Unconsolidated Zone Research Articles

Subsurface Characterization Using Downhole Refraction Survey: A Case Study of the Niger Delta

This study addresses the critical role of downhole refraction as a method for assessing subsurface characteristics, particularly in areas facing challenges such as ground roll issues and weak reflection signals during seismic data acquisition. Focused on the Agudama, Kenfa, and Yenegwe settlements in the Niger Delta region, where frequent engineering structure collapses occur, the research aims to understand the depth and velocity of unconsolidated zones through downhole refraction. The study emphasizes the limitations of relying solely on uphole refraction and highlights the necessity of downhole methods for accurate velocity determination. The research employs various techniques, including borehole drilling, velocity measurements, and seismic pulse generation. The study's primary objectives include investigating the causes of engineering structure failures, proposing geophysical solutions, and contributing valuable insights into the geological context of the Niger Delta region. The fieldwork involved a comprehensive approach, combining reconnaissance surveys, downhole refraction studies, and the use of specialized equipment such as a Geometrics Stratavisor NZXP seismograph and explosives for seismic sources. The results of the downhole refraction survey reveal a double-layer velocity model in the research areas, indicating variations in weathered or unconsolidated layer thickness and velocities. The study establishes a relationship between elevation, weathered layer thickness, and velocities in both weathered and consolidated layers, offering valuable information for engineering considerations. The research concludes that the downhole refraction method is crucial for evaluating weathered strata properties and provides cost-effective subsurface information. The study recommends drilling below the weathered zone for seismic energy source placement, excavation depths for stable structures, and future investigations focusing on closely spaced data points and additional soil properties. These recommendations aim to enhance the safety and durability of structures in the study area, contributing to the understanding and mitigation of engineering structure failures in the Niger Delta region.

Application of Complex Geophysical Methods for the Detection of Unconsolidated Zones in Flood Dikes

The flood levees in the vicinity of Krakow city (Poland) are, in some places, over 100 years old. Thereupon, in the flood dike, and its subsoil, can appear unconsolidated zones, which, during the flood stage, can be a simple way of water flow and/or even can be the place where the levee body will be destroyed. This phenomenon took place in Wawrzeńczyce village, near Krakow city, during the flood in 2010. The geophysical research was carried out, in order to develop a methodology of recognition of potential areas where the levee body can be damaged. The geophysical surveys were conducted with the use of electrical and electromagnetic methods, as well as utilizing the seismic method. The general identification of examined media was realized by the electrical resistivity tomography (ERT) method. The ERT surveys were supplemented by capacitively-coupled resistivity (CCR) measurements, in order to analyze the usefulness of the CCR method for the examination of river dikes and reduction of interpretation ambiguity. The ground penetrating radar (GPR) method detected small anomalies in the body dike, due to the very high resolution of this method, which were not detected by the ERT and CCR techniques. During GPR surveys, non-standard measurement techniques were applied. Finally, the high-resolution seismic reflection (HRSR) method provided a clear and high-resolution image of the dike structure up to the water table and assisted with the identification of the hazard non-consolidated zones.

WITHDRAWN: Application of GIS software in analyzing hydrodynamics of sub surface water demeanor zones in Gondwana sedimentary terrain of eastern India

Abstract Gondwana study terrain of Orissa, India has diverse geological, geophysical, hydrological, hydrogeological and meteorological information which have been integrated for extensive study. The study aims at acknowledging the geology and hydrogeology of the region backing up with the type and existence of aquifers around the region. To get the detailed features 225 observation wells, 40 National Hydrograph Network Stations (NHNS), 40 groundwater monitoring (GWM) stations and 83 exploratory wells were collected from different sources to analyse the groundwater occurrence in the study area. The data obtained were integrated and initiated for lithological distribution, groundwater flow directions, depth to water levels in pre- and post-monsoon. Limited aquifer thickness of unconfined aquifer and poor yield from deeper aquifers has been studied intricately. Groundwater occurrence has provided a paradigm to in-depth study in association with detailed lateral and vertical demarcation and behaviour of aquifers. Taking into consideration about lithology, the area can be hydrogeologically divided into consolidated, semiconsolidated and unconsolidated zones. The semi and unconsolidated zones are the groundwater potential zones where the aquifer remains under saturated condition. Though semiconsolidated zones bear abundant volume of water but hydrological parameters illustrate that they do have the potentiality for shallow water wells whereas the fissured and fractured zones in consolidated formations yield perennial source of groundwater illustrating deep borings.

