鄂尔多斯盆地北部致密砂岩储层特征及测井识别

鄂尔多斯盆地北部十里加汗地区上古生界广泛发育致密砂岩气藏,不同类型砂岩储层天然气富集程度不同,有效识别不同类型砂岩储层对于进一步研究气层的富集规律至关重要。利用岩心观察及薄片鉴定、扫描电镜、压汞等实验资料综合分析,主要含气层位下石盒子组盒1段、山西组山2段储层以岩屑砂岩为主,山西组山段储层主要为石英砂岩,石英砂岩储层孔隙度和渗透率数值均大于岩屑砂岩储层。通过不同类型砂岩储层测井响应评价,补偿中子(CNL)、光电吸收截面指数(Pe)、自然伽马(GR)、声波时差(AC)4条测井曲线特征差异明显,岩屑砂岩储层总体具有相对高CNL值、高Pe值、高GR值、高AC“四高”特征,石英砂岩储层总体具有相对低CNL值、低Pe值、低GR值、低AC“四低”特征。交汇图分析表明,岩屑砂岩储层CNL值、Pe值分别大于11%、2.10b/e,石英砂岩储层CNL值、Pe值分别小于12%、2.30b/e,结合GR值、AC值响应特征,能够有效识别岩屑砂岩储层和石英砂岩储层。

Characteristics of tight sandstone reservoirs and logging identificationin the Northern Ordos Basin

Tight sandstone gas reservoirs are widely developed in the Upper Paleozoic in the Shilikahan area in the northern Ordos basin. The natural gas enrichment degree of different types of sandstone reservoirs is different. Effective identification of different types of sandstone reservoirs is essential to further study the enrichment law of gas reservoirs. Based on the comprehensive analysis of core observation, thin section identification, scanning electron microscope, mercury intrusion and other experimental data, the reservoirs of the first Member of Shihezi Formation and the second Member of Shanxi Formation are mainly composed of lithic sandstone, and the first Member of Shanxi Formation is mainly composed of quartz sandstone. The porosity and permeability of quartz sandstone reservoir are greater than those of lithic sandstone reservoir. Through the evaluation of logging response of different types of sandstone reservoirs, the characteristics of the four logging curves of compensated neutron (CNL), photoelectric absorption cross section index (Pe), natural gamma (GR), and interval transit time (AC) are significantly different. The lithic sandstone reservoir is generally characterized by "four high", including relatively high CNL value, high Pe value, high GR value and high AC, the quartz sandstone reservoir is generally characterized by "four low", including relatively low CNL value, low Pe value, low GR value and low AC. The intersection diagram shows that the CNL value and Pe value of lithic sandstone reservoirs are greater than 11% and 2.10b/e respectively, and the CNL value and Pe value of quartz sandstone reservoir are less than 12% and 2.30b/e respectively. Combined with the response characteristics of GR value and AC value, the lithic sandstone reservoirs and quartz sandstone reservoirs can be effectively identified.