浅水型三角洲前缘钙质夹层的地质意义

1.长安大学 地球科学与资源学院,陕西 西安 710064; 2.陕西师范大学 旅游与环境学院,陕西 西安 710062

浅水型三角洲前缘; 钙质夹层; 水下分流泗道

Geological significance of reservoirswith calcareous intercalation in the shallow-water delta front
WANG Tao1,FU Chao-feng1,2

(1.College of Earth Sciences and Resources,Chang'an University,Xi' an 710064,China; 2.College of Tourism and Environment Science,Shaanxi Normal University,Xi' an 710062,China)

the shallow-water delta front; calcareous intercalation; underwater distributary channel

DOI: 10.13800/j.cnki.xakjdxxb.2017.0213

备注

浅水型三角洲前缘利于油气成藏,储层砂体中的钙质夹层对油气分布、储藏和运移有一定的影响。通过岩心观察、滴水滴酸、测井识别等技术,对王家川油田佛古源区长6储层的钙质夹层进行研究,进而确定钙质夹层对油藏的形成及开发的影响。研究认为:钙质夹层形成于水体不流畅的浅水蒸发环境的叠加砂岩中,后期洪水期,原废弃分流河道再次复活期; 钙质夹层非常致密,孔隙度、渗透率极低,是稳定的渗流屏障; 在测井曲线上,具有“三高三低”的典型识别特征,即高电阻、高密度与高微电极和低自然电位、低自然伽马与低声波时差; 在垂向上,钙质夹层常发育在三角洲前缘水下分流河道底部的小型的侵蚀—冲刷面处,还多见三角洲前缘河口坝顶部。水下分流河道砂体垂向上呈下部粒度粗,而上部粒度细的正韵律,初期泥质含量较低,砂岩粒度较粗,进而原生孔隙比较发育,孔隙水容易流动,容易形成钙质夹层,砂岩顶部和底部的钙质夹层厚度为0.5~1 m,砂岩内部的钙质夹层厚度较薄,为0.3~0.7 m,泥岩中的钙质夹层厚度多大于1 m; 在平面上,钙质夹层在水下分流河道的边部厚度一般大于河道内部。

The shallow-water delta front is favorable for oil and gas accumulation,and the calcareous intercalation in the reservoir sandbody has certain influence on the distribution,storage and migration of oil and gas.Through the observation of core,dripping acid and logging identification,the calcareous intercalation of Chang 6 reservoir in Foguyuan area of Wangjiachuan oil field was studied to determine the influence of calcareous intercalation on the formation and development of reservoir.It is concluded that the calcareous intercalation is formed in the superimposed sandstone where the water is not smooth in the shallow water evaporation environment.In the later flood period,the original waste diversion channel is resurrected again.The calcareous intercalation is very dense with low porosity and low permeability which is a stable seepage barrier; Logging curve has the typical features of “three high and three low”,which is high resistivity,high density,high microelectrode,and low natural potential,low natural gamma,low acousticwave.In the vertical direction,the calcareous intercalations often develop in the small erosional-erosion facies at the bottom of the underwater distributary channel of the delta front,but also at the top of the delta front dyke.Underwater distributary channel sandbody is vertical rhythm,the lower granularity is coarse,and the upper granularity is fine.In the initial stage,the clay content is low,the sandstone grain size is coarse,and the primary pores are more developed,the pore water is easy to flow and the calcareous intercalation is prone to the calcareous intercalation thickness of sandstone top and bottom is 0.5~1 m,sandstone internal calcareous intercalation thickness is thin with 0.3~0.7 m,the thickness is calcareous intercalation in mudstone is more than 1 m; On the plane,the thickness of the calcareous intercalation in the edge of underwater distributary channel is larger than that in the river.