水文地质条件对页岩气开采控制

通过对比页岩气定压开采与承压水定降深开采的相似性，建立起二者指标之间的对应关系；借鉴美国页岩储层典型参数及Barnnet页岩年产量变化规律，从水文地质的角度，建立起水文地质概念模型；利用GMS软件，对页岩气开采进行数值模拟。从模型结果看，11个拟合值中，6个相对误差在5%之内，4个在10%之内，只有一个接近20%，拟合结果较为理想。说明用水文地质方法研究页岩气开采是合理的；也表明开采过程中页岩气产量由游离气和吸附气组成，当游离气开采完毕后，产量主要由吸附气维持，解吸气还有再吸附现象。当盖层开启程度由微裂缝区的25%，50%，75%到100%依次增加时，开采年限按6 a，4 a，2 a，1 a依次减少；不同开启程度下，相同开采年的开采量也依次降低；在每种开启程度下，年产量与原来的年产量的比值也依次降低。任何侧向边界若出现断层，不论其开启程度为微裂缝区的25%，50%，75%还是100%，均达不到定压开采条件。从敏感分析可知，当页岩压裂达到一定程度时，页岩气的析出对页岩气产量影响是最关键的。最后对页岩气开采提出相应的建议。

Hydrogeological Conditions Control of Shale Gas Exploration

By comparing the similarities between constant pressure exploration of shale gas and fixed drawdown exploitation of confined groundwater, through the establishment of correspondence indicators between the two, exampled by typical shale reservoir parameters from the USA Barnett shale annual production variation pattern, studying from a hydrogeology perspective, a hydrogeological conceptual model was established to stimulate shale gas exploitation by using GMS(groundwater modeling system) software. The result of model identification and verification shows that, among the 11 fitting values, 6 relative errors are within 5%, 4 relative errors are within 10%, and only 1 is approximately 20%, which indicates that the fitting results are quite desired; it also illustrated that hydrogeological methods in shale gas exploitation are reasonable, and it also showed that in the process of mining, shale gas production is composed of free gas and adsorbed gas, after the entire collection of free gas, the gas yield is supported by the desorbed gas basically; the desorption gas will be re-adsorbed. If there exist fractures in the overlying layer, the number of years and yield for mining decrease along with the fracture increasing. If the fractures in the overlying layer increase as many as 25%, 50%, 75%, and 100% of microfractures zone (Ⅱ/Ⅲ zone), the number of years for mining will decrease to 6 years, 4 years, 2 years, and 1 year accordingly; in different circumstances, with the same mined year, the yield decreases accordingly too. In each case, the ratio of the annual output to that of the original decreases accordingly too. When the boundary conditions change, the lateral boundary (the lower boundary or the right boundary) is set to permeable fault respectively, whether its permeable abilities are 25%, 50%, 75% or 100% of the microfractures zone (Ⅱ/Ⅲ zone), the fixed drawdown (constant pressure) mining conditions can't be met. Thus, the boundary conditions have more influence on shale gas with respect to the overlying/underlying rock. The sensitivity analysis showed that the change of source and sink terms has much greater influence on the gas yield than that of permeability.It is concluded that to promote by all means the desorption of the adsorbed gas is crucial, even determinable, to shale gas production in a certain degree of fracturing. Some suggestion is proposed to exploit shale gas.