Carbonates and Evaporites最新文献

The recognition of incised valleys and the reconstruction of their filling history are significant for defining unconformity surfaces and their stratigraphic framework, particularly when detailed petrographic data are missing. However, little of such research is published so far on the characterization and factors influencing the development of incised valleys using three-dimensional seismic and well data. Thus, this work aims to examine and analyze the geometry and factors controlling the formation and sediments filling of an Eocene incised valley in a sequence stratigraphic frame using an integration of three-dimensional seismic and well data from NE Sirte Basin, Libya. The Eocene incised valley is defined by an unconformable sequence boundary underneath and contains sediments of the lowstand systems tract of Sequence 6. The incision deposits are thick limestones intercalated by thin shales and show a low-order stacking of serrated log motif. The thickness of the incised valley is 118 m and has an aerial extension of ~ 3.2 km in a southwest-northeast direction. Its uppermost width was found to be ranging between 950 and 1100 m and displays a moderately sinuous geometry with asymmetrical meanders occurring each 1 to 1.8 km. The amplitude of these meanders ranges from 500 to 700 m. No distinguishable tributaries are observed in the studied incised valley, indicating the formation of a singular stream or possibly the seismic data resolution not capable to identify small size tributaries. The geometry and stratigraphic architecture of the incised valley suggest a fluvial rather than tidal incisions. The incision primarily formed as a result of a falling sea-level that led to a subaerial exposure, while a successive rising sea-level caused the development of the lowstand deposits and infilling of the incised valley.

The main aim of this study is to integrate the results of sedimentology, strontium isotope with the results simultaneous inversion of 3D seismic data for rock characterization of Rupelian-Chatian Asmari Formation. Using the simultaneous inversion of prestack seismic data variations of rock properties in the Rupelian-Chatian Asmari Formation were interpreted. In this regard, lame coefficients, compressive velocity (Vp), shear velocity (Vs) and compressive-to-shear velocity ratio (Vp/Vs) were extracted from prestack 3D seismic data. Converting shear impedance (SI) and acoustic impedance (AI) to LMR (Lambda-Mu-Rho) provides a more comprehensive understanding of the subsurface rock properties. Based on AI, SI, and lame coefficients, the Rupelian-Chatian Asmari Formation was divided into the lower part and the upper part. The upper part of the Asmari Formation shows a relatively low lame parameters indicating sigmoid patterns composed of shale and sandstone. In contrast, the upper part of Asmari Formation is composed of cyclic carbonate sediments mainly mainly limestone and dolomite. This interval is associated with variations in the lame coefficients, P and S- impedances indicating clinoform patterns. The downlap and top lap termination observed in lame coefficient sections indicate the movement of clinoforms from southwest (shallow) to northeast (deep). The results of this study show that during the Rupelian Chatian time, the coastal part of the Asmari Sea was situated in the southwest of the Kopal Oilfield, while the deeper part was located in the northeast of the field. This study shows that the simultaneous inversion of seismic data combined with sedimentological and geochemical can effectively aid in lithology detection, sequence stratigraphy and depositional setting analysis.

In the geology of Pakistan, the Jurassic carbonate sequence is widely spread around the Upper Indus Basin periphery. Specifically, the indigenous Jurassic layers within the carbonate framework, known as the Samana Suk Formation, situated in the Kahi section Nizampur area, necessitate an extensive examination for future exploration. This investigation is prompted by the recent gas discovery in Jurassic carbonate rocks in the lower Indus Basin, indicating their potential as reservoirs. A thorough evaluation of these Jurassic carbonate units, specifically the Samana Suk Formation, within the Nizampur Basin of the Attock-Cherat ranges, involves a multifaceted approach encompassing observational aspects such as depositional history and diagenetic transformations. Field samples were collected from selected Dolomite beds, and a sedimentological analysis was performed on 20 samples. The current study of the Samana Suk Formation provides a detailed account of diagenetic alterations, delineating various variations in depositional environments represented as different facies: KS-1 Dolomitic Grainstone, KS-2 Bioclastic Wackstone-Mudstone, and KS-3 Bioclastic Peloidal Wackstone. The primary objective is to ascertain the paragenetic sequence of the carbonate succession concerning reservoir quality. The identified diagenetic processes encompass dolomitization, fluid circulation patterns, compaction, micritization, dissolution, and cementation. Notably, dolomitization significantly contributes to enhancing reservoir quality generally and about 50% of the whole world’s carbonate reservoirs are in dolomite. This study significantly enhances our capacity to comprehend the broader spectrum of depositional facies and diagenetic changes within the carbonate succession, thereby shedding light on their reservoir potential.

