LAGOA FEIA FORMATION (LOWER CRETACEOUS), CAMPOS BASIN, OFFSHORE BRAZIL: RIFT VALLEY STAGELACUSTRINE CARBONATERESERVOIRS - I

The Campos Basin is one of the coastal basins of eastern Brazil formed during the separation of the African and South American continental blocks. The Lagoa Feia Formation consists of the sediments deposited during the rift valley stage of the Campos Basin, and varies from 200 m to more than I, 500m in thickness. 17 microfacies were recognized, and are grouped into four main sequences, dominated respectively by terrigenous supplies, ostracods, pelecypods and basic volcaniclastics.
The vertical sequence of microfacies and the associations of syndepositional diagenetic minerals were used to reconstruct the general environment of deposition. It consisted of saline alkaline lakes, oscillating between a playa lake stage with ostracod microfacies and a pluvial lake stage with pelecypod microfacies.
Five diagenetic stages were recognized: syndepositional alteration of lithics to trioctahedral smectites, early dolomitization, early silicification, early cementation by bladed rim calcite and zeolites; fresh water vadose, consisting mainly of dissolution of bioclasts and lithics; fresh water phreatic, with sparite cementation and neomorphism; mixed saline-fresh water, represented mainly by silicification; and burial with compaction, late dolomitization and partial conversion of smectites to illite.
Pelecypod-rich limestones with primary interparticle, secondary intraparticle, moldic and moldic-enlarged porosities constitute the main potential reservoirs. The ideal conditions for the generation and preservation of such reservoirs consisted of periods of exposure followed by rapid lake expansion and burial. In this manner, the secondary porosity formed in the vadose fresh water environment was preserved or only partially occluded by calcite cementation during fresh water phreatic conditions.     

克拉玛依油田五2 西区油藏气水交替驱方案设计

针对克拉玛依油田五₂西区克下组油藏设计了23 个气驱方案并预测了各方案的开采动态指标,通过数值模拟对注气年限、日注气速度和气水交替周期等注入参数进行了敏感性分析论证。研究结果表明,五₂ 西区克下组油藏在气水交替驱开发方式下,气水交替周期的长短不是开发动态影响的敏感因素;气水交替年限和日注气速度对注气增产油量和气换油率影响较大。与注水开采相比,注气开采能够较大幅度提高原油采收率,是改善高含水油藏开采效果的有利手段。     

STRONTIUM ISOTOPE STRATIGRAPHY OF THE ASMARI FORMATION (OLIGOCENE - LOWER MIOCENE), SW IRAN

The Asmari Formation has been studied in the subsurface at the Bibi Hakimeh, Marun and Ahwaz oilfields and in an outcrop section from the Khaviz anticline. It consists of approximately 400 m of cyclic platform limestones and dolostones with subordinate intervals of sandstone and shale. The method of Sr‐isotope stratigraphy is well suited for dating these strata because of the rapid rate of change of marine ⁸⁷Sr/⁸⁶Sr during Asmari deposition (roughly 32‐18 Ma) and the common presence of well‐preserved macrofossils. Profiles of age against depth in the four areas show a decrease from higher stratigraphic accumulation rates in the lower Asmari to lower rates in the middle to upper part of the formation. There is also a trend towards less open‐marine depositional conditions and increasing early dolomitization and anhydrite abundance above the lower part of the formation. These changes reflect the dynamics of platform progradation across the areas studied, from early deposition along relatively high accommodation margin to slope settings to later conditions of lower accommodation on the shelf top. Ages of sequence boundaries are estimated from the age‐depth profiles at each locality, providing a framework for stratigraphic correlation. Asmari deposition began in early Rupelian time (34‐33 Ma) in the Bibi Hakimeh area, when the studied areas to the NW were accumulating basinal marl facies. Progradation of the platform across the Marun and Ahwaz areas took place in mid‐Chattian time (27‐26 Ma) and somewhat later (26‐25 Ma) in the more basinward Khaviz area. Depositional sequences have durations of 1‐3 Ma, whereas component cycles represent average time intervals of 100‐300 Ky. Sr analyses of most dolomite, anhydrite and celestite samples plot close to or below the macrofossil age‐depth trend for each locality, indicating formation from waters preserving seawater ⁸⁷Sr/⁸⁶Sr approximately contemporaneous with or slightly younger than the time of sediment deposition. Local deviations from this trend are interpreted as indicating episodes of seepage‐reflux and also a contribution of Sr from non‐marine sources during formation of the Gachsaran cap rock anhydrite.     

油田注入水中Cl~-、SO_4~(2-)和Ca~(2 )、Mg~(2 )的快速现场测定—离子色谱法

将ZIC-ⅡA型离子色谱仪改装为双输液泵、双流路、双检测系统以后,可以同时用稀释100倍的油田注入水、双柱离子色谱(带电渗析抑制器)法测定Cl~-、SO_4~(2-),用稀释20倍的水样、单柱离子色谱法测定Ca~(2 )、Mg~(2 )。方法简便快速、准确可靠,已用于中原开采油田现场分析。