The Zhang 22 well was drilled in the Ordos Basin, penetrating the Chang 7 Member of the Yanchang Formation, which has more than 80 m cumulative black organic-rich shale of oil window maturity. Utilizing seventy-six samples collected every 1 meter from the well the effects of stratigraphic fractionation and petroleum expulsion within five intervals of the Chang 7 shale were qualitatively and quantitatively documented. The organic-rich intervals-1,-2 and-5, having an average TOC content of 6.79 wt% and pyrolyzable hydrocarbon potential S2 of 9.40 mg/g rock, are defined as "generative units" in the Chang 7 shale system, compared to the "in-source reservoirs" or "sweet spots"-the third and fourth intervals-which contain lower average TOC content of 4.19 wt% and an average S2 value of 7.17 mg/g rock, but the highest amount of free oil (av. total oil of 7.35 mg/g rock). Geochemical and molecular compositions display distinctive differences between samples from these source and reservoir groupings. For example, bitumens from the generative units proportionally possess lower saturated hydrocarbons (56% to 66%) than those from the in-source reservoirs (up to 81%). The proportions of aromatic and polar compounds in the generative units are accordingly higher than in their counterpart. The individual molecular weight distribution of sample extracts displays more light-end moieties being enriched in the generative units. By applying the compositional mass balance calculation, the overall and compound-specific expulsion efficiencies in the in-source reservoirs are abnormally negative compared to the positive values in the generative 2 intervals. This finding in conjunction with the effects of the preferential retention of aliphatic hydrocarbons and the differential expulsion of light molecular weight compounds in the in-source reservoirs together indicate a short-distance intrasource migration of generated petroleum into the sweet spot intervals (intervals-3 and-4) from the overlying units (intervals-1 and-2) and the underlying interval-5. Furthermore, when quantifying the total amount of retained petroleum in the shale system, an amended assessment has been introduced to overcome the systematic misestimations if only unextracted S1 values were considered. Thus, the oil crossover effect, Tmax shift phenomenon and the HI being shifted to higher values after extraction all account for identifying the intervals-3 and-4 as the in-source reservoirs. In this study, we have not only identified a set of promising in-source target for shale oil exploration and production, but we also presented the chemical and molecular composition for these shale oils. We have additionally speculated for the intrasource migration model, and further discussed the different expulsion efficiencies in the shale system upon the compositional mass balance calculation, and the stratigraphic fractionation on differentiating the chemical compositions during migration. The improved oil quality by fractionation, the extra storage potential derived from microfos...
Deepwater/deep‐marine turbidite lobes are the most distal part of a siliciclastic depositional system and hold the largest sediment accumulation on the seafloor. As many giant hydrocarbon provinces have been discovered within deepwater lobe deposits, they represent one of the most promising exploration targets for hydrocarbon industry. Deepwater exploration is characterized by high cost, high risk but insufficient data because of the deep/ultra–deepwater depth. A thorough understanding of the deepwater turbidite lobe architecture, hierarchy, stacking pattern and internal facies distribution is thus vital. Recently, detailed outcrop characterizations and high–resolution seismic studies have both revealed that the deepwater lobe deposits are characterized into four–fold hierarchical arrangements from “beds”, to “lobe elements”, to “lobes” and to “lobe complex”. Quantitative compilations have shown that hierarchical components of lobe deposits have similar length to width ratios but different width to thickness ratios depending on different turbidite systems. At all hierarchical scales, sand–prone hierarchical lobe units are always separated by mud–prone bounding units except when the bounding units are eroded by their overlying lobe units thus giving rise to vertical amalgamation and connectivity. Amalgamations often occur at more proximal regions suggesting high flow energy. A mixed flow behavior may occur towards more distal regions, resulting in deposition of “hybrid event beds”. These synthesized findings could (1) help understand the lobe reservoir distribution and compartmentalization therefore benefit the exploration and development of turbidite lobes within the deep marine basins (e.g. South China Sea) and (2) provide rules and quantitative constraints on reservoir modeling. In addition, the findings associated with deepwater turbidite lobes might be a good starting point to understand the sedimentology, architecture and hierarchy of turbidites in deep lacustrine environment.
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