A Petrological, Geochemical, and Geochronological Study of Shuikou Ultrabasic Rock Mass in Wuding County, Yunnan Province, China

Geotectonically, the Shuikou ultrabasic-basic rock mass is located on the western margin of the Yangtze Platform. As revealed by field geological surveys, the Shuikou rock mass intrudes into the quartz sandstones of the Sinian Chengjiang Formation (Zac). It is dominated by pyroxenites and can be roughly divided into four lithofacies zones, namely gabbros at the outermost periphery and fine-, medium-, and coarse-grained pyroxenites from margin to center. With the transition from pyroxenites to gabbros, the Shuikou rock mass features gradual enrichment in silica and alkali overall, an increase in ΣREE and (La/Yb)N ratio, and a decrease in δEu values and Eu/Sm ratio, indicating that the Shuikou rock mass was formed from the continuous differentiation and crystallization of consanguineous magma and that low-degree partial melting occurred meanwhile. According to the U-Pb baddeleyite geochronology, the crystallization age of the Shuikou rock mass is 210.7 ± 3 Ma (MSWD = 1.01). Based on this, as well as the analysis of geochemical characteristics, the Shuikou rock mass occurred in a continental intraplate tensional environment, this is closely related to the activities of the Emeishan mantle plume during the same period.

Study on Reservoir Geological Characteristics and Potential Damage Mechanism of FIOC Oilfield in Sargiz

With the in-depth development of the Sargiz oilfield in Kazakhstan, oil layer protection plays an extremely important role in the development process. The petrological characteristics and pore types of the reservoir were analyzed by X-ray diffraction and electron microscopy. The average face ratio of the reservoir was 19.30%. The main pore type was intergranular pore and the face rate was 17.52%. The total amount of clay minerals in the reservoir core is 7% - 10%, and the clay minerals are mainly illite, Yimeng, kaolinite and chlorite;the shale content of the main oil-bearing layer is about 3% - 10%. Refer to relevant industry standards for speed, water, stress, acid, and alkali sensitivity experiments to study the potential damage mechanism of the reservoir. According to the above experiments, the oilfield reservoirs have no speed-sensitive damage and are weakly water-sensitive reservoirs;the reservoirs are highly stress-sensitive and easy to produce sand when the stress changes;they have moderately weak acid sensitivity and weak-medium weak alkaline.

Sedimentary Petrology Characteristics and Their Implications for Provenance of Flowerpot Basin Jurassic System in Yanqing County, Beijing

The characteristics of sedimentary petrology are significant in determining geological provenance. By using field outcrop observation and indoor identification of thin sections, the characteristics of Jurassic system Tuchengzi Formation clastic rocks exposed in the Beijing Yanqing “flowerpot” basin, which include rock types, clastic composition and cement type, etc. have been analyzed systematically to identify the provenance direction and tectonic setting and nature of the provenance. Research shows that the sedimentary rocks in this area belong to analluvial fan and braided river sedimentary rock system and include mainly conglomerates, lithic sandstone, and feldspathic lithic sandstone. The main compositions of the conglomerate are dolomite and limestone. Nearly 50% to 70% of the sandstones are mainly polycrystalline quartz;10% to 15% are feldspar;and 40% to 55% are composed of debris from mainly magmatic and metamorphic rocks. A Dickinson triangular diagram indicates that the provenance type in this area is recycled orogny evolving from clastic recycled orogeny such as a collisional orogenic belt to a transitional recycled orogeny. On the basis of the geographic position and tectonic setting, three types of provenance can be identified in the Jurassic system Tuchengzi Formation. The far source provenances are Archean erathem basement metamorphic rocks in the northern basin and granite or adamellite that intruded rocks of the Late Jurassic epoch of the Yanshanian period in the northeast. The nearby provenance is the Mesoproterozoic erathem Changchengian system and Jixianianian system dolomite in both the east and west.

Evolution of pore fluid of low porosity and permeability reservoir in Qinnan Sag:a case study of 29-2 structurein Qinhuangdao area

The southeast depression of Qinnan Sag is a potential oil-gas exploration region in the Bohai Sea area. With the analysis of large quantity of rock thin sections,scanning electron microscope and the physical property data of reservoir,the authors studied the petrological characteristics and the evolution of pore and fluid of sandstone in the deeper strata in 29-2 structure in Qinhuangdao area. The results show that the evolutionary tendency of Paleogene sandstone reservoir porous fluid in research area is changed from alkaline porous fluid to acidic porous fluid,and back to alkaline porous fluid. There are three stages of reservoir porous evolution in Qinhuangdao area,namely sharp decrease in porosity due to mechanical compaction,increase in porosity because of corrosion and dissolution,and remarkable reduction owing to carbonate cementation.

Experimental Study of the Main Influencing Factors in Mechanical Properties of Conglomerate

In recent years,with the success of exploration and development of conglomerate reservoirs in Mahu Depression,Junggar Basin,China,it is urgent to study the mechanical properties and its influencing factors of conglomerate which is considered as a new oil and gas reservoir.Based on the investigations of petrologic characteristics,heterogeneity and mechanical properties of conglomerate in Baikouquan formation,the content and geometric characteristics of gravel in conglomerate,the main factors in heterogeneity and the mechanical behavior in the triaxial compression experiment of conglomerate are analyzed in this paper.The results show that the size and content of gravel in conglomerate varies greatly,and conglomerate has strong heterogeneity under the influence of gravel content and size.An analysis of mechanical properties of conglomerate shows that conglomerate is characterized by plasticity.Besides,the sphericity is negatively correlated to the gravel content,while the heterogeneity increases with the increase of conglomerate plasticity.Due to the existence of heterogeneous gravel,local stress may concentrate in conglomerate when the stress is loaded.Consequently,a large number of micro-cracks appear at the edge of gravel,demonstrating the strong plasticity of conglomerate.This paper is of referential significance to the study of rock mechanical properties and the evaluation of engineering properties in conglomerate development.