Coupling Relationship between Lithofacies and Brittleness of the Shale Oil Reservoir: A Case Study of the Shahejie Formation in the Raoyang Sag

Analyzing the characteristics of rock brittleness in low-permeability mudstone and shale (MS) formations is imperative for efficient hydraulic fracturing stimulation. Rock brittleness depends on the mineral composition, organic matter abundance, and bedding structure. Based on the MS from Shahejie Formation mineral composition (clay mineral, felsic mineral, and calcareous mineral contents), total organic content, and bedding structure (laminated, laminar, and massive), six types of lithofacies were identified: clay-rich MS, felsic-rich MS, calcareous-rich MS, clay MS, felsic MS, and calcareous MS. The quartz, feldspar, calcite, and dolomite of the Shahejie Formation are brittle minerals. Consequently, lithofacies with high felsic and calcareous mineral contents are more brittle. In addition, laminated and laminar MS are also conducive to hydraulic fracturing. Therefore, laminated, organic-rich, and calcareous-rich MS are the dominant lithofacies for hydraulic fracturing in the Shahejie Formation. The lithofacies and brittleness index were predicted by the response characteristics between mineral compositions and logging curves. The 3521–3552 m section of well B11x is dominated by calcareous-rich MS with developed laminae, representing a favorable section for hydraulic fracturing. Fragile minerals and oil are widely developed in the lower part of the lower 1st member of the Shahejie Formation (Es1L) in the southwestern part of Zhaohuangzhuang-Suning, where hydraulic fracturing can be used to increase shale oil production.

Shale Heterogeneity in Western Hunan and Hubei: A Case Study from the Lower Silurian Longmaxi Formation in Well Laidi 1 in the Laifeng-Xianfeng Block, Hubei Province

Shale heterogeneity directly determines the alteration ability and gas content of shale reservoirs, and its study is a core research topic in shale gas exploitation and development. In this study, the shale from the Longmaxi Formation from well Ld1 located in western Hunan and Hubei is investigated. The shale’s heterogeneity is analyzed based on shale mineral rocks, microslices, geochemistry, and low-temperature N2 adsorption-desorption. It is found that the shales of the Longmaxi Formation from well Ld1 are mainly composed of siliceous shale, mixed shale, and clayey shale. The three types of shale facies exhibit strong heterogeneity in terms of the occurrence state of organic matter, organic content, mineral composition, microstructure and structure, brittleness, and micropore type. Sedimentation, late diagenesis, and terrigenous input are the main factors influencing the shale’s heterogeneity. With a total organic carbon (TOC) of 0.41%-4.18% and an organic matter maturity ( R o ) of 3.09%-3.42%, the shales of the Longmaxi Formation from well Ld1 are in an overmature stage, and their mineral composition is mainly quartz (5%-66%) and clay minerals (17.8%-73.8%). The main pore types are intergranular pores, intragranular pores, microfractures, and organic pores. The results of the low-temperature N2 adsorption-desorption experiment show that the shale pores are mainly composed of micropores and mesopores with narrow throats and complex structures, and their main morphology is of a thin-necked and wide-body ink-bottle pore. Based on the Frenkel-Halsey-Hill (FHH) model, the pore fractal dimension is studied to obtain the fractal dimension D 1 (2.73-2.76, mean 2.74) under low relative pressure ( P / P 0 ≤ 0.5 ) and D 2 (2.80-2.89, mean 2.85) under high relative pressure ( P / P 0 > 0.5 ). The shales of the Longmaxi Formation in the study area have a strong adsorption and gas storage capacity; however, the pore structure is complex and the connectivity is poor, which, in turn, imposes high requirements on reservoir reformation measures during exploitation. Moreover, the fractal dimension has a positive correlation with organic matter abundance, TOC, clay mineral content, and pyrite content and a negative correlation with quartz content. Since the organic matter contained in the shales of the Longmaxi Formation in the study area is in the overmature stage, the adsorption capacity of the shales is reduced, and the controlling effect of organic matter abundance on the same is not apparent.

