Fractured Basement Research Articles

GEOPHYSICAL INVESTIGATION OF GROUNDWATER CONTAMINATION USING DC RESISTIVITY TECHNIQUE AT THE MALE HOSTEL OF ISA KAITA COLLEGE OF EDUCATION DUTSIN-MA, KATSINA STATE, NIGERIA

A geophysical investigation involving Vertical Electrical Sounding (VES) using the Schlumberger array was carried out at the Isa Kaita College of Education specifically at the Male Hostel. The aim of the investigation is to explore the groundwater contamination of the area with the objectives: to determine the depth to basement of the study area, to determine the aquifer thickness, to determine the depth to aquifer, to determine the conductivity of the aquifer and to determine the thickness of topsoil and its variation in resistivity. A total of four (4) vertical electrical soundings were carried out using Schlumberger configuration. Terrameter signal averaging system (SAS) model 300 was the instrument used. The survey area is dominated by mainly four layers, namely: Topsoil, Weathered basement, fractured basement. The value of VES 03 and VES 04 have high electrical conductivities which likely shows they are contaminated, The topsoil resistivity along the profile ranges from approximately 1 to 154, The depth to basement (basement topography) Varies from 4.94 m to 7.59 m, The thickness of aquifer range from 1 m to 6.8 m. Therefore VES 02 has high Potential for groundwater because it has retaining capacity and good aquifer thickness and is therefore recommended for borehole establishment. It is recommended that the management of Isa Kaita College of Education should provide a concrete dumping site to avoid leaching of waste in ground thereby contaminating the groundwater.

Structure and Composition of Basement and Sedimentary Cover in the Southwestern Part of the Siljan Ring, Central Sweden: New Data from the C-C-1 Drill Core

The results from the geological and geophysical investigations of the Siljan Ring impact structure (central Sweden) have shown that the Paleozoic sedimentary succession and the Precambrian basement were strongly affected by complex deformational processes. Studies of a new drill core from the C-C-1 well provide valuable additional information necessary for the reconstruction of the geological setting in the southwestern part of the Siljan Ring. It was found that the contact between the basement and the sedimentary cover is tectonic, not normal sedimentary, in origin. The basement interval comprises Precambrian metavolcanic and metasedimentary rocks with a single mafic intrusion (gabbro-dolerite) in the upper part. The rocks have only been partially metamorphosed. The intercalation of calcareous mudstones, skeletal wackstones, and black shales in the sedimentary cover interval is not consistent with the regional lithostratigraphy scheme. Thus, more likely that the sedimentary sequence is not complete as a result of tectonic displacements, and a significant part of the Lower and Middle Ordovician succession is missing. The Post-Proterozoic tectonic reactivation and impact event also caused the formation of four types of fracture. The third type of fracture is accompanied by cataclastic zones and probably have an impact-related nature. In the highly fractured basement rocks, a dissolution along the second type of fracture has resulted in the development of open vugs. Open vugs and microporosity in cataclastic zones have been considered to be an effective storage space for hydrocarbons.

Geophysical Assessment of Groundwater Vulnerability to Diesel Contamination at a Telecommunication Mast in Adebayo Area, Ado-Ekiti, Southwestern Nigeria

Abstract An appraisal of the groundwater vulnerability to contamination risk at Adebayo in Ado-Ekiti, Southwestern Nigeria, was carried out using the electrical resistivity method of geophysical prospecting. Two traverses of length 100 m each were established for both vertical electrical sounding (VES) and dipole-dipole. Six (6) Vertical Electrical Sounding (VES) and 2-D dipole-dipole profiling techniques of the electrical resistivity method were adopted for the geophysical investigation. The results show variations in resistivity values, depicting four to five geologic layers: the topsoil, laterite, weathered layer, fractured, and the fresh basement. It was observed from the correlation of the geoelectric section and 2-D resistivity image along traverse 1 (TR1) that the groundwater in the study area flows towards the southwestern part, and the fractured basement serves as a migration pathway to the diesel oil in the same direction as groundwater flow. The fractured basement (Well 2) with no lateritic cover has higher resistivity values compare to the fracture zone that was found directly under the mast which was overlain by the laterite. Comparing the resistivity values of Well 1 and 2, Well 2 that was drilled into the fractured basement has more traces of the contaminant than Well 1.

