellbore cannot be effectively supported

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