THE ORIGIN OF DOLOMITE IN THE ASMARI FORMATION (OLIGOCENE-LOWER MIOCENE), DEZFUL EMBAYMENT, SW IRAN

Dolomitisation is an important factor controlling reservoir quality in the Asmari Formation in many producing fields in SW Iran. Dolostones have higher average porosities than limestones. Petrographic and geochemical studies have been used to determine the causes of Asmari dolomitisation at the Bibi Hakimeh and Marun fields and at the Khaviz anticline. The formation is generally characterized by a large‐scale trend of upward‐decreasing accommodation. Basal strata were deposited under relatively open‐marine, high‐energy conditions, whereas the Middle to Upper Asmari succession was deposited in relatively protected settings with more frequent evidence of exposure and evaporitic conditions. There is a general upward increase in the abundance of both anhydrite (occurring as nodules and cement) and dolomite. Two main types of dolomite fabric are recognised, reflecting the textures of the precursor limestones: (1) finely crystalline pervasive dolomite (commonly <20μ) replacing mud‐rich facies; and (2) combinations of finely crystalline replacive dolomite and surrounding areas of coarser dolomite cement (crystals up to 100μ) in grain‐supported facies. Fluid inclusion data indicate that finely crystalline dolomites formed at low temperatures (ca. <50°C), while the coarser dolomite formed at higher temperatures (50–;140°C). Whole rock‐carbonate oxygen and carbon isotope analyses of pure dolostone samples show no apparent correlation with either depositional or diagenetic textures: δ¹⁸O is generally 0 to 2.7‰ PDB, and δ¹³C is ?1 to 4‰ PDB. The importance of evaporated seawater to Asmari dolomitisation is indicated by the ubiquitous occurrence of felty‐textured anhydrite nodules in dolostone beds and the presence of high‐salinity fluid inclusions in dolomite. The derivation of dolomitising fluids from contemporaneous seawater is supported by the general correspondence between age estimates derived from the strontium isotope composition of anhydrites and dolomites and those derived from stratigraphic considerations. This suggested synsedimentary dolomitisation. Dolomitisation of the upper half of the Asmari Formation may have occurred as a result of two syn‐sedimentary mechanisms: (1) by the reflux of evaporative brines concentrated in shallow lagoons or sabkhas, through immediately underlying strata (mainly during highstands); and (2) by the flushing of platform‐top carbonates by basinal evaporated waters during lowstand/early transgression. Continued dolomitisation during deeper burial is supported by the presence of high‐temperature fluid inclusions and iron‐rich crystal rims. Dolomite within the lower part of the Asmari Formation probably mostly formed during burial as a result of compaction of, and fluid exclusion from, the underlying Pabdeh marls and shales.     

白云石制备纳米氧化镁的方法研究

以白云石为原料,采用消化-分散沉淀-超声震荡法处理后,灼烧制得了纳米氧化镁.对前驱体进行热分析(TG-DTG-DTA),确定了合适的煅烧温度为600℃.研究了分散剂种类及用量、沉淀剂种类、溶剂等对纳米氧化镁粒径的影响,并用原子吸收(AAS)、X射线衍射(XRD)、扫描电镜(SEM)等进行了表征.结果表明,该法制备的纳米粒子纯度高、分散性好,晶体粒子分布均匀,纳米颗粒粒径为12.5 nm.     