Detection of unconsolidated zones in coal mining site using resistivity data at Odagbo area, Kogi State, Nigeria

A coal mining site at Odagbo area located in Kogi State, Nigeria, was investigated using resistivity data to detect unconsolidated zones, majorly caused by the mining of coal seam deposit. The resistivity measurement was carried out with the aid of ABEM Terrameter SAS 4000 and electrode selector equipment (ES 464). The resistivity data was acquired along three (3) profile lines at an equal interval of 50 m apart. The electrode array that was used for data acquisition was dipole-dipole array at electrode spacing of 5 m. The data acquired along the three (3) profiles were inverted with RES2DINV software. The inverted models were able to map-out air-filled/water-filled voids and showed the boundary between the unsaturated and water-saturated zone. The air-filled/water-filled voids have high (553 - 4000 Ωm) and low (3 - 70 Ωm) resistivity values with an average thickness of 11 m respectively. The unsaturated zone is 7 m thick and mostly consists of materials with resistivity values ranging from 195 to 4018 Ωm. The weathered zone is 17 m thick and is majorly dominated by water-saturated materials. The study shows that the unconsolidated zones in the subsurface of the study area lies within the weathered layer. These zones are the cause of environmental hazard and might even affect the probable potential coal resources of the study area.

Consolidity Analysis of Wind Turbines in Wind Farms

Consolidity is an inner property of systems, which explains the behavior of the stable and controllable systems operating in fully fuzzy conditions. Wind energy conversion systems are considered man-made fully fuzzy systems, which have been designed to achieve satisfied conditions such as stability, reliability, high efficiency, high performance and high accuracy. Sometimes these systems fail during its operation due to some mechanical or electrical issues or both. The authors in this paper present a novel consolidity analysis of the wind turbine rotor at different values of wind speed, pitch angle and tip speed ratio. This analysis shows how the consolidity trajectory pathways of the wind-turbine system changes from the unconsolidated zone to the consolidated zone and vice versa. It is foreseen that the consideration of the consolidity pathways will allow wind turbine designs that avoid failure of the operation of the wind-turbine. Consolidity charts that are constructed using the non-linear power coefficient formulas are used to show the behavior of wind turbines during external ini¬‚uences such as wind speed and internal influences such as blade pitch angle. The consolidity analysis presented in this paper incorporates theoretical data obtained from literature at rated values and practical data obtained from wind farms at Zafarana and the Gulf of El Zayt. The consolidity analysis shows that the degree of the consolidity of wind-turbine rotors falls in the unconsolidated class for the three case studies. The consolidity pathway is found to move towards consolidity zone while increasing both wind speed and blade pitch angle.

Effect of Stratigraphic features on Deep-Water Cementing Operation – A Review

Drilling operations in deep-water environment is faced with technical challenges despite its massive record of huge hydrocarbon reserves when compared with onshore oil and gas fields. The weak, unstable formations coupled with adverse deep-water conditions poses as a challenge to cementing operations. Narrow pressure window conditions are encountered when the wellbore pressure required to contain subsurface pressures lies close to the pressure at which losses may be sustained. This is evidence in the ratio of pore pressure to vertical stress moving close to lithostatic condition. This can either be caused by porous formation or by the way of inducted fractures in weak or sheared or unconsolidated zones in the subsurface. This study showed an overview of some possible challenges faced in deep-water cementing operations in relation with stratigraphic features of the deep-water environment. From the review it was gathered that the stratigraphic nature of deep-water environment has a huge effect on cementing operations for oil and gas wells. The study also highlighted some gaps in the literature which require urgent attention to reduce loss circulation. These gaps include but not limited to: spacers generating sufficient downhole force to overcome the yield stress of the mud and the need for a new type of treatment for lost returns. Managed pressure cementing operations may control wellbore pressures.

