Method for predicting fracture pressure of coal open hole

Abstract

The invention discloses a method for predicting the fracture pressure of a coal open hole with consideration of the stress sensitivity and percolation effect. The method comprises the following steps:step one, collecting basic parameters; step two, with consideration of the induced stress of an open hole as superposition of a stress field generated by an in-situ stress, an induced stress field generated by wellhole injection and a stress field generated by the fluid percolation, carrying out superposition of three stress fields to obtain total stress distribution; step three, on the basis ofthe pore pressure distribution and tensile failure criterion with consideration of the stress sensitivity, carrying out calculation based on a continuous incremental stepwise iterative method by combining the total stress distribution and thus predicting the fracture pressure of the coal open hole. With the method disclosed by the invention, the influence on the fracture pressure of the coal openhole by the percolation effect and stress sensitivity is considered; the dynamic process of pore pressure changing caused by fluid percolation to the rock under the high pressure condition is reflected objectively; and the problem of fracture pressure prediction of the coal open hole is solved effectively. Therefore, the basis is provided for predicting the fracture pressure of the coal open hole;and the important parameters are provided for the hydraulic fracturing design.

Description

technical field [0001] The invention relates to the field of coal mine exploration and development, in particular to a method for predicting the rupture pressure of an open-hole well in a coal seam. Background technique [0002] The single well production of coalbed methane in China is generally low, which has become a bottleneck for the development of the coalbed methane industry. Only by increasing the volume and scope of coal bed reconstruction and accelerating the desorption rate of coal bed methane can single well production be increased. Hydraulic fracturing is not only an effective measure to develop coalbed methane resources, but also a reliable method to measure ground stress. As an important part of hydraulic fracturing design, accurate prediction of fracture pressure is crucial. [0003] At present, there are two methods for predicting the rupture pressure at home and abroad. The first is based on the theory of fracture mechanics, assuming that there is an init...

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Problems solved by technology

None of these three models can objectively reflect the dynamic process of pore pressure changes caused by fluid percolating into rocks under high pressure conditions.

[0005] At the same time, during the process of coal and rock fracture initiation, the formation pressure increases due to the wellbore fluid injection, so the difference between the effective overlying pressure of the rock skeleton and the pore pressure will gradually decrease with the increase of the reservoir pore pressure, making the reservoir The increase of permeability causes stress sensitivity, and the above method of predicting fracture pressure does not take into account the change of permeability caused by stress sensitivity effect

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