Hu Wenxuan

Mn content of reservoir calcite cement: A novel inorganic geotracer of secondary petroleum migration in the tectonically complex Junggar Basin (NW China)

Electronic probe microanalysis (EPMA) results of reservoir calcite cement from fourteen core samples in the Junggar Basin show that Mn-content varies largely between different samples from below the detect limitation to 4.14%, while it displays a generally good correlation with oil-gas shows. This, therefore, likely indicates that concentration of the Mn-content of the calcite cement has a close relation to the intensity of petroleum fluid charging during hydrocarbon secondary migration. In order to assess this hypothesis, oxygen and strontium isotopic measurements on sixteen calcite veins host in source sequences were carried out to investigate the feature of the oil-source petroleum fluid. Analytical results imply that during hydrocarbon generation and migration, deep hot fluid has dissolved volcanic minerals interlined between mudstone source rocks. As Mn is a kind of typical trace element enriched in volcanic rocks, it is reasonable to conclude that the petroleum fluid formed in the source sequences would be Mn-rich. Consequently, calcite cements precipitated from such Mn-rich petroleum fluid would be Mn-rich accordingly. Due to the geologic chromatographic effect during migration along reservoir rocks, the decreasing of the Mn-content of the reservoir calcite cements indicates the migration direction. Then, this novel geotracer was further successfully applied in the study of hydrocarbon migration in the Junggar Basin in combination with organic geochemical analyses during the hydrocarbon migration. The Mn content of the reservoir calcite cement appears promising as a novel inorganic geotracer for the petroleum migration. This paper represents a search for novel indicators of secondary petroleum migration in tectonically complex basins based on fundamentals of the reservoir fluid-rock interactions.

Effects of Deep Fluids on Hydrocarbon Generation and Accumulation in Chinese Petroliferous Basins

Deep fluids in a petroliferous basin generally come from the deep crust or mantle beneath the basin basement, and they transport deep substances (gases and aqueous solutions) as well as heat to sedimentary strata through deep faults. These deep fluids not only lead to large-scale accumulations of CO2, CH4, H2, He and other gases, but also significantly impact hydrocarbon generation and accumulation through organic-inorganic interactions. With the development of deep faults and magmatic-volcanic activities in different periods, most Chinese petroliferous basins have experienced strong impacts associated with deep fluid activity. In the Songliao, Bohai Bay, Northern Jiangsu, Sanshui, Yinggehai and Pearl Mouth Basins in China, a series of CO2 reservoirs have been discovered. The CO2 content is up to 99%, with δCCO2 values ranging from −4.1‰ to −0.37‰ and He/He ratios of up to 5.5 Ra. The abiogenic hydrocarbon gas reservoirs with commercial reserves, such as the Changde, Wanjinta, Zhaozhou, and Chaoyanggou reservoirs, are mainly distributed in the Xujiaweizi faulted depression of the Songliao Basin. The δCCH4 values of the abiogenic alkane gases are generally >−30‰ and exhibit an inverse carbon isotope sequence of δCCH4>δCC2H6>δCC3H8>δCC4H10. According to laboratory experiments, introducing external H2 can improve the rate of hydrocarbon generation by up to 147% through the kerogen hydrogenation process. During the migration from deep to shallow depth, CO2 can significantly alter reservoir rocks. In clastic reservoirs, feldspar is easily altered by CO2-rich fluids, leading to the formation of dawsonite, a typical mineral in high CO2 partial pressure environments, as well as the creation of secondary porosity. In carbonate reservoirs, CO2-rich fluids predominately cause dissolution or precipitation of carbonate minerals. The minerals, e.g., calcite and dolomite, show some typical features, such as higher homogenization temperatures than the burial temperature, relatively high concentrations of Fe and Mn, positive Eu anomalies, depletion of O and enrichment of radiogenic Sr. Due to CO2-rich fluids, the development of high-quality carbonate reservoirs is extended to deep strata. For example, the Well TS1 in the northern Tarim Basin revealed a high-quality Cambrian dolomite reservoir with a porosity of 9.1% at 8408 m, and the Well ZS1C in the central Tarim Basin revealed a large petroleum reserve in a Cambrian dolomite reservoir at ~6900 m. During the upward migration from deep to shallow basin strata, large volumes of supercritical CO2 may extract petroleum components from hydrocarbon source rocks or deep reservoirs and facilitate their migration to shallow reservoirs, where the petroleum accumulates with the CO2. Many reservoirs containing both supercritical CO2 and petroleum have been discovered in the Songliao, Bohaiwan, Northern Jiangsu, Pearl River Mouth and Yinggehai Basins. The components of the petroleum trapped with CO2 are dominated by low molecular weight saturated hydrocarbons.

Improved method to determine the molar volume and compositions of the NaCl-H2O-CO2 system inclusion

AbstractOn the basis of Parry’s method (1986), an improved method was established to determine the molar volume (Vm) and compositions (X) of the NaCl-H2O-CO2 (NHC) system inclusion. To use this method, the determination of Vm-X only requires three microthermometric data of a NHC inclusion: partial homogenization temperature n

Hydrothermal alteration dolomite reservoir in Tazhong area

(T_{h,CO_2 } )

Grains Containing Oil Inclusions in Different Hydrocarbon Production and Show Types of Sandstone Reservoirs from the Central Junggar Basin, Northwest China

n, salinity (S) and total homogenization temperature (Th). Theoretically, four associated equations are needed containing four unknown parameters: n

DEVELOPING CHARACTERISTICS OF KAOLINITE IN CENTRAL JUNGGAR BASIN AND THEIR EFFECT ON THE RESERVOIR QUALITY

X_{CO_2 }