Petroleum Wells Research Articles

CASPIAN SEA GEODYNAMICAL EVOLUTION EFFECT ON THE SEA LEVEL CHANGING ALONG THE QUATERNARY PERIOD

The Caspian Sea as the largest lake in the world has different characteristics considering geosciences (Fig. I). In fact sea level changing is the most important happening in this region. Annually fluctuation impact on surrounding coastal area has serious damage and human society meet frequent destroyed phenomena. In this paper we are trying to reconstruct rapid Sea level changing in Holocene epoch by use paleontology evidences such as: Mollusks fossil and sedimentary fades record. In this research 254 Quaternary sediment core samples from exploring petroleum wells (M-l, G3-A) have been evaluated considering above mentioned and also more than 130 sea bottom recent sediments on view of biofacies and biostratigraphy studied. Our investigation results show that in the Caspian Sea basin at the Holocene epoch there are many periodic sea level fluctuations and climatologie impact is most important agent for sea level changing in this basin. Data results are showing that in the studied area there were many periodic rapid sea levels changing during the Quaternary period. The Caspian Sea has several fluctuations along 10,000years ago and its latest begin about 25years ago. Finally we can conclude that Caspian Sea level fluctuation could continue at future similar past time and climatologie impact and tectonic movement are important agents for sea level changing in this region

Aeromagnetic study of buried basement structures and lineaments of Sahel region (Eastern Tunisia, North Africa)

This study presents original results regarding the use of aeromagnetic to explore deep subsurface structuring in southern part of Tunisian Sahel petroleum province (Eastern Tunisia, North Africa). Several filters and techniques were applied to the total magnetic intensity (TMI) grid. First, an adequate reduce to the pole (RTP) grid was generated. The RTP map shows 17 positive and negative anomalies associated with short- and long-wavelength amplitude anomalies. Positive anomalies correspond to high magnetic basement structures estimated from seismic lines in the area. Circular anomalies are also distinguished locally and can be explained by Cretaceous magmatic rocks recognized in numerous petroleum wells. Second, specific qualitative and quantitative filters (e.g., residual-regional separation, horizontal tilt angle (TDX), tilt angle (TILT), total horizontal derivative of tilt angle (THDTILT)) were applied to elucidate the form and the extent of buried magnetic anomalies and lineaments. The resulting deep structural map revealed the presence of NW-SE, N-S, and E-W regional magnetic basement structures and lineaments and a regional tectonic node surrounding Henchir Keskes-Agareb-Mahres-Hachichina area. Two magnetic inversion models calculated across the study area highlight west to east crustal thinning trend and permit depth to basement estimation. These results are valuable for future conventional and unconventional petroleum exploration in this underexplored southern part of Sahel plain.

A Paleozoic-sourced oil play in the Jura Mountains of France and Switzerland

Abstract The Jura region of France and Switzerland has significant hydrocarbon potential. This arcuate fold-and-thrust belt, located in front of the Western Alps, is composed of Mesozoic rocks, which overlie the North Swiss Basin Complex filled with Permo-Carboniferous sediments of Late Westphalian–Lower Permian (Autunian) age. The existence of three small producing gas fields, and the presence of recorded oil and gas shows in a number of petroleum wells, indicate the presence of an active petroleum system. Shows occur in stratigraphic horizons that lie beneath the regional Triassic evaporite seal. Very effective Permo-Carboniferous oil-prone source rocks include algal organically rich Autunian shale beds and Stephanian-aged bituminous shales. Carboniferous and Permian coals are also present, which would be excellent sources of gas. The primary reservoir target is the fluviatile Triassic Bunter Sandstone Formation, which is widely developed across the area and thickens to the NE. Reservoir quality is best developed in the cleaner channel sands. The La Chandelière oil field, discovered in 1989 by Exxon, is crucial evidence of the oil potential and trapping mechanism. Geochemical analysis demonstrates that the 41° API oil at La Chandelière is derived from Lower Permian Autunian shales. The trapping mechanism, interpreted from seismic and confirmed by structural modelling, is that of an unreactivated Mesozoic-aged structural high bounded by thrust faults, resulting in a large-scale rollover within the core of the structure. This combination of critical elements sets up the Paleozoic-sourced oil play within the Jura Mountains of France and Switzerland. The Jura is not generally regarded as a major petroleum province. It is a region of complex structuring and mountainous terrain. Switzerland, a country renowned for its beautiful mountain scenery, has no major oil and gas discoveries. However, this poorly explored region has active petroleum systems with good hydrocarbon shows and a number of small gas fields demonstrating hydrocarbon generation. Good-quality source rocks and excellent reservoir development have been proven by drilling, and seismic interpretation has demonstrated the existence of large closures at reservoir level. The La Chandelière oil discovery, in the French Jura, proves the presence of a Paleozoic-sourced oil play.

