Deep Exploration Wells Research Articles

Research of the problem of optimization and development of a calculation method for two-stage chain drives used in heavy industrial vehicles in conditions of economic efficiency

The article is dedicated to the problem of optimization of chain drives of the drilling unit. At present, increasing the power per machine to the optimal limits, reducing the material and energy consumption per unit capacity of the machine, as well as operating costs are considered topical issues. The machines that are designed and constructed to optimal limits must be very powerful and productive. The machines that are applied to perform drilling works in the oil and gas industry must be easy to operate, reliable and have ability to operate for a long time. When constructing such machines, their being lightweight, economical, as well as their preparation in a short time and at low cost should be taken into account in advance. In order to ensure the reliable operation of drilling rigs, it is more expedient to apply chain drive in their mechanical transmission. First of all, the application of chain drive in drilling units and hoisting mechanisms is considered. Then a calculation method was developed for the chain drives of the drilling unit used in deep exploration wells and the exploitation of wells, and, accordingly, the calculation of the chain drive was carried out. The chain drive consists of drive and driven sprockets and a chain that encompasses the sprockets and engages in their teeth. Chain drives with several driven sprockets are also used. In addition to the basic listed elements, chain drives include tensioners, lubricating device and guards. The chain consists of hinged links that provide mobility or “flexibility” of the chain. Chain drives can be performed in a wide range of parameters. The calculation took into account the quality of the material, the service life and durability of the chain drive construction

Yukon Flats Basin Tectono-Sedimentary Element, East-Central Alaska

Abstract Yukon Flats is a vast and remote lowland that straddles the Arctic Circle, and is located along the Yukon River in east-central Alaska. Seismic reflection and gravity data indicate that low-density sedimentary strata beneath Yukon Flats are as thick as 8 km and are underlain by Jurassic–Devonian oceanic rocks of the Angayucham–Tozitna terrane. On the basis of shallow core-hole penetrations and by analogy with nearby outcrops, the low-density strata are thought to consist of fluvial and lacustrine deposits of Neogene, Paleogene and, possibly, Late Cretaceous age. No deep petroleum exploration wells have been drilled in Yukon Flats, but a coalbed methane test reached a total depth of nearly 700 m and found small amounts of microbial methane. Geochemical data from outcrops and shallow core holes suggest that potential source rocks include non-marine coal, mudstone and shale, whereas potential reservoirs include non-marine sandstone and conglomerate. Numerous potential structural and stratigraphic traps are evident on seismic profiles. The United States Geological Survey estimates that undiscovered, technically recoverable, oil resources in the Yukon Flats Basin Tectono-Sedimentary Element range from 0 to almost 600 MMbo, and that undiscovered, technically recoverable, gas resources range from 0 to almost 15 Tcf.

Facies interpretation from well logs applied to Calub-Hilala field within Ogaden Basin, Ethiopia

The lithofacies and environments of deposition interpretations of the Calub-Hilala field towards central trough of Ogaden Basin have been carried out. Geophysical well logs from three deep exploration wells; Calub-1, Bodle-1 and Hilala-2 were used. A methodology was piloted in establishing the sedimentary facies, their successions and environments of deposition. Gamma ray, neutron, sonic and resistivity logs were used for lithologic and depositional environment identification respectively. An attempt were also made to identify formation tops and well to well lithostratigraphic correlation basing gamma ray log trends and correlating with cored interval of the wells for Lithological comparisons. Lithofacies interpretation was carried out with Schlumberger’s Petrel 2009TMsoftware. Correlation techniques were conducted to delineate the subsurface trends of these facies with electrafacies to compare facies interpretation results that were implied using the wire line log signatures.Ten (10) formations; Calub, Bokh, Gumburo, Adigrat, Transition, Hamanlei (Lower, Middle and Upper), Urandab, Gebredare, Gorrahei, Mustahil and Five (5) log facies; a cylindrical-shaped log trends representing aeolian, braded fluvial; a funnel-shaped facies representing a crevasse splay; a carbonate shallowing upward sequence and shallow marine sheet sand; bell-shaped facies representing transgressive marine shelf; a symmetrical- shaped facies representing sandy offshore and an irregular shaped facies representing fluvial floodplain were recognized. The environments of deposition delineated for the study area are alluvial and transgressive – regressive marine.

