Zhenxue Jiang

Geochemical characteristics of crude oil and oil-source correlation of the Paleogene "Red Bed" in the south slope of the Dongying Depression, Bohai Bay Basin, China

The Paleogene Red Bed in the South Slope of the Dongying Depression is a set of red clastic sediments of the lower section of 4th member of the Shahejie Formation and the Kongdian Formation, and is the alternative strata for oil and gas exploration in this area. The Red Bed crude oil of the South Slope of the Dongying Depression is divided into four types according to the assemblage characteristics of biomarkers from 17 oil sand samples and 3 crude oil samples. The Type I crude oil is generated from the source rocks of the lower section of 3rd member of the Shahejie Formation, with low phytane and gammacerane concentration, Ph/n-C18<0.6, relatively high ratios of Ts/(Ts+Tm) (>0.38) and hopanes/steranes (>3.4), high diasteranes concentration, and low C35 homohopane index. The Type II crude oil could be derived from the source rocks of the upper section of 4th member of the Shahejie Formation with abnormal high phytane and gammacerane concentration, Ph/n-C181, relatively low ratios of Ts/(Ts+Tm) (<0.38) and hopanes/steranes (<2.5), low diasteranes concentration, and high C35 homohopane index. The Type III crude oil is mixed oil consisting of the Type II crude oil charged in the early stage and the Type I crude oil charged in the late stage and mainly of the Type I crude oil. The Type IV crude oil is characterized by C29 sterane predominance and this feature has not been found in the crude oils and source rocks of the study area, therefore this type of oil is identified as a mixture of the Type II crude oil and an oil type from a shallow lake-swamp facies. The fault throw of oil transporting faults controls the distribution of crude oils with different genetic types, and the upthrown side of the faults is the favorable zone for the Red Bed oil and gas accumulation.

The characteristics of unconformity surface at the bottom of the Paleogene and its significance in hydrocarbon migration in the Sikeshu Sag of the Junggar Basin, Northwest China

The unconformity surface at the bottom of the Paleogene, located in the Sikeshu Sag of the Junggar Basin, Northwest China, is one of the most important hydrocarbon migration pathways and characterized by 3 layers of upper coarse clastic rock, lower weathering crust and leached zone. The upper coarse clastic rock displays features of higher density, lower SDT and gamma-ray logging while the weathering crust in the lower part displays opposite features. The formation water is of NaHCO3 type but at lower mineralization degree. The QGF indices are generally between 2.19 and 3.77 and the GOI parameters vary from 1% to 5%. From the southeast to the northwest of the sag, the content of saturated hydrocarbon increases from 30.81% to 53.74% while that of non-hydrocarbon and asphaltene decreases. The Pr/nC17 decreases from 0.65 to 0.47 while the Ph/nC18 decreases from 0.66 to 0.27, and the content of benzo[c] carbazole declines while the benzo[a] carbazole amount and (alkyl carbazole)/(alkyl+benzo carbazole) ratio both increase. These revealed that the hydrocarbons migrated from the sag to the ramp region along the unconformity surface.

Effects of organic matter and mineral compositions on pore structures of shales: A comparative study of lacustrine shale in Ordos Basin and Marine Shale in Sichuan Basin, China:

The pore structure of shale plays key role in oil and gas storage capacity and accumulation. Twelve representative samples were selected from Triassic Yanchang Formation in the Ordos Basin and Silurian Longmaxi Formation in the Sichuan Basin with different ages, depositional settings, and maturities to analyze shale pore structure using focused ion beam-scanning electron microscopy and high-pressure mercury intrusion capillary porosimetry. The results show that the pores of lacustrine shale with maturity Rou2009<u20091.3% from the Triassic Yanchang Formation were predominantly composed of pores with pore throat diameter of larger than 30u2009µm. The pores of marine shale with maturity Rou2009>u20091.3% from the Silurian Longmaxi Formation were predominantly composed of pores with pore throat diameter of smaller than 100u2009nm. For the porosity, the average porosity of low-mature lacustrine shale is 2.4%, while the average porosity of high-mature marine shale is 1.5%. For the pore type, intergranular inorganic pores predominantly occurred between mineral particles in the lacustrine shale, while the marine shale mainly developed organic pores with pore throat diameters ranging from 5 to 200u2009nm. Compared to the low-mature lacustrine shale, macropores of high-mature marine shale are less developed and micropores dominant. Importantly, brittle minerals (quartz, feldspar, and carbonate minerals) mainly affect the pore structure of lacustrine shale, while organic matter mainly affects the pore structure of marine shale.

Controlling Factors on Oil and Gas Accumulation and Accumulation Modes of the Paleogene “Red Bed” in the South Slope of the Dongying Depression, China

The Paleogene “Red Bed”, the alternative strata for oil and gas exploration in the South Slope of the Dongying Depression, refers to a set of red clastic sediments of the lower 4th member of the Shahejie Formation and the 1st member of the Kongdian Formation. And it has important significance to study the controlling factors on oil and gas accumulation and the accumulation modes for guiding the deep-layer oil and gas exploration in the area. In this paper, according to the statistics of oil and gas static characteristics, analysis of oil original types, study of pathway system and recovery of oil and gas accumulation, the controlling factors on the Red Bed oil and gas accumulation were summarized as follows: source rock controlling oil and gas distribution, physical features of reservoir bed controlling trap oiliness, faults controlling oil and gas source and trap conditions, and nose structural zone controlling oil and gas migration and enrichment zone. Based on these studies, three accumulation modes for the Paleogene Red Bed in the research area were built: joints of source rock and reservoir bed acting as lateral pathway for oil and gas accumulation, faults acting as vertical pathway for oil and gas accumulation, and high pressure of deeper depression resulting in oil and gas flowing downward to form accumulation.

Methane adsorption in the low–middle-matured Neoproterozoic Xiamaling marine shale in Zhangjiakou, Hebei

ABSTRACT The adsorption capacity of high–over-matured shale has been widely investigated, but the adsorption capacity and the main factors influencing low–middle-matured, type II kerogen-containing, and organic-rich marine shale have been rarely explored. This research conducts organic geochemistry, mineralogical composition, adsorption isotherm tests to reveal the adsorption and main influencing factors of the different geochemistry characteristics, mineralogical compositions, temperature and pressure conditions of the low–middle-matured Neoproterozoic Xiamaling marine shale in Zhangjiakou, Hebei. The investigated shale is in a low–middle maturity stage, contains type II kerogen and is rich in organic matter. The results show that the total organic carbon (TOC) content of the Xiamaling shale is positively correlated with the methane adsorption capacity, which is the most important influencing factor on the adsorptive property of shale. The methane adsorption capacity first decreases to the minimum value as the temperature reaches 360°C equivalent Ro (EqRo = 1.0%), then increases and reaches the maximum value at 620°C (EqRo = 3.28%) and finally decreases again as the temperature rises at the last simulation stage. The mineral components exhibit an insignificant influence on the methane absorbability because of organic-matter coatings. The TOC-normalised methane adsorption capacity is positively correlated with the illite–smectite and clay-mineral contents but shows no significant correlation with brittle minerals, such as quartz. Soluble organic matter and kerogen caused the methane dissolution and adsorbtion, respectively. The strong dissolution property of the soluble organic matter is the most important cause of the larger adsorption capacity of the original shale compared with that of the residual samples. Moreover, the methane adsorption capacity of the Xiamaling shale decreases with increasing temperature, and increases with pressure below the critical pressure but decreases exceeding the critical pressure.