Natural Fractures Characteristics of the Carboniferous Volcanic Reservoir in Northwestern Margin of Junggar Basin

Research on the regional fracture’s development is important for reservoir fracturing. This paper takes the Carboniferous volcanic reservoir in the northwestern margin of Junggar Basin as the research object. Based on understanding the regional tectonic faults and geological characteristics, the parameter characteristics of natural fractures are analyzed using imaging logging data, and natural fractures distribution characteristics are compared with regional faults and in-situ stresses, as well as the pattern of natural fractures formation is revealed. The results indicated that: (1) The Carboniferous in the northwestern margin of Junggar Basin area mainly develops 3 NE-trending reverse faults. The reservoir type is pore-fracture dual media type, with an average porosity of 7.64% and an average permeability of 1.16mD, which belongs to the medium-porosity and ultra-low permeability reservoir; (2) Reservoir fractures are generally well developed. High-conductivity fractures and high-resistance fractures coexist, but high-conductivity fractures are the main ones. The fracture width is between 0.053 and 0.23 mm, and the fracture density is between 0.5 and 1.68 strips/m. The length is between 0.54-1.88m, the fracture porosity is between 3.4×10-5-41×10-5, and the dominant fracture trend is mainly NE50°-NE80°; (3) The direction of the maximum horizontal in-situ stress of the reservoir is mainly NE30°-NE60°, in the direction of NEE, it differs from fracture strike by 10°-50°, and roughly the same as the strike of the three reverse faults.

Reservoir Characteristics and Main Controlling Factors of the Mesozoic Volcanic Rocks in the D Oilfield in Southern Gentle Slope Zone of the Laizhouwan Sag

The Mesozoic volcanic rocks are widely developed in the Bohai Bay basin. The D oilfield, located in the southeast of the Bohai Bay Basin, is a Cenozoic depression developed on the base of the Mesozoic. The types of the volcanic rocks are complex and the reservoir space is diverse. According to the characteristics of the volcanic reservoir, such as vertical multi-stage and strong heterogeneity, and based on the analysis of the volcanic core observation, thin section identification, logging data and seismic data, we analyzed the reservoir space type, physical property characteristics and reservoir physical property control factors of volcanic reservoir in the study area. The results show that the volcanic rocks in the study area are mainly volcanic breccia, andesite and tuff; the lithofacies types mainly include volcanic eruption facies, effusion facies and volcanic sedimentary facies, and the volcanic eruption facies is the most developed. Four types of volcanic reservoirs and 14 effective storage space types have been identified from the macroscopic and microscopic multi-scale, mainly intergranular pores, intergranular dissolution pores, intracrystalline pores, structural fractures and weathering dissolution fractures. Reservoir performance is mainly affected by lithology, lithofacies, tectonic activity and diagenesis. The primary pores in the upper part of exhalative and explosive facies are the most developed. Early cement filling is beneficial to the preservation of primary intergranular pore space and is an important prerequisite for the formation of secondary dissolution pores. Under the action of multi-stage tectonic movement and weathering leaching, the reservoir performance of volcanic rocks has been greatly improved, and the volcanic rocks with superimposed fractures and porosities are effective volcanic reservoirs.

REE Minerals as Geochemical Proxies of Late-Tertiary Alkalic Silicate ± Carbonatite Intrusions Beneath Carpathian Back-Arc Basin

The accessory mineral assemblage (AMA) of igneous cumulate xenoliths in volcanoclastic deposits and lava flows in the Carpathian back-arc basin testifies to the composition of intrusive complexes sampled by Upper Miocene-Pliocene basalt volcanoes. The magmatic reservoir beneath Pinciná maar is composed of gabbro, moderately alkalic to alkali-calcic syenite, and calcic orthopyroxene granite (pincinite). The intrusive complex beneath the wider area around Fiľakovo and Hajnáčka maars contains mafic cumulates, alkalic syenite, carbonatite, and calc-alkalic granite. Both reservoirs originated during the basaltic magma underplating, differentiation, and interaction with the surrounding mantle and crust. The AMA of syenites is characterized by yttrialite-Y, britholite-Y, britholite-Ce, chevkinite-Ce, monazite-Ce, and rhabdophane(?). Baddeleyite and REE-zirconolite are typical of alkalic syenite associated with carbonatite. Pyrochlore, columbite-Mn, and Ca-niobates occur in calc-alkalic granites with strong peralkalic affinity. Nb-rutile, niobian ilmenite, and fergusonite-Y are crystallized from mildly alkalic syenite and calc-alkalic granite. Zircons with increased Hf/Zr and Th/U ratios occur in all felsic-to-intermediate rock-types. If rock fragments are absent in the volcanic ejecta, the composition of the sub-volcanic reservoir can be reconstructed from the specific AMA and zircon xenocrysts–xenolith relics disintegrated during the basaltic magma fragmentation and explosion.

