构造煤渗透率对红外辐射功率响应变化试验研究

Experimental study on permeability response of structural coal to infrared radiation power

中国煤储层地质开采条件复杂,具有低压力、低渗透率、低饱和度以及含气量高等特点。众学者通过多种手段研究煤层气增产技术,实现了高速开采煤层气的目的,但由于对煤储层解吸渗流机理的不明确,未能实现大规模开采。通过温升实验,得到红外辐射下煤体温度变化规律,红外辐射功率越大,煤体升温速率越快,所能达到的温度也越高。分析得到煤体温度与红外辐射功率的关系式,该关系式为探究红外辐射下煤体的温升规律及后续的红外辐射下煤体的解吸-渗流实验提供参考。基于自主知识产权的红外辐射三轴加载实验系统开展煤体的解吸-渗流实验,该系统主要分为红外辐射子系统、三轴加载子系统、数据采集子系统。分别以轴压、围压、孔隙压力及红外辐射功率为变量对煤体的渗透率进行系统性研究,解决了红外场、应力场和渗流场不能同时加载的难题。该实验系统具有结构简单、安全性高、密封性好、压力范围大、数值稳定及参数可单独调控等特点。在现有研究基础上进行红外辐射作用下煤体渗流实验,定量分析煤体解吸渗流过程中的相关参数及演化规律。结果表明:在孔隙压力较低范围内,煤体渗透率随红外辐射功率整体呈上升趋势,渗透率最大增加45%。在相同孔隙压力条件下,低围压状态下煤体的渗透率普遍高于高围压状态下煤体的渗透率。推导得出煤体渗透率与红外辐射功率关系式,并对关系式中孔隙率相关参数k_(0)及热膨胀相关参数b进行分析,在红外辐射影响下,孔隙率相关参数随围压的增加而下降,煤体热膨胀相关参数在孔隙压一定时,随围压的增加变化范围在0.0045~0.0030。对红外辐射作用下煤体渗透率损失率进行分析,低孔隙压力条件下,煤体渗透率损失率随红外辐射功率的增加整体呈减小趋势。考虑红外辐射功率敏感性,在孔隙压力一定的条件下,煤体红外辐射功率敏感系数与红外辐射功率呈正相关。在孔隙压力不同的条件下,煤体红外辐射功率敏感性存在差异,说明红外辐射功率敏感系数不仅与红外辐射功率有关,更是孔隙压力与围压共同作用的结果。通过对红外辐射作用下煤体渗透率影响因素的分析得到红外辐射功率与渗透率的关系式及影响参数。

The geological mining conditions of coal reservoirs in China are complex because of the characteristics of low pressure,low permeability,low saturation,and high gas content.Many scholars have studied the CBM stimulation technology through various means to achieve the purpose of high-speed exploitation of CBM.However,due to the unclear mechanism of desorption and seepage in coal seams,a large-scale mining has not been realized.Through the temperature rise experiment,the temperature change law of the coal sample under infrared radiation was revealed.The greater the infrared radiation power is,the faster the temperature rise rate of the coal sample is,and the higher the temperature can be achieved.The relationship between coal sample temperature and infrared radiation power was obtained.The relationship provides a reference for exploring the temperature rise law of coal samples under infrared radiation and subsequent desorption seepage experiments under infrared radiation.The desorption seepage experiment of coal samples was carried out based on the infrared radiation triaxial loading experimental system with independent intellectual property rights.The system is mainly divided into the infrared radiation subsystem,three-axis loading subsystem,and data acquisition subsystem.The permeability of coal samples was systematically studied with axial pressure,confining pressure,pore pressure,and infrared radiation power as variables,the problem that infrared field,stress field,and seepage field cannot be loaded at the same time was solved.The experimental system has the characteristics of simple structure,high safety,good sealing,large pressure range,stable numerical value,and independent regulation of parameters.Based on the existing research,the coal sample seepage experiment under the action of infrared radiation was conducted to quantitatively analyze the relevant parameters and evolution law in the process of coal sample desorption seepage.The results show that in the range of low pore pressure,the permeability of coal samples increases with the infrared radiation power and the maximum permeability increases by 45%.Under the same pore pressure,the coal sample is in a state of low confining pressure,and the permeability is generally higher than that of high confining pressure.The relationship between coal sample permeability and infrared radiation power was derived,and the porosity-related parameters and thermal expansion-related parameters in the relationship were analyzed,under the influence of infrared radiation,porosity-related parameters decrease with the increase of confining pressure.When the pore pressure is constant,the variation range of coal expansion-related parameters with the increase of confining pressure is between 0.0045 and 0.0030.The permeability loss rate of coal under the action of infrared radiation was analyzed,under the condition of low pore pressure,the permeability loss rate of coal samples decreases with the increase of infrared radiation power.Considering the infrared radiation power sensitivity,under the condition of certain pore pressure,the infrared radiation power sensitivity coefficient of coal permeability is positively correlated with the infrared radiation power.Under the condition of different pore pressures,the power sensitivity of coal permeability is different,The power sensitivity coefficient is not only related to the infrared radiation power,but also to the result of the joint action of pore pressure and confining pressure.By analyzing the influencing factors of coal sample permeability under the action of infrared radiation,the fixed relationship and influencing parameters were obtained.