scholarly journals Formation environments and mechanisms of multistage paleokarst of Ordovician carbonates in Southern North China Basin

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Haitao Zhang ◽  
Guangquan Xu ◽  
Mancai Liu ◽  
Minhua Wang
Keyword(s):  
Carbonate Rocks ◽  
North China ◽  
Oil And Gas ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Geochemical Data ◽  
Near Surface ◽  
Oil And Gas Exploration ◽  
Pore Types ◽  
North China Basin

AbstractWith the reduction of oil and gas reserves and the increase of mining difficulty in Northern China, the carbonate rocks in Southern North China Basin are becoming a significant exploration target for carbonate reservoirs. However, the development characteristics, formation stages, formation environments and mechanisms of the carbonate reservoirs in Southern North China Basin are still unclear, which caused the failures of many oil and gas exploration wells. This study focused on addressing this unsolved issue from the Ordovician carbonate paleokarst in the Huai-Fu Basin, which is located in the southeast of Southern North China Basin and one of the key areas for oil and gas exploration. Based on petrology, mineralogy and geochemical data, pore types, distribution characteristics, and formation stages of the Ordovician paleokarst were analyzed. Then, in attempt to define the origins of porosity development, the formation environments and mechanisms were illustrated. The results of this study showed that pore types of the Ordovician carbonates in the Huai-Fu Basin are mainly composed of intragranular pores, intercrystalline (intergranular) pores, dissolution pores (vugs), fractures, channels, and caves, which are usually in fault and fold zones and paleoweathering crust. Furthermore, five stages and five formation environments of the Ordovician paleokarst were identified. Syngenetic karst, eogenetic karst, and paleoweathering crust karst were all developed in a relatively open near-surface environment, and their formations are mainly related to meteoric water dissolution. Mesogenetic karst was developed in a closed buried environment, and its formation is mainly related to the diagenesis of organic matters and thermochemical sulfate reduction in the Permian-Carboniferous strata. Hydrothermal (water) karst was developed in a deep-buried and high-temperature environment, where hydrothermal fluids (waters) migrated upward through structures such as faults and fractures to dissolve carbonate rocks and simultaneously deposited hydrothermal minerals and calcites. Lastly, a paleokarst evolution model, combined with the related porosity evolution processes, nicely revealed the Ordovician carbonate reservoir development. This study provides insights and guidance for further oil and gas exploration in the Southern North China Basin, and also advances our understanding of the genesis of carbonate paleokarst around the world.

scholarly journals Characteristics and evaluation of the Upper Paleozoic source rocks in the Southern North China Basin

2021 ◽  
Vol 13 (1) ◽  
pp. 294-309
Author(s):  
Fengyu Sun ◽  
Gaoshe Cao ◽  
Zhou Xing ◽  
Shuangjie Yu ◽  
Bangbang Fang
Keyword(s):  
Source Rock ◽  
North China ◽  
Oil And Gas ◽  
Source Rocks ◽  
Oil And Gas Exploration ◽  
Potential Source ◽  
Unconventional Oil ◽  
Upper Paleozoic ◽  
Unconventional Oil And Gas ◽  
North China Basin

Abstract The Upper Paleozoic coal measure strata in the Southern North China Basin have good potential for unconventional oil and gas exploration. However, there has been no systematic evaluation of potential source rock in this area; this affects the estimation of potential resources and the choice of exploratory target layers. In this study, full core holes ZK0901 and ZK0401, which perfectly reveal Upper Paleozoic strata in the study area, systematically collected and analyzed the samples for total organic carbon, rock pyrolysis, chloroform bitumen “A,” organic maceral, vitrinite reflectance, and kerogen carbon isotopes. The results showed that in addition to coal rocks, mudstones and carbonate rocks are also potential source rocks in the Upper Paleozoic strata. Vertically, the source rocks are continuous in Taiyuan Formation, the lower part of Shanxi Formation, and Lower Shihezi Formation. The organic matter type in the Upper Paleozoic coal rocks and mudstone source rock belong to type III or II. This phenomenon is mainly attributed to the special transgressive–regressive sedimentary environment of the carbonate rocks. The higher degree of thermal evolution in the Upper Paleozoic source rocks may be related to the structure or a higher paleogeothermal gradient in this area. The coal layer and its upper and lower mudstone of the Shanxi Formation and Lower Shihezi Formation are the main target layers of unconventional oil and gas exploration. The results from this study can be used as a reference for the study on potential source rock for unconventional oil and gas exploration in the Southern North China Basin.

