珠江口盆地陆丰南文五段低矿化度水化学特征及成因分析  

Geochemical characteristics and genesis of the low-salinity water layer in the fifth member of Wenchang formation in the southern Lufeng sag,Pearl River Mouth basin

作　　者：阙晓铭 雷永昌 汪旭东 贾连凯 宋伟 QUE Xiaoming;LEI Yongchang;WANG Xudong;JIA Liankai;SONG Wei(CNOOC China Limited,Shenzhen Branch,Shenzhen 518054,Guangdong,China)

机构地区：[1]中海石油(中国)有限公司深圳分公司,广东深圳518054

出　　处：《中国海上油气》2023年第2期23-32,共10页China Offshore Oil and Gas

基　　金：十四五重大科技项目“中国近海新区新领域勘探技术”子课题“近海重点潜在富烃洼陷评价技术(编号:KJGG-2022-0301)”部分研究成果。

摘　　要：珠江口盆地陆丰南地区文五段水层在测录井响应特征上与油层十分接近,增加了流体识别难度。为明确文五段地层水化学特征及流体成因,对LA-1dSa地层水地球化学特征和文五段水体环境进行分析。结果表明:①文五段地层水矿化度为5038~6944 mg/L,钠氯系数较低、脱硫系数小、变质系数和钙镁系数极高,源于陆相原始沉积水,表现出轻微富Ca^(2+)、贫Mg^(2+)、略微贫Na^(+)的特点,属于氯化钙IV型水,指示地层封闭性好,处于交替停滞带,有利于油气的聚集与保存。②低矿化度特征与本区裂陷湖盆演化密切相关:裂陷期陆相湖盆决定原始地层水为淡水;裂陷高峰期文四段区域性厚层泥岩的发育控制文五段地层形成相对封闭的水体环境,阻碍了深浅地层水的交替作用,影响水体向矿化度增大的演化进程;埋藏期文四段泥岩压实排水和黏土矿物脱水作用进一步淡化文五段地层水。受淡化程度、成岩作用及后期水体交互作用差异性影响,形成文五段现今地层水矿化度分布特征。The water layer in the fifth member of Wenchang formation in the southern Lufeng sag,Pearl River Mouth basin has similar logging response characteristics with oil layer,which brings difficulty in fluid property identification.In order to clarify the geochemical characteristics and genesis of the formation water in the fifth member of Wenchang formation,the geochemical characteristics of the formation water in well LA-1dSa and the water environment of the fifth member of Wenchang formation are analyzed in this paper.The results show that:①The formation water in the fifth member of Wenchang formation has a salinity of 5038~6944 mg/L,and has low sodium-chloride ratio and desulfurization coefficient value,high metamorphism coefficient and calcium-magnesium radio value.The formation water originally came from continental original sedimentary water,characterized by slightly rich Ca^(2+),poor Mg^(2+)and slightly poor Na^(+),belonging to calcium chloride IV-type water.All of these features indicate that the fifth member of Wenchang formation has effective sealing capability and is deposited in an alternative stagnation zone,which is conducive as well to oil and gas accumulation and preservation.②The formation of the low-salinity water is closely related to the rifting period evolution of the lake basin in this area:The lacustrine basin initial water environment is freshwater in the rifting stage;The regional thick mudstone in the fourth member of Wenchang formation controls the formation of relatively closed water environment in the fifth member of Wenchang formation during the peak rifting stage,which greatly hinders the alternation of deep and shallow formation water and effectively slows down the evolution process of water salinization;The mudstone compaction-released water and dehydrating of clay minerals in the fourth member of Wenchang formation in the burial stage further desalinates the formation water in the fifth member of Wenchang formation.Nowadays the water salinity distribution characteristics of the fi

关 键 词：珠江口盆地 陆丰南地区 文五段 地层水 低矿化度 地球化学特征 

分 类 号：TE133.2[石油与天然气工程—油气勘探]