Temporal variability of catches, distribution and dynamics of length of Russian sturgeon in waters of the Caspian Sea in 2015 –2020

The paper presents long-term data on catches, distribution and length dynamics of Russian sturgeon in the waters of the Caspian Sea for the summer-autumn periods in 2015-2020. When considering the catches in the different parts of the sea there is found their annual variability, which is especially noticeable in the shallow zone in the North Caspian (0.31-2.0 specimens/trawl) and in the Middle Caspian (0-1.31 specimens/trawl). In the course of determining the reasons for the interannual dynamics of catches there were revealed several decadal rises. The dependence of decadal catches on the temperature of the bottom water layer was analyzed. The highest rise in catches was observed in the first decade of September when the temperature of water lowered up to 20.0-15.0 °C. The increase was observed due to migrating individuals to the shallow zone of the Northern Caspian Sea from shallow waters. Despite the variability of catches, the localization of Russian sturgeon schooling in the northern and middle part of the sea during the summer-autumn periods of 2015-2020 has certain similar features and trends. Sturgeon species fed mainly on shallow banks and deep dumps, where the largest catches of sturgeon were recorded from 5.0 to 12.0 specimens/trawl. The absence of sturgeon at depths of up to 3.0 m isobath in the last five years is due to the water heating up to 27.6-28.8 °C. The decrease in the length of the Russian sturgeon observed in recent years is due to an increase in the proportion of youngsters (19.2-70.0%) against the background of a decrease in the adult population. It should be noted that from 2017 to 2019 there were not found the adult species in the catches by fishing nets, which indicates their continued re-moval from the population.

Machine Learning Technology to Improve Precision and Accelerate Screening Shallow Gas Potentials in Tunu Shallow Gas Zone, PT Pertamina Hulu Mahakam

Tunu is a giant gas field located in the present-day Mahakam Delta, East Kalimantan, Indonesia. Tunu gas produced from Tunu Main Zone (TMZ), between 2500-4500 m TVDSS and Tunu Shallow Zone (TSZ) located on depth 600 - 1500 m TVDSS. Gas reservoirs are scattered along the Tunu Field and corresponds with fluio-deltaic series. Main lithologies are shale, sand, and coal layers. Shallow gas trapping system is a combination of stratigraphic features, and geological structures. The TSZ development relies heavily on the use seismic to assess and identify gas sand reservoirs as drilling targets. The main challenge for conventional use of seismic is differentiating the gas sands from the coal layers. Gas sands are identified by an established seismic workflow that comprises of four different analysis on pre-stack and angle stacks, CDP gathers, amplitude versus angle(AVA), and inversion/litho-seismic cube. This workflow has a high success rate in identifying gas, but requires a lot of time to assess the prospect. The challenge is to assess more than 20,000 shallow objects in TSZ, it is important to have a faster and more efficient workflow to speed up the development phase. The aim of this study is to evaluate the robustness of machine learning to quantify seismic objects/geobodies to be gas reservoirs. We tested various machine learning methods to fit learn geological Tunu characteristic to the seismic data. The training result shows that a gas sand geobody can be predicted using combination of AVA gather, sub-stacks and seismic attributes with model precision of 80%. Two blind wells tests showed precision more than 95% while other final set tests are under evaluated. Detectability here is the ability of machine learning to predicted the actual gas reservoir as compared to the number of gas reservoirs found in that particular wells test. Outcome from this study is expected to accelerate gas assessment workflow in the near future using the machine learning probability cube, with more optimized and quantitative workflow by showing its predictive value in each anomaly.

Frictional stability of porous tuff breccia under subsurface pressure conditions and implications for shallow seismicity

Thick sediment layers frequently cover the Japan islands’ surface, and their frictional properties significantly affect the shallow slip behavior that occurs during earthquakes. However, laboratory data on the properties of the shallow zone remain limited. We collected tuff breccia samples from deep borehole cores in the Miocene “Green Tuff” formation, a major surface cover, and performed velocity-stepping friction tests on these samples under in situ stresses of 2 to 20 MPa to assess the velocity dependence of their frictional strength. The samples exhibit predominantly frictionally stable, velocity-strengthening behavior over the range of normal stresses tested, which supports the hypothesis that shallow sediment layers are seismically quiescent. This result is consistent with the low seismicity and attenuation of coseismic slip occurring in the shallow zone that is observed during regional earthquakes. Microstructural observations of the postmortem samples using optical and scanning electron microscopes indicate a fabric transition from boundary shear localization to distributed cataclastic flow with increasing normal stress. Our laboratory investigation of the depth-variable distribution of the frictional velocity dependence of a shallow sediment layer would provide further insight into the mechanical role for earthquake rupture dynamics and shallow seismicity.

