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Exploration, development, structural geology
Abstract Najmah-Sargelu Formations of Kuwait show considerable potential as a new unconventional hydrocarbon play and produces mainly from fractures. The key uncertainties which affect the productivity are the nature and distribution of permeable fracture networks, and the limits of oil accumulation. This paper presents the results from whole-rock elemental analysis of three cored wells in UG field. The main objectives of this study are to use high-resolution elemental chemostratigraphy to gain a better understanding of the detailed stratigraphy and correlation of the Najmah-Sargelu Formations, to assess the chemo-sedimentology for determining the intervals of high organic content, to estimate the mineralogy of the sequence using an algorithm developed for an analog formation in North America; and to determine the most likely intervals to contain fractures, using a brittleness algorithm. A clear chemo stratigraphic zonation is recognized within the Najmah-Sargelu Formation. The larger divisions are driven mainly by inherent lithological variation. The finer divisions are delineated by more subtle chemo stratigraphic signals (K2O/Th and Rb/Al2O3 ratios) and preservation of organic matter (high V, Ni, Mo, and U abundances). Zones of alternating brittleness and ductility are clearly identified within the interbedded limestones and marlstones of Najmah-Sargelu Formation. Two unexpected but important features of the Najmah-Sargelu limestones were elucidated by the elemental data. Brittle, high-silica spiculites, with virtually no clay or silt, are more common than previously recognized from petrophysical logs and core descriptions in the upper Najmah limestones. In addition, the limestones adjacent to the spiculites tend to contain bitumen as pore-filling are recognized by the trace metal proxies. Ternary plots of V, Ni, and Mo differentiate the combinations of kerogen and bitumen present in the Najmah-Sargelu Formations. The clarity and sensitivity of the chemostratigraphic signals are sufficient to enhance formation evaluation, and can also assist borehole positioning using the RockWise ED-XRF instrument at wellsite.
- North America (1.00)
- Asia > Middle East > Saudi Arabia > Saudi Arabia - Kuwait Neutral Zone ("Partitioned Zone") (0.41)
- Asia > Middle East > Kuwait > Ahmadi Governorate (0.41)
- Geology > Geological Subdiscipline > Stratigraphy > Chemostratigraphy (0.91)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.89)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock (0.72)
- North America > United States > Texas > West Gulf Coast Tertiary Basin > Eagle Ford Shale Formation (0.99)
- North America > United States > Texas > Sabinas - Rio Grande Basin > Eagle Ford Shale Formation (0.99)
- North America > United States > Texas > Maverick Basin > Eagle Ford Shale Formation (0.99)
- (8 more...)
- Reservoir Description and Dynamics > Unconventional and Complex Reservoirs > Shale gas (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.91)
- Reservoir Description and Dynamics > Reservoir Characterization > Sedimentology (0.87)
Abstract The offshore of the United Arab Emirates (U.A.E.) contains a number of diapiric islands. These islands owe their relief to the diapiric movement of salt which has pierced and deformed the overlying strata. These islands have similar shapes, stratigraphic sequences, aerial distribution of the identified stratigraphic units and general tectonic framework as following: 1. Infracambrian to Cambrian (Hormuz Group) composed of igneous and metamorphic rocks, salt, anhydrite, carbonate and clastics interbeds. 2. Miocene that is composed of sandstone, siltstone, shale, carbonate and evaporite interbeds, and 3. Pliocene to Recent sediments composed of mixed facies of clastics, carbonates and evaporites. One of the good examples is the pear-shaped Zirku Island with an approximately 5 km long and 2.5 km wide. A zone of very rugged hills with ridges is located in the centre and NNW with an elevated point of 163 meters. Zirku Island was formed by the movement of Cambrian (Hormuz) salt that was deposited and had moved progressively upward, puncturing through the younger overlying strata to create a dome structure. The surface expressions are composed of evaporites rocks, plus igneous rocks and quartzitic sandstone. The salt piercement is probably related to the Zagros Orogeny in the Pliocene to early Pleistocene and has brought in materials to the surface from considerable depths. On the Zirku Island the ‘exotic’ materials are represented by a rugged central region of lower Paleozoic contorted sandstones and siltstone of the Hormuz series. In the north east of the central core there is a sequence of steeply dipping lavas out-cropping the eastern flank of the ridge. Bordering the central zone is a gypsiferous breccia or mélange apparently formed around the margin of the Hormuz outcrop during emplacement from depth. The older Hormuz material has been eroded and partly incorporated into calcareous sediments formed along the shore of the ‘structural high’, probably in the late Tertiary period.
