大牛地气田盒一段低孔渗砂岩储层特征

Reservoir characteristics of low porosity and permeability sandstone of Member Ⅰ of Xiashihezi Formation in Daniudi gas field,Ordos Basin

鄂尔多斯盆地伊陕斜坡东北部大牛地气田下二叠统下石盒子组盒一段辫状河道砂岩储层以岩屑砂岩和岩屑石英砂岩为主,成分成熟度中等偏低,结构成熟度中等偏高,储层非均质性较强,砂岩孔隙度和渗透率主要分布区间分别在4%～14%和0.05×10-3～2×10-3μm2,属低孔低渗至致密砂岩储层。研究区砂岩储层成岩阶段达到晚成岩阶段A2亚期至晚成岩阶段B期,机械压实以及石英加大和方解石胶结是降低孔隙度的主要成岩作用,砂岩孔隙类型以粒间溶蚀孔隙为主,影响储层物性的主要因素有沉积作用和成岩作用。根据沉积微相、储层宏观和微观特征等多种参数,运用灰色关联分析法开展了储层综合评价,将盒一段砂岩储层划分为3类,其中Ⅰ类为相对高孔高渗天然气储层,Ⅱ类为相对中等孔渗储层,并预测了3类储层的分布区带,建立了盒一段砂岩储层评价标准体系。

Daniudi gas field is located in the northeastern part of Yishan slope in Ordos Basin. One of the major reservoirs is the braided channel sandstone in Member Ⅰ of the Lower Permian Xiashihezi Formation. The sand- stones consists mainly of lithic sandstones and lithic quartz sandstones with medium compositional and structural maturity. The sandstone reservoir is of strong heterogeneity. The porosity and permeability of the reservoirs are 4 -14% and （0. 05 -2）×10^-3 μm^2 respectively, which repsent the typical characteristics of low porosity and permeability reservoirs or even tight reservoirs. The reservoir is at A2 - B substage of the late diagenetic stage. Mechanical compaction, quartz overgrowth and calcite cementation are the main diagenesis for decreasing porosi- ty of sandstone. Intergranular dissolution pore is the major pore type. Sedimentary microfacies ,lithology and alia- genesis are the main factors influencing reservoir properties. Using grey relational analysis （GRA）method, this paper divides the reservoirs in Member Ⅰ of Xiashihezi Formation into three types based on multiple parameters such as sedimentary microfacies, reservoir macro-and micro-charac teristics. Type Ⅰ reservoirs have relatively high porosity and permeability, while type Ⅱ has relatively moderate porosity and permeability. The distributions of three different types of reservoirs are predicted and the evaluation criteria of the reservoirs in Member Ⅰ of Xiashihezi Formation are also established.