Distribution of Volcanic Rocks Porosity of Dissected Kromong Paleovolcano: Analogue of Volcanic Reservoir

The potentiality of unconventional play on the volcanic reservoir was evaluated for the purpose to deliver an integrated evaluation of shallow reservoir target associated with the Northwest Java Basin (NWJB). This study provides basis discovery for further exploration and dissemination of volcanic reservoir by presenting an overview of geometric and porosity type analysis of Kromong paleo-volcano complex deposits associated with the NWJB comprehensively. Furthermore, reservoir lithofacies and pore space deployment of Kromong volcanic deposits were studied. The detailed lithofacies analysis was carried out based on field observations from several dissected- and obscure dipping-outcrops in Kromong area associated with NWJB. Following this, a set of outcrop samples were processed for megascopic description integrated with thin-section analysis by using the polarized light microscope and XRF, respectively to assess different types of reservoir pore spaces and structure. Subsequently, the physical properties-porosity measurement was conducted using ImageJ software tools to understand the potentiality of high-quality reservoir formation. The results of this study show that rocks in Kromong area associated with NWJB can be comprehensively classified into reefal limestone for carbonate deposit and into 4 categories, including volcaniclastic lava, sheeting joint lava, pyroclastic breccia, volcanic intrusion, for volcanic deposits. The proposed volcanic reservoirs of volcanic play in this study are lithologically composed of autobreccia lava, sheeting joint lava, pyroclastic breccia to andesitic- and andescitic-dikes, which comprises explosive facies and intrusive facies. Pyroclastic breccia reservoirs are primary pore-type reservoirs with devitrified micropores as main reservoir space. Whilst volcanic dikes reservoirs are mainly porous-fractured-type reservoirs with cooling fracture porosity. In conclusion, following factors that control the presence of a volcanic reservoir are lithology, lithofacies, tectonism and vulcanism. Despite worldwide discoveries of volcanic reservoirs, neither the detailed potentiality evaluation nor the postulated assumption of volcanic reservoir development in NWJB field has been examined sufficiently. This contribution offers knowledge benefits by discussing the potentiality of the Cenozoic-Quarternary volcanic reservoir of the NWJB field and providing a reference for future exploration in the petroleum industry.

Investigation on the biodegradation levels of super heavy oils by parameter-striping method and refined Manco scale: a case study from the Chepaizi Uplift of Junggar Basin

The Carboniferous volcanic reservoir in the Chepaizi Uplift became an exploration hot target in recent years for its substantial amount of oils discovered. However, most of the Carboniferous heavy oils were biodegraded to PM7 or higher with orders of magnitude variation in oil viscosities. Two oil groups (I and II) exactly corresponding to the western and eastern Chepaizi Uplift were distinguished according to their source diagnose. Furthermore, three oil families (II1, II2 and II3), with the biodegradation level of PM7, PM8–8+, PM9+, respectively, were classified based on molecular compositions and parameter-stripping method of strongly bioresistant parameters. Allowing for this extremely high biodegradation case, more biodegradation refractory compound class were added to establish a refined Manco scale to quantitatively evaluate the biodegradation extent. Refined Manco number (RMN2) positively correlated with the oil density, NSO contents, and absolute concentrations of diasteranes and gammacerane, negatively correlated with the absolute concentrations of diahopane, summed tricyclic terpanes and pentacyclic terpanes. This refined scale showed higher resolution than the PM one to differentiate the biodegradation extent of Carboniferous heavy oils from the Chepaizi Uplift, especially those with same PM values but different oil viscosities.

Reservoir Formation Model and Main Controlling Factors of the Carboniferous Volcanic Reservoir in the Hong-Che Fault Zone, Junggar Basin

The Hong-Che Fault Zone is one of the important oil and gas enrichment zones in the Junggar Basin, especially in the Carboniferous. In recent five years, it has been proven that the Carboniferous volcanic rock has 140 million tons of oil reserves, and has built the Carboniferous volcanic reservoir with a capacity of million tons. Practice has proven that the volcanic rocks in this area have great potential for oil and gas exploration and development. To date, Carboniferous volcanic reservoirs have been discovered in well areas such as Che 32, Che 47, Che 91, Chefeng 3, Che 210, and Che 471. The study of drilling, logging, and seismic data shows that the Carboniferous volcanic reservoirs in the Hong-Che Fault Zone are mainly distributed in the hanging wall of the fault zone, and oil and gas have mainly accumulated in the high part of the structure. The reservoirs are controlled by faults and lithofacies in the plane and are vertically distributed within 400 m from the top of the Carboniferous. The Carboniferous of the Hong-Che Fault Zone has experienced weathering leaching and has developed a weathering crust. The vertical zonation characteristics of the weathering crust at the top of the Carboniferous in the area of the Che 210 well are obvious. The soil layer, leached zone, disintegration zone, and parent rock developed from top to bottom. Among these reservoirs, the reservoirs with the best physical properties are mainly developed in the leached zone. Based on a comprehensive analysis of the Carboniferous oil and gas reservoirs in areas of the Chefeng 3 and Che 210 wells, it is believed that the formation of volcanic reservoirs in the Hong-Che Fault Zone was mainly controlled by structures and was also controlled by lithofacies, unconformity surfaces, and physical properties.