Using Logging and Seismic Data to Identify Boundaries Between Different OWC Units in a Deepwater Carbonate Reservoirs

2021 ◽  
Author(s):  
Kangxu Ren ◽  
Junfeng Zhao ◽  
Jian Zhao ◽  
Xilong Sun
Keyword(s):  
Seismic Data ◽  
Carbonate Rocks ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Sedimentary Process ◽  
Core Samples ◽  
Tight Carbonate ◽  
Porosity And Permeability ◽  
Seismic Sections ◽  
Parameters Inversion

Abstract At least three very different oil-water contacts (OWC) encountered in the deepwater, huge anticline, pre-salt carbonate reservoirs of X oilfield, Santos Basin, Brazil. The boundaries identification between different OWC units was very important to help calculating the reserves in place, which was the core factor for the development campaign. Based on analysis of wells pressure interference testing data, and interpretation of tight intervals in boreholes, predicating the pre-salt distribution of igneous rocks, intrusion baked aureoles, the silicification and the high GR carbonate rocks, the viewpoint of boundaries developed between different OWC sub-units in the lower parts of this complex carbonate reservoirs had been better understood. Core samples, logging curves, including conventional logging and other special types such as NMR, UBI and ECS, as well as the multi-parameters inversion seismic data, were adopted to confirm the tight intervals in boreholes and to predicate the possible divided boundaries between wells. In the X oilfield, hundreds of meters pre-salt carbonate reservoir had been confirmed to be laterally connected, i.e., the connected intervals including almost the whole Barra Velha Formation and/or the main parts of the Itapema Formation. However, in the middle and/or the lower sections of pre-salt target layers, the situation changed because there developed many complicated tight bodies, which were formed by intrusive diabase dykes and/or sills and the tight carbonate rocks. Many pre-salt inner-layers diabases in X oilfield had very low porosity and permeability. The tight carbonate rocks mostly developed either during early sedimentary process or by latter intrusion metamorphism and/or silicification. Tight bodies were firstly identified in drilled wells with the help of core samples and logging curves. Then, the continuous boundary were discerned on inversion seismic sections marked by wells. This paper showed the idea of coupling the different OWC units in a deepwater pre-salt carbonate play with complicated tight bodies. With the marking of wells, spatial distributions of tight layers were successfully discerned and predicated on inversion seismic sections.

SECONDARY CHANGES IN CARBONATE ROCKS OF OIL AND GAS COMPLEXES

2020 ◽  
pp. 18-23
Author(s):  
M.A. Tugarova
Keyword(s):  
Carbonate Rocks ◽  
Oil And Gas ◽  
Carbonate Reservoirs ◽  
Fundamental Importance ◽  
Schematic Diagram ◽  
Reservoir Properties ◽  
Physico Chemical ◽  
Chemical Conditions ◽  
First Time

The article considers the secondary transformations of carbonate rocks of oil and gas complexes, which are of fundamental importance in the formation of reservoir properties. For the first time, a schematic diagram, illustrating the regularities of secondary processes in carbonate reservoirs and their relationship with the physico-chemical conditions of the stratosphere is proposed.

scholarly journals Prediction of Favorable Carbonate Reservoirs under Extremely Thick Salts via Poststack Facies-Controlled and Prestack Zoeppritz Equation Inversions in the Santos Basin of Brazil

Geofluids ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Sheng Zhang ◽  
Suoliang Chang ◽  
Handong Huang ◽  
Yinping Dong ◽  
Youyi Shen ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Large Angle ◽  
Low Frequency ◽  
Prediction Method ◽  
Approximate Equation ◽  
Carbonate Reservoirs ◽  
Linear Inversion ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Oil And Gas Exploration

Subsalt carbonate rocks in Brazil’s deepwater region have broad prospects for oil and gas exploration and development. Due to the low-frequency bandwidth of the seismic data and the poor signal quality for this kind of reservoir target, there is a demand for accurate seismic prediction methods. We employ the facies-controlled inversion using a low-pass filter matrix to ensure the accuracy of the low frequency and to improve the robustness of the inversion results. We integrated the concept of adaptive regularization constraint of the Zoeppritz equation into the generalized linear inversion theory framework, which overcomes the shortcomings of the approximate equation. Making full use of the large angle prestack seismic information, Zoeppritz equation inversion improves the accuracy of the inversion results. The application of this method in carbonate reservoirs under extremely thick salts in the Santos Basin of Brazil indicates the feasibility and practicality of the proposed integrated prediction method.

