鄂尔多斯盆地西峰和姬塬油田长8_1段低渗透储层迥异性

Diversity of the Triassic Chang 8_1 Low Permeability Reservoirs in Jiyuan and Xifeng Area,Ordos Basin

利用岩芯、薄片、测井等资料,从储层特征及孔隙演化角度对比分析了西峰和姬塬油田长8_1低渗透储层的迥异性。分析结果表明,两地区长8_1储层的共性为:1)储层砂体为浅水三角洲前缘的多期叠加的水下分流河道厚层砂体,且在空间上具有良好的连续性;2)砂体为岩屑长石砂岩和长石岩屑砂岩,属于细砂岩和极细砂岩,分选以较好为主;3)储层孔隙类型以粒间孔和溶蚀孔为主,原始孔隙度约38%,压实作用、胶结作用孔隙损失率约35%,最终储层孔隙度约7%。两地区长8_1储层存在以下差异:1)姬塬地区长8_1水下分流河道砂体叠加期次不明显,为"连续退积式"沉积模式,而西峰地区具有明显的垂向加积特征,为"顶牛"沉积模式;2)粒间孔、岩屑溶孔、晶间孔姬塬地区低于西峰地区,而溶蚀孔姬塬地区高于西峰地区;3)储层后期成岩演化过程中,姬塬和西峰地区长8_1砂体平均胶结孔隙度损失率为13.87%和11.99%,姬塬地区胶结孔隙度损失程度高于西峰地区,而溶蚀增孔率分别为3.71%和2.79%,姬塬地区溶蚀增孔率高于西峰地区。

Using the data of drilling cores,thin sections and well loggings,focused on the reservoir characteristics and pore evolution,this paper gives a comparative analysis about the diversity of the Triassic Chang 81 low permeability reservoirs in Jiyuan and Xifeng area. On the one hand,the commonalities of Chang 81 reservoirs in both areas are：1） Reservoir sand bodies are underwater distributary channel sands of shallow water delta front,which are thick sand bodies of multiphase superposition with great continuity on the space. 2） The sandstones are lithic arkose and feldspathic litharenite and belong to fine sandstones and very fine sandstones with good sorting in both areas. 3） Reservoir porosity is mainly composed of primary pores and dissolution pores. The original porosity is around 38% in the study area. The loss of primary pores accounts for about 35% because of compaction and cementation. The final reservoir porosity is 7%. On the other hand,the differences of Chang 81 reservoirs in both areas are： 1） The underwater distributary channel sands of Chang 81 in Jiyuan area hold the unobvious superposition and belong to ＂continuous retrogradation＂depositional model. In contrast,the sands in Xifeng area have the obvious vertical accretion and belong to ＂seesaw＂depositional model. 2） The intergranular pores,lithic dissolved pores and intracrystalline pores in Jiyuan area are inferior to Xifeng area. However,the dissolved pores in Jiyuan area are superior to Xifeng area. 3） In the late diagenetic evolution stages of reservoirs,the average cementation porosity loss ratio of Chang 81 sands accounts for about 13.87% and 11.99% in Jiyuan and Xifeng area,respectively. The degree of cementation pores loss in Jiyuan area is higher than Xifeng area. In addition,the dissolution pores increase ratio accounts for about 3. 71% and 2. 79% in Jiyuan and Xifeng area,respectively. The Jiyuan area is superior to Xifeng area.