New Insights on Characteristics of the Near-Wellbore Fractured Zone from Simulated High-Resolution Distributed Strain Sensing Data

Summary Rayleigh frequency-shift-based distributed strain sensing (RFS-based DSS) is a fiber-optic-based diagnostic technique, which can measure the strain change along the fiber. The spatial resolution of RFS-based DSS can be as low as 0.2 m, and the measuring sensitivity is less than 1 μɛ. Jin et al. (2021) presented a set of DSS data from the Hydraulic Fracture Test Site 2 project to demonstrate its potential to characterize near-wellbore fracture properties and to evaluate perforation efficiency during production and shut-in periods. Extensional strain changes are observed at locations around perforations during a shut-in period. At each perforation cluster, the observed responses of strain changes are significantly different. However, the driving mechanisms for the various observations are not clear, which hinders accurate interpretations of DSS data for near-wellbore fracture characterization. In this study, we applied a coupled flow and geomechanics model to simulate the observed DSS signals under various fractured reservoir conditions. The objective is to improve understanding of the DSS measurements and characterize near-wellbore fracture geometry. We used our in-house coupled flow and geomechanics simulator, which is developed by a combined finite-volume and finite-element method, to simulate strain responses within and near a fracture during shut-in and reopen periods. Local grid refinement was adopted around fractures and the wellbore, so that the simulated strain data can accurately represent the DSS measurements. The plane-strain condition is assumed. Numerical models with various fracture geometries and properties were constructed with representative parameters and in-situ conditions of the Permian Basin. The simulated well was shut-in for 4 days after producing 240 days, and reopened again for 1 day, following the actual field operation as shown in Jin et al. (2021). The characters of the strain changes along the fiber were analyzed and related to near-wellbore fracture properties. A novel diagnostic plot of relative strain change vs. wellbore pressure was presented to infer near-wellbore fracture characteristics. The impacts of permeability and size of the near-wellbore-stimulated region, fracture length, and near-perforation damage zone on strain responses were investigated through sensitivity analysis. The strain responses simulated by our model capture the observed signatures of field DSS measurements. During the shut-in period, clear positive strain changes are observed around the perforation locations, forming a “hump” signature. The shape of the “hump” region and peak value of each “hump” are dependent on the size and permeability of the near-wellbore fractured zone. Once the well is reopened, the strain changes decrease as the pressure drops. However, in one cycle of shut-in and reopen, the strain-pressure diagnostic plot shows path dependency. The discrepancy between the shut-in and reopen periods is highly influenced by the properties of near-wellbore fractured zones. The differences in the strain-pressure diagnostic plots can help to identify the conductive fractures. This study provides better understandings of the DSS measurements and their relations to the near-wellbore fracture properties, which is of practical importance for near-wellbore fracture characterization and completion/stimulation optimization.

Integrated geological-geophysical characterization of the zone of the Kherson—Smolensk transregional tectonic suture — deep long-lived magma- and fluid-conducting channel

The transregional Kherson—Smolensk suture has been established to be located between large meridional faults of the crystalline crust of the Ukrainian Shield (USh) in a strip of 50—70 km width and separates two microplates of different composition of the Precambrian basement. It is traced by subcrustal mantle heterogeneity in the lithosphere and a change in the relief of the main geodynamic boundary. The suture controls the USh large multiphase magmatic massifs and manifestation of the basic mafic magmatism in the Dniepr-Donets Depressin (DDD), which age decreases from south to north from the Early Proterozoic in the shield to the Devonian in the depression. On both sides of it, the crystalline crust differs in a set of parameters including a zone of low velocities in the area of the Novokonstantinovsky ore field of the USh to the east of the Kherson—Smolensk suture, where from DSS data its maximum thickness is 10—15 km in the upper crust. It appears to bea source of abiogenic hydrogen manifestations recorded by mining operations on this field. The Kherson—Smolensk suture, being a transregional mantle feature, unites the existing hydrocarbon manifestation in the USh with the promising hydrocarbon areas of the DDD. The inhomogeneities of the crystalline crust and the uppermost mantle give strong evidences to classify reasonably the transregional tectonic suture Kherson—Smolensk as a powerful mantle long-lived magmatic and fluid-conducting channel. Ores hows and modern degassing of methane are related to it, with methane beingmain greenhouse gas.