Improving Porosity–Velocity Relationships Using Carbonate Pore Types

2015 ◽  
Vol 23 (04) ◽  
pp. 1540006 ◽  
Author(s):  
Tingting Zhang ◽  
Yuefeng Sun ◽  
Qifeng Dou ◽  
Hanrong Zhang ◽  
Tonglou Guo ◽  
...  
Keyword(s):  
Pore Structure ◽  
Acoustic Impedance ◽  
Carbonate Rocks ◽  
Seismic Inversion ◽  
Carbonate Reservoir ◽  
Reservoir Rocks ◽  
Fluid Content ◽  
Fracture Fluid ◽  
Poroelastic Model ◽  
Pore Types

Acoustic impedance in carbonates is influenced by factors such as porosity, pore structure/fracture, fluid content, and lithology. Occurrence of moldic and vuggy pores, fractures and other pore structures due to diagenesis in carbonate rocks can greatly complicate the relationships between impedance and porosity. Using a frame flexibility factor ([Formula: see text]) derived from a poroelastic model to characterize pore structure in reservoir rocks, we find that its product with porosity can result in a much better correlation with sonic velocity ([Formula: see text] = [Formula: see text]) and acoustic impedance ([Formula: see text] = [Formula: see text], where A, B, C and D is 6.60, 0.03, 18.3 and 0.09, respectively for the deep low-porosity carbonate reservoir studied in this paper. These new relationships can also be useful in improving seismic inversion of ultra-deep hydrocarbon reservoirs in other similar environments.

Major Controls on the Evolution of the Cambrian Dolomite Reservoirs in the Keping Area, Tarim Basin

2013 ◽  
Vol 734-737 ◽  
pp. 377-383
Author(s):  
Qing Li ◽  
Xue Lian You ◽  
Wen Xuan Hu ◽  
Jing Quan Zhu ◽  
Zai Xing Jiang
Keyword(s):  
Tarim Basin ◽  
Significant Contribution ◽  
Oil And Gas ◽  
Geochemical Data ◽  
Acid Dissolution ◽  
High Quality ◽  
Secondary Porosity ◽  
Oil And Gas Exploration ◽  
Reservoir Evolution ◽  
Major Factors

The Cambrian dolomite reservoir is an important target in oil and gas exploration. The Penglaiba section in the Keping area is typically examined in studies dealing with the Cambrian dolomite reservoirs of northwestern Tarim Basin. Based on sedimentological, petrographic, and geochemical data, lithofacies and fluids are identified as the major factors that control the dolomite reservoir in the study area. Lithoacies are fundamental to reservoir evolution because they provide suitable channels for dolomitization and dissolution of fluids that, in turn, facilitate the formation of high quality reservoirs. The lithofacies which could form high-quality reservoirs in the study area are: slope slip (collapse) facies, gypsum related facies, and algae dolomite facies. The sources of fluids include seawater, meteoric freshwater, diagenetic/hydrocarbon fluid, and hydrothermal fluid. These fluids lead to dolomitization, penecontemporaneous meteoric dissolution, hypergene dissolution, organic acid dissolution and hydrothermal dissolution that result in secondary porosity, and as such, they have a significant contribution to reservoir evolution.

scholarly journals Optimization of Rock Physics Models by Combining the Differential Effective Medium (DEM) and Adaptive Batzle-Wang Methods in “R” Field, East Java

2019 ◽  
Vol 17 (2) ◽  
Author(s):  
M. Wahdanadi Haidar ◽  
Reza Wardhana ◽  
M. Iskan ◽  
M. Syamsu Rosid
Keyword(s):  
Elastic Modulus ◽  
Wave Velocity ◽  
Carbonate Rocks ◽  
Effective Medium ◽  
Carbonate Reservoir ◽  
P Wave ◽  
S Wave ◽  
P Wave Velocity ◽  
Reservoir Conditions ◽  
Pore Types

