Features of the Tien Shan newest orogen morphostructure

Research subject. The concept of morphostructure implies the presence of a relationship between the relief forms of segments of the Earth’s crust and their structural and material content. This article describes the geological ensembles of the Tien Shan orogen, the tectonic structure and modern relief of which differ in their parameters from the general morphostructural plan and which, therefore, belong to the category of morphostructural anomalies. Materials and methods. The data presented in the article were obtained in the course of field structural-geological and morphostructural study of key segments of the Tien Shan orogen, as well as an analysis of materials from previous research, including the results of geophysical sounding of the Earth’s crust and geodesical monitoring of relative modern movements of reference points on the surface.Results. The article demonstrates that, against the background of the general linear-wave morphostructure of the Tien Shan orogen, there are areas whose relief and tectonic structure do not agree with the general tectonic plan of the mountain. Wi thin the considered region, different types of morphostructural anomalies are identified and described, reflecting the speci fics of the evolution and geotectonic position of individual volumes of upper-crust rock complexes: zones of concentrated deformation and tectonic joining; centrally symmetric structures formed on the site of paleoatolls; neotectonic protrusions of the granite basement; trans-regional zone of the Talaso-Ferghana Fault and other structures. Conclusion. The formation of morphostructural anomalies is associated with the presence of non-trivial geodynamic environments operating against the background of the tectonic regime common to the Tien Shan. The modern morphostructure of the Tien Shan is the result of interference between various geodynamic regimes and settings: a regime common to the entire territory of the orogen and particular regimes that manifest themselves sporadically and are reflected in the modern relief.

Assessment of Paleocene to lower Oligocene formations and basement to estimate the potential hydrocarbon reservoirs using seismic inversion: a case study in the Upper Assam Shelf, India

The upper Assam shelf is a self-slope basin in north-east India, filled with nearly 7 km of sedimentary rocks of tertiary period with the granite basement and various oil fields along the border of the Naga thrust. The major producing fields are structural and strati-structural. The study area is placed in between the Mikir hills and Naga thrust. The objective of the study is to identify potential hydrocarbon reservoir zones in the geologically complex south upper of the Assam shelf using estimates of acoustic impedance and porosity derived by 3D post-stack seismic inversion. Well data, such as sonic velocity and density logs, from two wells (namely, KA and TE) are used in the inversion and validation of results. Inversion results are used to build a geological model in the form of acoustic impedance from which we derive 3D porosity cube which are used for hydrocarbon potential in the Paleocene to lower Oligocene sands, and the Precambrian basement. Although the amplitude maps provide an indication of potential reservoirs, the extent of these zones are much better identified in the inverted impedance maps and the corresponding estimated high-porosity zones. The analysis predicted the potential reservoir rocks in the Sylhet, Kopili and Barail formations, in which the Sylhet and Kopili appear to have good potential zones. Near the vicinity of the Naga thrust belt, the proximity of potential reservoir is predicted in the Kopili, Sylhet formation and in the fractured basement, respectively.

Oil exploration and discovery in the basement rocks of Bach Ho field: Documentation, facts and lessons

During the 40 years of operation and development (1981 - 2021), the Vietnam - Russia Joint Venture "Vietsovpetro" has witnessed many historical milestones, but the discovery of industrial oil for the first time from the fractured and weathered granite basement at exploration well BH-6 on 11 May 1987 is the most important one. From the first oil in the basement rock of Bach Ho field, Vietsovpetro consecutively discovered industrial oil in other fields in its area of operation, such as Dong Bac Rong (1991), Dong Nam Rong (1995), Nam Rong (2005), Nam Trung Tam Rong (2006), etc. At the beginning of 2018, the 2P (P1+P2) oil reserve from the basement rock accounted for 74% of Vietsovpetro's total balanced reserves at that time. As of 1 October 2021, the total oil produced from the basement reached 235 million m3 (195 million tons), accounting for 86% of Vietsovpetro's total oil output. Being encouraged by the success and experience of Vietsovpetro, other domestic and foreign oil and gas companies (PVEP, JVPC, Talisman, and Petronas, etc.) have explored and discovered oil and gas from the granite basement and put the fields of Rang Dong, Su Tu Den, Hong Ngoc, and Hai Su Den, etc. into operation. This fact has, at the same time, created a strong attraction for domestic and foreign investors, making important contributions to the rapid development of Vietnam's oil and gas industry which was still very young at the time. The above-mentioned shows that it is time to study data and documents, draw lessons from success and failure gained during the 40 years of basement exploration. The outcomes should be used as a basis to formulate an appropriate exploration strategy for Vietsovpetro in the coming decades with strong fluctuations in the oil and gas market expected, and the inevitable depletion of non-renewable resources worldwide.