Investigating the Impact of Caving on Longwall Mine Ventilation Using Scaled Physical Modeling.

In longwall mining, ventilation is considered one of the more effective means for controlling gases and dust. In order to study longwall ventilation in a controlled environment, researchers built a unique physical model called the Longwall Instrumented Aerodynamic Model (LIAM) in a laboratory at the National Institute for Occupational Safety and Health (NIOSH) Pittsburgh Mining Research Division (PMRD) campus. LIAM is a 1:30 scale physical model geometrically designed to simulate a single longwall panel with a three-entry headgate and tailgate configuration, along with three back bleeder entries. It consists of a two-part heterogeneous gob that simulates a less compacted unconsolidated zone and more compacted consolidated zone. It has a footprint of 8.94 m (29 ft.) by 4.88 m (16 ft.), with a simulated face length of 220 m (720 ft.) in full scale. LIAM is built with critical details of the face, gob, and mining machinery. It is instrumented with pressure gauges, flow anemometers, temperature probes, a fan, and a data acquisition system. Scaling relationships are derived on the basis of Reynolds and Richardson numbers to preserve the physical and dynamic similitude. This paper discusses the findings from a study conducted in the LIAM to investigate the gob-face interaction, airflow patterns within the gob, and airflow dynamics on the face for varying roof caving characteristics. Results are discussed to show the impact of caving behind the shields on longwall ventilation.

Hybrid Sand-Consolidation Fluid Offers Versatility in Treatment of Shallow Reservoirs

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 189548, “Tunu: From Laboratory to Field Application With a New Hybrid Inorganic/Organic Sand-Consolidation Fluid as Primary Treatment of Shallow Reservoirs,” by J. Andrieu, B. Kutzky, and B.T. Schackmann, Engineered nanoProducts Germany, and A. Mahardhini, SPE, I. Abidiy, SPE, and H.M. Poitrenaud, Total, prepared for the 2018 SPE International Conference and Exhibition on Formation Damage Control, Lafayette, Louisiana, USA, 7–9 February. The paper has not been peer reviewed. The Tunu giant gas field is in the Mahakam region of the South China Sea. Because of the maturity of the field, the producing layer has moved from the deep zone of consolidated sand into the shallow zone of unconsolidated sand. Hydrocarbon production from the shallow zone is unmanageable without primary sand control downhole. In this paper, a new type of sand-consolidation low-viscous binding material, based on a combination of inorganic and organic components, is presented. Introduction Tunu produces almost 40% of total gas production in the Mahakam region. Hundreds of wells have been drilled in the field. Its primary-zone reservoirs are between 2000 and 5000 m true vertical depth (TVD) and typically consist of medium to fine sandstone with strong consolidation and high porosity. Above the primary zone, between 1500 and 2000 m TVD, is the Intra Beta section, with high porosity and sufficient consolidation. In the top layer of the field, shallow reservoirs, above 1500 m TVD, are typically poorly consolidated, with high porosity (28%) and permeability (greater than 1 darcy). Tunu’s shallow zone is an unconsolidated zone that requires sand control; types that have been used include gravel pack, standalone screen, and sand consolidation. Sand consolidation can be a challenging option because of the difficulty in finding a balance between compressive strength and regained permeability after treatment. Field Application After the first laboratory-testing phase, detailed in the complete paper, showed promising results, the decision to perform field trials on five wells was validated. Wells in Tunu are typically completed using 3.5- or 4.5-in. tubingless completion inside 7- or 9⅝-in. casing. A coiled-tubing (CT) unit was chosen for pumping into the target reservoir. First Campaign (2012–2013). The primary objective of the first campaign was to acquire experience with the composite binding material in the field without taking the risk of plugging the wells. Therefore, a large amount [6 pore volumes (PV)] of overflush was used. Several tests and subsequent adjustments were developed to tailor the product to actual field conditions. The first campaign began in October 2012 and ended in July 2013 after treatment on five wells. On the basis of laboratory test results, the treatment comprises the following steps: Activation of binding material by dissolving the initiator Injection of preflush fluid (0.75-fold binding material volume) Injection of the binding system, followed by a small pill of spacer (maximum 0.5 bbl of preflush) Post-flushing or overflushing (six-fold binding material volume for first campaign)