The pore systems in carbonate reservoirs are more complex than the pore systems in clastic rocks. There are three types of pores in carbonate rocks: interparticle pores, stiff pores and cracks. The complexity of the pore types can lead to changes in the P-wave velocity by up to 40%, and carbonate reservoir characterization becomes difficult when the S-wave velocity is estimated using the dominant interparticle pore type only. In addition, the geometry of the pores affects the permeability of the reservoir. Therefore, when modelling the elastic modulus of the rock it is important to take into account the complexity of the pore types in carbonate rocks. The Differential Effective Medium (DEM) is a method for modelling the elastic modulus of the rock that takes into account the heterogeneity in the types of pores in carbonate rocks by adding pore-type inclusions little by little into the host material until the required proportion of the material is reached. In addition, the model is optimized by calculating the bulk modulus of the fluid filler porous rock under reservoir conditions using the Adaptive Batzle-Wang method. Once a fluid model has been constructed under reservoir conditions, the model is entered as input for the P-wave velocity model, which is then used to estimate the velocity of the S-wave and the proportion of primary and secondary pore types in the rock. Changes in the characteristics of the P-wave which are sensitive to the presence of fluid lead to improvements in the accuracy of the P-wave model, so the estimated S-wave velocity and the calculated ratio of primary and secondary pores in the reservoir are more reliable.

scholarly journals Pore characterization of marine-continental transitional shale in Permian Shanxi Formation of The Southern North China Basin

2020 ◽  
Vol 38 (6) ◽  
pp. 2199-2216 ◽  
Author(s):  
Xiaoguang Yang ◽  
Shaobin Guo
Keyword(s):  
Negative Correlation ◽  
North China ◽  
Gas Adsorption ◽  
Relative Content ◽  
X Ray Diffraction ◽  
Mesopore Volume ◽  
Positive Correlation ◽  
Pore Types ◽  
North China Basin ◽  
Adsorption Desorption

Organic-rich marine-continental transitional shale is widely developed in the Permian Shanxi Formation in the Southern North China Basin. In this study, shale samples from the southern and northern wells of the basin were characterized by X-ray diffraction, high-pressure mercury intrusion porosimetry, low-pressure gas adsorption (N2 and CO2) and argon ion polishing-field emissions scanning electron microscopy. The pore types and structures of shale micropores, mesopores and macropores are qualitatively described; their pore size distribution and volume are quantitatively characterized; and the influencing factors of the pore volume are analyzed. The results show that the marine-continental transitional shale pores exhibit an unbalanced multimodal distribution with four peaks at 0.4–0.8 nm, 2–4 nm, 10–50 nm, and >10 µm. The mesopore volume is dominant, accounting for 40–70% of pores. The mesopores of the samples are slit-shaped pores and ink bottle-shaped pores. Since there is a desorption hysteresis loop on the N2 adsorption-desorption curve, most of them belong to the H4 type, and ye23-8 belongs to the mixed H2 and H4 type according to the IUPAC classification scheme. The slit-shaped pores are mainly interlayer pores and interparticle pores in clays, and the ink bottle-shaped pores are tiny dissolved pores and organic matter pores. Ro has negative correlation with the volumes of the mesopores and macropores, but it does not affect the volume of micropores. TOC has a positive correlation with the macropore and micropore volumes, and it has a negative correlation with mesopore volume. The relative contents of kaolinite and I/S have a positive correlation with the mesopore and macropore volumes. The relative content of illite has a negative correlation with the mesopore and macropore volumes. The relative content of chlorite has a negative correlation with the mesopore volume.

Integrated processing and interpretation to image and derisk a carbonate reservoir clouded by shallow gas — A case study from offshore Vietnam

2021 ◽  
Vol 40 (5) ◽  
pp. 357-364
Author(s):  
Jaewoo Park ◽  
Craig Hyslop ◽  
Da Zhou ◽  
Arjun Srinivasan ◽  
Patricia Montoya ◽  
...  
Keyword(s):  
Oil And Gas ◽  
Model Building ◽  
Integrated Approach ◽  
Carbonate Reservoir ◽  
Carbonate Reservoirs ◽  
Shallow Gas ◽  
Hydrocarbon Production ◽  
Field Development ◽  
Processing Depth ◽  
Seismic Image