Hydrogeophysical investigation for the aquifers in part of Ilorin, Central Nigeria: Implication on groundwater prospect

Hydrogeophysical study involving the use of Vertical Electrical Sounding (VES) was carried out in part of the basement complex rocks of Ilorin, central Nigeria, with the aim of determining its geoelectric parameters and groundwater potential. A total of thirty (30) VES were carried out using Schlumberger electrode configuration, with half electrode separation (AB/2) varying from 1m to 100m. Information on the subsurface lithologies, overburden thickness and aquiferous layers were obtained from the different VES locations in the study area. From the quantitative interpretations of the data collected, using the method of curve matching with the Orellana-Mooney master curves and 1-D forward modeling with WinResist 1.0 version software, three to five lithologic units were identified in the study. These include: the topsoil, sandy/lateritic clay/laterite, the weathered basement, the fractured basement and the fresh bedrock which are predominantly of the ‘KH’ curve type (30%), followed by ‘H’ type (26.7%), other type curves include ‘QH’ (16.7%), ‘HKH’, ‘HA’ and ‘A’ (6.7% each) and KQ and KQH (3.3% each). The weathered layer and the fractured basement constitute the main aquifer units. The aquifers are of generally low resistivity values (mostly below 100 Ω-m). The depths to dry bedrock at the chosen VES locations vary from 2.7 to 62.7 m with a mean value of 13.02 m in the study area. The geoelectrical interpretations of data obtained in these areas have permitted the delineation of the study area into low and moderate groundwater potential zones. This study is expected to assist in future planning for groundwater resources.
 Keywords: Hydrogeophysical, Basement Complex, Groundwater, Electrical Soundings, Weathered, Fractured

Assessment of Leachate Contamination of Groundwater at Some Waste Disposal Sites in the Southern Guinea Savannah Ecological Zone of Nigeria Using Geoelectric Processes

This study aims at determining the leachate contamination of the groundwater resource at selected domestic wastes disposal sites in Minna, Nigeria for a population about 2.1 million, to locate aquifers and hydraulically active structures by tracing the movement of contaminant plumes and seepages in ground at the selected locations. Resistivity data was collected using a terrameter (SAS4000) while the Vertical Electrical Sounding (VES) mode was deployed using the Schlumberger array to enable investigation of the depth penetration of contaminant plume. The induced polarization (IP) was used to determine the level of contaminant plume. The VES readings measured at 50m intervals along each profile line and 100m inter-profile distance, with a maximum current electrode separation of 200m and potential electrode separation of 30m. There are equal numbers of three and four layers observed on the profile, which has ten VES points. The first layer has a resistivity range between 48.4 Ωm & 428 Ωm and thickness between 0.65m & 3.83m. However, isolated resistivity area such as VES; N5 (287Ωm), N6 (295Ωm) and N8 (428Ωm) also suggested sandy/soil rich in organic matter (humus material/soil). The second and third layer is the fractured basement which has very low resistivity values for most VES (N1–48.5Ωm, N2–38.7Ωm, N3–41.6Ωm, N5–61.5Ωm, N7–49.6Ωm, N8–60.7Ωm, N9–108Ωm and N10–97.6Ωm) that indicated leachate presence and contamination, which results from increased ionic concentration. In conclusion, it was discovered that the study area had high conductivity values for some of the locations using the resitivity determination method. This indicated the presence of water within the study area. It was also concluded that the IP which indicated high concentration of metals caused the lowering of the resisitivity values at some of the locations, thus indicating the presence of metals within the study area.