- North America > Canada (0.70)
- Asia > Middle East > UAE > Abu Dhabi Emirate > Abu Dhabi (0.16)
- Phanerozoic > Cenozoic > Quaternary > Pleistocene (0.55)
- Phanerozoic > Cenozoic > Neogene > Pliocene (0.45)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (1.00)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Sandstone (0.70)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Geologic modeling (0.94)
ABSTRACT: To identify suitable correlations between UCS and sonic velocity for a variety of lithologies, this paper analyzes the variations of formation lithology (e.g., shale, sand, or limestone) and the transitional lithology (e.g., sandy shale, shaly sand, tight limestone, and porous limestone) and examines their relations to the mechanical properties of the respective formation (e.g., UCS). Interpreting the characteristic responses from various wireline logs, such as gamma ray (GR), spontaneous potential (SP), resistivity (RES), sonic (DT), neutron porosity (NPHI), and formation density (RHOB), more accurate formation identification is sensibly obtained than the conventional method of using GR as the sole lithology indicator. The proposed methodology is illustrated using an actual wellbore stability case study in an oil field of the Gulf of Mexico (GOM). After the lithologies are defined, the correlated mechanical properties are determined (e.g., UCS, friction angle, cohesion, Young’s modulus, and Poisson’s ratio). The proposed method is used to evaluate the lower bound of safe mud weight windows in assessing the wellbore stability in drilling, invoking the shear failure gradient. The evaluation is based on each formation layer where the desired correlations between layer lithology and mechanical properties are provided. The calculated shear failure gradient will be used with the determined fracture gradient (or closure pressure) to define the safe mud weight window. With the reasonable sensitivity study, the match between the calculation and the observation can be ensured. 1. INTRODUCTION In the absence of mud logs, conventional wellbore-stability studies in layered formations rely on gamma-ray (GR) logs to identify lithology. An incorrect selection of properties can result in erroneous determinations of wellbore failure. Fig. 1 [1] illustrates this issue. This figure shows the responses from a GR log to three types of formation lithologies (shale, shaly sand, and sand).
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock > Shale (1.00)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Well Drilling > Wellbore Design > Wellbore integrity (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
Rock Mechanics Aspects Related to Cutting Efficiency of Mechanical Excavators, 25 Years of Experience In Istanbul
Bilgin, N. (Istanbul Technical University) | Balci, C. (Istanbul Technical University) | Copur, H. (Istanbul Technical University) | Tumac, D. (Istanbul Technical University) | Avunduk, E. (Istanbul Technical University)
Abstract: The mechanical excavation of utility tunnels in Istanbul started in 1985 with roadheaders and impact hammers. The first TBM application was started for a sewer-age tunnel in 1990. Since then, more than 60 km of tunnels including metro tunnels were excavated with mechanical excavators. A large amount of data was collected continuously by researchers in the Mining Engineering Department of Istanbul Technical University. Rock mechanics and engineering geological aspects of the rock formations affecting the efficiency of the mechanized excavation systems were also care-fully recorded; the performance prediction models were developed and modified continuously for impact hammers, roadheaders and TBMs. This paper will summarize briefly the works done in these respects emphasizing specially on the concept of in situ specific energy when using TBMs. A numerical example showing how to calculate net production rate of a TBM is given based on the model developed in a complex geology. 1 INTRODUCTION The geology of Istanbul is complex and some of the tunnels have been currently excavated in young Cenozoic formations and some of them in complex series of Paleozoic formations. The Paleozoic rock formations are cut frequently by andesite and diabase dykes, fracturing the main rock, decreasing the daily advance rates and increasing the tunneling cost tremendously. Sometimes in EPB (Earth Pressure Balance) TBM applications, excessive ground deformations may cause damages to the surrounding buildings like experienced in Otogar-Esenler metro tunnels which caused an extra cost of 35.6x106 $ to the project. The total length of the tunnels planned to be excavated in Istanbul in near future is 127 km for metro tunnels and 47 km for utility tunnels. Majority of the tunnels will be excavated with tunnel boring machines and the total cost of the operation is estimated to be around 10x109 Euros.