Carbonate reservoirs are increasingly becoming an important resource for hydrocarbon production because they contain the majority of remaining proven oil and gas reserves. In this context, carbonate reservoirs could represent new opportunities; however, there is still a lack of understanding of their subsurface status and characterization. Carbonate reservoirs are more difficult to evaluate than their siliciclastic counterparts because many aspects of carbonate rocks make their seismic image signature complex and difficult to interpret. Moreover, the presence of complex overburden such as shallow gas accumulation can exacerbate amplitude and phase fidelity at the reservoir, which introduces an additional imaging challenge. This makes field development of carbonate reservoirs extremely difficult because field development requires detailed delineation of characteristic karst features to avoid drilling hazards and sudden water breakthrough. In this paper, we demonstrate that a tight integration of signal processing, depth model building, and imaging, as well as near-real-time seismic interpretation feedback, is the key to success for imaging complex carbonate reservoirs with overburden challenges. Our findings show that such an integrated approach can result in a substantially better image, reduced depth uncertainty, and better delineation of karst and fractures. It can also aid in well placement and improve reservoir property modeling.

Multi-episodic recrystallization and isotopic resetting of early-diagenetic dolomites in near-surface settings

2021 ◽  
Vol 91 (1) ◽  
pp. 146-166
Author(s):  
Brooks H. Ryan ◽  
Stephen E. Kaczmarek ◽  
John M. Rivers
Keyword(s):  
Carbonate Rocks ◽  
Isotopic Exchange ◽  
Early Diagenesis ◽  
Geochemical Data ◽  
Near Surface ◽  
Lower Eocene ◽  
Gypsum Formation ◽  
History Of ◽  
Mineral Replacement ◽  
Diagenetic History

ABSTRACT The lower Eocene Rus Formation in Qatar reflects carbonate deposition in a semirestricted to fully restricted marine setting on a shallow ramp. Petrographic, mineralogical, and geochemical evidence from three research cores show early diagenesis has extensively altered nearly every petrological attribute of these rocks despite not having been deeply buried. In southern Qatar, the lower Rus (Traina Mbr.) consists of fabric-retentive dolomite intervals that preserve mudstone, wackestone, and packstone textures that are interbedded with depositional gypsum beds. In northern Qatar, the same member is dominated by fabric-destructive planar-e dolomite, and evaporites are absent. In both northern and southern Qatar, the upper Rus (Al Khor Mbr.) is composed of fabric-retentive dolomite intervals as well as limestone intervals rich with Microcodium textures that display evidence of dedolomitization. Geochemical analysis reveals that the limestones have an average δ18Ocal of –10.73‰ VPDB and δ13Ccal of –7.84‰ VPDB, whereas average dolomite δ18Odol is significantly higher (–1.06‰ VPDB) but δ13Cdol values (–3.04‰ VPDB; range –10 to 0‰) overlap with δ13Ccal values. Additionally, δ13Cdol trends toward normal marine values with depth away from the calcite–dolomite contact in all three cores. Petrographic observations demonstrate that dolomite crystals are commonly included in calcite and partially to completely replaced by calcite in these intervals and suggests that dolomite formed before calcite in the Microcodium-bearing intervals. Furthermore, the dolomites are commonly cemented by gypsum in the Traina Mbr. in southern Qatar, suggesting that dolomitization may have also occurred before, or concurrent with, bedded gypsum formation and indicates that dolomitization occurred early. Early dolomites were subsequently replaced by Microcodium-bearing limestones at and immediately below paleo-exposure surfaces, and at greater depths recrystallized in mixed marine–meteoric fluids, producing a negative δ13Cdol signature that trends toward more positive values away from the limestone–dolomite contact. Lastly, the dolomites underwent another phase of recrystallization in either marine-dominated fluids or possibly a well-mixed aquifer setting, resulting in a near-0‰ δ18Odol signature but retaining the negative δ13C signature. These findings thus have implications for reconstructing the diagenetic history of carbonate rocks, as they suggest that early diagenesis of carbonates can be extremely complex, resulting in multiple stages of mineral replacement and isotopic exchange in meteoric and shallow marine fluids before significant burial. Furthermore, this study shows that dolomitization of a limestone does not necessarily prevent additional early diagenesis and multiple recrystallization events. Lastly, it emphasizes the importance of incorporating petrographic observations with geochemical data when interpreting the diagenetic history of carbonate rocks.

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