Subsurface Investigation of Basement Structures Using Electrical Resistivity Methods at Zainawa Village Kano, Nigeria

Electrical Resistivity Methods involving Schlumberger Vertical Electrical Sounding (VES) and Wenner Electrical Profiling (EP) were carried out to map the Geological features of the earth subsurface in Zainawa Area of Kano State, Nigeria. Five profiles were established; consist of six (6) VES points at each profile. GEOPULSE resistivity meter (SAS 300) was used for the data acquisition. The field data obtained have been analyzed using computer software (IPI2win) which gives an automatic interpretation of the apparent resistivity. A maximum of three geoelectric subsurface layers were delineated from the VES master curves. The geoelectric section beneath the study area was composed of top soil (clayey-sandy and sandy-lateritic), weathered layer, partly weathered (fractured basement) and fresh basement. The resistivity value for the topsoil layer varies from 20 Ωm to 600 Ωm with thickness ranging from 0.5 to 7.2 m. The weathered basement has resistivity values ranging from 15 Ωm to 593 Ωm and thickness of between 2.75 to 33.04 m. The fractured basement has resistivity values ranging from 201 Ωm to 835 Ωm and thickness of between 11 to 20.4 m. The fresh basement (bedrock) has resistivity values ranging from 1161 Ωm to 3115 Ωm with infinite depth. The depth to basement map was produced to give a good picture of the basement topography within the study area. The depth to basement ranges from 11 m around VES 01 to 85 m around VES 25 m. The map also reveals linear structures (VES 05, 21, 22 and VES 23) which trends in the NE-SW direction. These structures suggest a basement depression at these points. However, the depth from the topsoil to the bedrock surface varies between 2.5 to 37.75 m.

Fractured, altered, and faulted basement in northeastern Oklahoma: Implications for induced seismicity

Due to a decade of wastewater injection-triggered seismicity, the crystalline basement of northern Oklahoma has become the subject of intensive research, almost all of which has relied upon remote sensing or analog models and materials due to a near total absence of outcrops. This study reports relevant characteristics of material in drill cores from the area, the best available analog for seismogenic northern Oklahoma basement. Fractures are present in all cores, remain abundant over 100 m below the top of basement, commonly have steep inclinations (≥70°) and are nearly universally mineralized. Many fractures show evidence of slip such as slickenlines, vein offset, brecciation, and in one core injectite formation. Fractures are mineralized by carbonates and/or phyllosilicates along with various other minerals, some contain vugs, and many contain multiple generations of minerals. Color changes suggestive of redox processes, including possible paleoweathering, are associated with fractures and proximity to the basement unconformity. Paragenesis of fracture minerals and variations in geochemical analyses of altered rocks indicate complex histories of deformation and fluid activity. The abundance of fractures in cores indicates that the upper basement of northeastern Oklahoma is much less “intact” than commonly assumed; it instead shows similarities to fractured basement plays, which may provide a more reasonable comparison for future work.

Combined GPR, DC resistivity, and hydrogeochemical data for hydrogeological exploration: a case study at the Red Sea coast

This study presents an approach of information on ground-penetrating radar (GPR), DC resistivity, and hydrogeochemical data for monitoring the potential of fresh groundwater zone, both quantitatively and qualitatively. This is applied in new urban area located at the coast of the Red Sea. First, a GPR survey is conducted to provide the preliminary data on the lithology, subsurface structure, and accumulation of groundwater in the aquifer. Then, a DC resistivity enabled the mapping of several geoelectric layers with info, water table, depth, and thickness of each water-bearing layer. Vertical electrical sounding is acquired and calibrated using available data of observation boreholes as well as the near GPR profiles to verify the results. In addition, water samples from drilled wells and springe are collected to evaluate hydrogeochemical characteristic and hydrogeological setting of the aquifers. Geophysical and hydrogeological datasets indicated the presence of two aquifers; the first aquifer occupies the zone of wadi deposits, and the second aquifer occurs in the fractured basement rock. The salinity in these aquifers shows heterogeneous distribution, but generally increases with depth, and is basically dependent to the prevailing structural framework and geological conditions. Such data integration shows the potential of the proposed approach in exploring and evaluating groundwater resources in semi-arid coastal plains using hydrogeological, DC resistivity, and GPR data.

