Distal Bar Research Articles

Characteristics and origin of the relatively high-quality tight reservoir in the Silurian Xiaoheba Formation in the southeastern Sichuan Basin.

A mature understanding of the sandstone gas reservoir in the Xiaoheba Formation in the southeastern Sichuan Basin remains lacking. To assess the reservoir characteristics and the origin of the high-quality reservoir in the Xiaoheba Formation, this paper uses systematic field investigations, physical property analysis, thin section identification, scanning electron microscopy and electron microprobe methods. The results indicate that the Xiaoheba sandstone is an ultra-tight and ultra-low permeability reservoir, with an average porosity of 2.97% and an average permeability of 0.56×10−3 μm2. This promising reservoir is mainly distributed in the Lengshuixi and Shuangliuba regions and the latter has a relatively high-quality reservoir with an average porosity of 5.28% and average permeability of 0.53×10−3 μm2. The reservoir space comprises secondary intergranular dissolved pores, moldic pores and fractures. Microfacies, feldspar dissolution and fracture connectivity control the quality of this reservoir. The relatively weak compaction and cementation in the interbedded delta front distal bar and interdistributary bay microfacies indirectly protected the primary intergranular pores and enhanced late-stage dissolution. Late-stage potassium feldspar dissolution was controlled by the early-stage organic acid dissolution intensity and the distance from the hydrocarbon generation center. Early-stage fractures acted as pathways for organic acid migration and were therefore important factors in the formation of the reservoir. Based on these observations, the area to the west of the Shuangliuba and Lengshuixi regions has potential for gas exploration.

Sedimentary characterization of a braided delta using well logs: The Upper Triassic Xujiahe Formation in Central Sichuan Basin, China

The image logs played a key role in interpreting the lithology and sedimentary structures of uncored units. An integrated analysis of the borehole images and open-hole logs, which are calibrated with core observations, is conducted to reveal the detailed sedimentary characteristics of the Upper Triassic Xujiahe Formation in the Central Sichuan Basin. To establish borehole image interpretation guidelines, the interpretations of sedimentary textures and lithology from cores and outcrops are calibrated with borehole images and conventional logs. Lithologies in the Xujiahe Formation include conglomerates, fine to medium-grained sandstones, siltstones, mudstones and coals. Sedimentary structures in terms of bedding, scour surface and stacking style of beds are interpreted from the image and open-hole logs. Depositional microfacies are defined on the basis of grain size and sediment texture, sedimentary structures, thickness, basal and upper contacts derived from core observations, openhole logs and image logs. The Xujiahe Formation sandstones in Central Sichuan Basin are deposited in a braided delta front, of which the depositional microfacies consist of underwater distributary channel, river mouth bar, distal bar or sand sheet and underwater interdistributary bay. The depositional microfacies is predicted in a single well using a combination of openhole conventional logs, borehole images, and cores. The distributary channels, which show box-shaped or bell-shaped GR log character, are generally infilled with fine to medium-grained sandstone with massive, tabular, wedge-shaped or trough-cross-laminated bedding. Repeated fining-upwards cycles, as well as the stacked nature of individual bedsets and the presence of scour surfaces represent multistory, amalgamated, channel-fill deposits. The underwater distributary channel deposits can also be overlain by interdistributary bay mudstones, known as channel abandonment. Mouth-bar deposits, which are characterized by coarsening- up successions, infill the channels as they migrate laterally, and sometimes could be overlain by a channel deposit. The methodology has potential application to other braided delta front reservoirs with appropriate calibration and scaling.

The Impact of Distal Cantilever Extension on the Stress Around Four Implants Connected by a Bar Retained Palateless Overdenture (In Vitro Stress Analysis)

Aim: This in vitro research was aimed to compare the impact of distal cantilever extension on the stress around four implants retained palateless overdenture by means of a bar. Materials and methods: Four implants were placed bilaterally in lateral incisor and the first premolar positions of edentulous acrylic resin maxillary model; connected bar with 7 mm distal cantilever extension with soft liner female retentive element was used. Eight strain gauges were bonded to the acrylic resin at the mesial and distal surfaces of each implant, stress was measured, then the 7 mm cantilever extension was trimmed and the stress measured for the bar without distal cantilever extension. Results: Bar with distal cantilever extension demonstrate a significant increase in stress compared to the bar without distal cantilever extension in unilateral loading and bilateral loading. During unilateral loading in bar with distal cantilever extension and bar without distal cantilever extension the maximum stress was recorded at mesial side of posterior implant of loading side. Conclusion: The four implants connected with the bar without distal cantilever extension demonstrates lower stress than bar with distal cantilever extension.

