准噶尔盆地二叠系上乌尔禾组退覆式扇(辫状河)三角洲前缘-滩坝复合砂砾岩沉积特征及控制因素^*

Sedimentary characteristics,controlling factors and genesis of retrogradational fan(braided)delta front-beach bar composite gravel body in the Permian Upper Urho Formation in Junggar Basin

摘要

近年来准噶尔盆地的油气勘探从源外常规圈闭逐渐走向源内岩性圈闭,二叠系上乌尔禾组是该盆地增储上产的主力层系,沉积体系展布对上乌尔禾组岩性油气藏分布具有控制作用。利用岩心数据、薄片资料等,并结合地震数据和钻测井资料,对准噶尔盆地二叠系上乌尔禾组的沉积相类型及沉积体系分布特征进行了识别和刻画,总结了大型退覆式扇(辫状河)三角洲-滩坝复合砂砾岩体的沉积模式,并分析了其控制因素。研究表明: (1)研究区发育扇三角洲、辫状河三角洲、滨浅湖滩坝等沉积相类型,扇三角洲平原亚相和扇三角洲前缘亚相主要发育在盆地西部,辫状河三角洲平原亚相和辫状河三角洲前缘亚相主要发育在盆地东部和北部,滩坝相叠置在扇三角洲和辫状河三角洲前缘之上或在其前端独立分布; (2)准噶尔盆地上乌尔禾组各段沉积体系是在整体湖侵的背景下发育的,乌一段沉积时期湖盆面积较小,沉积的砂体较厚,延伸距离近,靠近凹陷的中央; 乌二段沉积时期物源持续供应,湖盆水体加深,湖盆面积增加,沉积砂体厚度薄,分布广; 乌三段沉积时期湖侵作用增强,湖盆面积进一步扩大,湖盆内广泛发育湖泛泥岩; (3)扇三角洲与辫状河三角洲前缘在湖平面不断变化与湖浪的改造下,形成了扇(辫状河)三角洲前缘-滩坝复合砂砾岩体; (4)准噶尔盆地上乌尔禾组沉积时期,沉积体系的主要控制因素为气候、物源供给、湖平面变化和沉积时的古地形坡度和古地貌。该研究为上乌尔禾组油气勘探提供了地质依据。

Abstract

In recent years,oil and gas exploration in the Junggar Basin has gradually shifted from conventional traps outside the source to lithological traps within the source. The Upper Urho Formation is currently the main exploration target for boosting reserves and production in the basin. The distribution of sedimentary system has a controlling effect on the distribution of lithological reservoirs in the Upper Urho Formation. Using drilling cores,thin sections,combined with seismic data and drill cuttings and wireline logs,this study identified and characterized the sedimentary facies and depositional systems of the Upper Urho Formation in the Junggar Basin,and summarized the large-scale transgression. The sedimentary model of fan(braided river)delta-beach bar composite sandy conglomerate body was analyzed,and its controlling factors were analyzed. The results show that: (1)The study area is characterized by various sedimentary facies,including fan delta,braided river delta,and shallow lake beach bar. Among them,fan-delta plain and fan-delta front are mainly developed in the west of the basin,while braided river-delta plain and braided river delta front mainly developed in the east and north of the basin,and beach-bar is mainly superimposed on fan-delta and braided river-delta fronts or occurs independently at their front ends. (2)The depositional system of each member of the Upper Urho Formation developed under the background of overall lacustrine transgression. During the first member of Urho Formation,the basin was relatively small,and the deposited sand bodies were thick and of limited lateral extent,located in proximity to the depression center;during the second member of Upper Urho Formation,with continuous sediment supply and increased water depth the area of the lacustrine basin increased,with thinner but more extensive sand bodies deposited;during the third member of Upper Urho Formation,lacustrine transgression was enhanced,basin area was thus further expanded,and lacustrine mudstone was widely developed in the basinal area. (3)The fan(braided river)delta front-beach-bar composite gravel body was formed under continuous change of lake level and transformation of lake waves in the fan delta state and braided river delta front. (4)During the depositional period of the Upper Urho Formation in the Junggar Basin,the main controlling factors of the depositional system were climate,source supply,lake-level changes,and palaeotopographic slope and palaeogeomorphology at the time of deposition. This study provides a geological basis for oil and gas exploration in the Upper Urho Formation.

关键词

准噶尔盆地 / 上乌尔禾组 / 扇三角洲 / 辫状河三角洲 / 滩坝 / 复合砂砾岩体 / 沉积模式

Key words

Jungger Basin / Upper Urho Formation / fan delta / braided river delta / beach bar / composite gravel body / sedimentary model

基金资助

*国家自然科学基金面上项目(编号: 42072115)、新疆油田公司科技外协项目“盆地二—三叠系古地貌控砂、控圈与控藏作用机理研究与模式建立”联合资助