Influences of the petroleum-recovering activity on the arsenic level in groundwater of Kuitun, Xinjiang, China

ABSTRACTIncreasing demands of groundwater in petroleum-recovering regions could elevate the level and mobility of arsenic in groundwater as a result of the enhanced dissolution of arsenic-bearing iron or manganese oxide due to the accelerated sulfate reduction by microorganisms in a reductive environment. To substantiate this possibility, groundwater samples were collected from 220 water wells in the nearby petroleum wells in Kuitun. Dissolved arsenic, iron, manganese, and sulfate levels and pH in groundwater samples were analyzed. The dissolved arsenic levels in groundwater varied from <2.3 to 789.4 μg·L−1, in which approximately 96.4% of the measured values exceeded the allowed limits of the World Health Organization. An inverse relation existed between dissolved arsenic and sulfate levels. Most of the high arsenic-level samples (>300 μg·L−1) were found in wells at close proximity to petroleum wells where a high iron or manganese level was also detected. The oil-exploring activity in the study region seemed to have enhanced the microbial reduction of sulfate in underground environment and hence the level of arsenic in groundwater. The microbial sulfate reduction coupled with the reduction of arsenic-bearing iron oxides in the groundwater environment may explain the spatial heterogeneity of the arsenic level in groundwater.

Evidence of hotspot paths below Arabia and the Horn of Africa and consequences on the Red Sea opening

Rifts are often associated with ancient traces of hotspots, which are supposed to participate to the weakening of the lithosphere. We investigated the expected past trajectories followed by three hotspots (Afar, East-Africa and Lake-Victoria) located around the Red Sea. We used a hotspot reference frame to compute their location with respect to time, which is then compared to mantle tomography interpretations and geological features. Their tracks are frequently situated under continental crust, which is known to strongly filter plume activity. We looked for surface markers of their putative ancient existence, such as volcanism typology, doming, and heat-flow data from petroleum wells. Surface activity of the East-Africa hotspot is supported at 110 Ma, 90 Ma and 30 Ma by uplift, volcanic activity and rare gas isotopic signatures, reminiscent of a deep plume origin. The analysis of heat-flow data from petroleum wells under the Arabian plate shows a thermal anomaly that may correspond to the past impact of the Afar hotspot. According to derived hotspot trajectories, the Afar hotspot, situated (at 32 Ma) 1000 km north-east of the Ethiopian–Yemen traps, was probably too far away to be accountable for them. The trigger of the flood basalts would likely be linked to the East-Africa hotspot. The Lake-Victoria hotspot activity appears to have been more recent, attested only by Cenozoic volcanism in an uplifted area. Structural and thermal weakening of the lithosphere may have played a major role in the location of the rift systems. The Gulf of Aden is located on inherited Mesozoic extensional basins between two weak zones, the extremity of the Carlsberg Ridge and the present Afar triangle, previously impacted by the East-Africa hotspot. The Red Sea may have opened in the context of extension linked to Neo-Tethys slab-pull, along the track followed by the East Africa hotspot, suggesting an inherited thermal weakening.

