伊拉克哈法亚油田白垩系Nahr Umr组碎屑岩沉积特征及沉积环境研究

Sedimentary characteristics and depositional environment of clastic deposits:the Cretaceous Nahr Umr formation,Halfaya oilfield,Iraq

为了满足进一步勘探开发的需求,以测井、地震、岩心等资料为基础,结合普通薄片、X射线衍射(X-ray diffraction,XRD)等手段,详细研究了哈法亚油田Nahr Umr组碎屑岩的岩石学和沉积学特征,明确了其为海陆过渡带潮控三角洲环境的沉积产物。Nahr Umr组碎屑岩以细砂岩、粉砂岩夹泥岩及页岩为主,砂岩的结构和成分成熟度高,表明沉积期研究区气候炎热、湿润,地形平缓,具备潮控三角洲发育的有利条件;碎屑岩内部发育过渡性层理(脉状、波状及透镜状)、羽状交错层理、泥披层等与潮汐作用相关的典型沉积构造,并可划分为3种主要的岩石组合:泥岩-砂岩(脉状、波状和透镜状层理泥岩-砂岩亚类)、砂岩(交错层理正粒序、反粒序砂岩亚类)、泥(页)岩(粉砂质泥岩和水平层理页岩);根据岩石类型组合特征及沉积序列,Nahr Umr组碎屑岩整体为1个“海侵—海退—海侵”的沉积序列,可识别出潮控三角洲平原、前缘和前三角洲(或陆棚)3种亚相类型;根据平面相分布,其存在东、西2个物源,且以西部物源为主,三角洲整体沿NEE向呈“漏斗状”向海方向展开。

In order to meet the requirements of further exploration and development,the petrological and sedimentological characteristics of the clastics of the Nahr Umr formation in the Halfaya oilfield and suggested them as deposits of tide-dominated delta in a transitional environment between terrestrial and marine were studied based on well-logging,seismic and core data,thin-section identification and X-ray diffraction(XRD)analysis.The clastics are characterized by fine sandstones and siltstones interbedded with mudstones and shales,and the high textural and compositional maturities of sandstone indicated that the study area is very flat and with moist and hot climate during depositional stage,which is favorable for the formation of tide-dominated delta.Some typical sedimentary structures related to tide influence,such as transitional beddings(flaser,wavy and lenticular beddings),herringbone cross bedding,mud drapes etc.,occurred in the clastics,and the clastics can be divided into three major rock associations:mudstone-sandstone(flaser-bedded,wavy-bedded and lenticular-bedded mudstone-sandstone),sandstone(normally-graded,cross-bedded sandstone and inversely-graded,cross-bedded sandstones)and mudstone(shale)(silty mudstone and horizontal-bedded shale).The clastic of Nahr Umr formation follows a“transgression-regression-transgression”sequence,and 3 subfacies(tide-dominated delta plain,delta front and prodelta/shelf)are recognized.There are two provenances(the east and west)in the study area,and the west one is the main provenance forming a tide-dominated delta with a“funnel-shaped”mouth to sea(NEE direction).