On the Use of Electrical Resistivity Method in Mapping Potential Sources and Extent of Pollution of Groundwater Systems in Lapai Town, Niger State, Nigeria.

<p>Electrical resistivity method employing the Schlumberger array was used to occupy forty four (44) vertical electrical sounding points in Lapai town with the aim of determining the depth to aquifers, aquifer thicknesses and aquifer protective capacity. The G41 Geotron resistivity meter was used in obtaining the apparent resistivity data which was processed using Interpex 1XD resistivity interpretation software. The results revealed four lithologic sections which include top lateritic soil, sandy clay, fractured basement and fresh basement. Both confined and unconfined aquifers were identified within the area, with four classes of aquifer proactive capacities as high, moderate, weak and poor. While the aquifer at VES 20 was highly protected, twenty other aquifers were moderately protected, eight others had weak protection and fifteen aquifers were poorly protected. The aquifers were generally of good thicknesses and at varying reasonable depths, making them good reservoirs of water in appreciable quantity. The average aquifer thickness was estimated to be 48.36m while the average depth to aquifers was estimated to be 56.68m.</p>

Development of numerical model for simulating resistivity and hydroelectric properties of fractured rock aquifers

Studying fractured aquifers have been always a challenging subject due to the complexity of their physical and hydrogeological properties. In this study, it is therefore aimed to investigate the electrical conductivity of the saturated fractures as conductive zones and the role of these zones in changing and reducing the host rock resistivity. To achieve this goal and estimate the hydro-electrical characteristics of these aquifers, a 3D numerical modeling (Comsol Multiphysics Model, CMM) was developed for simulating the resistivity and hydro-electrical properties of these aquifers by applying the Vertical Electrical Sounding technique (VES). The calibration between the analytical solution and numerical model showed an error percentage less than 0.03%. The resulted VES-curves depending on porosity increasing, which in its turn is depending on increasing in fractures density, distribution and their orientation, confirmed that the resistivity of fractured aquifer decreases with increasing the fractures density and porosities. The results were considerably representative exhibiting the nature of the relationship between porosity and resistivity of fractured aquifers. This relationship was found to be linear and inverse with high evidence and correlation results. Corresponding to these findings the resulted empirical equation can be used in predicting the porosity with taking into account the saturated weathered and fractured basement rocks resistivity which ranges between 7-85 Ω.m. The error percentages should also ranging between 0.0015%–0.0668%. Accordingly, this model produces reliable solutions of the resistivity method forward problem for arbitrary electrical resistivity in the subsurface depending on the fractures density and porosity of fractured aquifers. The apparent resistivity curve obtained from this model was compared with the measured field apparent resistivity curve of the fractured aquifer. The results are consequently testifying the effectiveness of Comsol Multiphysics Model in studying, solving, and understanding the different electrical and hydrogeological conditions of these aquifers.

The potential use of remote sensing and GIS techniques for sustainable development in the coastal plain between Halayb and Shalateen, Egypt