Porosity Evolution In Lacustrine Organic-Matter-Rich Shales With High Claly Minerals Content

Pore structure is a major factor affecting the storage space and oil-bearing properties of shales. Mineralogy, organic matter content, and thermal evolution complicate the pore structures of lacustrine shales. In this study, the porosity evolution of organic-matter-rich shales from the Cretaceous Nenjiang Formation in the Songliao Basin, Northeast China, are investigated using thermal simulation experiments and in-situ scanning electron microscope analysis. Three findings were obtained as follows: 1) The pore system of shales from the Nenjiang Formation is dominated by inter-granular dissolution pores of plagioclase and intra-granular pores of illite-smectite mixed layers. Few organic-matter pores are observed. 2) New pores developing during thermal evolution are primarily organic matter pores and clay mineral pores, with diameters greater than 18 nm. Clay mineral pores with diameters of 18–50 nm are the principal contributors to porosity at temperatures between the low maturity stage and the oil-generation window, and organic matter pores with diameters of greater than 50 nm comprise the majority of pores generated between the gas-generation window and the high-/over-mature stages. 3) Porosity increases continuously with maturity, and the pore system varies at different maturity stages. Porosity evolution is controlled by illite content and organic matter abundance. Total pore volume correlates positively with illite content but negatively with organic matter abundance. These findings could provide guidance on shale oil evaluation in the Songliao Basin and assist in the ‘sweet-spotting’ of lacustrine shale systems across China.

Source Rocks Characterization Of Agbada And Akata Formations In The Niger Delta, Nigeria

The geochemical analysis was performed on twelve (12) core samples from 6 wells of different formations (Akata, Agbada, and Akata/Agbada) of the onshore Niger Delta Basin. The study was essentially based on the results of the Rock-Eval 6 Pyrolysis to evaluate organic matter abundance, quality, and thermal maturity. The Total Organic Carbon (TOC) varies between 0.6 and 3.06 wt% and the Hydrogen Index (IH) of the studied samples ranges from 38 to 202 mgHC/g TOC, indicating predominantly Type III (gas prone) and mixed type II/III (gas and oil-prone) kerogen. This suggests terrigenous and a mixture of marine and terrigenous organic matter deposited in a paralic marine setting. The organic matter is immature to early mature according to the thermal maturity parameter (414<Tmax<432). The well Isan 9 from Agbada (6760 ft) and Agbada/Akata (8680 ft) shows petroleum generation potential of fair (2,5 < S2 < 5 mg HC/g rock) to good (5 < S2 < 10 mgHC/g rock) and poor for the other wells. The maturation of the kerogen indicates a very early stage of maturation (Tmax= 432°C). The results indicate that the shales from Agbada and the transition zone between the upper and lower parts of the Akata Shales are more shaly and perhaps the more mature part of the Agbada formation can be the potential source rocks of Niger Delta Basin.