Analysis of subsurface structural trend and stratigraphic architecture using 2D seismic data: a case study from Bannu Basin, Pakistan

The present study is focused on the subsurface geology of Bannu Basin, a part of western Indus foreland Pakistan. For this purpose, some regional seismic profiles and deep exploratory wells data have been used in integration.A total of ten mappabale seismic reflection events have been identifed which are representative of specific geological units. In general, based on the seismic the formation trends, the horizons are dipping in the northwest direction of the study area. The area generally deepens toward the northwest due to sediments load toward the northwest. The seismic profile MWI-83 shows a unique faults bounded anticlinal structure that has also been mapped on the two-dimmensional contour maps. This could be regarded as potential hydrocarbon entrapment. The regional seismic profiles are contoured for the entire grid in both time and depth domain to obtain the clearer image of the subsurface individual stratigraphic units. The 2D contour maps for Lower Permian aged Warcha Sandstone, Middle Triassic aged Tredian Formation and Early Jurrasic aged Datta Formation have been prepared using gridded TWT of the seismic profiles. The time and depth contour maps of the Datta Formation and Tredian Formation show a four way clouser oriented in the southeast dierction. The area of the closure was computed which is 24 Sq km approximately. Furthermore, the formation tops of the five wells have been used to correlate the wells for understanding the lateral and vertical variations in the stratigraphic layers. The correlation shows that the Datta Formation’s thickness increases at the centre of the basin whereas decreases on the east and south flanks of the basin. Reasons of Wells failure were concluded on the basis of the final well report and concluded that these well failure occur due to poor quality of the data and also due to some mechanical problems. Reservoircharacterization using statistical rock physics and petrophysics coupled with core data analysis can provide further insights into the hydrocarbon exploration.

Planktonic foraminiferal biostratigraphy and lithology of the Upper Cretaceous (upper Campanian-Maastrichtian) and Palaeogene succession of the Palmyrides (Syria)

An upper Campanian to upper Oligocene stratigraphic succession has been examined from six deep exploration wells in the Palmyrides area of Syria. Most of the sedimentary succession contains rich and well to moderately preserved planktonic foraminiferal assemblages that enable successful age determination. The upper Campanian and Maastrichtian planktonic fauna is highly diverse with domination of warm water taxa such as Globotruncana aegyptiaca, Gansserina gansseri, Globotruncanella havanensis, Globotruncanita angulata and Pseudotextularia elegans. The most dramatic turnover occurred across the Cretaceous/Palaeocene boundary when most planktonic foraminiferal species became extinct. The oldest Palaeocene planktonic foraminiferal assemblage, rich in the number of specimens, but not very diverse, includes the following species: Eoglobigerina eobulloides, Globanomalina archeocompressa, Chiloguembelina morsei, Woodringina claytonensis and Parasubbotina pseudobulloides. The late Palaeocene is marked by origination of the morozovellids, acarininids and globanomalinids, while the early Eocene is characterized by a tropical assemblage, dominated by muricate species, and by intensive speciation of Acarinina and Subbotina in the latest part. Most of these species continue into the middle Eocene and become a significant component of the planktonic community. The middle Eocene is characterized by intensive speciation and domination of warm water genera such as Acarinina, Morozovelloides, and to a lesser degree Turborotalia, Globigerinatheka and Hantkenina. The middle/late Eocene boundary is marked by double extinction of the last muricate taxa Acarinina mcgowrani and Morozovelloides crasssatus, which indicate a variable climate, water column instability, and loss of surface habitats. In contrast, Turborotalia and Globigerinateheka become more important in the late Eocene. The Eocene/Oligocene boundary is marked by the extinction of most warm water taxa including Turborotalia cerroazulensis group, Hantkenina, Globigerinatheka and some subbotinids. The beginning of the early Oligocene is indicated by the domination of cool water taxa such as Dentoglobigerina, Globorotaloides, Tenuitella and Chiloguembelina. Speciation of the spinose surface dweller Ciperoella ciperoensis group reflects warming in the late Oligocene. The combined observations of lithology with the diversity and composition of planktonic foraminifera assemblages indicate that the Palmyrides area in Syria was a Tethyan bioprovince with a tropical to subtropical climate from the late Campanian to the end of the Eocene with deposition in deep sea environments (upper bathyal to outer shelf). In contrast, Oligocene deposits and their microfossil content suggest temperate to warm climate conditions and sedimentation in middle to inner shelf environments.

