A coal seam open hole fracture pressure prediction method

Abstract

The invention discloses a method for predicting the rupture pressure of open-hole wells in coal rocks considering stress sensitivity and percolation effects. The main steps are: 1) collecting basic parameters; 2) considering the induced stress of open-hole wells as the stress field generated by in-situ stress, The superposition of the induced stress field produced by wellbore fluid injection and the stress field produced by fluid percolation, through the superposition of the three stress fields, the total stress distribution is obtained; 3) Based on the stress-sensitive pore pressure distribution and tensile failure criteria, combined with The total stress distribution is solved by the continuous incremental step-by-step iteration method to predict the fracture pressure of coal rock open hole wells. This method can consider the impact of percolation effect and stress sensitivity on the fracture pressure of open-hole coal seam wells, and can objectively reflect the dynamic process of pore pressure changes caused by fluid seepage into rock under high pressure conditions, effectively solving the problem of coal seam open-hole well fracture pressure prediction. Therefore, it provides a basis for predicting the fracture pressure of open-hole wells in coal seams, and provides important parameters for 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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