Evaluating the Effect from Constructing Binary Geothermal Power Units Based on Spent Petroleum and Gas Boreholes in the South Regions of Russia

The article substantiates the possibility of efficiently harnessing the geothermal resources available in the North Caucasian region through constructing binary geothermal power plants (GeoTPPs) using idle petroleum and gas wells. The power capacities of GeoTPPs are evaluated, and the basic characteristics of these power plants in case of constructing them in the promising areas are determined. The overall useful GeoTPP capacity equal to approximately 330 MW can be obtained from using the entire fleet of idle wells available in these areas. Diagrams confirming the possibility of reaching the optimal flowrate of geothermal heat carrier circulating in the geothermal circulation system loop are presented. This flowrate corresponds to a binary GeoTPP’s maximal useful power output. The article shows, taking the Ternair geothermal field as an example, that it is inefficient to use medium-enthalpy thermal waters for generating energy at a binary GeoTPP involving reinjection of a spent heat carrier. It is shown that good prospects can be expected from applying a hybrid geothermal and combined-cycle technology, by means of which it is possible to use lowenthalpy (80–100°С) thermal waters for generating electricity in a highly efficient manner. In accordance with such technology, geothermal heat is used in the binary GeoTPP cycle for heating low-boiling working fluid to its evaporation temperature. The working fluid is evaporated and superheated by using the heat of exhaust gases from a gas turbine power unit. Owing to combined use of the thermal water heat potential and the heat of exhaust gases from a gas turbine power plant in a hybrid process system, it becomes possible to obtain high power performance indicators of hybrid geothermal and combined-cycle power plants. This conclusion is confirmed by the results from numerical evaluations carried out as applied to the Ternair geothermal field. With the fully harnessed resource potential of the Ternair field, the total capacity of hybrid geothermal and combined-cycle power plants may reach 60 MW, a level that would make it possible to relieve a significant part of energy, environmental, economic, and social problems faced by the city of Makhachkala.

Seismic reflection and structuring characterization of deep aquifer system in the Dakhla syncline (Cap Bon, North-Eastern Tunisia)

The Dakhla syncline is located in the North-Eastern Tunisia. It is bounded by Abd El Rahmene anticline to the North-West, El Haouaria Graben to the North-East, Grombalia Graben to the South-West and the Mediterranean Sea to the East. The main aquifer reservoirs of Dakhla syncline are constituted by stacks of fluvial to deltaic Neogene sequences and carbonates. The interpretation of eight seismic reflection profiles, calibrated by wire line logging data of three oil wells, hydraulic wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of aquifers and their distribution in elevated structures and subsurface depressions. Lithostratigraphic correlations and seismic profiles analysis through the syncline show that the principal aquifers are thickest within the central and northern part of the study area and thinnest to the southern part of the syncline.Seismic sections shows that the fracture/fault pattern in this syncline is mainly concentrated along corridors with a major direction of NW-SE and secondary directions of N-S, E-W and NE-SW with different release. This is proved by the complexity structure of Eastern Tunisia, resulted from the interaction between the African and Eurasiatic plates. Isochron maps of aquifers systems exhibited the structuring of this syncline in sub-surface characterized by important lateral and vertical geometric and thickness variations. Seismic sections L1, L2, L3, L4, L5 and petroleum wells showed an heterogeneous multilayer aquifers of Miocene formed by the arrangement of ten sandstone bodies, separated by impermeable clay packages. Oligo-Miocene deposits correspond to the most great potential aquifers, with respectively an average transmissivity estimated: Somaa aquifer 6.5 10−4 m2/s, Sandstone level aquifer 2.6 10−3 m2/s, Beglia aquifer 1.1 10−3 m2/s, Ain Ghrab aquifer 1.3 10−4 m2/s and Oligocene aquifer 2 10−3 m2/s. The interpretation of spatial variations of seismic units and the recognition of tectonic structures and their development may reveal some new insights for hydrogeological aspects.

Two-stage genetic algorithm for parallel machines scheduling problem: Cyclic steam stimulation of high viscosity oil reservoirs

In this paper, the problem of optimal assignment of trailer-mounted steam generators for cyclic steam stimulation (CSS) of petroleum wells is formulated as a parallel uniform machines scheduling (PMS) problem with release dates. The total weighed tardiness is used as the goal of the optimization process. The distinctive features of the proposed PMS formulation include: jobs with variable weights, variable machine setup time, constraint capacity of drilling pads (where machines are allocated), and modified tardiness criterion. A two-stage scheduling algorithm combining heuristic and genetic algorithms is proposed for solving it. A chromosome representation, crossover and mutation operators generating only feasible solutions and thus avoiding the use of any repair mechanism are discussed. The performance of the algorithm is tested on a real-world data set from the oilfield asset located in the coastal swamps of the Gulf of Mexico. The experiments indicate that the proposed approach gives good results in optimization of the operational costs and petroleum recovery. The algorithm is implemented as a part of the software platform for optimization of CSS and currently is in use by oilfield engineers.

