Characteristic Law of Borehole Deformation Induced by the Temperature Change in the Surrounding Rock of Deep Coalbed Methane Well

Abstract

The borehole stability of the coalbed methane (CBM) well has always been vital in deep CBM exploration and development. The borehole instability of the deep CBM well is due to many complicated reasons. The change in the surrounding rock temperature is an important and easily overlooked factor among many reasons. In this research, we used methods that include experiment and numerical simulation to study the characteristic law of the borehole deformation induced by the changes in the surrounding rock temperature of deep CBM well. The experimental results of the stress–strain curves of five sets of experiments show that when the experimental temperature rises from 40 °C to 100 °C, the average stress when coal samples are broken gradually decreases from 81.09 MPa to 72.71 MPa. The proportion of plastic deformation in the entire deformation stage gradually increases from 7.8% to 25.7%. Moreover, the characteristics that some key mechanical parameters of coal samples change with the experimental temperature are fitted, and results show that as the experimental temperature rises from 40 °C to 100 °C, the compressive strength, elastic modulus, and main crack length of coal samples show a gradually decreasing trend. By contrast, the Pois-son's ratio and primary fracture angle show a gradually increasing trend. Moreover, the relativity of the linear equations obtained by fitting is all close to 1, which can accurately reflect the corresponding change trend. Numerical simulation results show that a high temperature of the surrounding rock of the deep CBM well results in a high range of stress concentration on the coal seam borehole and high deformation.

Geological Controls on the Gas Content and Permeability of Coal Reservoirs in the Daning Block, Southern Qinshui Basin

“…The Qinshui Basin covers an area of approximately 27 000 km 2 and is formed during the period from the middle Jurassic to early Cretaceous, 32 and it is a large synclinorium with an axis strike of NNE-SSW. 5 The Daning block covers an area of approximately 39 km 2 and is situated in the SQB (Figure 1b), tectonically surrounded by the Zhongtiao mountain uplift in the west and Taihang mountain uplift in the east.…”

“…The global resources of coalbed methane (CBM) are very rich and amount to 263.8 trillion m 3 . , As a clean energy and a significant supplement to conventional natural gas, the CBM has received extensive attention in many countries worldwide. − The United States, Canada, and Australia are currently the most successful countries in terms of CBM development in the world . The CBM in China is very abundant, with resources up to 30.05 trillion m 3 , ranking the third in the world .…”

Damage characteristics of gas extraction boreholes under different crustal stresses and their effects on gas extraction

“…Li et al and Zhang et al [16][17][18] comprehensively considered the effects of effective stress, temperature, moisture, and other factors, and established a coal rock permeability model based on this. Li et al 19 used a combination of experimental and numerical simulation to study the characteristic law of well wall deformation caused by the temperature change of surrounding rock in deep CBM wells. The numerical simulation results show that the high temperature of the surrounding rock of deep CBM wells leads to a large stress concentration range and deformation of the coal bed borehole.…”

Research on Hole Collapse Monitoring Technology of Coal Seam Gas Extraction Boreholes

“…A fiber grating strain sensor is a high-precision monitoring element with an optical signal as the transmission carrier; this has the advantages of extreme anti-electromagnetic interference, corrosion resistance, water and moisture resistance, and low transmission loss and is widely used in underground engineering fields, such as rock and coal mines. Studies [30][31][32] have monitored borehole surrounding rock pressure by strain-grating sensors. Studies [33][34][35][36][37][38][39] have applied fiber-optic grating monitoring technology to mine pressure monitoring, such as sudden water in the roof and floor of coal seams.…”