川北地区灯影组四段优质储层特征及控制因素

为了解决川北地区震旦系灯影组四段储层特征和控制因素认识不清的问题,基于四川盆地北缘露头剖面及岩心观测,通过薄片鉴定、扫描电镜、包裹体、阴极发光、储层物性等研究,分析了灯四段储层岩石学、储集空间、成岩作用及物性等特征,并利用地震资料恢复古地貌,探讨了优质储层发育的控制因素。结果表明：川北地区灯四段储层的岩石类型以颗粒粘连白云岩、藻叠层白云岩及粉-细晶白云岩为主,储集空间以藻黏结格架孔、晶间溶孔及近顺层溶蚀孔洞为主,储层总体具有低孔、低渗特征,但局部地区仍具有发育中孔、中高渗优质储层的条件。受裂陷槽边缘古地貌高地控制发育的台缘丘滩、台内丘滩相带是优质储层发育的物质基础,在中-深埋藏阶段与烃源岩热演化有关的埋藏溶蚀作用是控制灯四段储层大量溶蚀孔洞发育的关键,而表生岩溶作用的影响较弱。优质储层位于绵阳-长宁裂陷槽东缘的元坝西-阆中区块,为台缘丘滩与埋藏溶蚀作用叠加部位,它是川北地区灯四段油气勘探的有利区带。     

四川震旦系灯影组天然气藏储渗体的再认识

通过对四川资阳、威远地区震旦系灯影组11口井岩心分析,结合地面剖面研究后认为,震旦系末的桐湾运动引起的地表和近地表古岩溶所形成的地表风化残积砾屑白云岩、近地表50m左右地层内的岩溶洞、岩溶漏斗、岩溶管、漏滴状小溶洞及溶洞崩塌角砾岩的角砾间几乎全被来自风化面下渗的沉积物、渗流粉砂及胶结物充填满,现存的22种孔、洞、缝中最主要的储集空间有:①重结晶白云岩的晶间孔、洞;②沿40°左右裂缝扩溶的成排、成串溶洞,经白云石半充填后的残余洞;③沿构造裂缝溶解,经多种形式,若于世代白云石成花边状胶结后的残余孔、洞;④70°～80°方向的张裂隙。它们发生的初始时期可能分别为海西期、印支期、晚加里东期和喜山期。     

鄂尔多斯盆地苏里格地区奥陶系马家沟组白云石化

苏里格地区马家沟组为一套碳酸盐岩为主,夹蒸发岩的地层,沉积于超盐度的局限陆表海环境。白云石分为以泥晶结构为主的,以细—中晶结构为主和充填于孔、缝中3类。白云石Na含量(0~2099)×10^-6,Sr含量(0~70)×10^-6,Mn含量(0~112)×10^-6,Fe含量(39~86746)×10^-6,以变化较大的Na含量、低的Sr和Mn含量、高的Fe含量为特征。白云石δ¹⁸O值在-16.00‰~-5.73‰之间,δ¹³C值在-11.46‰~1.90‰之间,说明碳酸盐岩经历了淋滤作用和埋藏作用。大多数孔、缝充填白云石较围岩组分有较低的δ¹⁸O和δ¹³C值,说明孔缝充填的白云石形成较晚。白云石以低的有序度,非理想配比的CaCO₃和MgCO₃含量为特征。白云石的⁸⁷Sr/⁸⁶Sr值为0.707977±0.000070至0.711791±0.000064,绝大部分高于全球中、上奥陶统分界线对应的⁸⁷Sr/⁸⁶Sr值。微生物白云石化是形成白云石的机理。     

The relationship between dolomite textures and their formation temperature: a case study from the Permian-Triassic of the Sichuan Basin and the Lower Paleozoic of the Tarim Basin

Study of dolomite texture can contribute to understanding the process of dolomitization. This research reports textures and homogenization temperatures of dolomites from the Permian–Triassic strata in the Sichuan Basin and the Lower Paleozoic strata in the Tarim Basin, which provided insights into relationships between dolomite textures and their formation temperatures. Our results are summarized as follows: 1) dolomites with well-preserved texture indicate low dolomitization temperature. However, in certain diagenetic environments, the hydrothermal dolomitization may completely or partially preserve the original texture of dolomites. 2) The formation temperatures of non-planar dolomites are always higher than those of planar dolomites. 3) The formation temperatures of dolomite cements are generally higher than those of replacive dolomites. 4) Although the formation temperatures of saddle dolomite cements have a wide range, they show higher values than those of the planar subhedral to euhedral dolomite cements. Thus, saddle dolomites could generally be an indicator of high precipitation temperature. 5) The fluid Mg/Ca ratio is another element controlling dolomite morphology. Micritic dolomites, which precipitate from hypersaline fluids with a high Mg/Ca ratio in a subaerial environment could also have features of non-planar anhedral crystal shape because of rapid nucleation and crystallization during dolomitization.     