- Geology > Geological Subdiscipline > Geomechanics (0.70)
- Geology > Rock Type > Sedimentary Rock > Clastic Rock > Mudrock (0.31)
- Energy > Oil & Gas > Upstream (0.48)
- Materials > Metals & Mining (0.35)
- Well Drilling > Wellbore Design > Rock properties (0.70)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.70)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.47)
Abstract: The Portoro "marble" is a fine variety of black limestone from the La Spe-zia area, in Liguria (North-western Italy), which consists of a Liassic limestone with limonite and calcite veins. The Portoro typically crops out close to the Portovenere village and Poets' Gulf area, which is very known and sensitive in terms of scenery and tourist appeal. Even if few stone quarries are still working, it is evident how quar-rying must be done with special care. So underground excavation is more and more developing, in order to control waste production, environmental impact and slope in-stability: big blocks are mined in large underground chambers whose roofs are sup-ported by pillars. In this study a numerical modeling, based on a distinct element method was used, in order to compare stresses and displacements with the in situ measurements and to reach an optimum quarrying design. This research mainly aimed at improving the working conditions, as regards different topics: work safety in under-ground environment; prevention of fracturing of intact rock, induced by excessive stress concentration; improvement of the extraction process, to quarry intact, bigger stone blocks and produce less waste material; providing the underground chambers with long-term stability conditions, for possible future use. 1 INTRODUCTION This study deals with the underground quarrying of ornamental stone in the promontory of La Spezia, in Italy (Fig. 1). This area gives spectacular sights on the La Spezia Gulf, the Portovenere harbour and the Palmaria Isle, and on the Ligurian Sea. Several quarries have been active here since the 19th century, excavating stone materials for different uses, among which the ornamental and construction purposes have prevailed. At present very few of them are still active, for mining the Portoro ornamental stone, a Jurassic black stone with intense yellow and veins.
- Phanerozoic > Mesozoic > Triassic (0.46)
- Phanerozoic > Cenozoic (0.46)
- Geology > Geological Subdiscipline > Geomechanics (1.00)
- Geology > Structural Geology (0.96)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.49)
- Energy > Oil & Gas > Upstream (1.00)
- Information Technology (0.94)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Reservoir geomechanics (0.94)
- Health, Safety, Environment & Sustainability (0.89)
- Data Science & Engineering Analytics > Information Management and Systems (0.86)
Exploration for a cave by magnetic and electrical resistivity surveys: Ayvacık Sinkhole example, Bozdağ, İzmir (western Turkey)
Balkaya, Çağlayan (Süleyman Demirel University) | Göktürkler, Gökhan (Dokuz Eylül University) | Erhan, Zülfikar (Dokuz Eylül University) | Levent Ekinci, Yunus (Çanakkale Onsekiz Mart University)
ABSTRACT Geophysical survey techniques have been successfully applied to near-surface cave detection in karstic terrains. We used magnetic and electrical resistivity surveys to delineate the karstic structure of the Ayvacık Sinkhole, which may be considered to be a vertical cave. The magnetic-total-field-anomaly map helped reveal the metamorphic and sedimentary units in the study area. The total-horizontal-gradient map, which was based on a calculated pseudogravity anomaly, successfully identified the contact between the limestone unit and the cave system. Using these results, we positioned and carried out a vertical electrical sounding (VES) survey with a Schlumberger array along a line that consisted of 11 stations. The VES data were then processed using a 1D global optimization technique, which used a genetic algorithm and a 2D linearized least-squares algorithm. The results were generally in good agreement with each other, and together they pointed out three geologic layers: (1) an overburden layer (), (2) an approximately 25-m-thick alluvial fill (100–316 Ωm), and (3) a limestone unit (316–3162 Ωm); and also suggested the existence of a high-resistive anomaly (), possibly a karstic cave, located at the depth of approximately 40 m. Also, the results suggested that the buried limestone unit had an undulating karstic topography including a probable pinnacle structure. A synthetic modeling study was carried out, and it validated the reliability of the results. Finally, our findings indicated that the geophysical survey techniques used here were successful in detecting a cave located deep enough to make human exploration difficult.
- Research Report > New Finding (0.68)
- Research Report > Experimental Study (0.54)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.67)
- Geophysics > Gravity Surveying (1.00)
- Geophysics > Electromagnetic Surveying (1.00)
- Geophysics > Magnetic Surveying > Magnetic Acquisition (0.46)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.92)
- (2 more...)
ABSTRACT We investigated how changes induced in the microstructure of carbonate rocks by the injection of -rich water affect pore-network properties. In particular, we investigated from multiple perspectives the microstructural changes and types of porosity that alter the observable geophysical properties. We thereby refined our understanding of induced modification of the pore network. Our experimental protocol included a suite of time-lapse acoustic, transport, and nuclear magnetic resonance (NMR) measurements, along with scanning electron microscopy (SEM) and CT-scan images; these gave us complementary sensitivity to changes in different properties of the pore space. Induced porosity variations were smaller than in previous reported results because of chemomechanical compaction resulting from dissolution under pressure. No porosity enhancements larger than 0.8 pu were observed. Results indicated that dissolution occured primarily in the grain-coating cement and the microporosity of the micritic phase. Both caused the formation of cracklike pores around larger grains leading to a more compliant frame, causing both velocity reductions and an increased sensitivity of velocity to pressure. Chalky micritic facies exhibited velocity reductions of , whereas micritic limestones, less prone to compaction and grain sliding, experienced smaller velocity reductions (). Because porosity enhancement was minimal, we hypothesized that the reductions were due to injection-induced reduction of grain-contact stiffness. Dissolution-induced compaction played an integral role also in the permeability response during injection. Compaction in pressure-sensitive chalky facies strongly counteracted the effects of dissolution, leading to negligible permeability and NMR response changes. In contrast, stiff micritic limestones with little dissolution-induced compaction exhibited larger permeability increases (). This work demonstrated the advantages of utilizing a suite of concurrent and independent measurements to build a more comprehensive interpretation of microstructure changes induced by injecting fluids that are in chemical disequilibrium with the host formation.
