Basin architecture and lithosphere structures of Western Central Asia – Uzbekistan: from geophysical studies

This paper presents an integrated geophysical study of the Western Central Asia (WCA) in the Uzbekistan area. It presents new interpretations of deep seismic sounding (DSS) data and new analyses of potential fields data. An integrated model of the physical properties and lithosphere structures displays distinct features that are related to tectonic history of the study WCA-Darius area. Task-oriented complex geological and geophysical research revealed in the lithosphere of western Uzbekistan series of crust blocks with abnormal petrophysical characteristics and established some correlation dependences between the distribution and placement of these objects (in plan) with deposits of minerals.

Identifying Subsurface Structures beneath the Sumani and Sianok Segments of the Great Sumatran Fault using Combined Geophysical Methods

The 1900 km long Great Sumatran Fault is a complex active fault system that is divided into segments that include the Sumani and Sianok segments in a rather densely populated area of the West Sumatra Province. Major earthquakes have occurred in these two segments that include the March 2007 Sumatra earthquake. Mitigating future risks requires a better understanding of these complex segments. To identify the subsurface structures beneath the Sumani and Sianok segments, we are conducting combined geophysical study that include gravity and magnetic. Gravity data were obtained from the published regional Bouguer anomaly map of the area around these two segments. The measurements from which the map was derived were rather sparse. Thus, more detailed magnetic measurements were carried out in this study. Magnetic measurements were also expected to be more sensitive as the predominant rocks in the study area are volcanic as well as other type of intrusive rocks. These gravity and magnetic analyses were complemented by seismicity data that include relocated seismicity data that will enhance the modelling of subsurface structures. Progress of this study will be reported. Challenges and obstacles will also be presented.

Integrated geological and geophysical study of the Tagil river valley morphology in its middle course

Relevance. Integrated geological and geophysical studies of a bridge in the Makhnevo village area are considered in the frame of the Urals eastern slope geology. Research objective is to study the lithology of the underlying part of the valley floor, determine soil physical and mechanical characteristics, and study a complex of fluvial terraces. Results. Relief elevations across the river valley have been studied, and four main fluvial terrace levels typical of the Urals eastern slope have been identified. An unstable section of the streambed with a canyonshaped valley above the neotectonic unwarping zone has been identified. The geological section of the river’s floodplain and streambed were studied based on geological and geophysical data. A change in the physical properties of glauconite sandstones and clays of Paleogene age in the recent underlying part of the river valley has been established. Layers of sand and glauconite sandstone that can be developed have been found at the new bridge site near the existing sand and gravel deposit. Conclusions. A complex of terraces of the Tagil river valley in its middle course is typical for the Urals eastern slope. The paleovalley is cut into a Paleogene glauconite sandstone layer. In the underlying part of the valley floor, changes in sandstones and clays physical properties have been recorded, and the presence of hypogene minerals was revealed. These are the signs of possible neotectonic processes in the series of the Cenozoic and Quaternary deposits.

Success story of integrated subsurface study to deliver a successful infill drilling: Buntal-5 case study

Buntal is a mature gas field located in South Natuna Sea Block B PSC. The field was discovered by well Buntal-1 and delineated by appraisal well Buntal-2. The field consists of multi-stacked sandstone reservoirs, which were deposited under fluvial deltaic environment. The major Buntal reservoirs have been produced since 2004 from two subsea wells. Buntal-3 was producing from zones Beta-1 and Beta-2, while Buntal-4 was a horizontal well producing from Zone-1C. Both of those wells had loaded up prior to Buntal-5 drilling. This paper describes the details of a multidisciplinary approach taken for the proposal of Buntal-5 infill drilling. An integrated geological and geophysical study were carried out to quantify resources and uncertainties of the remaining thin unproduced zones. In total, there are 8 virgin zones as Buntal-5 initial target namely Beta-0, Zone-1A, Zone-1B, Zone-1D, Zone-1E, Zone-2B, Zone-3 and Zone-3A. Max-trough seismic amplitude was utilized to identify geological features across for each Buntal reservoir. The result was then combined with geological concept based on its depositional environment to justify a reasonably higher hydrocarbon volume which can not be estimated only by wells’ data. A reservoir simulation study was also carried out to not only to evaluate production potential from the virgin zones but also to capture upside potential from the produced zones. Simulation history matching result on Zone-1C revealed early water breakthrough experienced by Buntal-4 well due to water cresting phenomena which left significant gas reserves. This result added upside potential to Buntal-5 which initially only targeted marginal remaining unproduced zones. The well was drilled at the end of 2019 and proven to be a major success. Buntal-5 open hole logs data indicate thicker and better virgin zones reservoir quality as expected by integrated geological and geophysical study. Furthermore, significant remaining gas was encountered in Zone-1C with actual gas water contact was within the simulation result proving the water cresting theory, the zone itself add well’s gas-in-place by 30% on top of the unproduced zones’ gas-in-place.

Pre-Jurassic Formation Lithological Composition and Reservoir Characteristic Variation Analysis. Core and Field Tests Analysis in Frolovsky and Shaimsky Petroliferous Regions

Analysis of the lithology of rocks of the pre-Jurassic complex and changes in the reservoir properties of rocks is one of the most important and difficult tasks for the formation of a petrophysical model for the interpretation of well logging data. Despite the long history of geological and geophysical study of deposits of the pre-Jurassic complex, a number of issues related to the reflection in the geophysical parameters of rocks and characteristics of reservoir properties have been studied insufficiently. This is due to the high variability of the lithological composition, textural and structural heterogeneity of the volcanic-sedimentary strata of the Turin Group. At present, the sediments of the pre-Jurassic complex are being actively studied - a representative core is purposefully selected, which is studied using an SCAL, including special methods, modern precision electrical, radioactive and acoustic studies are included in the complex of geophysical studies. The results of new studies are a good information base for refining the petrophysical model of an extraordinary object of study. The aim of this work was to analyze the lithology and reservoir properties of rocks, as well as to identify and classify the main groups of rocks that are possible reservoirs in the sediments of the pre-Jurassic complex within the Frolovsky and Shaimsky petroliferous regions.

ROMNY SALT DOME STRUCTURE (DNIPRO-DONETS BASIN): GEOLOGICAL HISTORY AND HYDROCARBON POTENTIAL

The geological structure of the Romny salt dome and related the Romny oil field as the first discovered one in the Eastern region of Ukraine are described. The history of its discovery and development of the field are featured. The geological and geophysical study of this area is characterized. Under generalization of geological and geophysical data, paleotectonic and peleogeothermal reconstructions on the Romny structure derived from the results of drilling of Gerasymivska-1 exploration well. The cyclic intermittent development of the salt dome structure is demonstrated. It is proved that the upper intersalt Frasnian source rocks could generate hydrocarbons starting from the early Visean time. According to the results of seismic surveys the uplifted block is outlined in the area of the northern edge of the salt dome. The presence of hydrocarbon pools in of the Visean and Serpukhovian granular reservoirs as well as in the salt breccia is predicted applying seismic attributes analysis for this block. The carbonate reservoirs of the lower part of the Bashkirian sequence, the productivity of which is established at the nearest located Velyki Bubny field, can be potentially oil and gas-bearing.