量化指标在煤层气开发潜力定量评价中的应用

等温吸附曲线蕴藏了丰富的煤储层信息,对于认识煤层气开发潜力至关重要。为了更好地挖掘等温吸附曲线蕴含的丰富信息,定量评价煤层气开发潜力,首先对不同盆地/地区煤岩等温吸附曲线进行了对比分析,探讨了含气饱和度和临储比比值指标的意义和局限性,在此基础上,提出临储压差、临废压差和有效解吸量3个量化指标,并结合具体实例对其应用效果进行分析和论述。研究表明,含气饱和度和临储比是比值指标,可以用来对比评价不同区块、不同煤层、不同井之间开发潜力的优劣和定性评价煤层气开发潜力;相比而言,临储压差、临废压差和有效解吸量可应用于区块和单井不同层次煤层开发潜力定量评价中,能够更好地反映煤层气开发潜力。实例分析表明,寿阳区块15号煤储层有一定的开发潜力,但因其煤岩吸附时间长(扩散速度低),需在见气后通过较长时间的缓慢排采,实现产气潜力的释放;恩洪EH-C6井需要较长时间的前期排水降压过程,但其开发潜力比较乐观。

Application of quantitative indexes in quantitative evaluation of coalbed methane development potential

The isothermal adsorption curve containing abundant coal reservoir information is vital to recognize coalbed methane development potential. To deeply explore the rich information from isothermal adsorption curve and quantitatively evaluate the coalbed methane development potential, this study first performs a comparative analysis on the isothermal adsorption curves of coals in different basins or regions, and then discusses the significance and limitation of both gas saturation and the ratio of desorption pressure/reservoir pressure. On this basis, three quantitative indexes are proposed, i.e., desorption-formation pressure difference, desorption-abandonment pressure difference and effective desorption quantity, and their application effects were analyzed and discussed using concrete examples. Research shows that the gas saturation and the ratio of desorption pressure/reservoir pressure are relative indexes, which can be used to comparatively evaluate the development potential between different blocks, different coal seams and different wells and qualitatively evaluate CBM development potential. In contrast, the desorption-formation pressure difference, desorption-abandonment pressure difference and effective desorption quantity can be applied to quantitatively evaluate the CBM development potential of CBM blocks and/or single wells, thus better reflecting the CBM development potential. The case analysis shows that coalbed No.15 in Shouyang CBM block has certain development potential, but needs a long period of drainage before and after initial gas production to release the gas development potential due to its long sorption time. Well EH-C6 also has great development potential even if a long-term drainage and relief process is required in advance.