Distribution of organic matter and evaluation of brittleness index of the Lower Silurian shales of west Lithuania based on interpretation of well logs

There is little known of the basic parameters of the Lower Silurian graptolitic black shales that are considered the most prospective unconventional gas reservoir in west Lithuania, situated in the deep central part of the Baltic sedimentary basin. Hundreds of deep oil exploration wells have been drilled in the area of interest, owing to extensive exploration of oil fields. The lower and middle Llandovery interval was mainly drilled with coring, while most of the section was covered by only logging. Therefore, the knowledge of major parameters of the Lower Silurian shales is rather obscure and is based on scarce rock sample data. The gamma-ray, electrical resistivity and sonic logs were utilised, together with mineralogical studies of rock samples to document vertical and lateral distribution of organic matter. Also, the brittleness index was defined to characterise the whole Lower Silurian section. Some unexpected trends were identified that may redirect exploration strategy in west Lithuania. The combined application of mineralogical studies and well logs indicate a much higher exploitation quality of the Lower Silurian shales than previously believed. A higher organic matter content and brittleness were derived from logging data in the Lower Silurian shales.

Numerical and thermodynamic modeling for estimating production capacity of NW Sabalan geothermal field, Iran

In this paper, a new estimate of the power production capacity of the NW Sabalan reservoir is presented based on an evaluation of the recent field data. An improved three-dimensional numerical model (EOS1) was created utilizing the Tough2 simulator code. A rectangular prism with a length of 11.5 km and a width of 8 km (92.9 km) and a depth of 5.11 km is assumed for modeling. Also, 17 horizontal layers were considered for the model, with a layer thickness ranging from 100 to 1000 m, extending from the elevation of -1000 to 4110 masl. The model was validated using temperature and pressure profiles at ten deep exploration wells. The best-fit model of the natural state demonstrated the existence of an upflow of high-temperature fluid in the southern part of the area (with a recharge rate of 108 kg/s). For evaluating and predicting the power production, a thermodynamic model of the single-flash geothermal power plant was developed for the NW Sabalan field. The optimum separation pressure of approximately 5.1 bar was obtained, assuming the quality of the turbine outlet steam is equal to 0.86. At this pressure, the system yields about 31 MW of electricity as a best estimate. Then simulations of four scenarios of 25, 50, 100, and 150 MWe were carried out for 30 years using the TOUGH2 code. The results of the scenarios showed that the main factors controlling the production capacity in the NW Sabalan field are the expected pressure drop and the enthalpy of the produced fluid. This field cannot provide the required enthalpy of the produced fluid for more than 150 MWe. The field can provide enough high enthalpy fluid for a maximum capacity of 114 MWe for 70 years. For this capacity, a limit of 3.125 km2 was identified on the area of the main production zone.