The frequency of water inrush disasters severely affects tunnel construction, lives, and property. As a result, accurate forecasting of the danger of water inrush during construction is critical. This paper aims to create a progressive evaluation model for assessing water inrush risk during two stages: pre-construction and construction. The proposed model provides a static pre-construction estimation and allows dynamic updates based on previous predictions for unexcavated sections during construction. Initially, comprehensive multi-water inrush information was presented by analyzing 65 tunnel accidents of water during construction, including 12 evaluation indexes encompassing hydrogeology and excavation monitoring. Subsequently, the assessment model was constructed using a combined weighting method and non-linear attribute recognition theory. The information from dynamic monitoring on surrounding rock and seepage pressure is integrated, and feedback site data is used to dynamically modify the weighting of the indicators and update the projected predictions. This approach has been employed as a case study to evaluate the water inrush risk during the Qinling water transmission tunnel. The results demonstrate that the prediction outcomes of dynamic weights align well with on-site holes, exhibiting higher forecasting accuracy than other methods. This approach offers a novel perspective for accurately evaluating water inrush risk in tunnel construction.

Attention to carbonate rocks is important in the contemporary geoheritage studies, although the related knowledge is yet to be complete. The consideration of the already published information can help to fill this gap. The present study offers interpretation of crinoidal limestones (encrinites) in the terms of geoheritage. A total of 180 literature sources (chiefly articles in international journals) were selected, and their content was analyzed. These sources trace the history of crinoidal limestones from the Ordovician to the Cretaceous; these carbonate rocks were especially common in the Carboniferous and Jurassic. Nonetheless, crinoidal limestones are relatively rare in the world’s sedimentary records, and, thus, they constitute a geoheritage resource. The multiple lines of evidence imply that these rocks can be assigned to ten geoheritage types. The existing works stress their scientific and educational utility. Their touristic importance is linked, particularly to the colors of these rocks, which associate with the common people’s emotions. The collected literature suggests that crinoidal limestones are chiefly a potential, not yet proven geoheritage resource. However, several in-situ and ex-situ geoheritage objects representing these rocks have already been established. Generally, the present study demonstrates a novel perspective for the application of carbonate sedimentology.

Late Cretaceous-Miocene foraminiferas were recovered from the BG-1 well in the offshore Eastern Dahomey Basin. Four (4) lithostratigraphic units comprising Ogwashi-Asaba, Upper Araromi, Lower Araromi and Afowo Formations have been delineated and assigned based on the textural characteristics of the sediments. Forty-nine (49) foraminiferal species were identified, with a total count of 47 calcareous species (96%) comprising both planktonic and benthic forms and two arenaceous forms (3%). Seven (7) foraminiferal zones were recognised and dated from the Upper Cenomanian to Late Miocene age. The Globotruncana aegyptica zone, marked by the disappearance of the Maastrichtian forms at 3060 ft, coincided with the appearance of the Early Paleocene benthic forms such at the Anomalinoides umboniferus- Anomalinoides midwayensis zone. The Cretaceous-Paleogene (K-Pg) boundary was recognised at 3060 ft. Seven MFSs and SBs dated from the Upper Cenomanian and Upper Miocene ages were identified in the sequence stratigraphic analysis. The stacking patterns of the lowstand and highstand systems tracts reveal the interplay of progradational and aggradational parasequence signatures of siltstones and sandstone lithologies. The paleodepositional sedimentary packages of the BG-1 well are recognised from the Inner-Neritic to Bathyal environment. The sequence stratigraphic integration of lithofacies and foraminifera assemblages in this study has created a model of the distribution of the elements in the hydrocarbon system of the offshore Eastern Dahomey basin. Therefore, this study will underscore the critical role of sequence biostratigraphy in enhancing the accuracy and efficiency of exploration and development efforts in the hydrocarbon industry.

