Formation Water Geochemistry and Its Controlling Factors: Case Study on Shiwu Rifted Sub-basin of Songliao Basin, NE China

A common way to trace fluid flow and hydrocarbon accumulation is by studying the geochemistry of formation water. This paper focuses on the spacial distribution of the geochemical features of the formation water in the Shiwu Rifled Basin and its indication of the water-rock interaction processes. The hydrodynamic field controls the spacial distribution of formation water. Due to the penetration of meteoric water, the salinity is below 4,500mg/L at the basin margin and the severely faulted central ridge and increases basin ward to 7,000-10,000mg/L. The vertical change of formation water can be divided into 3 zones, which correspond respectively to the free replacement zone （〈1,250m）, the obstructed replacement zone （1,250m-1,650m） and the lagged zone （〉 1,650m） in hydrodynamics. In the free replacement zone, the formation water is NaHCO3-type with its salinity increased to 10,000mg/L. The formation water in the obstructed replacement zone is Na2SO4-type with its salinity decreased to 5,000mg/L-7,000mg/L because of the dehydration of mud rocks. The formation water in the lagged zone is CaC12-type, but its salinity decreases sharply at a depth of 1,650m and then increases vertically downward to 10,000mg/L. This phenomenon can be best explained by the osmosis effect rather than the dehydration of mud rocks. The relationships between Cl^--HCO3^- and Na^＋＋K^＋-Ca^2＋ show that the initial water-rock interaction is the dissolution of NaCl and calcium-beating carbonate, causing an increase of Na^＋-K^＋-Ca^2＋-Cl^- and salinity. The succeeding water-rock interaction is albitization, which leads to a decrease of Na^＋ and an increase of Ca2＋ simultaneously, and generates CaCl2-type fluid. The above analysis shows that the geochemical evolution of formation water is governed by the water-rock interactions, while its spacial distribution is controlled by the hydrological conditions. The water-rock interaction processes are supported by other geological observations, suggesting that formation water geochemistry is a viable method to trace the fluid-rock interaction processes and has broad applications in practice.

松辽盆地十屋断陷反转构造样式及其油气勘探意义

利用三维高精度地震资料,通过对松辽盆地十屋断陷典型剖面进行精细解释和研究,剖析了四个反转构造带各具特色的反转构造特征及样式。孤家子后五家户反转构造带以“欺压式断层”为特色,小五家子四家子反转构造带中、浅层表现为箱形背斜,深层发育有“欺压式逆断层”,秦家屯反转构造带为发育在早期半地堑之上的“尖棱状”背斜,皮家毛北张家屯反转构造带表现为小型背斜或向斜。这些反转构造发育在深层生烃凹陷附近,生、运、聚、储的配置关系极佳,是重要的油气圈闭。

松南地区十屋断陷构造-岩性复合圈闭样式

根据构造 -岩性复合圈闭所涉及到的构造、岩性两个重要因素的相互关系将复合圈闭样式划分为 4种样式 ,即单斜 -岩性复合式、背斜 -岩性复合式、断块 -岩性复合式和鼻状 -岩性复合式。松南十屋断陷中央构造带实际资料研究 ,发现了几个构造 -岩性复合圈闭 ,即SN85井西构造、SN87井北构造、孤家子北构造。这些构造 -岩性复合圈闭是下步勘探的有利目标。

断陷盆地构造枢纽部位油气富集规律

以十屋断陷为例,根据其构造演化、主要断层特征及油气成藏条件分析,揭示多旋回断陷盆地构造枢纽带与油气富集关系。结果表明:十屋断陷枢纽部位经历了断陷期、断拗过渡期、拗陷期、萎缩隆升期等复杂的构造演化,多期差异构造变形及断裂活动导致了小宽枢纽带南段和北段具有相似性及差异性,后期构造反转发育部位多为早期断层发育部位,且主要集中在主干断层上,构造运动产生位移被断裂和褶皱吸收;不同阶段的隆起部位相叠加,使枢纽部位与构造高点相对位置发生变化,枢纽部位相对位置由原来的古隆起演变为斜坡部位;枢纽部位早期为油气的有利指向区,晚期具有良好的保存条件,同时发育多类型圈闭、有利沉积相组合及生储盖组合,围绕枢纽带可形成复式油气聚集带。

松辽盆地南部十屋断陷层沉积体系类型及特征

十屋断陷为一西断东超的箕状断陷,桑树台断裂是主要的控盆断裂,控制了十屋断陷的形成与演化,控制了断陷沉积层序的岩性特征及时空分布特征,在靠近断裂一侧,沿陡坡快速堆积了冲积扇、水下扇、扇三角洲等粗碎屑沉积物,向断陷中心迅速过渡为半深湖—深湖沉积,并伴有深水浊流沉积。在断陷缓坡带,水体变浅,沉积物减薄,沉积相由半深湖—深湖相逐渐转变为滨浅湖、扇三角洲相及河流相。断陷两侧沉降深度差异较大,形成不对称式充填。此外,断陷北侧的端部存在较大的物源,形成纵向扇三角洲朵体。

十屋断陷构造发育特征及油气分布研究

十屋断陷为西断东超箕状断陷,经历多次构造运动改造,构造运动控制盆地的演化、油气的生成、构造圈闭的形成、原生油气藏的破坏及浅部次生油气藏的形成。沉积环境控制源岩、储层的发育特征、油气区域分布层位及原生油气藏的形成。断裂停止活动处于休眠期时,不是油气垂向运移通道,但是能形成断鼻、断块圈闭聚集油气形成油气藏;断裂只有在嫩末活动时期,才能作为垂向运移通道,并在浅部形成断鼻、断块次生油气藏。

松辽盆地十屋断陷沉积体系空间展布及演化规律研究

通过对岩心、录井、测井及地震资料的综合研究,识别出冲积扇和扇三角洲等8种沉积相类型,并组合为冲积沉积体系、河流—三角洲沉积体系、水下扇—扇三角洲沉积体系和湖泊—深水重力流沉积体系等4种类型。研究表明在箕状单断凹陷的构造背景下,十屋断陷早期以冲积沉积体系为主,从沙河子组沉积期至泉头组沉积期,西部断裂带及北部陡坡带沉积体系由冲积沉积体系演化为水下扇—扇三角洲沉积体系,东南缓坡带的沉积体系由滨—浅湖相沉积体系演化为辫状河三角洲—河流相沉积体系,中部沉积类型多样。