Search

Abstract Petroleum geology and deposition features of the fine grain phase region in the second member of the Kongdian Formation were investigated using traditional petroleum geology and sedimentary petrology. New theories for shale oil and gas formation, based on data from 500 m continuous coring, systematic analysis of over ten thousand core samples, and logging data in the center of the lake basin in the Cangdong Sag (Bohai Bay Basin, China) were developed to determine the distribution of shale oil and provide a basis for shale oil exploration deployment. Results showed that a wide distribution of semi-deep to deep lake sub-facies fine-grained sediment (shale) was deposited in the study area during the largest lake flooding period. This sediment consists of felsic shale, mixed shale, and dolomites, but no clay shale. The shale features multiple rock components with few dominant minerals; high clastic mineral content and low clay mineral content; rich analcite and lean pyrite; rich brittle minerals with lean quartz; diverse rock types with limited shale oil; more tight reservoirs and fewer reservoirs with no fractures; more high-quality source rock with less non-hydrocarbon source rock; and more high frequency cycles with fewer monolithic deposits. Results indicate that dolomites are located in strips on the plane and are locally enriched, contradicting the understanding that only hydrocarbon source rock, and no reservoirs, develop in the middle of a continental closed lake basin. The study region demonstrates good conditions for shale oil formation, a favorable configuration of source rock and reservoirs, and 260 km2 of sweet spots, indicating high exploration value. Several prospecting wells have obtained industrial oil flow with guidance based on geological knowledge and engineering technology support. Highlights • Continental shale oil exploration in China has been a breakthrough, the highest daily oil is 53.1t. • Continental shale have complex mineral compositions, lots of pores, high brittleness. • The source rocks of continental shale series are of good quality and generally contain oil. • Shale oil enrichment is mainly affected by source reservoir and its configuration relationship. • Shale oil resources of Ek2 is more than 300 million tons with high exploration potential. [ABSTRACT FROM AUTHOR]

To study nano-scale inorganic pore systems in shale plays, the removal of soluble organic matter (SOM) using solvent extraction is an important pre-treatment step to reduce the in-situ petroleum blockage effect in shale oil samples. However, factors controlling the extraction efficiency are not well-understood, making the reliability and consistency of this extraction process questionable. In this work, an oil window mature organic-rich lacustrine shale in the Bohai Bay Basin of East China was prepared in six different sample sizes (from 1 cm cubes down to <75 μm powder), extracted for different times (1 day–25 days), and analysed for chemical composition to assess the extraction efficiency and behaviour, in order to arrive at a consistent workflow for sample pre-treatment for pore structure characterization. In general, the smaller the sample is used and the longer the sample is extracted, the higher the extract yield is obtained. The maximum extraction efficiency (based on the amount of extract after 25 days for the powder sample) is highly correlated with the sample size, indicating that there would always be residual soluble material in larger-sized samples even after extraction for a month. Molecular examination of the extract reveals that the early extract is dominated by saturated hydrocarbons, and these in turn are enriched in n-alkanes, while the saturated hydrocarbon content declines relative to aromatic and polar fractions, and the saturates are more dominated by branched and cyclic hydrocarbons, as extraction time increases. Such a knowledge about the extraction time- and sample size-dependencies of the extraction rate are fundamentally important in designing the solvent extraction protocol prior to carrying out nano-petrophysical studies. • The time- and sample size-dependencies of solvent extraction yields from a lacustrine shale have been quantified. • Extraction times varied from 1 to 25 days, and sample sizes from 1 cm cubes to 200 mesh. • Only about half of the soluble material at 200 mesh was extracted from the 1 cm-sized cubic samples after 25 days. • With increasing extraction time, the extracts are characterized by more and more aromatic and polar compounds. [ABSTRACT FROM AUTHOR]

Nine as-received core samples were selected from four wells drilled in the lacustrine Kongdian Formation, which is a source rock located in Cangdong Sag, Bohai Bay Basin, China, and their geochemistry and pore structure characteristics were investigated by Rock-Eval pyrolysis, low-pressure nitrogen physisorption (LNP), mercury intrusion porosimetry (MIP), and spontaneous imbibition (SI) tests. Various models were employed to investigate the fractal characteristics of pore systems, and discuss the relationships between pore structure parameters and fractal dimension (D f). The results show that the samples can be divided into two groups (A and B) according to the different types of hysteresis loops from LNP isotherms, as well as geochemistry and pore structure parameters of samples. Negative relationship among BJH (Barrett-Joyner-Halenda) pore volume and S 1 value, and obviously higher average pore diameter of Group B samples with significantly higher S 1 values, indicate a blockage of residual hydrocarbons on small pores. According to the different D f − MIP values from MIP tests, the pore-throats of samples can be divided into four categories of A to D in the following sequence: microscopic (diameters less than 50 nm), small (50 nm-8 μm), medium (8 μm–20 μm) and large (greater than 20 μm) pore-throats/pores. The difference of D f from LNP and MIP tests is probably due to different sample sizes used and pore types assessed, while the difference of D f between MIP and SI tests is attributed to the mixed wettability of pores in shale samples. In addition, from the results of LNP tests with a measurable pore size of 2–200 nm, obvious positive relationships exist between D f − LNP − C (LNP test-derived D f value for Region C) and BJH pore volume, BET (Brunauer-Emmett-Teller) surface area and average pore size, as well as microscopic pore volume and percentage. The D f − LNP − C can be considered as an effective parameter to reflect the degree of development of microscopic pores in samples. • Paleogene-aged Lacustrine Kongdian shale was studied for pore structure characteristics. • Fractal analyses on various laboratory tests were used to link with shale properties. • Two groups of shale were derived from different hysteresis loops of N 2 physisorption. • Four categories of pore-throats were obtained from mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]