不同含水率下白云岩损伤本构关系研究

通过对干燥和不同浸水状态下白云岩进行常规单轴压缩试验,得到了岩石应力—应变曲线和抗压强度、弹性模量、泊松比等参数随浸水时间及含水率的变化规律;通过定义浸水时间为损伤变量,分析了该变量随抗压强度和弹性模量的变化情况,将变化规律代入本构关系中,获得了以浸水时间为变量的本构关系。研究表明:1)将由本构关系绘出的应力—应变曲线与实际曲线对比,结果表明大多数与实际情况吻合较好,模型能够充分反映不同浸水时间下的白云岩损伤过程,此种情况下,Weibull分布参数m决定了本构模型理论曲线的形状;2)建立了考虑峰值强度随着浸水时间变化的岩石损伤统计本构模型,由模型应力—应变曲线可知,εc取值为定值时,Weibull分布参数m值随着浸水时间的增加出现先减小后变大的趋势,浸水条件下的参数m值始终小于干燥条件下的,此种情况下m不能决定本构模型理论曲线的形状。     

BURIAL HISTORY RECONSTRUCTION USING LATE DIAGENETIC PRODUCTS IN THE EARLY PERMIAN SILICICLASTICS OF THE FARAGHAN FORMATION, SOUTHERN ZAGROS, IRAN

In spite of the increasing importance to hydrocarbon exploration and production of the Palaeozoic succession in the Zagros area of SW Iran, few burial history and palaeothermal modelling studies of the interval have been carried out. This paper attempts to assess the burial and palaeotemperature history of the Lower Permian Faraghan Formation which is composed of stromatolitic dolomites overlain by mainly cross‐bedded sandstones. The formation grades up into the thick bedded carbonates of the Upper Permian Dalan Formation. The Faraghan and Dalan Formations are major hydrocarbon reservoir units in SW Iran and are time‐equivalents of the Unayzah and Khuff Formations in Saudi Arabia, respectively. The Faraghan Formation consists of shallow‐marine siliciclastics and foreshore deposits, including tidal‐flat and tidal‐channel, estuarine, sabkha, shoreface and offshore facies. In this study, diagenetic constituents are used to evaluate the formation's burial history in the Southern Zagros, an area for which only limited subsurface data is available. A burial history diagram for the formation was constructed for well Finu # 1 using WinBury^TM software. The diagram shows that the formation underwent progressive burial at variable rates between its deposition and the mid‐Tertiary, since when it has undergone rapid uplift. Burial diagenetic products in the Faraghan Formation comprise saddle, ferroan and zoned dolomites, together with dickite, illite/sericite and chlorite minerals. Additional burial‐related features include stylolites and dissolution seams. Isotopic signatures (δ¹⁸O versus δ¹³C) of the ferroan dolomites suggest a burial trend for the formation. Reconstruction of the paragenetic sequence together with the burial history diagram suggests a maximum burial depth of about 5000 m and a wide palaeotemperature range of 80‐160°C. However considering the saddle dolomites as a palaeothermometer, the temperature range narrows to 78 to 138 °C. The burial depth and temperature ranges closely correlate with the main stage of oil generation to the dry gas zone.     

渤中13-1油田薄层生屑云岩分布特征及成因分析

渤中13-1油田古近系沙河街组沙一段顶部发育一套薄层生屑云岩油气藏.由于该储层具有厚度薄、埋藏深、横向变化快、预测难度大等特点,给油田钻探部署带来了极大的困难.运用类比分析及相控储层预测技术,对薄层生屑云岩的分布特征和成因进行了系统分析,并预测生屑云岩储层有利区带,优化钻前井位部署.经钻探证实均获良好效果,钻探成功率达...