Frictional Stability of Porous Tuff Breccia Under Subsurface Pressure Conditions and Implications for Shallow Seismicity

Thick layers of unconsolidated sediments are widespread in the Japan island’s surface, and their frictional properties significantly affect the shallow slip behavior during earthquakes. However, laboratory data on the properties of the shallow zone remain limited. We collected tuff breccia samples from deep borehole cores of the Miocene “Green Tuff” formation, a major surface cover, and performed velocity-stepping friction tests on them under in situ stresses of 2 to 20 MPa to assess the velocity-dependence of frictional strength. The samples exhibit predominantly frictionally stable, velocity-strengthening behavior over the range of normal stress tested, which supports the hypothesis that shallow sediment layers are seismically quiescent. The result is consistent with the low seismicity and attenuation of coseismic slip in the shallow zone observed for the regional earthquakes. Microstructural observations of the postmortem samples through optical and scanning electron microscopies indicate a fabric transition from boundary shear localization to distributed cataclastic flow with increasing normal stress. Our laboratory investigation on depth-variable distribution of friction velocity dependence of a shallow sediment layer would provide further insight into the mechanical role for earthquake rupture dynamics and shallow seismicity.

Correlation analysis of heavy metals content in bottom sediments of the shallow zone Sheksninskaya spur of the Rybinsk reservoir in the city of Cherepovets (Russia, Vologda oblast)

The paper presents the results on the content of heavy metals in the bottom sediments of shallow areas of the Sheksninsky spur and the correlation dependences on the content of heavy metals. Significant differences in the content of heavy metals on different banks of the Sheksninsky spur were found only for lead (p=0.042). The matrices of paired correlations were constructed, the analysis of which showed that a greater number of dependencies with heavy metals were found on the right bank. The sorption of mercury by organic matter plays a greater role than the sorption of other elements, the correlation is significant r=0.70. Single exceedances of maximum permissible concentrations (MPC) of lead and copper in bottom sediments of the right bank were detected. Exceedances of element clarks determined for the earth crust were observed for lead, zinc, copper for bottom sediments of the right bank. A decreasing series of distribution of heavy metal concentrations in bottom sediments of the Sheksninsky spur was determined.

Idle Wells Revival Guidance to Optimize Remaining Gas in Shallow zone of Tunu field, Mahakam: Taking Advantage from Reservoir Re-Equilibrium

Shallow Zone reservoir of Tunu Field (TSZ) which was initially identified as drilling hazards, has now been extensively developed since 2009 with more than 600 Bscf of cumulative gas. The zone consists of widespread and scattered gas-bearing sand reservoirs, with strong aquifer drive mechanism. Today, more than 280 development wells have been drilled, and as the field is aging up, there are more than 62% wells have been died or idle. As an impact from driving mechanism, most of idle wells are related to water influx from reservoir to wellbore. These wells have been studied and revival program is performed by considering the strong aquifer support and reservoir re-equilibrium process in the reservoir. Based on trial phase that have been conducted, global strategy to revive the dead well have been developed, in order to optimize remaining reserves and also to support field production target. To implement this initiative, several supporting items were prepared: well candidate selection workflow, static condition requirement by dynamic well simulation, automatic monitoring tool for well candidate selection based on static condition requirement, campaign categories, job preparation (i.e. dedicated deltaic swamp testing barge), and regular monitoring & evaluation. Continuous implementation from this initiative has given additional production gain and recovered volume significantly to support field production target. Guidance from this best practice could give an initiative idea for other gas field with typical characteristics for optimizing each standard cubic feet of gas volume from existing idle wells.

Reaction of Gammaridae to oxygen contained in low water level in the North Caspian

The research of bottom invertebrates Gammaridae was carried out in 2013-2017 in the western part of the North Caspian. The purpose of the study was to determine the environmental tolerance of the organisms to oxygen. Oxygen deficit was caused by temperature and salinity stratification of water masses.Hypoxia was formed mainly in some areas of the shallow zone (up to 5 m) on the border of the Northern Caspian – Middle Caspian, as well as in areas with fine-grained sediments.Representatives of Gammaridae are characterized by high frequency of occur-rence.During the research period the number and biomass of the studied organisms widely varied. Gammarus Fabricius dominated by the total number, Dakerogammarus Stebbing – by the total biomass.The maximum frequency of occurrence was characteristic for Niphargoides similis (G. O. Sars).The limits of tolerance to oxygen of individual Gammaridae species living in the Northern Caspian sea have been presented.The minimum concentration of oxygen recorded for the entire period of research (1.29ml/l; 21%) is not critical for one species – Niphargoides similis (G. O. Sars). The low concentration (3 ml/l) does not inhibit the development of Niphargoides macrurus (Sars), Gammarus ischnus Stebbing, Gammarus pauxillus Grimm and Dikerogammarus haemobaphes (Eichwald). Other Gammaridae representatives living in the western part of the Northern Caspian were found in the environment with absolute oxygen concentration over 3.63 ml/l and with relative oxygen concentration over 59%.Wide ecological valency for oxygen is typical for Niphargoides similis (G. O. Sars), Gammarus pauxillus Grimm, Dikerogammarus haemobaphes (Eichwald), Gammarus ischnus Stebbing, and Niphargoides macrurus (Sars).

