Geochemical characteristics and applications of 18α(H)-neohopanes and l7α(H)-diahopanes

Distribution and geological significance of 17α(H)-diahopanes from different hydrocarbon source rocks of Yanchang Formation in Ordos Basin

“…Based on analysis of formation mechanism, the redox attributes for deposition and diagenetic environment are the important factors that affect C 30 * relative abundance in hydrocarbon generation rocks [1,[6][7][8][9][10][11][12] . As reflected by the geological and geochemical data concerning hydrocarbon generation rocks of the Yanchang Formation (Table 1), Chang 6-9 black mudstone and Chang 7 oil shale, even with remarkable differences in C 30 * relative abundance, show similar organic precursor types (I-II 1 ), similar sedimentary water type (freshwater to slightly saline water), and similar balanced preponderance of both pristane and phytane, low gammacerane index, low Sr/Ba ratio [14,16] ), but maximum differences in rock fabrics and redox environment resulted from different sedimentary facies zones.…”

“…C 30 * is characterized by high thermal stability [3][4][5] , and its precursors could possibly be bacterial hopanoids, which were regarded as being resulted from rearrangement of hopanes with functional groups on D rings [6] . Currently, many scholars have explored the formation conditions and geochemical attributes of diahopanes, and the majority held that sub-oxidizing environment, acidic media and catalysis facilitated by clay minerals are favorable for formation of C 30 * [1,[6][7][8][9][10][11] , while some scholars considered that catalysis by clay minerals under appropriate alkaline conditions is helpful to formation of C 30 * [12] . Bacterial hopanoids are generally regarded as biological precursors for diahopanes.…”

“…As a result, arguments continue regarding precursors for diahopanes. As diahopane parameters show geochemical attributes like maturity [5] and sedimentary-organic facies [11] , the relative abundance of diahopanes can be used for oil-source correlation [12] and regarded as a parameter for maturity [5,11] . Generally speaking, lithology, biogenic sources, redox attributes, sedimentary and diagenetic media conditions, thermal maturity of hydrocarbon generation rocks are important factors that affect the relative abundance of diahopanes.…”

Source of the condensates from the Hetianhe Field and the genetic relationship between the condensates and their associated gases

“…Another two cross-plots, Ts/(Ts+Tm) vs. C 29 Ts/(C 29 Ts+ C 29 H) and Ts/(Ts+Tm) vs. 4-/1-MDBT, were applied here to evaluate the maturity of Hetianhe condensates ( Figure 8(c), (d)), which are suitable for high-post mature oils (Moldwoan et al, 1984;Wang C J et al, 2000;Wang et al, 2005). As shown in Figure 8(c) and (d), the Ts/(Ts+Tm) parameters of Hetianhe condensates show a good positive correlation with C 29 Ts/(C 29 Ts+C 29 H) and 4-/1-MDBT parameters, verifying the validity of maturity assessment of the investigated oils.…”

Geochemical Characteristics and Oil-Source Correlation of Oil-Sand Extracts of Kelatuo Anticline in the Northern Kashi Sag, NW Tarim Basin, China

“…614 Worthy of mention is the relatively higher amount of 17(α) C 30 diahopane in Middle and Lower Jurassic strata that is commonly discovered in the Ordos Basin and the Keche Basin. Many investigators have concluded that a combination of a suboxidizing environment, an acidic medium and the catalytic action of clay minerals benefits the formation of 17(α) C 30 diahopane (Peters and Moldowan, 1993;Philp and Gilbert, 1986;Farrimond and Teln, 1996;Zhu et al, 2007;Zhao and Zhang, 2001;Wang et al, 2000). However, some think that moderate alkaline conditions for catalytic action of clay minerals may be important (Xiao et al, 2004).…”