Principles of trap development and characteristics of hydrocarbon accumulation in a simple slope area of a lacustrine basin margin: An example from the northern section of the western slope of the Songliao Basin, China

The western slope of the Songliao Basin is a gently dipping monoclinal slope featured by stratum overlap, gradual change of stratum inclination and limited fault development, which formed during basin depression interrupted by a tectonic inversion stage. Structure, sedimentation and reservoir characteristics show that the development of the slope and its sand bodies’ depositional genesis determined the types, distribution and evolution of traps. Up-dip wedge-out traps in distributary channels, lenticular traps in distal sand bars and sand sheets in the delta front are the main lithologic trap types and usually have thin reservoir beds, small areas, and are distributed in clusters and belts. The episode of tectonic inversion led to the formation of structural traps and combination traps. The combination traps are characterized by large numbers of thin oil-bearing beds occurring along fold belts. Matching axial directions of distributary channel sand bodies in delta fronts with channel morphology during the period between deposition of sand bodies and sealing by an unconformity above is the key to the search for large scale traps in a simple slope area.

Sedimentary characteristics of 1st member of Yaojia Formation in Zhaoyuan-Taipingchuan region of Songliao Basin

Through integral studies on cores, seismics, well-logs and laboratory sediment analysis a new sequence stratigraphic framework of the Late Cretaceous first member of the Yaojia Formation in the Songliao Basin, in China's Zhaoyuan-Taipingchuan (Zhy-Tpch) region, has been reconstructed. In this study, the first member of Yaojia Formation is divided into 3 three-order depositional sequences, each composed of three systems tracts, i.e. the lowstand systems tract (LST), the transgressive systems tract (TST) and the highstand systems tract (HST). Using a dense network of cored boreholes data and data acquired from a combination of spontaneous potential and electric resistivity logging methods, the paper studies the characteristics and distribution of sedimentary environments within the cyclic patterns (systems tracts) of the major depositional sequences, and ascertains that deposition of sediments in a predominantly shallow lake delta environment which prevailed in the region during the Late Cretaceous period was responsible for the creation of the first member of the Yaojia Formation. Results show that this formation is mainly composed of three sub-facies namely, the delta plain, delta front and prodelta (the shore shallow lake). Each sub-facies is further subdivided into eleven sedimentary environments including distributary channels, natural levees, crevasse splays, inter-distributary channels, flood plains, subaqueous distributary channels, inter-distributary bays, subaqueous crevasse splays, mouth bars, distal bars and sheet sands. The delta plains and delta fronts are widely developed. Deposited with frequent bifurcations, the distributary channels gradually moved towards the center of the lacustrine basin where prodelta sedimentation had hardly occurred. Meanwhile, subaqueous channels were frequently developed within the shallow water areas of the delta fronts. Sandstone facies in the distributary and subaqueous distributary channels mutually interacted and stacked up to form dendritic-like sands. Distributary channel sands formed the most favorable reservoirs available today and are considered to be the most important exploration targets for the oil industry. Overall, this study is crucial for improving the understanding of the geological and paleo-geographic record in the Zhy-Tpch region including the facies types, relationships and cyclicity in response to changes in depositional environments (i.e. sedimentation and base-level changes) that prevailed in the region during the Late Cretaceous period and hence important for the predictive aspects of the economic petroleum exploration and development in the Songliao Basin.

Fine-grained and coarse-grained Paleogene sublacustrine fan systems in Fushan Depression, Beibuwan Basin, South China Sea: implications for sedimentary characteristics and depositional processes

The Fushan Depression is a hydrocarbon-bearing half-graben rift sub-basin located in the southeast of the Beibuwan Basin, South China Sea. The sublacustrine fan systems in the Paleogene Liushagang Formation have recently become important targets in this depression, while the depositional process and detailed characterization of these systems are little known. Analysis of drilled cores, wire-line logs, and 3-D seismic survey suggest that the Fushan Depression develops two different types of sublacustrine fan systems. The fine-grained sublacustrine fan system located in the western area is mainly composed of fine- to medium-grained light gray sandstones interbedded with layers of silt-rich shales. This kind of sediment slumped from the distal bar of the delta front due to high sediment pore pressures at the slope edge as well as the activity of the Meitai Fault. By contrast, the coarse-grained sublacustrine fan system formed in the eastern area is characterized by medium to coarse gray sandstones and conglomerates with the development of various deformed lenticular beddings, deformed pillow structures, and micro-faults. Further study suggests that its sedimentation process is closely related to the geomorphology of flexure slope-break belt. The slope changed abruptly from 3°~5° to 7°~9° across the flexure slope point, increasing the accommodation space under the flexure belt. The coarse-grained sublacustrine fan formed when coarse-grained sediment spillover the slope-break toward the increased accommodation space. As the reservoir quality of these sublacustrine fan systems is well controlled by the sedimentary characteristics and sedimentation processes, our results should be of great significance for the development of future exploration.