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.

Towards an Open Access European Database for Deep Seismic Sounding data

<p>Controlled source seismic data acquisition experiments have produced a vast amount of Deep Seismic Sounding (DSS) data since its development in the late 50’s. These datasets provide critical information on the structure and nature of the crust and the lithosphere, which constitutes a fundamental research tool within Solid Earth Sciences. The DSS datasets are unique and constitute the output of an expensive (in time, effort and cost) scientific process, which evidences the need for their preservation, both the recently acquired and the legacy data. Furthermore, the new developments in processing and imaging techniques generate new possibilities for re-use of the vintage datasets. The availability and accessibility of these datasets, therefore, is of foremost importance for scientists, decision-makers and the general public.</p><p>The research community, aware of the value of these data, has pushed forward Open Data policies based on the FAIR principles of data management (Findable, Accessible, Interoperable and Reusable). In this respect, a long-term plan has been launched by the European Plate Observation System (EPOS, https://www.epos-ip.org/) e-infrastructure. The focus is to streamline the integrated use of scientific data, data products and services. In close link with EPOS, the Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe (SERA, http://www.sera-eu.org/home, a Horizon 2020 project) includes a working package to set up a network on DSS data and products management. This initiative ensures the traceability of the data allowing that third parties can freely access, exploit and disseminate the data by means of permanent, international identifiers: a Digital Object Identifier (DOI) and a Uniform Resource Identifier (URI) or handle. Furthermore, the current aim is to go beyond the FAIR principles by linking the data with its related peer-reviewed publications, other scientific contributions and technical reports, facilitating its re-use.</p><p>A prototype DSS data exchange system has been developed jointly between the DIGITAL.CSIC (the Spanish National Research Council) services and the Institute of Earth Sciences Jaume Almera-CSIC (https://digital.csic.es/handle/10261/101879, last access January 2020). Within the platform, each dataset includes the acquired raw data and a metadata file. The metadata provides information of the nature of the data itself, list of authors, the context of the data (time and location of the experiments), funding agencies and other relevant legal aspects. The technical information includes the acquisition parameters, data processing and format of the data (SEGY standard in this case - www.seg.org-, broadly used in the geophysics community). In the developed storage protocol, a permanent identifier is assigned once it has been checked that the data meets all the described requirements. This permanent identifier ensures that any visit or download is accounted for. This information is entered into a statistics referencing database and can also be used as a measure of the impact of the data and/or data product.</p><p>This work is funded by the European Commission (Grant Agreement no: 676564-EPOS IP, Call H2020-INFRADEV-2014-2015/H2020-INFRADEV-1-2015-1, SERA 730900).</p>

DEPTH STRUCTURE FEATURES OF THE EASTERN STANOVOY FRAGMENT OF THE 8-DV GEOLOGICALGEOPHYSICAL SURVEY – BASE LINE (ACCORDING TO THE DSS DATA)

The materials of deep seismic operations on the Vostochno-Stanovoy fragment of the survey base geophysical profile 8-DV within large tectonic zones – the Selengino-Stanovoy and Amur fold regions of the Central Asian fold belt are presented. It is shown that longitudinal waves from the boundaries in the earth’s crust and the surface of Mohorovichich were recorded from explosions on a 700-kilometer geophysical profile. An inhomogeneous structure was established according to the data of longitudinal waves of the upper part of the earth’s crust to depths of 15–20 km and the surface of Mohorovichich. In general, the thickness of the earth’s crust at the profile is 37–42 km; the effective velocities of longitudinal waves in the crust and refractor ones along the mantle surface change at the profile, respectively, from 6.35 to 6.5 km/s and from 7.9 to 8.5 km/s. The results obtained are discussed and established features of the seismic structure are compared with the tectonics of the region and materials from other studies.