Understanding the production dynamics characteristics is crucial in regulating the development potential of tight oil in lacustrine limestone reservoir. However, the development characteristics of oil wells with low production and long-cycles has hindered their commercial development in Da’anzhai Member of Sichuan basin. Here we carried out X-ray diffraction (XRD), focused ion beam scanning electron microscope (FIB-SEM), high-pressure mercury injection, nuclear magnetic resonance (NMR), and nano-CT experiments to study the factors controlling the production characteristics in the Da’anzhai Member in central Sichuan Basin. We found that the lacustrine limestone reservoir contains three types of pores and fractures: non-stratigraphic control, shell control, and matrix control. The lacustrine limestone reservoir developed various pore-throat systems, including along-fracture, dissolution pores, fracture-type pores, and isolated pores. Additionally, the small number, small size, dispersed distribution, and poor connectivity of the pores and throats lead to poor sorting, low mercury saturation, and high displacement pressure. The flow capacity is mainly affected by the size of the mainstream channel, the number of pores and throats, and the development degree of intergranular (interparticle) pores. We further demonstrate at least three types of pore-throat distributions corresponding to at least three types of exploitation model. Our work provides a promising route to evaluate the enormous development potential of tight oil in Sichuan basin.

The oncoids possess dual properties, namely “spherical stromatolite” and coated particles resembling ooids but with a larger particle size, which has garnered significant attention from the academic community. In this study, we focused on investigating the oncoids in the Zhangxia Formation of the Cambrian Miaolingian at the Jiguanshan section of Shandong Province, North China Platform applying sedimentological methods. Our findings reveal that these oncoids formed during the FRST (forced regression system domain) phase, representing products of a continuously submerged shallow sea high-energy environment. Two notable characteristics are observed: (1) the volume of the oncoids gradually increases from the bottom to the top; (2) the numerous clots between individual oncoid. Microscopic analysis demonstrates that laminae development is either undeveloped or indistinct in these oncoids. Morphologically speaking, they can be classified into giant and ordinary types based on their appearance. Abundant Girvanella fossils found within the oncoids and clots suggest that the interactions between microbes and the sedimentary environment played a crucial role in oncoid formation. Studying oncoids can reveal their depositional conditions and the role of microbial activity in their formation. Consequently, our study provides compelling evidence supporting microbial involvement in oncoid formation while also serving as a valuable reference for future studies exploring similar sedimentary environments of oncoids.

Abstract

The key obstacles to developing the four wells in the Pariwali Block of the Potwar Basin in Pakistan continue to be an accurate age diagnosis of the reservoir intervals, facies variation, and locating the hydrocarbon target for future development wells. The purpose of this work is to offer integrated biostratigraphic, facies, and sequence stratigraphic information from well cuttings to more fully characterize the carbonate reservoirs. The diagnosis of exact stratigraphic units, their ages, and order of cyclicity were constrained by larger benthic foraminiferal biostratigraphy, and the facies integration has made it possible to identify the sequence stratigraphic architecture. The Paleogene Lockhart, Sakesar, and Chorgali Formations were diagnosed, which were deposited on a ramp carbonate platform in a range of environments, including tidal flats, the inner ramp, the proximal middle ramp, and the outer ramp. Integrated sequence stratigraphic analysis has demarcated two third-order cycles (TR1 and TR2), two depositional Sequences (Sequence 1 and Sequence 2) having two transgressive systems tracts (TST 1 and TST 2) which are separated from the Two regressive Systems tracts (RST 1 and RST 2) by Maximum Flooding Surfaces (MFS 1 and MFS 2), respectively. The diagenetic analysis and nanoporosity information was helpful in delineating sweet spots for the hydrocarbons in the Lockhart, Sakesar, and Chorgali formation that lies within the larger benthic foraminiferal–algal wackestone–packstone and dolomitized mudstone–wackestone facies. The occurrence of lime mudstone facies controlled the reservoir compartmentalization at repeated intervals in different wells.