Two new marine cyst genera from Upper Cretaceous Brookian megasequence strata in the North Slope of Alaska

ABSTRACTTwo new genera, comprising three new species, of marine algal cysts are described here. The extinction horizons of all three occur with a high degree of consistency in many petroleum wells in the Alaska North Slope region. These horizons provide useful correlation events within the overall progradational sediments which filled a large and complex depositional basin during Cenomanian–Turonian time. The newly described taxa are Paranelsoniella woodii gen. et sp. nov., P. minuta gen. et sp. nov. and Xanthocysta ovata gen. et sp. nov.

Deepwater sedimentation and Cenozoic deformation in the Southern New Caledonia Trough (Northern Zealandia, SW Pacific)

Abstract The New Caledonia Trough (NCT) is a 2000–3000 m deep bathymetric feature that extends 2500 km from Taranaki, New Zealand, to the western margin of New Caledonia (Northern Zealandia, SW Pacific). The underlying sedimentary basin originates from Cretaceous extension, but underwent a significant Eocene tectonic event that shaped its present physiography. We present an analysis of the basin based on multibeam data, seismic profiles and rock samples collected on the TAN1312 and TAN1409 Expeditions onboard R/V Tangaroa, combined with legacy data. We focus on the southern part of the basin, where new data reveal a link between compressive deformation of Paleocene strata and their potential reworking into the basin. On the western basin side, Upper Cretaceous to Paleocene strata were deformed by local reverse faults and folds that created a sub-circular bathymetric ridge and seabed exposure. This folded unit (seismic Unit 2) is sharply overlain by a restricted interval imaged as chaotic high-amplitude reflections that are interpreted as syntectonic mass-transport deposits due to slope oversteepening (seismic Unit 1b). This unit is stratigraphically below the main basin onlap surface and seismic mapping revealed that it rapidly thins away from the mouth of a present day submarine canyon imaged on the western slope of the basin, and that is diverted by exposures of Unit 2 deformed strata. Deformed and syntectonic intervals are in turn overlain by a flat-lying unit (seismic Unit 1a) we interpret as reflecting a passive basin fill. Our new data provide insight into an extensive deep-water basin that is remote from terrigenous sediment sources, and new constraints on its Cenozoic tectonic history. Stratigraphic ages are constrained by seismic ties to Taranaki basin petroleum wells and biostratigraphic dating of dredged samples. This specific site has particular significance for understanding tectonic events in the southwest Pacific. Indeed, our observations show that deformation is younger than the Paleocene and is envisaged to be a local expression of a widespread Cenozoic compressive event (called “TECTA”, Tectonic Event of the Cenozoic in the Tasman Area), which affected the region after the Mesozoic rifting. On a regional perspective, this study provides new insights on the evolution of the submerged Zealandia continent and associated geodynamic processes such as Gondwana break-up and initiation of the Tonga-Kermadec subduction.

