钻孔绳索取芯煤层气损失量估算方法研究

Abstract: The production practices reflect that the coalbed methane (CBM) content measured in the coalfield exploration period is universally lower than the actual gas content in coal seams. The theoretical analysis and indoor simulation test results all indicate that the main cause resulted in the lower CBM content test is resulted from the lower estimation value of the CBM loss quantity. With respect to this practical problem, this project takes the CBM desorption process during the wireline coring in borehole as the study object, to improve and make prefect the existed CBM desorption test unit, let it has the self-control, even and quick de-pressure functions, simulate and measure the CBM desorption quantity of coal core in the wireline coring process, and analyze the CBM desorption and escape regularities of coal core in the wireline coring process. It takes the disciplines such as the coal geology, CBM geology, thermodynamics, mathematic, physics and isothermal adsorption theory and so on as the theoretical basis, establishes the CBM desorption estimation model of coal core under the constant temperature and variable pressure conditions, and suggests the estimation model and method of the CBM loss quantity of coal core in the wireline coring process. In the typical mining areas, it adopts the means of the closed coring technique and indoor simulation test, to compare and analyze the differences among the CBM loss quantity estimated by this estimation method, the measured CBM loss quantity and the CBM loss quantity estimated by the United States direct method, and inspect the reliability of this estimation model and method. The successful develop of this project can provide the technical support for the exploration and development of the CBM resources and the safe and high-effective mining of the coalmines.

生产实践反映了煤田勘探时期测得的煤层气含量普遍低于煤层中实际的气含量，理论分析和室内模拟测试结果均表明了造成煤层气含量测试偏低的主要原因是由煤层气损失量估算偏低所致。针对这一实际问题，本项目以钻孔绳索取芯煤层气解吸过程为研究对象，对现有煤层气解吸试验装置进行改进完善，使其具有自控、均匀、快速降压的功能，模拟测定绳索取芯过程中的煤芯煤层气解吸量，分析绳索取芯过程中的煤芯煤层气解吸逸散规律。以煤田地质学、煤层气地质学、热力学、数学物理学和等温吸附理论等学科为理论基础，建立恒温变压条件下的煤芯煤层气解吸估算模型，提出绳索取芯过程中的煤芯煤层气损失量估算模型及方法。在典型矿区，采用密闭取芯技术和室内模拟测试等手段，分别对比分析本估算方法估算的煤层气损失量与实测的煤层气损失量和美国直接法估算的煤层气损失量的差异，考察本估算模型及方法的可靠性。为煤层气勘探开发和煤矿安全高效开采提供技术支撑。

生产实践反映了煤田勘探时期测得的煤层气含量普遍低于煤层中实际的气含量，理论分析和室内模拟测试结果均表明了造成煤层气含量测试偏低的主要原因是由煤层气损失量估算偏低所致。针对这一实际问题，本课题以钻孔绳索取芯煤层气解吸过程为研究对象，对现有煤层气解吸试验装置进行改进完善，使其具有均匀、快速降压的功能，模拟测定绳索取芯过程中的煤芯煤层气解吸量，分析绳索取芯过程中的煤芯煤层气解吸逸散规律。以煤田地质学、煤层气地质学、热力学、数学物理学和等温吸附理论等学科为理论基础，建立恒温变压条件下的煤芯煤层气解吸估算模型，提出绳索取芯过程中的煤芯煤层气损失量估算模型及方法。课题研究取得了如下几个方面的研究成果和认识：.（1）建立了能够模拟绳索取芯过程高压匀速降压、注水驱气和及时测定煤层气损失气量的试验装置，并提出了测定煤层气损失气量的试验方法。.（2）模拟试验实测了钻孔提芯阶段和地面暴露阶段煤层气损失气量，揭示了高压匀速降压过程中损失气和解吸气量变化规律及影响因素。结果表明：损失气-解吸气曲线呈明显的“三段型”，提芯和地面暴露阶段损失气量产出速率比罐中解吸阶段解吸气产出速率大得多，前者呈非线性快速增加，而后者的早期时间则呈平缓线性增加。不同粒度煤样的煤层气损失气量和解吸速率差异很大。.（3）对比研究了采用USBM法直接法估算的损失气量和损失气含量和模拟试验实测得的损失气量和损失气含量。对比结果显示：采用USBM法直接法估算的损失气量和损失气含量比模拟试验实测得的损失气量和损失气含量小很多，并分析了其产生的主要原因。.（4）建立了地面钻孔绳索取芯方式线性变压边界的煤层气扩散解吸地质模型和数学模型，得出了地面钻孔绳索取芯煤层气损失气量估算模型的形式表达式。