The Red Sea coastal plain between Halayb and Shalateen represents one of the localities with great potential for future sustainable development. The area is almost flat with Quaternary deposits from the western wadies towards the Red Sea shoreline. Due to the general character of the area, it is promising for reclamation, tourism, and industrial activities. This paper highlights the environmental characteristics of the area for sustainable development using remote sensing and GIS techniques. Geomorphological analysis, assessment of soil pollution (radiological and heavy metal distribution), groundwater assessment, and detection of change to the shoreline have been carried out. Geomorphologically, the most suitable part of the study area for future planning is the southeastern region. The northern area is not appropriate as it is classified as third-order drainage and will be exposed to flash floods that threaten the infrastructure of the native settlements, newly built tourist villages, and the coastal roads. The groundwater aquifers in the study area are Quaternary sediments and fractured basement rocks. All groundwater samples have acceptable soluble sodium percentages (SSPs) with relatively low sodium and very high saline, making them suitable for salt-tolerant crops on soil with good permeability and special leaching. The Wadi Diit area is in the safe range of radioactivity with a maximum effective dose rate of 0.37 mSv year−1, which does not represent any harm to living organisms. Furthermore, the soil studied from the area under consideration reflects heavy metal concentrations lower than the maximum allowable levels. The change detection study showed that there is a balance between erosion and accretion rates with no significant change in the shoreline morphology that would affect future planning in the coastal area.

Fracture characterization with fieldwork data and its implication for basement fracture reservoir at Muaro Silokek Granitic Outcrops

The Muaro Silokek Area is a location that is quite complex in geological structure and consists of granitic rocks which vary in mineral composition, so it’s fit to do fieldwork for fracture characterization for analog basement fracture reservoir. This research was continuance of previous study about granitic basement fracture at around Sumatra, now especially with fieldwork data. The aim of the study is to determining fracture characteristics like fracture spacing, fracture aperture, fracture length by using fieldwork data to determine fractal analysis and relate it to fracture reservoir. Those research conducted by using scanline and windows scan method with total 2700 cm scan line and 490000 cm2 area of widows scan in five location damage zone. The result shows generally shear fracture have three main orientations, there were NE – SW, NNW – SSE, ENE – WSW and NNE – SSW, W – E, NW – SE for joint orientation. Cumulative distribution of fracture spacing, fracture aperture, fracture length at five location scan line and window scan following power law. Statistically, fracture porosity and permeability result shows linier data distribution with cubes calculation methods. This fracture permeability has exponential distribution relationship with fracture aperture, and fracture porosity has power distribution relationship with fracture spacing.

Hydrogeophysical appraisal of groundwater potential in the fractured basement aquifer of the federal capital territory, Abuja, Nigeria

In this study, eighteen (18) vertical electrical sounding (VES) data points were located in the Federal Capital Territory (FCT), Abuja, Nigeria with ABEM Terrameter using Schlumberger array to delineate potential groundwater development areas. Groundwater flow direction map was produced using the elevation of the water level from sea level with GIS Arc/Info Point coverage. The investigated areas have four geoelectric sections, categorized as topsoil, clay, fractured/weathered basement, and fresh basement. The groundwater is mainly confined in the fractured/weathered basement. It generally flows from NW to SE, but this flow is not steady. It has been obstructed and reoriented towards the south, whereas some portion flows towards the northern parts of the aquifer system peradventure due to the variation in aquifer depth from place to place. Out of the 18 VES points, 9 points located around the NE and SE peripherals of the study area have groundwater development potentials at depths ranging from 40 - 80 m and aquifer thickness of 25 – 65 m, characterized by resistivity values that varied from 80 – 680 Ωm, whilst the other nine in the SW and central parts do not show promising groundwater development potentials because they lack fractured/weathered zones. The northern and SE zones, which comprise areas such as Bwari, Kuje, Idu CITEC, Sherete, and GTSSC are the preferred targets for water well drilling than the southern zone. However, other communities including Gwagwalada and Gugugu in the southern zone also offer promising groundwater potentials.

