11/3/2022 0 Comments B amazing mazeLost circulation zones (LCZ) encountered while drilling through non-matrix features suggest they are not only open, but connected and with considerable flow capacity. The main non-matrix components include faults and fractures, pervasive networks of touching vugs, cm-scale vugs and caves. Observations across multiple datasets reveal a multi-scale, non-matrix pore system that is identifiable and important to include in geologic models when considering reservoir performance. We integrate static (core and wireline logs) and dynamic (drilling losses and well tests) datasets using a consistent workflow to investigate the types and distribution of non-matrix excess permeability away from wellbore control. We use publicly available data from the Pre-Salt to screen for non-matrix presence and dynamic potential. Therefore, early recognition of non-matrix deeply impacts field development strategies. The findings are further corroborated by additional insight from optical petrography and cathodoluminescence microscopy, as well as fluid inclusion analysis of secondary calcite crystals related to the cave forming phase.Įxcess permeability in carbonate reservoirs is typically related to the presence of dual-porosity multi- scale non-matrix features that can result in early water production or breakthrough of injected fluids. Macedonia), we apply for the first time, both conventional and clumped stable isotope analysis, and identify two different isotope alteration trends, reflecting two distinct hydrothermal events: an older, hotter one, where isotope alteration was likely related to isotope diffusion, lowering the δ18O values of the carbonate and a younger one, related to the cave formation by low-temperature CO2-rich thermal waters, with dissolution-reprecipitation as the alteration mechanism, causing decrease in δ18O values, and unexpected increase in δ13C values. Clumped isotope composition (Δ47) of carbonates is an independent measurement of temperature, and if combined with the conventional stable isotopes, can provide information on the paleowater stable isotope composition. If combined with a prior information on the paleowater stable isotope composition, further insights can be obtained on the temperature and the source of the paleowater. With the boreholes drilled as controls and checks for anomalies, the cavities filled with some geo-materials were detected at depths between 6 and 10.5 m in the subsurface.Īlteration of conventional carbonate stable isotopes (δ18O, δ13C) in cave walls has been shown to be a useful tool to identify cave formation driven by deep-seated processes, i.e., hypogene karstification. For the reduced field data, a number of important gravity anomalies with the cavities system as the major feature were obvious on the residual anomalies map. The numerical modelling results showed the shape and depth of the reconstructed cavities model were obtained with a model misfit of 3.18 mGal. The raw gravity observations were reduced to the Bouguer gravity anomaly after a number of corrections were carried out. Furthermore, for a comprehensive understanding of the geological settings and characterization of the cavities in the study area, we carried out microgravity surveys at 358 stations using a Scintrex CG5 Autograv gravimeter. The inverted subsurface geological cavities system was obtained iteratively by adjusting the model parameters until a good fit was attained between the calculated and observed gravity values. In this effort, modelling using synthetic data where a spherical structure of known depth extent and size was assumed as the initial model approximating the cavities systems was carried out using an interactive GRAV2DC program. Addressing these issues using geophysical microgravity technique motivated this present study. Subsurface concealed voids such as cavities do not only pose threats to geotechnical/engineering structures but also difficult to know their real positions in the subsurface.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |