Quantitative assessment of areal geological complexity

Background. The article presents a new approach to assessing the geological complexity — quantitative assessment of areal complexity, as well as an alternative methodology for assessing complexity in 1D. Aim. Developing a numerical metric for assessing the geological complexity and creating an algorithm for complexity maps construction. Materials and methods. Generally, complexity describe the reservoir in one number, that often underestimates the real complexity of the deposit. Geological complexity, presented in the article consists of 5 groups: structuraltectonic, facies-lithological, permeability and porosity, secondary alteration and fluid properties, 13 characteristics describe the complexity space of these groups. Each of these characteristics could be presented not only in 1D but also in 2D. The proposed methodology was tested on the company’s assets. Results. The presented examples of complexity maps for several fields show the advantage of 2D complexity estimation in comparison with 1D. The analysis of decomposed complexity estimation (for individual groups) on the company’s assets showed that the key groups of complexity are structural-tectonic, facies-lithological characteristics. Therefore, characteristics that describe these groups should be taken into account during the decision-making process and assets ranking. Conclusion. A methodology of quantitative assessment of areal geological complexity has been developed. This areal assessment allows identify the most “problematic” areas, analyzing existing sources of uncertainty, and also ranking and screening company assets when making strategic decisions.

A Fast Gridding Method for Capturing Geological Complexity and Uncertainty

Summary In this paper, we introduce an efficient method to generate reservoir simulation grids and modify the fault juxtaposition on the generated grids. Both processes are based on a mapping method to displace vertices of a grid to desired locations without changing the grid topology. In the gridding process, a grid that can capture stratigraphical complexity is first generated in an unfaulted space. The vertices of the grid are then displaced back to the original faulted space to become a reservoir simulation grid. The resulting inversely mapped grid has a mapping structure that allows fast and easy fault juxtaposition modification. This feature avoids the process of updating the structural framework, which may be time-consuming. There is also no need to regenerate most of the reservoir properties in the new grid. To facilitate juxtaposition updates within an assisted history matching workflow, several parameterized fault throw adjustment methods are introduced. Grid examples are given for reservoirs with Y-faults, overturned beds, and complex channel-lobesystems.

A Fast Gridding Method for Capturing Geological Complexity and Uncertainty

In this paper, we introduce an efficient method to generate reservoir simulation grids and modify the fault juxtaposition on the generated grids. Both processes are based on a mapping method to displace vertices of a grid to desired locations without changing the grid topology. In the gridding process, a grid that can capture stratigraphical complexity is first generated in an unfaulted space. The vertices of the grid are then displaced back to the original faulted space to become a reservoir simulation grid. The resulting reversely mapped grid has a mapping structure that allows fast and easy fault juxtaposition modification. This feature avoids the process of updating the structural framework and regenerating the reservoir properties, which may be time-consuming. To facilitate juxtaposition updates within an assisted history matching workflow, several parameterized fault throw adjustment methods are introduced. Grid examples are given for reservoirs with Y-faults, overturned bed, and complex channel-lobe systems.

Analysis of Hypocenter Relocation by Using Double Difference Method in a Deep Underground Mining

Hypocenter relocation is one of the keys to success in the analysis of seismicity induction in underground mines. Overburden thickness, topography, geological complexity, and mining activities can result in newly induced seismicity that can endanger the safety of underground mine workers. The relatively narrow underground mine area requires the most accurate hypocenter location information possible. The double-difference algorithm approach is one of the keys to overcoming this problem. The double-difference method is a relative location method that tries to minimize the residuals between the observed and calculated travel time differences for pairs of microseismic events at each station, by adjusting the differences between all pairs of events at each station repeatedly. In this study, we utilized microseismic measurement data in the deepest underground mine in Indonesia. A total of 1783 seismic events were successfully relocated. The relocation results show the rock mass stress which is illustrated by the distribution of events around the cave, especially the abutment area and underground mining tunnels.

Retrospective Analysis of Geological Exploration 2010 - 2020

Oil and gas companies’ future production profile is shaped by their exploration strategy and resource base development. Gazprom Neft's production profile will include 40% of current exploration projects by 2030. Geological exploration, on the other hand, is a high-risk business because it involves a lot of uncertainty due to the geological complexity of the targets being explored, as well as a lot of risky capital. Taking these factors into account, the Company will need to expand its exploration function as well as its approaches to managing exploration projects in order to meet its lofty aims. To determine the key areas of growth and a strategy for the exploration function development in the coming years, it was decided to first analyze the geological exploration activity in the Company in 2010 – 2020 period. The knowledge of achievements, success stories, and development areas is the fulcrum for future victories. Therefore, retrospective analysis is an important tool for the development of any system of activity - individual, organization, or state.

Geochemical and Isotope Characterisation of Thermo-Mineral Springs of Corsica Island: From Geological Complexity to Groundwater Singularity

Understanding hydrogeological processes at the origin of thermal and mineral groundwater are necessary to ensure their sustainable management. However, many processes are involved in their genesis and often only one or two processes are investigated at the same time. Here, we propose to use an innovative combination of geochemical, isotopic (34S, 14C, 18O, 2H) and geothermometry tools to identify, for the first time in a multi-composite geological context, all processes at the origin of diversified thermo-mineral waters. 19 springs covering a wide range of temperature and chemical composition emerging on a restricted area of Corsica Island (France) were selected. Geochemical results highlight five geochemical provinces, suggesting a common origin for some of them. Geothermometry tools show the unexpected involvement of a common deep groundwater reservoir within this non-active zone. Water stable isotopes highlight a contrasted altitude in recharge areas supplying lowland springs. This suggests that different flow patterns have to be involved to explain the wide geochemical diversity observed and to allow the design of a very first conceptual groundwater-flow model. This paper demonstrates the efficiency of the combination of the selected tools as tracers of water–rock interaction, independently of flow depth, intrinsic water properties, geological conditions and interaction time disparities.

