鄂尔多斯盆地东缘上古生界致密砂岩有效气源岩下限与储层分级评价

Lower limits of effective gas source rock and reservoir grading evaluation of tight sandstone in the Upper Paleozoic in the northeastern margin of the Ordos Basin

基于物质平衡法对鄂尔多斯盆地东缘临兴—神府气田上古生界源岩的排气强度进行定量评价,通过建立源岩排气强度与TOC含量的关系,确定出临兴地区本溪组、太原组、山西组有效源岩TOC下限分别为2.2%、3.3%、6.3%;神府地区本溪组和太原组有效源岩TOC下限分别为6.3%和9.0%,山西组源岩无法有效排气,属于无效源岩。基于试气产能法与力学平衡法厘定出临兴—神府气田上古生界致密砂岩气储层界限,以此为依据对储层质量进行分级评价。其中,常规储层:孔隙度>15%,渗透率>0.78×10^(-3)μm^(2);一类致密储层:孔隙度为8%~15%,渗透率为(0.3~0.78)×10^(-3)μm^(2);二类致密储层:孔隙度为6%~8%,渗透率为(0.1~0.3)×10^(-3)μm^(2);三类致密储层:孔隙度<6%,渗透率<0.1×10^(-3)μm^(2)。综合气源岩下限、储层分级评价、测井评价与产能分析结果,表明临兴—神府气田上古生界烃源岩品质、储层质量、层间断层输导通道3个要素的区别配置是天然气差异富集的控制因素。源内和近源层系中临近有效源岩的常规/一类致密储层含气饱和度通常较高,易获得产能;远源层系中和层间断层输导通道匹配的常规储层的含气饱和度相对较高,可作为勘探目标,层间断层稀疏发育区域的远源层系勘探潜力有限。

The expulsion gas intensity of Upper Paleozoic source rocks in the Linxing-Shenfu Gas Field at the eastern margin of the Ordos Basin is quantitatively evaluated based on the material balance method.The lower limits of TOC for effective source rocks of the Benxi,Taiyuan,and Shanxi formations in the Linxing region were determined to be 2.2%,3.3%,and 6.3%,respectively;the lower limits of TOC for effective source rocks of the Benxi and Taiyuan formations in the Shenfu area were 6.3%and 9.0%,respectively,and the source rocks of the Shanxi Formation were ineffective source rocks because they can not be effectively expel gas.Based on the test gas capacity method and mechanical balance method,the Upper Paleozoic tight sandstone reservoir quality boundaries of the Linxing-Shenfu Gas Field were determined,and the reservoir grading was evaluated based on this method.Among them,conventional sandstone reservoir:porosity>15%,permeability>0.78×10^(-3)μm^(2);Class I tight sandstone reservoir:porosity 8%-15%,permeability(0.3-0.78)×10^(-3)μm^(2);Class II tight sandstone reservoir:porosity 6%-8%,permeability(0.1-0.3)×10^(-3)μm^(2);Class III tight sandstone reservoir:porosity<6%,permeability<0.1×10^(-3)μm^(2).The comprehensive gas source rock lower limit,reservoir grading evaluation,logging evaluation,and well production capacity analysis show that the differential configuration of the three elements of hydrocarbon source rock quality,reservoir quality,and inter stratigraphic fault migration channels in the Upper Paleozoic of the Linxing-Shenfu Gas Field is the controlling factor of differential gas enrichment.The gas saturation of conventional/class I tight sandstone reservoirs in the insource rock and near-source rock formations near the effective source rocks is usually high and easy to obtain production capacity;the gas saturation of conventional reservoirs in the distant-source rock formations matching the inter stratigraphic fault transport channels is relatively high and can be used as exploration targets,and the exploration potential of distant-source rock formations in areas with sparse development of inter stratigraphic fault migration channels is limited.