Numerical simulation of proppant transport in hydraulic fractures

A central issue in hydraulic fracturing treatment in petroleum wells is the transport of proppant particles by the injection fluid. In this paper, we present an innovative proppant transport model in a fixed rectangular- and elliptic-shaped slots. The proposed model is an improvement to the current modeling of proppant transport by applying a non-oscillatory numerical scheme which has high accuracy everywhere in solution domain, even close to the steep gradients. In addition, inertia, fracture wall, and concentration effects on proppant settling along with slurry evolution as a function of proppant concentration has been considered.This paper introduces the mathematical equations that govern the proppant transport phenomenon and discusses special front capturing numerical techniques, boundary conditions, coupling between proppant and slurry mass conservation equations and time stepping restrictions required for the solution stability. We incorporated published correlations obtained from proppant transport laboratory experiments in our numerical model to better capture the physics of the problem. 5th- order WENO scheme was used to avoid oscillation and diffusion at the proppant front since traditional finite difference discretization was found to be insufficient in solving the hyperbolic transport partial differential equations. Results show that the technique used in this study can capture the proppant distribution with minimum oscillation and diffusion.A series of sensitivity analysis was conducted to explore the legitimacy of these assumptions and to provide guidelines that allow more accurate predictions of the proppant and fluid transfer. Numerical results are presented to show how proppant distribution is impacted by the injection fluid viscosity, density difference between proppant particles and injection fluid, proppant size, and fluid flow injection rate. Results of the sensitivity analysis illustrate the significance of choosing appropriate viscosity of the injection fluid as small changes in the viscosity may cause noticeable effects on the concentration distribution. In addition, we found that variation of proppant size and density within a reasonable range have a modest effect on proppant concentration distribution.Furthermore, we also investigated the amount of gravity driven vertical motion of proppant which is driven by density differences (convection) and compare it to a second gravity driven motion which is proppant settlement. Both of these two well recognized mechanisms can occur inside a fracture during proppant placement, however, the importance of each mechanism as a function of proppant injection design parameters is not fully understood.

Modeling of subsurface structure in Utique basin with integration geological and geophysical data, Northastern Tunisia: investigations for natural resources

The Utique basin is situated in the northeastern Tunisia, It is borded by Jebel Hakima and Jebel en Nadour to the north, the Gulf of Tunis to the east, Jebel Amar and Jebel Nahli to the south and Jebel Kechabta to the west. The sedimentary series in the study area present the main potential deep and shallow aquifers in the Utique basin. The interpretation of nine sections seismic reflection profiles, calibrated by wire line logging data of five petroleum wells and geologic field sections highlighted the impact of tectonics on the structuring geometry of sedimentary series (Triassic and Neogene series) and their distribution in surface and subsurface of Utique basin. The Depth and the thickness of Triassic and Neogene to Quaternary series are characterized by important vertical and lateral geometric variations. In fact, the Triassic and Late Miocene to Quaternary deposits have important aquiferous potentialities (groundwater resources and hydrothermal water). In the northeastern Tunisia, shallow and deep groundwater and hydrothermal water such as hot spring of Ain el Hammam (Andolssi et al. 2015) continues to be an increasingly important resource. The objective of the study is to combination geological, structural data and geophysical method in order to evaluate and characterize the surface and subsurface in the Utique region. The study of the three dimension of the Utique region show folded structures and subsiding areas, delimited from different direction by major faults. Added, this paper to examine the Quality water and soil thermal of hot spring Ain El Hammam, characteristics and investigates the thermal waters. The results can be utilized a many applications such as agriculture, spas, medical therapy and green house heating.

Numerical analysis of downhole heat exchanger designed for geothermal energy production

A traditional way of geothermal energy production implies hot brine extraction from the reservoir to a surface facility. This method is economically profitable only for high enthalpy reservoirs associated with shallow depths and high temperatures. The low enthalpy geothermal (LEG) projects are out of consideration due to the high cost of produced electric power related to expensive drilling, cost of the binary cycle system, and long term installation cost. This paper presents a new zero mass extraction method utilizing downhole heat exchanger (DHE) with no geo-fluid production to the surface. The well design stays as a single horizontal well with coupled production and injection sections. The brine pump is located between the sections providing hot brine circulation through the DHE. The coupled fluid flow and heat transfer mathematical model was developed and simulated using nodal analysis method. The LEG reservoir prototype located in South Louisiana was used to study several cases of the DHE lengths, inclination angles, reservoir permeabilities, and flow rates optimization. According to the analysis, the power unit is able to provide 160 kW of net electric power with CO2 working fluid circulating inside a single lateral well. Increasing the reservoir temperature and the number of laterals, the available power production rises up to 600 kW with an attractive electricity cost of $21.84/MWh at 7000 m well depth. This methods opens a new prospective for the depleted petroleum wells converting them to the electricity production units.

Shallow Geology of the CO2CRC Otway Site: Evidence for Previously Undetected Neotectonic Features?