An unsaturated three-dimensional model of fluid flow and heat transfer in NW Sabalan geothermal reservoir

This paper presents a 3D numerical model for the north-west (NW) Sabalan geothermal system, including the unsaturated vadose zone overlying the system, based on a conceptual model derived from data gathered from 10 deep exploration wells. To achieve the goal, the EOS3 (water-air state equation) module of the Tough2 simulator was utilized to develop the model. The model was constructed from a rectangular prism, which is 11.5 km long, 8 km wide, and variable depths ranging from 3.8–5.11 km. The 21 horizontal layers with a thickness range of 100−1000 m were expanded from the maximum height of 4110 to -1000 masl. A total of 22 rock types were distributed within the model based on the availability of rock units and geological structures derived from the exploration wells. The permeability of these rock types varied from 1.0 × 10−17 to 9.0 × 10-13 m2. The model was initially run to match the natural state of the reservoir. A close agreement was obtained between the measured data from the exploration wells, and the model results for subsurface temperatures and pressures. In the calibrated model, a high temperature upflow zone was required in the southeast part of the area (below the exploration sites D and E). This flow rises to the land surface through permeable zones, faults, and fractures, and finally appears on the earth’s surface as hot springs in the northwestern part of the area. This model was then used as the initial model to predict the reservoir performance for the 50 MWe scenario. The results showed that the reservoir can generate about 45 MWe by assigning two makeup wells and remain at this level for more than 30 years.

Novel geothermal gradient map of the Croatian part of the Pannonian Basin System based on data interpretation from 154 deep exploration wells

As part of EU strategy to tackle climate changes, energy transition from fossil fuels to renewable resources is necessary. During the last few years, in the Republic of Croatia there is a strong tailwind towards promoting activities of geothermal energy exploration and exploitation. As geothermal sector was often neglected in a favour of petroleum business in the past, there is still a somewhat knowledge gap in groundwork related to defining geothermal resources potential. Since initial investigation related to defining hot spots in geothermal gradient were conducted more than 40 years ago, there was a need to remodel older imprecise maps with a completely new groundwork research in this area. More than 150 deep oil&gas exploration wells scattered in the Croatian part of the Pannonian Basin were elaborated. From the historical well development records and temperature measurements, obtained with different methods, a novel geothermal gradient map was constructed. Furthermore, to define local potential sites for direct heat utilization and electricity production, temperature maps were designed for a depth of 1000 and 2000 m, respectively.

Geomechanical Analysis for Deep Shale Gas Exploration Wells in the NDNR Blocks, Sichuan Basin, Southwest China

The abundant reserve of shale gas in Sichuan Basin has become a significant natural gas component in China. To achieve efficient development of shale gas, it is necessary to analyze the stress state, pore pressure, and reservoir mechanical properties such that an accurate geomechanical model can be established. In this paper, Six wells of Neijiang-Dazu and North Rongchang (NDNR) Block were thoroughly investigated to establish the geomechanical model for the study area. The well log analysis was performed to derive the in-situ stresses and pore pressure while the stress polygon was applied to constrain the value of the maximum horizontal principal stress. Image and caliper data, mini-frac test and laboratory rock mechanics test results were used to calibrate the geomechanical model. The model was further validated by comparing the model prediction against the actual wellbore failure observed in the field. It was found that it is associated with the strike-slip (SS) stress regime; the orientation of SHmax was inferred to be 106–130° N. The pore pressure appears to be approximately hydrostatic from the surface to 1000 m true vertical depth (TVD), but then becomes over-pressured from the Xujiahe formation. The geomechanical model can provide guidance for the subsequent drilling and completion in this area and be used to effectively avoid complex drilling events such as collapse, kick, and lost circulation (mud losses) along the entire well. Also, the in-situ stress and pore pressure database can be used to analyze wellbore stability issues as well as help design hydraulic fracturing operations.