- North America > United States > Texas (0.46)
- North America > United States > Kansas (0.28)
- North America > United States > California (0.28)
- Geology > Geological Subdiscipline (1.00)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (0.46)
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (1.00)
- Geophysics > Time-Lapse Surveying > Time-Lapse Seismic Surveying (0.95)
- North America > United States > Kansas > Hall-Gurney Field (0.99)
- North America > United States > Texas > Frio Formation (0.94)
- North America > United States > Louisiana > Downdip Tuscaloosa-Woodbine Trend Basin > Tuscaloosa Formation (0.94)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (1.00)
- Reservoir Description and Dynamics > Improved and Enhanced Recovery > Chemical flooding methods (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Open hole/cased hole log analysis (1.00)
- (3 more...)
In hard-rock aquifers, fractured zones constitute adequate drinking water exploitation areas but also potential contamination paths. One critical issue in hydrogeological research is to identify, characterize, and monitor such fractured zones at a representative scale. A tracer test monitored with surface electrical resistivity tomography (ERT) could help by delineating such preferential flow paths and estimating dynamic properties of the aquifer. However, multiple challenges exist including the lower resolution of surface ERT compared with crosshole ERT, the finite time that is needed to complete an entire data acquisition, and the strong dilution effects. We conducted a natural gradient salt tracer test in fractured limestones. To account for the high transport velocity, we injected the salt tracer continuously for four hours at a depth of 18 m. We monitored its propagation with two parallel ERT profiles perpendicular to the groundwater flow direction. Concerning the data acquisition, we always focused on data quality over temporal resolution. We performed the experiment twice to prove its reproducibility by increasing the salt concentration in the injected solution (from 38 to ). Our research focused on how we faced every challenge to delineate a preferential flow and solute transport path in a typical calcareous valley of southern Belgium and on the estimation of the transport velocity (more than ). In this complex environment, we imaged a clear tracer arrival in both ERT profiles and for both tests. Applying filters (with a cutoff on the relative sensitivity matrix and on the background-resistivity changes) was helpful to isolate the preferential flow path from artifacts. Regarding our findings, our approach could be improved to perform a more quantitative experiment. With a higher temporal resolution, the estimated value of the transport velocity could be narrowed, allowing estimation of the percentage of tracer recovery.
- Overview (0.67)
- Research Report > New Finding (0.34)
- Geology > Rock Type > Sedimentary Rock > Carbonate Rock > Limestone (1.00)
- Geology > Geological Subdiscipline > Environmental Geology > Hydrogeology (0.89)
- Europe > Belgium > Namur Basin (0.89)
- Europe > Belgium > Dinant Basin (0.89)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (1.00)
- Reservoir Description and Dynamics > Formation Evaluation & Management > Tracer test analysis (1.00)
- Data Science & Engineering Analytics > Information Management and Systems (1.00)
- Reservoir Description and Dynamics > Reservoir Characterization > Faults and fracture characterization (0.93)
In this study, we suggest the use of a finite difference (FD) forward solution with triangular grid to incorporate topography into the inverse solution of direct current resistivity data. A new inversion algorithm was developed that takes topography into account with finite difference and finite element forward solution by using triangular grids. Using the developed algorithm, surface topography could also be incorporated by using triangular cells in a finite difference forward solution. Initially, the inversion algorithm was tested for two synthetic data sets. Inversion of synthetic data with the finite difference forward solution gives accurate results as well as inversion with finite element forward solution and requires less CPU time. The algorithm was also tested with a field data set acquired across the Kera fault located in western Crete, Greece. The fault location and basement depth of sedimentary units were resolved by the developed algorithm. These inversion results showed that if underground structure boundaries are not shaped according to surface topography, inversion using our finite difference forward solution with triangular cells is superior to inversion using our finite element forward solution in terms of CPU time and estimated models.
- Asia > Middle East > Turkey (0.31)
- Europe > Greece (0.25)
- Data Science & Engineering Analytics > Information Management and Systems (0.94)
- Reservoir Description and Dynamics > Reservoir Characterization > Exploration, development, structural geology (0.68)
- Reservoir Description and Dynamics > Reservoir Characterization > Seismic processing and interpretation (0.51)