Success Deployment and Operation of Downhole Casing Valve Improves Tripping and MPD Operation While Saving 5 Drilling Days Through Total Loss Circulation in Basement

Southern part of Sumatra is known for its high deliverability hydrocarbon gas formation with flow rate up to 200 MMSCFD produced from a single well. The fractured network present mainly in its granite basement formation posed as the primary hydrocarbon contributor aside to the carbonate zone. High formation pressure with massive gas reservoir as its driving mechanism combined with total loss circulation due to geological fault in the same section, lead to operation with various hazard combined which demands potent solution. Advanced technologies required to execute the operation in safest and efficient manner. Downhole Casing Valve (DCV) is one of Managed Pressure Drilling (MPD) equipment used to support operation with deep and high-pressure formation, installed alongside with casing to provide sealing of the well at depth. Equipped with flapper type valve and full borehole size, DCV which is surface controlled, enables operator to seal the well in the absence of any string. The seal created by DCV allows the string to be pulled out preventing to kill a live well. The South Sumatra blocks depicts enormous potential gas reservoir. Located in the fault of basement where total loss circulation will occur in highest probable manner. Utilization of chemical mixed mud was impractical considering the total loss circulation. Thus, pressure exerted from fluid column and pumping flow rate from string needs to be compensated by surface backpressure. In addition, to accommodate deep footage penetration of the section, hard basement formation, complex completion running sequence, and multiple tripping for BHA changes, requirement of DCV shifted from nice-to-have into a must-have segment. Without the need of killing the well nor changing the mud system, DCV allows tripping operation to be completed safely and efficiently by sealing the well with its flapper, saving costs and time on each tripping operation. DCV utilization successfully supports drilling high-pressure gas reservoir through basement fault until target depth reached safely and efficiently.

Diffraction imaging for basement fault-fracture prediction: Application to an oil field in Cuu Long basin

Improvement to the image of fractured granite basements is among the most sought-after goals for processing seismic data in Cuu Long basin, the most proliferous petroleum basin. Unlike a clear layering structure of the sediment, fuzzy images of the granite basement are often the source of confusion for interpreters to identify which structures are presented inside it. In such a low signal to noise ration (SNR) environment, extracting geological information such as fault systems and fracture becomes challenging. In this study, diffraction imaging is employed in an effort to identify and enhance the fault system inside the basement. The comparison of the study result with various standard post-stack attribute approaches shows the effectiveness of the diffraction imaging method.

Diffraction imaging for basement fault-fracture prediction: Application to an oil field in Cuu Long basin

Improvement to the image of fractured granite basements is among the most sought-after goals for processing seismic data in Cuu Long basin, the most proliferous petroleum basin. Unlike a clear layering structure of the sediment, fuzzy images of the granite basement are often the source of confusion for interpreters to identify which structures are presented inside it. In such a low signal-to-noise ratio (SNR) environment, extracting geological information such as fault systems and fracture becomes challenging. In this study, diffraction imaging is employed in an effort to identify and enhance the fault system inside the basement. The comparison of the study result with various standard post-stack attribute approaches shows the effectiveness of the diffraction imaging method.

LA-ICP-MS Zircon U-Pb dating of Early Jurassic granite basement in Chagan Area of the Northest Guangdong and its geological implications

Rencha basin is one of the typical Mesozoic-Cenozoic volcanic fault basins in northeastern Guangdong. The borehole data indicate that the basement is mainly composed of Paleozoic metamorphic rocks and Wenxiang granite. At present, the basement granite has been lacking in precise years. In order to discuss its formation age and improve the understanding of the geological evolution of the area, LA-ICP-MS zircon U-Pb isotopic dating of Wenxiang granite cores from two boreholes in the Chagan area of the basin is carried out, and the two harmonic ages are 179+1 Ma and 186 Ma, respectively. The results show that the basement Wenxiang granite in Rencha Basin was formed in late Early Jurassic, which is the product of the first volcanic activity of Yanshan. This age not only deepens the understanding of the formation and evolution of Rencha Basin, but also provides new chronological data for the lack of magmatic activity in the Early Jurassic in northeastern Guangdong, China.