Quantifying vertical movements in fold and thrust belts: subsidence, uplift and erosion in Kurdistan, northern Iraq

Abstract Traditional structural analysis in fold and thrust belts has focused on quantifying horizontal movements. In this paper, the importance of quantifying vertical movements is illustrated using a case study from Kurdistan, northern Iraq. The subsidence history of this area can be determined by analysis of the stratigraphic record from deep exploration wells. A phase of thermal subsidence from Middle Permian to Late Cretaceous (tectonic subsidence 1.8–1.9 km) was followed by flexural subsidence in the Late Cretaceous and Cenozoic (tectonic subsidence >0.6 km) in response to the closure of the Neo-Tethys Ocean. The main phase of continental collision during the Neogene resulted in the development of the Zagros fold and thrust belt; the amount of uplift at individual anticlines can be estimated from their amplitude (up to 3 km), but regional cross-sections indicate that approximately 1 km of additional basement-involved uplift is present NE of the Mountain Front. The timing of basement-involved uplift is interpreted to be coeval with the deposition of a Pliocene–Quaternary growth sequence adjacent to the Mountain Front. The amount of erosion resulting from the uplift can be estimated from vitrinite reflectance and cross-sections; these estimates show a similar pattern, with maximum erosion in the mountains NE of the Mountain Front (>1.5 km) and lesser erosion in the adjacent foreland basin (generally <0.8 km). The results provide a quantitative understanding of subsidence, uplift and erosion, and have been used to define prospective and high-risk areas for petroleum exploration.

The Geothermal Regime in Sirt Basin, Libya: The Geological Role and Heat Flow Studies

Bottom hole temperatures (BHTs) and static formation temperatures (DSTs) of 70 deep exploratory wells are used to evaluate the geothermal regime in the northeastern part of Sirt Basin. A linear regression was derived between the BHT’s and the DST’s, for correcting the bottom hole temperatures from the drilling factors that lower them from the true formation temperatures. The geothermal gradients were calculated using the corrected BHT’s and the heat flow has been estimated. Interpretation of the geothermal data, utilizing subsurface maps and isothermal geologic cross section, revealed a shallow, local semi-thermal reservoir of Oligo-Miocene age (at depths 1000 m). The geothermal gradients and heat flow values of this reservoir are ranging from 40 - >60°C/Km and from 80 up to >130 mW/m2, respectively. At deeper depths (>1000 m until the maximum depth of investigation), the area has more or less moderate to low geothermal gradients that range from 40 to 2. The study indicates that the vertical and the lateral variations of the formation temperatures, geothermal gradients and the heat flow values are controlled by the structural, groundwater movements as well as lithological and thermal characteristics of the subsurface sequence.

PETROLEUM GEOLOGY OF THE NOGAL BASIN AND SURROUNDING AREA, NORTHERN SOMALIA: PART 1, STRATIGRAPHY AND TECTONIC EVOLUTION

In this study, 92 closely‐spaced reflection seismic profiles (∼4000 line‐km) were tied to biostratigraphic and lithological data from six deep exploration wells in the poorly‐known Nogal rift basin, northern Somalia, and were integrated with outcrop and aeromagnetic data to investigate the basin stratigraphy and tectonic evolution. Aeromagnetic data show NW‐SE trending magnetic anomalies which are interpreted as plutonic bodies intruded during the Early Cretaceous, probably contemporaneously with a pre‐Cenomanian uplift phase. The aeromagnetic data also suggest a change of basement type from Inda Ad Series metasediments in the SE of the study area to igneous and high‐grade metamorphic basement in the NW. Biostratigraphic data and seismic reflection profiles define the Nogal Basin as a WNW–ESE striking half‐graben, approximately 250 km long and 40 km wide, which formed as a result of mainly Cenomanian–Maastrichtian and Oligocene–Miocene intracontinental rifting. The depocentre contains at least 7000 m of Mesozoic and Cenozoic sediments and is located in the centre of the basin (east of well Nogal‐1), to the south of the Shileh Madu Range. To the north, the basin is bounded by a major border fault along which significant variations in the thickness of sedimentary units are observed, suggesting that the fault controlled basin architecture and patterns of sedimentation. Oligocene–Miocene normal faults which resulted in north‐tilted fault blocks are widespread within the main basin; smaller‐scale sub‐basins oriented NW‐SE to WNW‐ESE are observed to the NW of the basin and probably developed contemporaneously.The Late Jurassic rift phase which has been documented elsewhere in northern Somalia is either missing in the Nogal Basin or is preserved only in localised grabens in the western and central parts of the basin. This is probably due to the pre‐Cenomanian uplift and erosion which removed almost the entire Jurassic and Lower Cretaceous successions over a wide area referred to as the Nogal‐Erigavo Arch. A more pronounced rifting episode followed this erosional event in the Cenomanian–Maastrichtian and resulted in the deposition of well‐sorted fluvio‐deltaic sandstones (Gumburo and Jesomma Formations), more than 2000 m thick. In wells in the Nogal Basin, these formations are between two and three times thicker than in wells drilled in footwall locations, and include excellent reservoir rocks sealed by transgressive mudstones and carbonates. A final rifting event in the Oligocene–Miocene was related to the opening of the Gulf of Aden. A rift sag phase which accommodated the Early Oligocene continental sediments of the Nogal Group initially developed at the centre of the basin. This was followed by a period of strong rotational faulting and tilting, which reactivated the Cenomanian–Maastrichtian structures.