Microgravimetric and GPR surveys for detection of unconsolidated zones in a levee

Selected results of complex geophysical surveys carried out on the Vistula river flood levee in Cracow are herein presented. Two complementary geophysical methods were applied for detection of potential unconsolidated zones in the body of the levee, i.e. microgravimetry and ground-penetrating radar (GPR). The surveys were carried out in 2D mode, along a profile at the crown of the flood levee. Microgravimetric data reveal anomalies showing zones of decreased bulk density. These zones provide information about poor quality of the levee. The main anomaly was interpreted in a quantitative manner using gravity modelling. Non-standard GPR processing and visualization of radargrams were employed to better extract information concerning the distribution of unconsolidated zones. High resolution GPR surveys allow to outline such zones which was the basis for construction of the 2D model used in the gravimetric modelling. Integration of these two geophysical methods provided important information about the spatial variations of mass density in several unconsolidated zones within the body of the flood levee.

Failure analyses of a reinforced embankment by Strength Reduction and Limit Equilibrium Methods considering hardening of soft clay

A 7.6 m high reinforced embankment-wall system was constructed in stages on very thick soft clay. The reinforced structure incurred a deep-seated global failure at the end of backfill loading. The Strength Reduction Method (SRM) and the Limit Equilibrium Method (LEM) were employed to analyze the stability of the structure. It was found that the SRM captured the deep-seated global failure of the structure through a coupled mechanical and hydraulic Finite Element (FE) modeling. The stability of the reinforced structure was much underestimated or overestimated by the LEM using unconsolidated-undrained or consolidated-undrained shear strength values. However, the stability of the structure could be still captured by the LEM with the increased shear strength values assigned to the consolidated zone directly beneath the reinforced structure and with the unconsolidated-undrained shear strength values assigned to the unconsolidated zone beyond the structure. In practice, both the SRM and the LEM are recommended for stability analyses of geosynthetic-reinforced structures on soft ground considering hardening of the soil so that the results from the two methods can be cross-examined.

Temperature distribution and anomalies in the crystalline basement of the tataria arch

We made temperature measurements in the crystalline basement of the superdeep and deep boreholes located in the central-eastern part of the East European platform. The basement in the studied region is characterized by an average heat flow of 60 mW m−2. Our experiments have revealed temperature anomalies in the crystalline basement that we interpreted as unconsolidated zones. The studies indicate that fluid injection anomalies, sheet flow and overflow zones and gas anomalies can be detected by temperature measurements.

Construction of the Seikan undersea tunnel—II. execution of the most difficult sections

Abstract This paper describes the three main problems associated with the difficult sections of the work which were encountered and for which solutions were found during construction of the Seikan Tunnel: (1) the excavation of squeezing ground; (2) water inflow accidents; and (3) the excavations of unconsolidated zones. Squeezing ground, which appeared in the F-10 fault with an earth pressure as high as 2 MPa, was excavated employing spring line drifts and the short bench method with steel pipe supports filled with reinforcing hoop-shaped steel bars and grouted with a high-strenth mortar. The most serious water inflow incident (maximum rate of 70 m 3 /min.) occurred in the service tunnel on the Hokkaido side in May 1976, causing inundation of 3 km of the service tunnel and 1.5 km of the main tunnel. By correctly judging the situation and making strenuous efforts over the next 5.4 months, the remedial work—which included water drainage—was safely completed. There were no fatalities or serious injuries resulting from the accident. The unconsolidated soft sand layer of the Kuromatsunai Formation, which existed in the middle of the Tsugaru Straits, was excavated without any water inflow accidents. This was accomplished with the aide of water-seal grouting and by carrying out construction procedures with care. Although different measures were required for each problem, the difficulties were overcome by careful investigation and construction management.