地层因素对陆相沉积储层特征的控制(英文)

在相同沉积相和沉积环境中 ,沉积记录中作为地层位置函数的不同尺度的地层学与沉积学性质的变化是有序的并可以预测。诸多沉积学和地层学性质 ,从孔隙度、渗透率到地质体的规模和非均质性对于储集性能和产能都是重要的。地层导致的上述性质的变化与由于原始沉积环境的差异产生的变化同等重要。运用地层观点对沉积物某种或多种性质变化进行分析 ,表明这些变化具有规律性并有向一些界限呈单向变化的趋势。与此对照 ,运用对时间和地层位置并不敏感的“相”对这些性质进行分析会发现数值具明显的非相关离散特征。因此 ,仅根据沉积环境或相组成对储集性能进行评价会造成预测的准确性和精确性变差。由此 ,文中提出了能够提高储层表征准确性和精确性的一种新的分析思路 ,即运用地层观点评价相的诸多性质。上述原理可用陆相地层中的一些实例加以说明。以河道砂岩储层为例 ,在地层剖面上 ,随着可容纳空间与沉积物补给的比值 (A/S)的增大 ,槽状交错层组的厚度和层的厚度向上增大 ,孔隙度、渗透率、保存下来的河道的宽度、连续性和连通程度降低 ,而底形多样性、相的分异性、相的保存程度和非均质性增加。这些性质所表现出来的单向变化趋势多数是由于作为A/S值函数的原始地貌单元的保存程度的变化而产生的。同时 ,地

STRATIGRAPHIC CONTROLS ON RESERVOIR ATTRIBUTES IN CONTINENTAL STRATA

Numerous sedimentologic and stratigraphic attributes of all scales change systematically and predictably as a function of stratigraphic position, even though facies and depositional environment remain constant. Many of these attributes, from porosity and permeability to geometry, volume and heterogeneity, are important for reservoir characterization and production. Stratigraphically induced variations in these attributes are as great as variations induced by differences in the original depositional environments. Analysis of variations in single and multiple attributes from a stratigraphic perspective manifests regular organization and unidirectional tendencies toward limits. By contrast, analysis from a time and stratigraphically insensitive facies perspective shows an apparent incoherent scatter of values. Assessment of reservoir attributes solely on the basis of depositional environment or facies composition produces unnecessarily imprecise and inaccurate predictions. A more accurate and precise procedure of reservoir characterization arises when facies attributes are assessed from a stratigraphic perspective.These principles are illustrated with several examples from continental strata. For channelbelt sandstone reservoirs, as trough cross stratification set thickness and bed thickness increase through a stratigraphic section of increasing accommodation:sediment supply (A/S) ratio, porosity, permeability, preserved channelbelt width, continuity and connectivity decrease, whereas macroform diversity, facies diversity, degree of preservation, and heterogeneity increase. Most of these unidirectional tendencies in multiple attributes arise from variable preservation of original geomorphic elements as a function of the A/S regime. Stratigraphic controls also affect the composition and morphology of the original environment. Alluvial ridge height and crevasse splay thickness increase with increasing A/S conditions, and crevasse splays become sandier and have steeper clinoforms. Construction of an analog ruler based upon A/S regime is recommended for determining the degree of analogy between outcrops described in reservoir characterization studies and producing fields.