A three-dimensional numerical model to simulate Iranian NW Sabalan geothermal system

The plan for electricity generation from north-west (NW) Sabalan geothermal field, Iran has been presented since 1994. Now construction of the first pilot plant is running with a capacity of 5 MWe in this site. A three-dimensional (3D) numerical model of fluid flow and heat transfer of the geothermal reservoir was developed using Tough2 simulator code on the basis of the updated conceptual model from the field recent data. The aim of this study was to present an updated 3D model of the geothermal reservoir in this area by taking ten deep wells data into account and validate an existing model in which the data obtained from only three wells were included. The model covers an area of 92 km2 and extends to an approximate depth of 5.11 km from the land surface. The model includes 17 horizontal layers, (AA through QQ). The thickness of the layers range between 100 m and 1000 m. The model extends from a minimum level of -1000 to a maximum level of 4110 masl. The model has 12,784 grid blocks, in total. Each layer has 752 grid blocks with horizontal dimensions of 250 m × 250 m and 500 m × 500 m. Altogether, 21 rock types were used in the model to assign different horizontal permeability values from 1.0 × 10−17 to 9.0 × 10-13 m2 based on the conceptual model. The model was first calibrated by varying the permeability, the total magnitude and location of the recharges and well bottom pressure of discharge zones. It was further validated by the profiles of temperature and pressure distribution at 10 deep exploration wells data. A close agreement was obtained between the model predictions and the measured downhole temperature and pressure data in the exploration wells. In the best-fitted model, the natural state simulation proved the presence of a high temperature upflow zone in the southern part (Below the ground, between Pads D and E). High temperature fluid at a rate of 108 kg/s and with an enthalpy of 1056.43 kJ/kg (244 °C) recharged over an area of 2.25 km2 from 36 grid blocks from the bottom layer in southern part of the field. The overall natural discharge is about 43 kg/s from hot springs which was simulated using the pressure dependent deliverability method. The results show that there is mostly one inflow of geothermal water at the level of -1000 m at southeast below the land surface between the Pad D and Pad E. The fluid flow moves upward by the fracture zones and faults toward the northwest of area. The faults NW5, NW3 and NNW2 play a major role in this system. Finally, the geothermal fluid discharging by the surface manifestations can be seen as hot springs at the land surface. This model can be used to simulate future production scenarios to evaluate the sustainability of the reservoir.

Deep Resistivity Structure of Basalt‐Covered Central Part of Paraná Basin, Brazil, From Joint 3‐D MT and GDS Data Imaging

