基于渗流新模型分析页岩气流动影响因素及规律

Analysis of the influencing factors and rules of shale gas flow based on a new porous flow equation

储层条件下Langmuir吸附模型不足以描述页岩气的超临界高压吸附特征,故含Langmuir吸附模型的渗流方程不利于描述超临界高压吸附解吸作用下页岩气的流动特征,因此建立了考虑超临界高压吸附模型的页岩气渗流方程,并与考虑Langmuir吸附模型的渗流方程进行了对比,同时分析了渗透率、孔隙度及吸附解吸作用对页岩气流动的影响规律及程度。研究表明:与Langmuir吸附模型相比新吸附模型能更加准确地描述页岩的超临界高压等温吸附特征;基于新吸附模型的渗流方程拟合实验结果的精度更高,更利于描述吸附解吸对流动的影响;当平均压力下降小于32.70%时,日产量影响程度排序为渗透率>孔隙度>吸附解吸作用;当平均压力下降为32.70%~42.58%时,日产量影响程度排序为孔隙度>渗透率>吸附解吸作用;当平均压力下降大于42.58%时,日产量影响程度排序为孔隙度>吸附解吸作用>渗透率;孔隙度、渗透率仍为页岩气传质输运的主控因素,但不可忽略吸附解吸作用对页岩气井生产中后期的影响。

Langmuir model cannot describe the supercritical high-pressure adsorption under the reservoir condition,so the flow equation with Langmuir model cannot describe the flow characteristics of shale gas effectively.Therefore,we establish a new porous flow equation which contains a high-pressure adsorption model,outcomes of the new equation are compared to the flow equation with Langmuir model,then we analyze the influence of permeability, porosity and adsorption function on shale gas flow and the influence rule of these factors.Results show that the new supercritical adsorption model can represent the supercritical adsorption isotherm on shale precisely 〉 the new porous flow equation based on the new adsorption model can fit the experiment data with a higher precision and express the adsorption/desorption effect more clearly ; when average pressure declining is less than 32.70% ,influence extent for gas production per day is permeability〉porosity〉adsorption and desorption〉when average pressure declining is between 32.70% and 42.58 %, the influence extent is porosity〉permeability〉adsorption and desorption〉when average pres- sure declining is more than 42.58% ,the influence extent is porosity〉adsorption and desorption〉permeability.Although permeability and porosity are still the main factors,we should not neglect the function of adsorption and desorption.