ANALISIS TEKSTUR SEDIMEN DAN BAHAN ORGANIK TERHADAP KELIMPAHAN MAKROZOOBENTHOS DI MUARA SUNGAI JAJAR, DEMAK

Sungai Jajar merupakan salah satu sungai besar yang aliran sungainya banyak dimanfaatkan penduduk sekitar. Kondisi ini akan berdampak terhadap kualitas perairan yang dapat mengakibatkan suatu pencemaran. Makrozoobentos merupakan hewan yang hidup di dasar perairan dan dapat dijadikan sebagai bioindikator karena habitat hidupnya relatif menetap. Tujuan dari penelitian ini adalah untuk mengetahui tekstur sedimen, kandungan bahan organik, kelimpahan makrozoobentos, hubungan tekstur sedimen dengan bahan organik; tekstur sedimen dengan kelimpahan makrozoobenthos; dan hubungan bahan organik dengan kelimpahan makrozoobenthos. Penelitian dilaksanakan pada bulan Maret-April 2018 menggunakan teknik purposive random sampling dengan total 6 stasiun. Sampel yang diambil adalah substrat dan makrozoobenthos. Hasil penelitian menyatakan bahwa nilai fraksi sand berkisar antara 3,66 -8,40%; fraksi silt berkisar antara 1,29-1,80% dan fraksi clay berkisar antara 89,89-94,81%. Jenis makrozoobentos yang ditemukan dikelompokkan dalam 3 kelas, yaitu: Gastropoda (Cerithidea sp, Terebra sp, Pila sp, Murex sp, Urosalpinx sp, Filopaludina sp dan Telescopium sp), Bivalvia (Anadara sp, Mesodesma sp, Mytillus sp) dan Polychaeta (Nereis sp). Kelimpahan individu berkisar antara 280-2320 ind/m2 dengan kelimpahan tertinggi terdapat pada stasiun III dan kelimpahan terendah pada stasiun I. Kandungan bahan organik berkisar antara 6,73-9,4 %. Hubungan bahan organik dengan tekstur sedimen memiliki korelasi yang cukup erat. Hubungan antara tesktur sedimen dengan kelimpahan makrozoobenthos memiliki korelasi yang rendah. Hubungan bahan organik dengan kelimpahan makrozoobenthos menunjukkan hubungan yang cukup erat dengan nilai koefisien korelasi sebesar 0,557. Sungai Jajar is one of the major rivers where the river flows are widely used by local people. This condition will have an impact on water quality which can cause a pollution. Macrozoobenthos are organism that live in the bottom of the water and can be used as bioindicators because their habitat is relatively sedentary. The purpose of this study was to determine sediment texture, organic matter, abundance of macrozoobenthos, sediment textures relationship with abundance of macrozoobenthos; relationship of organic matter with sediment texture; and the relationship of organic matter with abundance of macrozoobenthos. The study was conducted in March-April 2018 using purposive random sampling method technique with a total of 6 stations. The samples taken were substrate and makrozoobenthos. The result refers that sand fraction value ranged from 3,66%-8,40%; Silt fraction ranged from 1,29%-1,80% and clay fraction ranged from 89,89%-94,81%. Macrozoobenthos found in three classes are: Gastropods (Cerithidea sp, Terebra sp, Pila sp, Murex sp, Urosalpinx sp, Filopaludina sp and Telescopium sp), Bivalvia (Anadara sp, Mesodesma sp, Mytillus sp) and Polychaeta (Nereis sp). Individual abundance ranged from 280-2320 ind/m2 with the highest abundance found at station III and the lowest abundance at station I. The content of organic material ranges from 6,73% -9,4%. The relationship of organic matter with sediment texture has moderate correlation. The relationship between sediment texture and abundance of macrozoobenthos has low correlation. The relationship of organic matter with abundance of makrozoobenthos shows a fairly strong relationship with a correlation coefficient of 0,557.

Evaluation of Source Rock in Xihu Sag in the East China Sea

Xihu Sag is the largest petroliferous sag in China offshore area, which is also the main oil and gas exploration battlefield in the East China Sea shelf basin. Source rock is the main material basis for oil and gas generation, its study has important significance on oil and gas exploration in Xihu Sag. By taking source rock of the Eocene Pinghu Formation and Oligocene Huagang Formation of Pingbei area in Xihu Sag as the research object, static characteristics of source rock in Pingbei Area are evaluated and analyzed in the following three aspects: organic matter abundance, types and maturity. The results show that, based on the organic matter abundance, lower member of Pinghu Formation has a high organic matter abundance, mainly gas, while lower member of Huagang Formation is mainly medium-better source rock, with a common hydrocarbon generating potential. Based on the organic matter types, Huagang Formation and Pinghu Formation are mainly type II and type III kerogen, having a certain hydrocarbon generating potential. While, from the point of view of maturity, lower member of Pinghu Formation is under low mature - mature stage, and the lower part of Huagang Formation mainly under mature to high mature stage. Its hydrocarbon generation peak is basically at present.