Lithofacies Types, Assemblage Characteristics, and Sedimentary Evolution Model of Lacustrine Shale in Dongyuemiao Formation of Fuxing Area

The identification and classification of lithofacies’ types are very important activities in shale oil and gas exploration and development evaluation. There have been many studies on the classification of marine shale lithofacies, but research on lacustrine shale lithofacies is still in its infancy. Therefore, in this study, a high-resolution sequence stratigraphic framework is established for the lacustrine shale of the Jurassic Dongyuemiao Formation in the Fuxing area using detailed core observations, thin section identification, XRD analysis, major and trace element analysis, wavelet transform analysis, and detailed identification and characterization of the fossil shell layers in the formation. In addition, the lithofacies’ types and assemblages are identified and characterized, and the lithofacies’ characteristics and sedimentary evolution models in different sequence units are analyzed. The significance of the lithofacies assemblages for shale oil and gas exploration is also discussed. The results show that the shale of the target interval can be divided into 8 parasequence sets; further, 9 types of lithofacies and 6 types of lithofacies assemblages are identified. The 9 lithofacies are massive bioclast-containing limestone shoal facies (LF1), thick-layered fossil shell–containing limestone facies (LF2), layered mud-bearing fossil shell–containing limestone facies (LF3), laminated fossil shell–containing argillaceous shale facies (LF4), laminated fossil shell–bearing argillaceous shale facies (LF5), argillaceous shale facies (LF6), massive storm event–related bioclast-containing facies (LF7), massive argillaceous limestone facies (LF8), and massive mudstone facies (LF9). The sedimentary evolution models of different lithofacies are established as follows: Unit 1 (LF1-LF6) of the Dong-1 Member corresponds to the early stage of a lake transgressive system tract, and Units 2–4 (LF4-LF7) correspond to the middle to late stage of the lake transgressive system tract, which was an anoxic sedimentary environment. The Dong-2 Member (LF7-LF8) and the Dong-3 Member (LF5+LF9) correspond to a lake regressive system tract, which was an oxygen-rich sedimentary environment. Based on the characteristics of the shale lithofacies, sedimentary environment, and the quality of the reservoir, the lithofacies assemblage of LF4–LF7 in Unit 4 is the most favorable type for oil and gas exploration, followed by the lithofacies assemblage in Unit 2; the lithofacies assemblage in the Dong-2 and Dong-3 Members are the worst.

Sedimentary Evolution Characteristics of Fine-Grained Lithofacies under the High-Resolution Isochronous Shelf System: Insights from the Wufeng-Longmaxi Shales in the Sichuan Basin

The deposition and evolution of fine-grained sediments is a hot topic in fine-grained sedimentary rock studies and is important for accurately evaluating shale gas sweet spots. In this paper, the fine-grained deposition and evolution characteristics of the Wufeng-Longmaxi shales, major targets for Chinese shale gas exploration, were studied by using core observations, thin section analyses, scanning electron microscopy, geochemical analysis, and fossil identification. This work accurately identified six typical lithofacies; among them, the organic matter-rich siliceous shale facies (OMRSSF), the high-organic matter siliceous argillaceous shale facies (HOMSASF), and the medium-high organic matter low calcareous siliceous shale facies (M-HOMLCSASF) are favorable facies for shale gas exploration. The high-resolution isochronous unit in the shelf fine-grained sedimentary system was established, and the differential evolution of lithofacies in the system tract was discussed. The lithofacies deposition and differentiation in the transgressive system tract were controlled by the transgressive scale and tectonics under increasingly shallow water conditions. The lithofacies deposition and differentiation in the regressive system tract were controlled by tectonics and the preexisting lithofacies. The lithofacies in the regressive system tract had more frequent facies transitions and greater differentiation than those in the transgressive system tract, and they exhibited significant spatiotemporal inheritance. Sequential differential sedimentary sequences and symmetric differential sedimentary sequences were distinguished in the continental shelf sedimentary system. The lithofacies depocenters and subsidence centers were consistent in the transgressive system tract, while the tectonically active paleocontinent was important in the regression system tract. This study is of great significance for further high-resolution exploration of marine shale and improvement of the theory of shelf fine-grained sedimentary systems.

