摘要
本文以东营凹陷盐家地区盐22块古近系沙四上亚段砂砾岩体为研究对象,综合运用岩心,测井及分析测试等资料,对其储层特征进行了系统研究。
通过对岩心的详细观察描述将研究区沙四段发育的岩石相类型归纳为中粗砾岩、细砾岩、含砾砂岩、砂岩和泥岩五类。在对岩心进行精细归位的前提下,主要根据AC和CNL测井响应特征,建立了岩石相定量识别标准,对研究区沙四上亚段的岩石相类型进行了逐井识别。
研究区沙四段发育近岸水下扇相沉积,其内扇亚相包括主沟道和沟道侧缘微相,中扇亚相包括辫状沟道、沟道前缘和沟道间微相,外扇亚相包括深切水道、末端和外扇泥微相。根据各类沉积相识别标志,对单井沉积微相进行了细致划分。在研究区沙四段砂砾岩沉积期次划分及沉积微相展布特征研究的基础上,认为纵向上,研究区沙四上亚段沉积相自下而上呈内扇-中扇-外扇的正旋回。北部物源区砂砾岩厚度最大,总体上向南、东、西三个方向减薄。平面上,随着水体加深,湖盆面积扩大,扇体发育范围缩减,主沟道和辫状沟道逐渐萎缩。
以岩心观察、薄片鉴定、物性分析和扫描电镜观察等技术手段,对盐22区块砂砾岩储层的成岩作用类型、成岩阶段划分和储集空间类型进行了研究。研究区砂砾岩储层整体处于中成岩A期,储集空间类型以次生孔隙和孔隙-裂缝复合系统为主。认为研究储层物性主要为中孔低渗-特低渗、低孔特低渗和低孔超低渗,纵向上发育多个次生孔隙带。根据储层孔隙结构参数及压汞曲线特征将孔隙结构划分为大-中孔中细喉型、中-小孔细喉型和小孔微细喉型三类。研究区砂砾岩储层物性的主要受控于沉积作用、成岩作用及储层孔隙结构特征。结果表明,在酸性溶解作用下,发育于中扇辫状沟道微相的,具大-中孔中细喉型孔隙结构的颗粒支撑砾岩物性最好。
通过对储层“四性”关系的综合分析,认为研究区沙四段砂砾岩储层的有效物性下限较低(孔隙度5%,渗透率0.1×10-3μm2)。对研究区沙四段砂砾岩储层进行综合评价,将储层划分三类:I类中孔低渗储层、II类低孔特低渗储层和III类低孔特低渗-超低渗储层,储集性能和含油性依次降低。有利储层主要发育在II砂组3-5小层中。
In this paper, reservoir characterisics of sandy conglomerate body in the 4th member of Shahejie formation, Paleogene, Yan 22 block of Yanjia area in Dongying Depression are systematically studied by comprehensive use of core, logging, and analysis of testing data. Rock types of the 4th member of Shahejie formation in this area are divided into five types through detailed observations of cores.Based on the fine core location, quantitative identification standards of rocks are set up according to AC&CNL logging response characteristics, and the rock types developed in every well were identified.
Nearshore subaqueous fan developed in research area, the 4th member of Shahejie formation, which includes inner fan, middle fan and outer fan sub-facies.The inner fan is devided into main channel and main channel edge micro-facies. The middle fan is devided into braided channel, frontchannel and interchannel micro-facies. The outer fan is devided into deep-cutting channel, end sand of channel and outer fan mud. Based on kinds of facies marks, single well microfacies were carefully divided. Stratigraphic division and development of micro-facies features are studied, which shows that in the longitudinal direction,sedimentary facies have a positive rhythm of inner-middle -outer fans form below whit thickness thinning. Thickness of sandy conglomerate body is maximum in northern source area, and it’s thinning in southern, eastern,and western directions.In the plane, area of nearshore subaqueous fan decreased with the increasing of lake area and depth.
The diagenesis types, diagenesis stage and reservoir spaces are studied by means of core observation, thin section analysis, physical property analysis, scanning electron microscopy. Sandy conglomerate reservoir of this area is in middle diagenesis stage A.Solution pore and pore-fracture compound system are the main reservoir spaces. Sandy conglomerate reservoir of this area are mainly medium-porosity low&extra-low- permeability, low-porosity extra-low-permeability and low porosity extra-low& super-low permeability. There are several pore zone in Sandy conglomerate reservoir of Es4 member. Pore structures are divided into 3 types of macro-medium pore with medium-fine throat, medium-small pore with fine throat and small pore with microthroat by using pore structure parameters and mercury injection curve. Reservoir physical property is mainly controlled by sedimentation, diagenesis and pore structure characteristics. The results show that, under the influence of acid dissolution, the physical property of grain-supported conglomerate with macro-middle pore and medium-fine throat developed in braided channel of inner fan is best.
The reservoir lower limit is porosity of 5%, and permeability of 0.1×10-3μm2 according to comprehensive analysis of four properties ' relations. Sandy conglomerate reservoirs of Es4 in Yan 22 area are classified into 3 types: medium-porosity low permeability, low-porosity extra-low-permea- bility and low porosity extra-low& super-low permeability reservoirs, and their reservoir properties and oiliness decrease gradually. Favorable reservoirs mainly distribute in braided channel sediments of middle fan subfacies in 3-5 subzone of sand set II.
引文
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