Hydrogen in Australian natural gas: occurrences, sources and resources

Natural or native molecular hydrogen (H2) can be a major component in natural gas, and yet its role in the global energy sector’s usage as a clean energy carrier is not normally considered. Here, we update the scarce reporting of hydrogen in Australian natural gas with new compositional and isotopic analyses of H2 undertaken at Geoscience Australia. The dataset involves ~1000 natural gas samples from 470 wells in both sedimentary and non-sedimentary basins with reservoir rocks ranging in age from the Neoarchean to Cenozoic. Pathways to H2 formation can involve either organic matter intermediates and its association with biogenic natural gas or chemical synthesis and its presence in abiogenic natural gas. The latter reaction pathway generally leads to H2-rich (>10mol% H2) gas in non-sedimentary rocks. Abiogenic H2 petroleum systems are described within concepts of source–migration–reservoir–seal but exploration approaches are different to biogenic natural gas. Rates of abiogenic H2 generation are governed by the availability of specific rock types and different mineral catalysts, and through chemical reactions and radiolysis of accessible water. Hydrogen can be differently trapped compared to hydrocarbon gases; for example, pore space can be created in fractured basement during abiogenic reactions, and clay minerals and evaporites can act as effective adsorbents, traps and seals. Underground storage of H2 within evaporites (specifically halite) and in depleted petroleum reservoirs will also have a role to play in the commercial exploitation of H2. Estimated H2 production rates mainly from water radiolysis in mafic–ultramafic and granitic rocks and serpentinisation of ultramafic–mafic rocks gives a H2 inferred resource potential between ~1.6 and ~58MMm3 year−1 for onshore Australia down to a depth of 1km. The prediction and subsequent identification of subsurface H2 that can be exploited remains enigmatic and awaits robust exploration guidelines and targeted drilling for proof of concept.

Geophysical and Contamination Assessment of Soil Spatial Variability for Sustainable Precision Agriculture in Omu-Aran Farm, Northcentral Nigeria

The Spatial and temporal variability of soil properties (fluid composition, structure and water content) and hydrogeological properties employed for sustainable precision agriculture can be obtained from geoelectrical resistivity methods. For sustainable precision agricultural practices, site-specific information is paramount, especially at the planting season. An integrated one-dimensional (1D) and two-dimensional (2D) electrical resistivity surveys have been adopted to characterize the subsoil parameters and delineate the aquifer unit of large farm area, especially in precision agricultural practices. Also, contamination assessment reveals the soil quality status of farmlands. This study aims to determine the site-specific soil parameters of a commercial farm in Omu-Aran, Northcentral, Nigeria. The subsoil features from the geoelectrical resistivity surveys indicate 3 to 4 distinctive lithology to a depth of 43.4 m into the subsurface of the farm. The ID (Vertical Electrical Sounding) and 2D resistivity inversion models results have revealed the heterogeneity nature of the topsoil also known as the stone zone comprising of reworked clayey soil and sandy gravelly soil, the weathered/saprolite zone (gravelly sandy/ sandy soil), the fractured basement and the fresh basement rock. Contamination factor (Cf), pollution load index (PLI) and Nemerow integrated pollution index (NIPI) were used to assess the contamination index on the farmland. Toxic elements such as arsenic, cadmium, chromium, cobalt, lead, manganese, nickel, and zinc have low to moderate contamination in the farm. The depth of investigation (≤ 3m) covers the upper root zone of significant crops grown in the area. The findings can assess soil contamination, delineate basement features, subsoil variability, soil profiling, and determine the subsoil hydrological properties.

GEO-ELECTRICAL DELINEATION FOR GROUNDWATER RESOURCES OVER GIDAN-DOYA BASEMENT AREA, CENTRAL NIGERIA

Groundwater development is very important in the survival of the human. This research was carried out in a newly developing area with population increase and agricultural development hence the need for this study. The objective is to carry out a geophysical investigation, delineate aquiferous zones, and groundwater potential for the study area. An electrical resistivity method for groundwater investigation using the Vertical electrical sounding (VES) technique was adopted. The survey involved three profiling and seven VES points using the Schlumberger configuration to delineate the subsurface lithologies and aquiferous zones within the study area. It was observed that the study area is composed of highly weathered and fractured rocks; hence there is a tendency for groundwater migration and accumulation in the weathered fractured horizons. Two geo-electric sections and a basement map were produced. The area generally showed four to five lithology units; which include topsoil, laterite, weathered basement, fractured basement, and the fresh basement. The thickness of the overburden ranges from 0 - 12.8m and the saturated layers have resistivity values ranging from 19.7Ωm - 849.8Ωm with depths to water range of 10.5m – 61.1m respectively. VES points 2, 4, and 5 showed good potential for groundwater with aquiferous unconfined zones ranging depths of about 45.0m - 60.0m. It was also deduced that areas, where thick overburden complemented with the presence of weathering and fractures within the study area, are zones for groundwater accumulation.

