Formation of the Zengmu and Beikang Basins,and West Baram Line in the southwestern South China Sea margin

The Zengmu and Beikang basins,separated by the West Baram Line(WBL)in the southwestern South China Sea margin,display distinct geological and geophysical features.However,the nature of the basins and the WBL are debated.Here we explore this issue by conducting the stratigraphic and structural interpretation,faults and subsidence analysis,and lithospheric finite extension modelling using seismic data.Results show that the WBL is a trans-extensional fault zone comprising normal faults and flower structures mainly active in the Late Eocene to Early Miocene.The Zengmu Basin,to the southwest of the WBL,shows an overall synformal geometry,thick folded strata in the Late Eocene to Late Miocene(40.4-5.2 Ma),and pretty small normal faults at the basin edge,which imply that the Zengmu Basin is a foreland basin under the Luconia and Borneo collision in the Sarawak since the Eocene.Furthermore,the basin exhibits two stages of subsidence(fast in 40.4-30 Ma and slow in 30-0 Ma);but the amount of observed subsidence and heat flow are both greater than that predicted by crustal thinning.The Beikang Basin,to the NE of the WBL,consists of the syn-rift faulted sub-basins(45-16.4 Ma)and the post-rift less deformed sequences(16.4-0 Ma).The heat flow(~60 mW/m2)is also consistent with that predicted based on crustal thinning,inferring that it is a rifted basin.However,the basin shows three stages of subsidence(fast in 45-30 Ma,uplift in 30-16.4 Ma,and fast in 16.4-0 Ma).In the uplift stage,the strata were partly folded in the Late Oligocene and partly eroded in the Early Miocene,which is probably caused by the flexural bulging in response to the paleo-South China Sea subduction and the subsequent Dangerous Grounds and Borneo collision in the Sabah to the east of the WBL.

Characterization of Baram and Tanjung sands as potential proppants

Baram and Tanjung sands were evaluated for potential use as proppants.Experiment was conducted on Baram and Tanjung sands following ISO and ASTM recommended standards.Results showed that Baram and Tanjung sand mineralogy is predominantly quartz with presence of metal oxides.Shape descriptors of both sands for sphericity and roundness were above 0.7.Baram sand was retained by 20/40 mesh size with mean size of 448.2 mm,bulk density of 1.32 g/cc,acid solubility of 1.5%and crush resistance of 4000 psi.While Tanjung sand was retained by 30/50 mesh size with mean size of 383.2 mm,bulk density of 1.30 g/cc,acid solubility of 1.20%and crush resistance of 8000 psi.This indicates that Baram sand has larger grain size that supports high permeability at low closure stress,making this sand suitable for shallow depth hydraulic fracturing operations,whereas Tanjung sand is more suitable for deeper domains with high closure stress.Experimental results and economic comparison with commercial frac sand and other proppant types support using Baram and Tanjung sands as potential proppants.

巴兰三角洲地区构造特征及其成因机制

处于主动大陆边缘的巴兰三角洲地区,在构造格局上具有南北分带的特征,其北部发育挤压应力作用下的NE—SW向叠瓦状逆冲推覆构造,中部发育拉张应力作用下的NE向生长断层及其控制下的滚动背斜,南部为压扭作用下早期生长断层发生反转而形成的反转构造。针对北部挤压应力区收缩量大于中部拉张应力区伸展量这一现象无法用理想的被动大陆边缘三角洲体模型来解释的情况,现结合区域构造背景、研究区应力特征及构造恢复结果的分析认为,巽他古陆、菲律宾板块、印澳板块及欧亚板块推挤作用产生的区域压应力的远距离效应与三角洲发育过程中重力驱动的综合作用,是产生该现象的主要原因。

曾母拉分盆地的油气成藏规律:廷贾-西巴兰线断裂的控制

南海南部廷贾-西巴兰线断裂是一条规模巨大的北西向走滑断裂,渐新世开始活动,早期具有强烈的右旋走滑特征,晚中新世以来走滑方向变为左旋,更新世至今,走滑方向变为右旋,是曾母盆地与北康盆地、南沙海槽的分界。为了理清廷贾-西巴兰线断裂特征与曾母盆地油气成藏的关系,通过对断裂两侧地震剖面特征、重磁特征、地热流分布特征以及地壳性质和岩石圈厚度的分析,探讨该断裂在曾母盆地形成演化及油气成藏中的控制作用。研究表明:断裂活动为曾母盆地后期的沉积提供了丰富的物源,断裂走滑作用导致曾母盆地具有良好的圈闭,后期的反向走滑使得盆地的沉积中心由南向北迁移;断裂沟通深部热源,有利于油气生成,形成的伴生断层是盆地油气运移的主要通道。

生物扰动对砂岩储集层物性的影响--以马来西亚沙捞越巴拉姆三角洲为例

以马来西亚沙捞越巴拉姆三角洲为研究对象,进行取样岩心和薄片分析,结合EDX(能量色散X射线)、FESEM(场发射扫描电镜)、压汞测孔隙度和点状渗透率测量等方法评估生物扰动对储集层孔隙度和渗透率的影响。岩心取自巴拉姆三角洲W-1井和W-6井,分析结果显示,W-1井样品主要发育双杯迹潜穴(Diplocraterion),为强烈—剧烈生物扰动,可见沉积物充填,沉积物充填活动将宿主沉积物中的细粒物质(黏土和有机物)混入潜穴充填物和潜穴衬里,降低沉积物的均质性和分选性,导致潜穴中局部区域孔隙度和渗透率降低;W-6井样品主要发育蛇形迹潜穴(Ophiomorpha),为强烈—剧烈生物扰动,黏土和泥质被清除出潜穴充填物和宿主沉积物,聚集于潜穴衬里,潜穴生物的沉积物清除活动导致潜穴内部沉积充填物的分选性变好、孔隙度和渗透率升高。生物扰动对储集层孔隙度和渗透率的影响由潜穴及其充填物和潜穴活动的类型决定。

巴兰三角洲地区构造特征及其成藏控制因素

巴兰三角洲地区位于西北婆罗洲活动大陆边缘,其构造格局具有南北分带的特征,即北部挤压应力下叠瓦状逆冲推覆带、中部拉张应力下伸展沉降带、南部压扭作用下挤压反转带。与位于被动大陆边缘三角洲发育的地区不同,其北部三角洲前端收缩量大于中部三角洲末端伸展量的1.8%左右,而这无法用理想的被动大陆边缘三角洲体模型来进行解释。在研究区区域构造背景、应力特征分析的基础上,认为这种现象是区域压应力远距离效应与三角洲发育过程重力驱动综合作用的结果。受构造南北分带的影响,研究区发育的上部、中部和下部油气成藏组合分布于不同构造带内;各构造带不同应力背景形成了各自内部独特的构造圈闭类型,而作为油气运移通道的长期继承性发育的断层则控制了研究区内油气的垂向运移。这些研究结果对巴兰三角洲地区油气地质研究、油气勘探部署及优选有利勘探新领域具有一定的借鉴和指导意义。