AbstractThe deep structure beneath the basalt‐covered sediments of Paraná basin is not well understood. Magnetotelluric (MT) broadband (1,000 to 0.001 Hz) data recorded at 296 selected stations along three new survey lines were first inverted in three dimensions to reveal the local scale resistivity structure of the central part of the basin where there are three deep exploration wells with resistivity logs for model validation. The 3‐D MT inversion model correctly identified the resistive (>100 Ωm) flood basalts and postvolcanic cover layer, the underlying electrically conductive (~10 Ωm) sediments, and the highly resistive (>1,000 Ωm) crystalline basement at the well locations and provides a reliable average crustal resistivity structure consisting of ~20–24 km thick highly resistive upper crust and ~20 km thick conductive lower crust above a resistive mantle. Subsequent basin‐scale joint inversion of highest quality MT data sets (261 stations) and geomagnetic depth sounding array data imaged two prominent subparallel belts of N‐S and NNE‐SSW trending steep conductors in the deep crust and upper mantle, one located directly beneath the present‐day axis of thickest sedimentary deposits in the basin and another near the coastal location where dolerite dyke swarms intrude the outcropping Precambrian basement. Other roughly orthogonal bands (E‐W to NW‐SE) of linear crustal conductors radiate from these two main belts. The resulting networks of steep conductors at upper to midcrustal level seem to mark the fossil plumbing system of Paraná magmatic province and are interpreted as preexisting shear zones exploited by the voluminous Early Cretaceous magmatism in the region.

Characterizing Seismo-stratigraphic and Structural Framework of Late Cretaceous-Recent succession of offshore Indus Pakistan

Abstract Regional seismic reflection profiles and deep exploratory wells have been used to characterize the subsurface structural trends and seismo-stratigraphic architecture of the sedimentary successions in offshore Indus Pakistan. To improve the data quality, we have reprocessed the seismic data by applying signal processing scheme to enhance the reflection continuity for obtaining better results. Synthetic seismograms have been used to identify and tie the seismic reflections to the well data. The seismic data revealed tectonically controlled, distinct episodes of normal faulting representing rifting during Mesozoic and transpression at Late Eocene time. A SW-NE oriented anticlinal type push up structure is observed resulted from the basement reactivation and recent transpression along Indian Plate margin. The structural growth of this particular pushup geometry was computed. Six mappable seismic sequences have been identified on seismic records. In general, geological formations are at shallow depths towards northwest due to basement blocks uplift. A paleoshelf is also identified on seismic records overlain by Cretaceous sediments, which is indicative of Indian-African Plates rifting at Jurassic time. The seismic interpretation reveals that the structural styles and stratigraphy of the region were significantly affected by the northward drift of the Indian Plate, post-rifting, and sedimentation along its western margin during Middle Cenozoic. A considerable structural growth along the push up geometry indicates present day transpression in the margin sediments. The present comprehensive interpretation can help in understanding the complex structures in passive continental margins worldwide that display similar characteristics but are considered to be dominated by rifting and drifting tectonics.

Seismic stratigraphy of the Mianwali and Bannu depressions, north-western Indus foreland basin

Regional seismic reflection profiles, deep exploratory wells, and outcrop data have been used to study the structure and stratigraphic architecture of the Mianwali and Bannu depressions, north-western Indus foreland basin. Synthetic seismograms have been used to identify and tie the seismic horizons to the well data. Nine mappable seismic sequences are identified within the passive and active margin sediments. In general, the Mianwali and Bannu depressions deepens towards north due to the flexure generated by the loading and southward shifting of the thrust sheets of the North-western Himalayan Fold and Thrust Belt. The seismic profiles show a classic wedge shaped foreland basin with a prominent angular unconformity which clearly differentiates the active and passive margin sediments. The onlap patterns in the Late Cretaceous sediments suggest the initial onset of foreland basin formation when the Indian Plate collided with Eurasian Plate. As the collision progressed, the lithospheric flexure caused an uplift along the flexural bulge which resulted in onlaps within the Paleocene and Eocene sequences. The tectonic activity reached to its maximum during Oligocene with the formation of a prominent unconformity, which caused extensive erosion that increases towards the flexural bulge.