In–situ quantification of mechanical and permeability properties on outcrop analogues of offshore fractured and weathered crystalline basement: Examples from the Rolvsnes granodiorite, Bømlo, Norway

Fractured and weathered crystalline basement units below erosional unconformities potentially represent unconventional reservoirs for georesources (oil, mineral and water). The reservoir properties and characteristics strongly depend on secondary processes connected to the local structural and alteration/weathering history. Here we present the results of in–situ field quantification of mechanical (uniaxial compressive strength) and petrophysical (permeability) properties of a fractured and weathered crystalline basement at selected outcrops on the island of Bømlo (western Norway). The Bømlo outcrops are believed to represent an onshore analogue of the unconventional oil reservoir hosted in the offshore Utsira High granodioritic fractured basement (northern North Sea). The off– and onshore crystalline basements have both undergone surficial weathering during the Mesozoic, as shown by the occurrence of a dated, variably thick saprolitic profile on top of fresh fractured basement blocks. The Bømlo crystalline basement is characterized by a complex and highly permeable fracture network. Fault rocks within its fault zones are characterised by an anisotropic mechanical strength and by an average permeability that is two orders of magnitude larger than that of the host rock. The matrix permeability and mechanical strength are significantly affected by alteration/weathering products. Analysis of the textural and mineralogical characteristics of the weathered outcrops allowed us to constrain the variation of permeability and mechanical strength as a function of increasing alteration and to infer their distribution in the, now eroded, top–basement weathering profile on Bømlo. Weathering enhances permeability and drastically decreases the mechanical strength. Nevertheless, evolved saprolitic horizons may act as low–permeability top–seal units to the fractured and weathered crystalline basement reservoir. The obtained permeability and mechanical data are finally used to better constrain the potential reservoir rocks, the fluid migration pathways, and to discuss their role in the geomechanics of a conceptualised fractured and weathered crystalline basement unconventional reservoir.

Hopes of Basement Bonanza Drowned by Bad Modeling

A British independent bet its future on proving that fractured basement formations could produce large amounts of oil and gas. Based on its first two wells, the proposition that these highly fractured layers of awful-quality reservoir rock can produce billions of barrels of oil is looking very unlikely, but there might be something of value down there. Last April, Hurricane Energy predicted those two development wells could easily produce 17,000 B/D of oil from rock it said held “half a billion barrels of oil.” Now Hurricane’s ambitious plans and its identity as “basement reservoir specialists” are in tatters. The initial wells were productive but much of what was coming out of the lower one - 205/21a-7z - was water. After 8 months of production the water cut reached 46% from a well that was supposed to be hundreds of meters above the boundary between the oil and water aquifer. That was not the only evidence suggesting there was something wrong with the plan to develop discoveries in the Lancaster field along Rona Ridge in the West of Shetland area. On 8 June, Hurricane’s founder and Chief Executive Officer Robert Trice, a geologist with a keen interest in fractured basement rock, resigned, and the company launched a review of the technical work underlying the plan. Experts were added to the subsurface team, which then made major changes. The most significant change pushed up the depth of the contact point between the oil and water levels by around 300 m, within 1 m below the toe of the lower well. In other words, three-quarters of the reservoir in the original plan was under water. The presentation by Beverley Smith, the company’s interim chief executive officer, was a reminder of how a long-term production test can change a reservoir model, even one based on years of work and the drilling of multiple wells. “Let me start by reminding everyone that we are dealing with a unique and challenging reservoir that was always subject to great uncertainty and where data acquisition has long been problematic,” Smith said. Lowered Expectations Hurricane’s remaining Lancaster well (205/21a-6) is producing more than 12,000 B/D, providing critical cash flow for the company, whose future looks altogether different than it did in the days when it predicted its discoveries could potentially produce 2.6 billion bbl of oil, making it the largest undeveloped resource base in the UK Continental Shelf (UKCS).

