基于采动影响条件下煤层气数值模拟方法研究

Coalbed methane extraction from ground wells is the main direction of the future of coal-bed gas exploitation, there is an urgent need to develop the numerical method under consideration coalbed methane mining conditions affecting to guidance the coalbed methane production. Proposed by theoretical analysis, field testing and the coal sample, summarized the law, such as mining mining scope, Construction of the stress field, the permeability field and seepage field three fusion, quantitative characterization the effective stress and fracture and permeability field. By using the dynamic mesh technique described mining working face move forward, based on increased dynamic virtual wells located in the Mesh refinement working face, the well move with the working face together to simulate the exchange of material around the working face advancing mining area; Using moving boundary technology to distinguish the grid number between the mining area and the other grid system, based on the dynamic mesh make the working face regional settings for the outer boundary, deal the grid at the working face advancing as the local flow boundary representation mining influence. Using two different processing methods to characterize the impaction on properties nearby the mining coal face during the process of mining, combined with three coal-bed methane mining law to establish a simplified coal-bed methane mining model. According to the current maturity of numerical simulation of coalbed gas flow, two simplified model under influence of mining coalbed methane was established, the model were carried out by using finite difference method, establishment numerical simulation methods of coal bed methane considered the Mining influence for our conditions.

煤层气地面井抽采是未来煤层气开采的主要方向，迫切需要开发考虑采动影响条件下煤层气数值模拟方法指导煤层气开采。拟通过理论分析、矿场测试和煤样实验总结采动影响范围等采动规律，构建应力场、渗透率场与渗流场融合三场，实现有效应力与裂隙和渗透率场的定量表征。采用动态加密网格技术描述采动工作面推进，基于在工作面所在加密网格增加动态虚拟井，该井随工作面一起推进达到模拟工作面推进后采动对于周围区域的物质交换；采用动边界处理技术，采动区网格编号与其余网格系统进行区分，基于动态网格将工作面推进区域设置为外边界，将工作面推进处网格作为局部可流动边界表征采动影响。利用两种不同处理方法表征采动过程中对工作面附近煤层物性影响，结合三场规律建立煤层气采动简化模型。根据目前成熟煤层气数值模拟建立流程建立两种简化模型下采动影响煤层气数学模型，利用有限差分方法对模型分别进行求解，最终建立适合我国采动条件下煤层气数值模拟方法。

煤层气地面井抽采是未来煤层气开采的主要方向，需要开发考虑采动影响条件下煤层气数值模拟方法对于指导煤层气开采具有重要意义。提出了采用测井资料等多元信息融合计算原始地应力的方法，采用室内凯赛尔声波实验等建立修正的岩石力学参数计算模型，根据压裂资料等建立修正的构造应力系数，基于测井资料利用修正的岩石力学计算模型和构造应力系数可以计算单井地应力曲线。将计算的单井地应力曲线作为测井曲线，利用建模软件采用随机建模的方法可以建立区块三维地应力分布模型，实现了应力场的三维表征，为应力场与渗透率场耦合提供了保障。构建采动条件下煤层气抽采物理概念模型，建立了网格系统不变，基于动态虚拟井和变渗透率场耦合的数学模型并进行了求解，利用动态虚拟井达到采动巷道到外部的能量物质传导，建立传导率随时间变化模拟采动巷道推进来模拟渗透率场和渗流场改变模型，模型中渗透率场对于工作面区域采用赋值的方法动态推进，对于工作面推进外区域采用应力场与传导率耦合方式确定传导率。根据Langmuir方程和fick扩散定律建立煤层气吸附与解吸模型，考虑模型简化中工作面推进对三场的影响和流体状态方程等状态方程，基于守恒方程建立采动条件下煤层气抽采数学模型，基于有限差分方法建立对应的差分方程组，并对各边界条件进行处理，离散化，最后对线性方程组利用IMPES方法求解。根据建立的模型和求解方法，利用VB语言编写了数值模拟软件，利用编写软件结合实际生产参数进行模型验证并优化模型，得到了前述变渗透率场范围和传导率调整系数。利用自编数值模拟软件结合实验研究从目前的初步结果看，在采动工作面前后30-60m左右范围内渗透率显著增加，而当工作面推进过后渗透率会有一定的恢复原始状态的倾向，但是从目前的认识看并不是完全降到初始值。最终该部分工作通过实验得到岩心力学参数与应力场的关系和数值模拟逆向分析两方面研究。初步建立了考虑三场融合采动条件下煤层气数值模拟方法。