Development of an updated geothermal reservoir conceptual model for NW Sabalan geothermal field, Iran

In this paper, a conceptual model has been developed for NW Sabalan geothermal field using exploration indicators. These indicators include the data and results of subsurface and surface investigations comprising geology, geophysics , hydro-geochemistry, hydrology and temperature and pressure distribution. The subsurface information was obtained from 10 deep exploration wells as well as from the results of previous studies in this field. All available data together with the stratigraphy and 1:20,000 geological map covering the study area were combined to produce a two-dimensional geological cross section. Also, a subsurface three-dimensional geological model was developed using available drilling logs. NW Sabalan geothermal field is one of the 18 detected potential areas in Iran that is located in Northwest of the country. This field includes a deep geothermal reservoir with a temperature range of 230–242 °C. The reservoir is covered by a cap rock with an approximate thickness of 500 m. There are four major geological units identified in the study area including Quaternary alluvium, fan and terrace deposits; Pleistocene post-caldera trachyandesitic Flows; Pleistocene syn-caldera trachydacitic to trachyandesitic domes and Pliocene pre-caldera trachyandesitic lavas, tuffs and pyroclastic. A hydraulic conductivity zone has been assessed by magnetotelluric surveys at deeper zones, suggesting that the main outflow direction is towards west and north of the area. The fluid chemistry is consistent with high chloride, neutral pH and immature liquids that partially equilibrated with host rock and they are classified as mixed water. The results of exploration and geological studies during a 10-year period have been integrated together to build a new overall conceptual model of the field.

Nonlinear inversion of isostatic residual gravity data from Montage Basin, northern Gulf of California

The flexural isostatic response to surface loads is used to estimate the crustal thickness in northwestern Mexico and Southwestern USA. This estimate is used to compute an isostatic regional gravity, which, subtracted from Bouguer gravity anomalies, led to the isostatic residual gravity anomaly at Montage Basin. This basin is located between the southern portion of the Mexicali Valley and the northern Gulf of California, it roughly has an extension of [Formula: see text] wide, and it shows a gravity minimum reaching approximately [Formula: see text]. Montage Basin is within the extensional province of the Gulf of California, where rifting is currently an ongoing geologic process, and deep exploratory wells drilled by Petróleos Mexicanos have shown that the basin accommodates thick sedimentary sequences greater than 5 km. The interpretation of the isostatic residual gravity anomaly is considered as a nonlinear inverse problem, constrained using density as a function of depth derived from Gardner’s equation applied to dual time [Formula: see text]-logs, assuming isostatic equilibrium and considering the basin as a subsurface load that is compensated at depth by a mass of unknown shape and density. The outcome of the inverse problem suggests that Montage Basin accommodates as much as 7.5 km thick sedimentary sequences and a compensating mass at a minimum depth of 13 km.

Evaluating the Baluti Formation at Sararu village, Ora Anticline, Iraqi Kurdistan: a stratigraphic and geochemical approach

Here, we report that a lithostratigraphic unit that outcrops at Sararu village, 6 km northeast of Qumri village that had previously been assigned to the Baluti Formation is not Triassic in age and therefore can not be a correlative equivalent of the Baluti Formation. The outcropping unit at Sararu comprises intercalation of calcareous mudstones and limestones, and is indeed lithologically similar to the Baluti Formation (Late Triassic). The Baluti Formation (also known as the Baluti Shale) is known from a typical section found at the Gara Anticline and from many deep drilled oil exploration wells. It is generally composed of alternations of the shales, limestones, dolomites, and dolomitic limestones. It is underlain by the Kurra Chine Formation (Upper Triassic) and overlain by the Sarki Formation (Lower Jurassic). In this study, detailed field observations, an assessment of stratigraphic successions, studies of microfossils such as age-specific planktonic foraminifera (e.g., Globotruncana bulloides), and age-specific biomarkers (oleanane index and C28/C29 regular sterane index) reveal that the lithostratigraphic unit at Sararu village can not be a correlative equivalent of the Baluti Formation, and it is more likely from the Upper Cretaceous. There are a number of Upper Cretaceous formations found in this part of Kurdistan, but based on fossil-type and palaeoenvironmental associations, the Hadiena Formation, from the Upper Cretaceous, is considered as the most likely correlative equivalent to the calcareous mudstone and limestone succession found at Sararu village.