Review of Underground Space Utilization and its Relevance in Nepal

Underground space, both open-cut and fully underground method, has been in use throughout the world for mining, storage, waterway, transport, and others from past centuries. But still the clear demarcation of ownership in terms of surface and underground is not clear in most parts of the world. The concept of underground space utilization is an evolving concept. The developed nations have opted for this option to accommodate growing urbanization need. Two modes of space utilization are reviewed for this paper, open excavation and full underground excavation. Also world case scenario is presented and is compared to the situation in Nepal. Social factors and geological factors in the context of Nepal are also addressed that have been crucial in case of some completed projects. Ambiguous underground rights in relation to surface ownership in Nepal is taken in account and example of some cities like Singapore, Tokyo, Helsinki is presented to make it clear how right segregation is possible and is needed for better underground space utilization. Historical evolution of Tunneling in Nepal is discussed along with the future designed and scheduled projects. Despite the geological complexity and lack of experienced manpower in the context of Himalayan geology the importance of underground space is highlighted because emerging researches and technological innovation around the world and also in Nepal have been confirming this concept now and again. As a conclusion for betterment and well managed cities in Nepal underground space would be an undefeated option in the long run.

Addressing Molybdenite187 Re Parent- 187 Os Daughter Intra-Crystalline Decoupling In Light of Recent In-Situ Micro-Scale Observations

Every so often, an analytical advancement or challenging geological occurrence necessitates re-evaluation of well-established geochronological methods. Rhenium-osmium (Re-Os) dating of sulfide minerals, especially molybdenite, by isotope dilution-negative thermal ionization mass spectrometry (ID-NTIMS) yields demonstrably accurate, robust ages. Difficulty in determining an age is caused by either 1) geological complexity including intra-crystalline heterogeneity or 2) inadequate analytical capabilities. Established, systematic methods overcome most of these difficulties, with exceptions. With respect to molybdenite, geological complexity is encountered as macro-scale polyphase overgrowths. Micro-scale complexity is observed as primary Re oscillatory zoning and secondary intra-granular 187Re parent-187Os daughter decoupling. Macro- and micro-scale geologic heterogeneities are overcome by systematic, targeted sampling protocols built upon careful hand sample and microscopic observations linking molybdenite crystallization to the host rock's geologic history.Advances in instrumentation permit more accurate and precise determination of elemental and isotopic compositions at the micro-scale, which ultimately reveals geological complexity and heterogeneity. Yet, newly produced high-resolution data must be carefully scrutinized and interpreted correctly. Two new micro-scale analytical techniques have been proposed: (1) to use NanoSIMS imaging to reveal heterogeneities that could preclude micro-scale geochronology (spot dating) methods, and (2) enable micro-scale geochronology using LA-ICP-MS/MS to distinguish the interfering masses of parent Re and daughter Os isotopes. We turn first to NIST Reference Material 8599, Henderson molybdenite, to compare its Re-Os characteristics and ID-NTIMS results with the newly published Re-Os molybdenite data. We identify the "best possible results" by quantifying the homogeneity of the NIST molybdenite, including model age variability, precision of ID-NTIMS analyses, and statistical treatment. Subsequently, we examine the limitations of the two newly proposed methods. We demonstrate that parent-daughter decoupling cannot be precluded by visual inspection of NanoSIMS isotopic maps. In addition, we prove mathematically that the quantifying the contribution of 187Os to the total measured mass 187 by LA-ICP-MS/MS is far too imprecise to achieve high-precision geochronology. Statistical data treatment and reporting can also result in misguided conclusions and applications.

Short communication: Inverse isochron regression for Re–Os, K–Ca and other chronometers

Conventional Re–Os isochrons are based on mass spectrometric estimates of 187Re/188Os and 187Os/188Os, which often exhibit strong error correlations that may obscure potentially important geological complexity. Using an approach that is widely accepted in 40Ar/39Ar and U–Pb geochronology, we here show that these error correlations are greatly reduced by applying a simple change of variables, using 187Os as a common denominator. Plotting 188Os/187Os vs. 187Re/187Os produces an “inverse isochron”, defining a binary mixing line between an inherited Os component whose 188Os/187Os ratio is given by the vertical intercept, and the radiogenic 187Re/187Os ratio, which corresponds to the horizontal intercept. Inverse isochrons facilitate the identification of outliers and other sources of data dispersion. They can also be applied to other geochronometers such as the K–Ca method and (with less dramatic results) the Rb–Sr, Sm–Nd and Lu–Hf methods. Conventional and inverse isochron ages are similar for precise datasets but may significantly diverge for imprecise ones. A semi-synthetic data simulation indicates that, in the latter case, the inverse isochron age is more accurate. The generalised inverse isochron method has been added to the IsoplotR toolbox for geochronology, which automatically converts conventional isochron ratios into inverse ratios, and vice versa.