Can applied external fixators be sterilized for surgery? A prospective cohort study of orthopaedic trauma patients

BackgroundTemporary external fixators are often used to stabilize fractures when definitive fracture surgery must be delayed. Sometimes, external fixators are left in place during repeat operations, including definitive internal fixation of tibial pilon and tibial plateau fractures. It is unknown how well current surgical preparation sterilizes these devices, which become part of the surgical field. Our hypothesis was that our institution’s standard surgical preparation creates a low rate of culture-positive environments on external fixators at the time of surgical skin incision. MethodsWe prospectively consented and enrolled patients to obtain cultures (48 patients, 55 external fixators, 165 sets of culture data). After standard preparation and immediately before incision, cultures were obtained from three sites on each external fixator: 1) most distal pin 1cm from pin-skin interface, 2) most distal bar at midpoint between pin and clamp connectors, and 3) most distal clamp at bar-clamp interface. Our standard preparation for patients with external fixation in place is to don sterile gloves and wipe down all components of the external fixator with 70% alcohol-soaked sterile 4×4in gauze sponges before skin preparation. The skin and external fixator are then prepped in the usual fashion with ChloraPrep for closed wounds or with povidone iodine scrub and paint for open wounds. Swabs were processed and organisms from cultures identified. Clinicians were blinded to study results until study completion. ResultsTwo of 165 cultures (1.2%; 95% confidence interval [CI]: 0–2.9%) were positive for common pathogens sometimes observed in surgical site infection. Four cultures (2.4%; 95% CI: 0–4.8%) had pathogens that are rarely associated with surgical site infection, and four (2.4%; 95% CI: 0–4.8%) had nonpathogenic organisms. ConclusionUsing 70% alcohol on external fixators plus either ChloraPrep for closed wounds or povidone iodine for open wounds seems to result in a low rate of positive cultures. Most species that were isolated are infrequently identified as sources of surgical site infections. This preparation protocol might be effective at producing a relatively clean environment at the time of surgery for patients with external fixators already in place.

Origin and classification of the composite sand bodies of the delta front in K1q4 of the Quantou Formation in the central region of the Fuyu oil field

This study discusses the formation mechanisms of the delta front reservoir of K1q4 of the Quantou Formation in the central region of the Fuyu oil field and summarizes the types of deposition based on an analysis of facies markers and a comprehensive study of the sedimentary microfacies using well cores, logs, and geologic data. The results show that K1q4 of the Quantou Formation mainly formed through shallow-water sedimentation on a delta front and includes five sedimentary microfacies: underwater distributary channels, underwater natural levees, underwater diversion bays, river mouth bars, and distal bars. Due to the effects of allocyclicity, the composite sand body evolved by vertical overlaying, whereas because of the effects of autocyclicity, the composite sand body evolved by horizontal transport. Three main types of composite sand bodies are located in the study area, including composite underwater distributary channels without levees, composite underwater distributary channels with natural levees, and composites of underwater river mouth bars with distributary channels.

Heterogeneities and Intra Sand-Body Compartmentalization in Late Oligocene Delta-Front Deposit, Niger Delta, Nigeria