Pre-Tertiary Basement Subcrops Beneath The Malay And Penyu Basins, Offshore Peninsular Malaysia: Their Recognition And Hydrocarbon Potential

Following the successful production from fractured basement in similar Tertiary basins, the basement play was pursued in the Malay Basin, particularly during the 2000-2010 period but, unfortunately, that effort fell short of expectations. The only oil discovery in fractured basement reservoir was Anding in the southwestern part of the basin. Despite its development being delayed due to economic reasons, the Anding discovery had been the basis for the basement play concept: namely, a fractured reservoir formed of pre-Tertiary metamorphic rock, charged from overlying Tertiary lacustrine source rocks in an adjacent half-graben and sealed by a transgressive shale unit. This paper examines seismic, gravity and well evidences on the pre-Tertiary basement geology, with the aim of assessing further the hydrocarbon potential of pre-Tertiary basement. The pre-Tertiary basement subcrops beneath the Malay and Penyu basins represent a continuation of the onshore geology of Sundaland Mesozoic terrane. Wells that penetrate the Base-Tertiary Unconformity (BTU) indicate a variety of rock types including igneous, metamorphic and sedimentary. Seismic data show the widespread presence of layered rocks beneath the BTU which could include potential new plays. Gravity modelling was carried out to help distinguish between pre-Tertiary layered rocks and Tertiary synrift sediments. Fractured reservoirs, like those discovered at Anding, seem to be associated with major strike-slip fault zones which are identifiable on high-quality seismic. Carbonate structures such as paleokarsts and buried hills are also recognisable and could potentially be mapped with seismic. These pre-Tertiary plays also rely on hydrocarbon charge mainly from the overlying Tertiary source rocks. Although Palaeozoic-Mesozoic source rocks may have passed their hydrocarbon generation stage, their gas potential cannot be ruled out.

Geological characterization of the Patterson CO2 storage site from 3-D seismic data


 Approximately 26 square miles of new 3-D seismic data were acquired in July 2019 over the Patterson Site (Kearny County, Kansas) to assess its potential for carbon dioxide (CO2) storage. Seismic interpretation revealed that the Patterson Site contains multiple structural closures that lie on uplifted fault blocks, bounded by two reverse faults that strike nearly perpendicular to each other. These faults offset Precambrian through Pennsylvanian sections, including several primary reservoir and seal intervals. Fault displacements are maximum at the Precambrian basement and decrease upward. Data indicated a range of structural and combination traps exists at the Patterson Site in the Cambrian-Ordovician Arbuckle through Mississippian Osagian reservoirs. The three-way closures along the NW–SE fault have structural relief of ~130 ft (40 m), and the four-way closures contain relief of ~60 ft (18 m). Erosional surfaces and multiple basement fractures also are observed on the top of the Precambrian. A Mississippian-aged incised valley system also was observed at the Patterson Site. The incised valleys formed during the Meramecian-Chesteran Stages with an incised depth up to 250 ft (76 m). The motion of the reverse faults likely captured existing meandering and linear channels, causing the current deeply incised morphology. The incised valleys observed at Patterson are similar in age, structural style, shape, incision depth, and seismic attribute properties to incised valleys observed by other workers at Pleasant Prairie South, Eubank, and Shuck oil fields (southwest Kansas). Further research should focus on estimating reactivation tendency and sealing characteristics of the reverse faults to evaluate the seal integrity of the saline reservoirs. This will reduce uncertainty concerning the risk of CO2 migration during injection and storage. Further reservoir description, modeling, and simulation are also underway to characterize the storage potential at the Patterson Site.