Australia's CO2CRC Otway Site hosts a carbon capture and storage (CCS) demonstration facility that has, to date, injected over 80,000 tonnes of CO2 into two separate geological reservoirs. The reservoir geology is well understood and the site has been the subject of several seismic investigations, though relatively little is known about the near-surface geology and how potential leaks from the injection wells would migrate, particularly within the Port Campbell Limestone. No shallow core has been taken from relevant petroleum wells or water bores, and although there is extensive exposure in the prominent sea cliffs, these are mostly inaccessible. In order to further define the structure and geology of the Port Campbell Limestone at the Otway site, a high-resolution, shallow focused, 3D seismic survey has recently been conducted. The assessment of the near-surface geology described in this paper was used to assist with planning the survey. Using available data, the Port Campbell Limestone is assessed as a series of laterally continuous intercalated limestone, marl, and marly limestones. Interpretation of three previously acquired 3D seismic surveys using a minimum similarity attribute demonstrates evidence for a shallow, steeply east-dipping fault striking approximately NNW-SSE directly below the Otway site. This is observed from approximately 100 m to 380 m depth below surface, where it appears to die out. In the shallow section, the fault is undetectable primarily due to low seismic resolution, and so it is unknown how shallow it propagates. Extrapolation of the fault to the surface projects to between the wells Naylor-1 and CRC-1. A recently acquired high-resolution 3D seismic survey over the study area will allow for this fault to be further delineated.

Geothermal Energy Extraction from Abandoned Wells

Abstract Below the surface of the earth, there exist geothermal resources with the potential to make a significant contribution to the global demand for energy in an environmental friendly way. Seemingly an endless resource, it could be capable of replacing other sources of energy if treated wisely. A main challenge with the industry is related to the capital expensive costs of drilling the geothermal wells, hence the introduction of abandoned petroleum wells is of interest. In this paper, we seek to investigate the potential amounts of heat extracted from beneath the surface, by retrofitting a double pipe heat exchanger in an abandoned petroleum well. The working fluid of choice is proposed to be circulated down through the annulus, then up through an inner, insulated geostring. By making use of a numerical simulator, we asses parameters of interest and obtain knowledge on how they affect the outlet temperature of the circulating working fluids and the accumulated heat extracted from the geothermal wells.

Open tensile fractures at depth in anticlines: A case study in the Tarim basin, NW China

AbstractUnderstanding fracture openness in the Earth's crust is crucial for understanding fracture properties and their impact on fluid flow and potentially also in reservoir modelling. Here, we present cases showing the presence of open tensile fractures at depth in anticlines by integrating borehole imaging logs, core observations, casting sections, physical modelling, in‐situ stress analysis and production data in petroleum wells, and analysing the time of fracturing by fluid inclusion analysis. The data come from the Cretaceous Bashejiqike Formation in the Kuqa Depression, Tarim basin; its current depth varies between 6,000 and 8,100 m. The results show that tensile fractures are the main fracture type in the studied formation and that their hydraulic conductivity is poorly affected by the current maximum horizontal stress direction. Furthermore, we find that fracture development is uninterrupted during continued anticline folding, although there is a dominant time of fracturing.

Evaluating The Effect of Temperature and Polymer Concentration on Properties of Hydroxyethyl Cellulose Gravel Pack Fluid

The commercial success of petroleum wells depends greatly on the type of completion, especially the choice of gravel packing fluid system for wells with gravel pack completions. Currently several polymers are in use to viscosify gravel pack fluids. These polymers are expected to exhibit acceptable properties such as good solubility, viscosity yield, rheology, sand carrying capacity, thermal stability, break profile, low residue content and others, to match the job requirements, in order not to jeopardize the sand control process or cause hydrocarbon production impairment. Hydroxyethyl cellulose (HEC), one of the most commonly used polymers used in formulating gravel pack fluids has so many good qualities, such as very low solid residues and easy clean out. In this paper, gel break time was investigated for 40lbs/1000gal and 60lbs/1000gal HEC polymer concentrations at 140°F, 160°F and 180°F, using Sodium Persulfate as gel breaker at concentrations of 1.0lbs/1000gal, 5.0lbs/1000gal, 10.0lbs/1000gal and 20.0lbs/1000gal. The proppant carrying capacity at different temperatures was also investigated. Test results indicated that gel break is a function of temperature, breaker and polymer concentrations. At higher temperatures and higher breaker concentrations, gel break is faster, but slower for higher polymer concentration.