Sequence stratigraphic analysis of the Surma Group in X Gas Field, Surma Basin, Bengal Delta

This study builds a high-resolution sequence stratigraphic framework for the Surma Group in the X Gas field. At first, electrofacies and depositional sequences were interpreted from wire line logs. Then, the field wide configurations of these sequences have been identified in seismic using reflection terminations (of flap, onlap, top lap and down lap relationship). Finally, wire line log and seismic interpretations were integrated to establish sequences stratigraphic framework in the Surma Group. Electrofacies analysis has revealed four major facies associations namely: (i) Bell shaped fining upward facies corresponds to retrogradational shoreface to tidal flat deposits, (ii) Funnel shaped coarsening upward facies corresponds to progradational shoreface to tidal flat, (iii) Cylindrical aggradational facies interpreted as stacked channel and (iv) Symmetrical or Bow shaped facies corresponds to heterolithic unit. The succession of Surma group of about 3100+ m has been divided into twelve depositional sequences. With exception of depositional sequence 1, 11 and 12, most of them are composed of three system tracts: sandy lowstand system tract, shaley transgressive system tract and heterolithic to shaley highstand system tract. Repetitive occurrence of incised valley, shoreface sand as well as tidal channel sand separated by transgressive system tract shelfal mud resulted in sand-shale alternation in the Surma Group. The lower depositional sequences (up to sequence-6) are shale dominated and equivalent to the Lower Surma Group. The upper six sequences are sand dominated, have more channel incisions and sequence boundary representing the Upper Surma Group

Shale facies from the Wufeng-Lower Longmaxi Formations in the Huangying section of Wulong County, southeastern Sichuan Basin, China

With the increasing interest on shale oil and shale gas around the world, it is essential to discover alternative economic shale gas fields outside the Fuling gas field, which is China’s first large-scale shale gas field with 100 billion cubic meters of reserves in the Sichuan Basin (China). Based on comprehensive analysis of dozens of black shale samples, the Wufeng Formation and the Lower Longmaxi Formation in the Huangying section of Wulong County showed good prospects for shale gas. An integrated study of petrology, organic geochemistry, trace element analysis, and sedimentology reveals that the sea level during the Early Silurian period was relatively high. Consequently, carbon-rich and high-silica lithofacies were deposited, corresponding to argillaceous-siliceous deepwater shelf microfacies. During deposition of the Guanyinqiao bed (latest Ordovician), the sea level was relatively low, resulting in the formation of moderately high carbon and high-silica shale facies, corresponding to argillaceous shallow shelf microfacies. A complete transgressive-regressive third-order sequence was recorded in the Longmaxi Formation. Carbon-rich and high-silica lithofacies, which are associated with carbonaceous deepwater shelf microfacies and siliceous-argillaceous deepwater shelf microfacies, respectively, dominated the transgressive system tract. Compared with the Fuling area with a record of high shale gas productivity, the Wufeng Formation and the transgressive system tract of the Longmaxi Formation in the study area demonstrate great potential for shale gas.

KAJIAN HUBUNGAN DIAGENESIS DAN SIKUEN STRATIGRAFI FORMASI NANGGULAN BERDASARKAN ANALISIS PETROGRAFI BATUPASIR

Proses diagenesis yang terjadi pada batuan memiliki hubungan yang erat dengan konsep sikuen stratigrafi. Proses diagenesis awal (eogenesis) yang terbentuk pada suatu batuan dipengaruhi oleh posisi stratigrafi batuan tersebut dalam tataan sikuen stratigrafi. Eogenesis tersebut dapat diteliti dengan menggunakan data petrografi batupasir mengenai proses diagenesis yang terdapat pada batuan, dan juga dengan melihat posisi batuan dalam tataan sikuen stratigrafi. Formasi Nanggulan yang tersingkap di Kulon Progo, Yogyakarta merupakan salah satu formasi yang dengan beberapa interval litologi batupasir. Analisis mengenai sikuen stratigrafi Formasi Nanggulan telah diteliti sebelumnya dengan menggunakan analisis batuan inti. Studi lebih lanjut mengenai Formasi Nanggulan bertujuan untuk mengetahui karakteristik batupasir dan proses diagenesisnya, serta mencari hubungan antara proses diagenesis dan sikuen stratigrafi. Penelitian dilakukan dengan menggunakan analisis petrografi dari data batuan inti dan singkapan permukaan dengan tujuan untuk mengetahui hubungan antara diagenesis dan sikuen stratigrafi pada batupasir Formasi Nanggulan.Berdasarkan analisis petrografi terhadap diagenesis pada Formasi Nanggulan, dapat dikonfirmasi bahwa Formasi Nanggulan terdiri dari 3 system tract yaitu lowstand system tract (LST), transgressive system tract (TST), dan highstand system tract (HST). Tahapan proses diagenesis yaitu eogenesis, mesogenesis dan telogenesis telah mempengaruhi Formasi Nanggulan. Karakteristik diagenesis pada Formasi Nanggulan bervariasi sesuai dengan system tract dan marker batas sikuen pada tataan sikuen stratigrafi. Berdasaran penelitian ini dapat diketahui bahwa sikuen stratigrafi Formasi Nanggulan dapat dikonfirmasi dengan data diagenesis.