Transformation of first mode breather of internal waves above the bottom step in a three-layer fluid

In the present study we consider propagation of a localized internal perturbation in the form of an oscillating wave packet (breather) of the first mode in a three-layer fluid with an uneven bottom shaped as a smoothed step. The study is carried out by methods of numerical simulation within a fully nonlinear two-dimensional (vertical plane) set of NavierStokes equations. A set of calculations was carried out for different widths and heights of the bottom step. Inhomogeneity of the medium leads to transformation of the internal wave field with the formation of weak reflected waves and one or two first-mode breathers passed to the shallow zone. By analyzing linear stability in terms of Richardson and Froude numbers, it was revealed that potentially unstable regions arise at the smallest values of the step width. An amplitude and energy analysis of secondary reflected nonlinear waves was performed. The vertical mode composition of the fully nonlinear wave field is analyzed. It is shown that the first mode makes the largest contribution to the vertical structure of the full-nonlinear packet, though the fourth, second and the third modes also contribute noticeably.

UNLOCKING HIDDEN POTENTIAL OF SHALLOW RESERVOIR AT 1955-2342 mSS, IN RUHOUL FIELD

<p>As a human, live in the ever-changing environment, with the abundant amount of human movement, increasing population, and advancing technology, consumpting high energy is inevitable. Indonesia has been working to obtain better energy to fuel the world. As the multinational energy company, Pertamina Hulu Mahakam, located in East Kalimantan, operate world wide to extract oil and gas from the reservoir in Mahakam Delta, which already used high technology and qualified human resource to support the safe, efficient, and effective production process.</p><p>The petroleum system models, the contribution of marine shales to the generation of liquid and gaseous hydrocarbons in the Mahakam was considered negligible. The production of the oil fields has started quite early, however the major development phase of gas accumulation started within the last decade, with increasing activity since.</p><p>Ruhoul is an offshore gas field belongs to Pertamina Hulu Mahakam that located in Mahakam Delta, East Kalimantan, Indonesia. It covers an area of 350 km² and has a gross thickness of the payzone over 2000 m. Structural architecture of Ruhoul field is multilayered un-faulted anticline. Stratighraphycally, Ruhoul reservoirs are divided into two intervals which are Ruhoul Main Zone and Ruhoul Shallow. This study is only focused in Shallow zone area, they are Sh-8a, Sh-8c, and Sh-8d, as it is considered as remaining prospective area for Ruhoul field. For more specific, Sh-8a was produced by wells RJ-16A-M and RJ-2G-M.T3, Sh-8c was produced by well RJ-2G-M.T3, and Sh-8d was produced by well RJ-2G-M-T3.</p><p>Over time, the gas production in Ruhoul Field keep decreasing, therefore hidden gas production potential needs to be re-evaluated. The evaluation can be done by doing the dynamic synthesis analysis based on completion type used, production history, and well correlation.</p><p>The main objective of this study is to evaluate hydrocarbon potential in Ruhoul Shallow specific area. Several approaches will be used to assess Ruhoul Shallow zone prospect such an updated database, zone change inventory, and well correlation based on netpay map by layer with software Geolog 7.2.</p><p>Perform Dynamic Synthesis Analysis and P/Z Straight Line Material Balance Calculation are chosen as the methodology to assess the prospect zone of this field. The results of this process are candidates to be the re-opening zone, the value of GIIP, EUR, RR, RF, also the drive mechanism applied to each layer. Not only that, the results also obtained the Plateau rate stage curve in each layer.</p><p>The results showed two categories of re-opening candidates, P/Z methodology to calculate the value of GIIP and RF, and Plateau stage in each layer. Along with this study, the only well that suit to be the candidate for re-opening zone was only RJ-2G-M.T3 in Sh-8a, while the other layers and wells were not suit to be the candidate for re-opening zone. From the P/Z Straight Line calculation, the GIIP for the candidate (Sh-8a produced by RJ-2G-M.T3) is 1.15 BSCF, with 1.02 BSCF Gp max, and 89% RF, and has depletion drive as its drive mechanism. Based on Plateau stage with 4 MMSCFD as the plateau rate, the decline in RJ-2G-M.T3 (Sh-8a) started on July 2015.</p><p> </p>

Application of aerial photography with visible atmospherically resistant index by using unmanned aerial vehicles for seagrass bed classification in Kung Krabaen Bay, Thailand

The aim of this research was to study seagrass classification by using aerial photography with Visible Atmospherically Resistant Index (VARI) in the Kung Krabaen Bay, Chanthaburi, Thailand, which covers an area of 5.59 km2 and has an average depth of 2.5 m in the shallow zone. The classification based on VARI resulted in three classes, namely (i) long-leaved species (E. acoroides), (ii) short-leaved species (H. pinifolia and H. uninervis), and (iii) other objects. Results showed that aerial photographs could clearly differentiate seagrass species having different digital number value ranges with the VARI approach. The overall accuracy of visual interpretation (86.36%) was higher than that of supervised classification (46.97%). This technique could be useful for seagrass species mapping in other areas. The results also showed that H. pinifolia and H. uninervis were distributed on sandy clay and seashell substrates while E. acoroides was distributed only on sandy areas.