Potential for gas hydrate formation at the northwest New Zealand shelf margin - New insights from seismic reflection data and petroleum systems modelling

In this study we provide evidence for methane hydrates in the Taranaki Basin, occurring a considerable distance from New Zealand's convergent margins, where they are well documented. We describe and reconstruct a unique example of gas migration and leakage at the edge of the continental shelf, linking shallow gas hydrate occurrence to a deeper petroleum system. The Taranaki Basin is a well investigated petroleum province with numerous fields producing oil and gas. Industry standard seismic reflection data show amplitude anomalies that are here interpreted as discontinuous BSRs, locally mimicking the channelized sea-floor and pinching out up-slope. Strong reverse polarity anomalies indicate the presence of gas pockets and gas-charged sediments. PetroMod™ petroleum systems modelling predicts that the gas is sourced from elevated microbial gas generation in the thick slope sediment succession with additional migration of thermogenic gas from buried Cretaceous petroleum source rocks. Cretaceous–Paleogene extensional faults underneath the present-day slope are interpreted to provide pathways for focussed gas migration and leakage, which may explain two dry petroleum wells drilled at the Taranaki shelf margin. PetroMod™ modelling predicts concentrated gas hydrate formation on the Taranaki continental slope consistent with the anomalies observed in the seismic data. We propose that a semi-continuous hydrate layer is present in the down-dip wall of incised canyons. Canyon incision is interpreted to cause the base of gas hydrate stability to bulge downward and thereby trap gas migrating up-slope in permeable beds due to the permeability decrease caused by hydrate formation in the pore space. Elsewhere, hydrate occurrence is likely patchy and may be controlled by focussed leakage of thermogenic gas. The proposed presence of hydrates in slope sediments in Taranaki Basin likely affects the stability of the Taranaki shelf margin. While hydrate presence can be a drilling hazard for oil and gas exploration, the proposed presence of gas hydrates opens up a new frontier for exploration of hydrates as an energy source.

Characterising the present-day stress regime of the Georgina Basin

ABSTRACTThe onshore Georgina Basin in northern Australia is prospective for unconventional hydrocarbons; however, like many frontier basins, it is underexplored. A well-connected hydraulic fracture network has been shown to be essential for the extraction of resources from the tight reservoirs that categorise unconventional plays, as they allow for economic flows of fluid from the reservoir to the well. One of the fundamental scientific questions regarding hydraulic stimulation within the sub-surface of sedimentary basins is the degree to which local and regional tectonic stresses act as a primary control on fracture propagation. As such, an understanding of present-day stresses has become increasingly important to modern petroleum exploration and production, particularly when considering unconventional hydrocarbon reservoirs. This study characterises the regional stress regime in the Georgina Basin using existing well data. Wellbore geophysical logs, including electrical resistivity image logs, and well tests from 31 petroleum and stratigraphic wells have been used to derive stress magnitudes and constrain horizontal stress orientations. Borehole failure features interpreted from wellbore image and caliper logs yield a maximum horizontal stress orientation of 044°N. Integration of density log data results in a vertical stress gradient of 24.6 MPa km–1. Leak-off and mini-fracture tests suggest that this is the minimum principal stress, as leak-off values are generally shown to be at or above the magnitude of vertical stress. The maximum horizontal stress gradient is calculated to be in the range of 31.3–53.9 MPa km–1. As such, a compressional stress regime favouring reverse/reverse–strike-slip faulting is interpreted for the Georgina Basin.

Sobral y la geología del Ã?irihuau

Sobral fue el Jefe de la comisión que exploró y desarrolló dos pozos petroleros en el Ã?irihuau desde fin de 1932 a mediados de 1934. Durante ese lapso reconoció la estructura de la comarca del cerro La Buitrera, realizando también observaciones menores entre Ingeniero Jacobacci y Pilcaniyeu, la zona del río Foyel y los alrededores de Bariloche, además de colaborar en la descripción de las perforaciones Ã?irihuau 1 y 2. El detalle de sus interpretaciones sobre la geología de la zona permaneció inédito en sus libretas de campo. Se comentan las notas y dibujos insertos en ellas y reproducen parcialmente, poniendo de relieve su valor histórico y geológico.