Facies Changes Between Kolosh and Sinjar Formations Along Zagros Fold–Thrust Belt in Iraqi Kurdistan Region

The present study is concerned with lateral and vertical facies changes between Kolosh (Paleocene) and Sinjar (or Khurmala) (Paleocene-Early Eocene) Formations in Sulaimani and Duhok area, Kurdistan Region, NE-Iraq. The latter and former formations are belonging to basinal clastic (turbidite) and reefal carbonate facies respectively. The facies changes are documented in six sections by field studies and evaluation of previous ideas and data which are critically discussed and compared to the result of the present study. The special attention is directed towards the contact between the two Formations in relation to conformity. All the studies achieved before 2002 showed conformable contact between the two formations while the most recent study found large a gap (erosional unconformity) between the two formations which persisted for 5million years. According to latter study, the sea level fall associated with this unconformity assigned to be type one and type two sequence boundaries in the east of Darbandikhan, north of Koya towns and the Bekhme gorge.Conversely, the present study has not recorded gaps in the sedimentation in the studied sections either in Sulaimani or Dohuk area. The contact can be regarded as transgressive system tract which represented by green marl or sandstone, which changes to limestone of Sinjar or Khurmala Formation (HST).The conglomerate beds that are recorded in the previous studies at the contact of the two formations are not proved in the present study. The previously recorded conglomerate is located inside the upper part of the Kolosh Formation not in the contact and it represents submarine fan feeder channel. In contrast to previous studies, neither incised valleys nor erosional unconformity are found at the contact between the two formations in the studied area. The one meter intraformational conglomerate that are found (in some previous studies) in the Bekhme gore is not found in the present study. It is observed that the Kolosh Formation, at Bekhme Gore consists of green marl and sandstone with one bed of Khurmala Formation. The green marl is changes totally to dolomitic limestone of the latter Formation toward northwest at the north of Saru Kani village near Bujeel town. This proves that both formations are deposited in one basin and Khurmala formation has the age of Lower Paleocene to Lower Eocene.

Sequence Stratigraphic Analysis of Badaowan Formation in Dishuiquan Area, Junggar Basin

In the light of the principle and method of sequence stratigraphy, the sequence stratigraphic framework of Badaowan formation in the Dishuiquan area was established. The results show that the sequence of Badaowan formation is one and half, including 5 system tracts. The whole experiences the process of retrogradation, progradation and then retrogradation again. There develop three types of sedimentary facies such as braided river, braided river delta and lakes, five types of sedimentary subfacies and 10 types of sedimentary microfacies. Most of JSQ1 sequence lowstand system tract is braided rivers, the lacustrine transgressive system tract mainly develops shore-shallow lacustrine sediment and most of highstand system tract is braided river delta; lowstand systems tract of JSQ2 sequence mainly develops braided river delta, most of the lacustrine transgressive system tract is shore-shallow lacustrine sediments.

Towards an integrated stratigraphy of the Gramame Formation (Maastrichtian), CIPASA quarry, Pernambuco-Paraíba Basin, NE Brazil

This study presents the integrated biostratigraphic (calcareous nannofossils and foraminifera), petrographic, geochemical and ichnological analyzes of the Gramame Formation (Maastrichtian) at the CIPASA Quarry section, in the Pernambuco-Paraíba Basin, northeastern Brazil. A high resolution calcareous nannofossil biostratigraphic study has been carried out, allowing to subdivide the studied section into three subzones of Maastrichtian age: CC25A, CC25B, and CC25C. Each biostratigraphic unit was further characterized by petrographic, geochemical and ichnological parameters. During the Maastrichtian the area was characterized by a dry and warm climate with low influx of terrigenous sediments. These conditions were fundamental to the widespread development of a carbonate ramp system in an outer neritic to bathyal setting, with deposition of alternating calcareous mudstones and argillaceous mudstones of the Gramame Formation. The Gramame Formation belongs to the transgressive system tract of second-order type, characteristic of a Passive Margin Sequence. The studied section consists of part of a third order deposicional cycle, which is arranged in a transgressive systems tract and a highstand systems tract. The lowstand systems tract was not characterized.