This paper presents the study of the heterogeneity in lithofacies, porosity, permeability, mineral grain density, pore-throats sizes and hydraulic rock types and the intra sand-body compartmentalization in cored delta-front deposit of Greater Ughelli depobelt of Niger Delta. Sedimentological study of core samples results in the identification of nine lithofacies and the interpretation of environments of deposition as mainly proximal and distal delta-front mouth bar. The sand unit indicates moderate to excellent reservoir quality with core porosity between 16.2 and 29.5% and permeability between 16.8 and 7,560 md. Dykstra-Parsons core permeability distribution coefficient of 0.97 indicates that the studied reservoir sand-body is vertically highly heterogeneous, with high potential for vertical intra sand-body compartmentalization. Graphical cluster analysis of Flow Zone Indicators (FZI) led to the identification of nine Hydraulic Flow Units (HFU) with distribution controlled by depositional facies. The prediction of permeability, porethroats (r35) and flow zone indicator values of the reservoir in an uncored-well using predictive mathematical models developed with multiple regression analysis enabled the inter-well correlation of hydraulic flow units and indicates lateral continuity of reservoir compartments. An intra sand-body compartmentalization evaluated with core permeability values, Winland r35 coefficients and flow zone indicators was corroborated with formation pressure data analysis. Results show that the studied delta front-mouth bar reservoir is vertically compartmentalized by intercalated shales. Fractures in over-pressured zones were found to reduce vertical reservoir fluid compartmentalization by intercalated shales. However, reduction in reservoir pressure due to hydrocarbon production can result in dynamic compartmentalization and consequently, reduction in hydrocarbon recovery.

The response of deltaic systems to climatic and hydrological changes in Daihai Lake rift basin, Inner Mongolia, northern China

Delta systems are ubiquitous around lacustrine rift basins. Its peripheral geometry, progradation structures and sedimentary successions were controlled by both tectonic settings and climatic changes. Peripheral geometry of a delta was strongly influenced by depositional gradients which formed the fan-shape delta on the steep slopes and developed the lobe-shape delta on the gentle slopes. Due to the discharge feed rivers can change rapidly driven by climatic variations, and the nearshore area of deltas display considerable facies variability. The rise of annual rainfall, which suggests the rivers feeding deltas are continuous, and result in distributary mouth bars that are prevalent in the front of deltas since the down-slope flows are greater than the along-slope currents. On the contrary, when the annual rainfall decreases and evaporation increases, the rivers only can feed deltas ephemerally. If the along-slope currents were in a dominant position, the distal bars were deposited. Progradation structure and sedimentary successions of deltas were controlled by the gradients of slopes. On gentle depositional slopes, shingle foreset beds predominate with fine sediments and small-scale sedimentary structures or vice versa.

Stress on external hexagon and Morse taper implants submitted to immediate loading

Background/AimsThis study aimed to evaluate the stress distribution around external hexagon (EH) and Morse taper (MT) implants with different prosthetic systems of immediate loading (distal bar (DB), casting technique (CT), and laser welding (LW)) by using photoelastic method. MethodsThree infrastructures were manufactured on a model simulating an edentulous lower jaw. All models were composed by five implants (4.1mm×13.0mm) simulating a conventional lower protocol. The samples were divided into six groups. G1: EH implants with DB and acrylic resin; G2: EH implants with titanium infrastructure CT; G3: EH implants with titanium infrastructure attached using LW; G4: MT implants with DB and acrylic resin; G5: MT implants with titanium infrastructure CT; G6: MT implants with titanium infrastructure attached using LW. After the infrastructures construction, the photoelastic models were manufactured and a loading of 4.9N was applied in the cantilever. Five pre-determined points were analyzed by Fringes software. ResultsData showed significant differences between the connection types (p<0.0001), and there was no significant difference among the techniques used for infrastructure. ConclusionThe reduction of the stress levels was more influenced by MT connection (except for CT). Different bar types submitted to immediate loading not influenced stress concentration.

Prevention of distal extension cantilever fracture in mandibular overdentures

ObjectivesFractures of distal bar extensions, supporting a mandibular overdenture, do occur with significant functional and economic consequences for the patient. This study therefore aims to evaluate the effect of different bar cross-sectional shapes and surfaces, bar extension lengths and the placement of a support rib under the distal bar extension on fracture resistance. Materials and methodsThe 2nd moment area and static strength were calculated for 11 frequently used bar designs using finite element analysis (FEA). For two specific designs (Ackermann round Ø 1.8mm and Dolder-Y macro, the former with and without a support rib) additional physical static and fatigue strength tests were included. ResultsThe FEA static strength data corresponded well to the 2nd moment area (a similar ranking when maximum allowed force was considered). The application of a rib support (Ackermann Ø 1.8mm) and limitations of the bar extension length (6mm for the Ackermann Ø 1.8mm, 8mm for the Dolder-Y macro) allowed the bars to exceed 5×106 cycles of 120 and 250N, respectively, before fracture. The region of highest stresses in FEA corresponded well with the locations of the fractures observed in static- and fatigue-testing. ConclusionsWith some simple guidelines/modifications, the number of bar extension fractures can be reduced significantly. Clinical significanceThis study focusses on distal bar extensions which improve the positioning of an implant supported overdenture. By combining laboratory testing and finite element simulations we aim to: (1) explain why fractures occur (dependent on physical characteristics of the bar), and (2) give clinical guidelines on how to prevent such fractures.

Vertical structure and dominating factors of sand body during Late Triassic Chang 9 time of Yanchang Formation in Ordos Basin, NW China

Based on a synthetic geological study of drilling, well logging and core observations, two main genetic types of Chang 9 sand body in Odors Basin were recognized, which included two effects, that is, delta environment and tractive current effects that lead to the development of mouth bar, distal bar, sheet sand and other sand bodies of subaerial and subaqueous distributary channel, natural levee, flood fan and delta front, and shore-shallow lake environment and lake flow transformation effects that result in the development of sandy beach bar, sheet sand and other sand bodies. Chang 9 sand body mainly developed five basic vertical structures, namely box shape, campaniform, infundibuliform, finger and dentoid. The vertical stacking patterns of multilayer sand body was complex, and the common shapes included box shape + box shape, campaniform + campaniform, campaniform + box shape, infundibuliform + infundibuliform, campaniform + infundibuliform, box shape + campaniform, box shape + infundibuliform, and finger + finger. Based on the analysis on major dominating factors of vertical structure of sand body, sedimentary environment, sedimentary facies and rise, fall and cycle of base level are identified as the major geological factors that control the vertical structure of single sand body as well as vertical stacking patterns and distribution of multistory sand bodies.

The Law of Reservoir Property Change both before and after Water Flooding in Liaohe Oilfield

In order to explore the change laws of physical properties and pore throat radius of reservoir both before and after water flooding to guide the oilfield in-depth fluid diversion, the reservoir properties are analyzed on the basis of core data of early exploratory well and inspection well in the middle and later stages of oilfield development. The theory of reservoir geology and development geology is used to study the change laws of reservoir properties both before and after water flooding in May 20th Development Area of Liaohe oilfield. The research result indicates that reservoir physical properties and pore throat radius have changed in the different period and different microfacies types of sand body [1-3].The permeability is changed far outweigh porosity in the physical properties of reservoir. And with the increase of time, the biggest change is the porosity and permeability of distributary channel, the next are margin of channels, mouth bar. The thin layer of channels and distal bar of physical properties have changed lesser or not. The pore throat radius has declined following distributary channel, mouth bar, thin layer of channels and distal bar in the sedimentary microfacies [4-5].The study results are helpful for the establishment of production measures at the later stage of oilfield development.

Finite element stress analysis study for stresses around mandibular implant retained overdenture MIR-OD

Background: It has been well known that the success of mandibular implant- retained overdenture heavily depends on initial stability, retention and long term osseointegration this is might be due to optimal stresses distribution in surrounding bones. Types of mandibular implant- retained overdenture anchorage system and number of dental implants play an important role in stresses distribution at the implant-bone interface. It is necessary to keep the stresses below the physiologic tolerance level of the bone .since. And it is difficult to measure these stresses around bone in vivo. In the present study, finite element analysis used to study the stresses distribution around dental implant supporting Mandible implant retained overdenture Materials and methods: Eight models were constructed including four designs of anchorage system (ball-cup, ball-O Ring, bar without distal extension and bar with distal extension).The first group of models were supported by four dental implant and second group of models were supported by two dental implant only. Models constructed from the data obtained directly from patient The contour of bone was obtained from C.T scan image of patient, then data transferred to ANSYS program for modeling then load applied and solve the equation by the program, Specified nodes were selected at the rings of crestal bone (cortical bone) and cortical cancellous interface around each dental implant and fixed for all models to monitor the stress change in that regions of different design of MIR-OD.. After load application, Specified nodes were selected at the rings of crestal bone (cortical bone) and cortical cancellous interface around each dental implant and fixed for all models to monitor the stress change in that regions of different design of MIR-OD . Results: In the present study the stress distribution and maximum stresses value around dental implant had a relationship to the number of dental implant. , The result appeared that the maximum stresses and means of stresses value was lower in the first group of models (which was supported through the use four dental implant) than the second group of models (which was supported through the use of two dental implant only). For the first group of models the maximum stresses value around mesial implant was11.67, 10.51, 10.98 and 10.72 Mpa, while the maximum stresses around distal implant was 21.33, 18.51, 18.86, and17.56 Mpa for models 1,2,3 and 4respectively ,and the stresses around implant supporting second group of models was 22.52, 22.16, 20.51 and 19.60 Mpa for models 5,6,7and8 respectively .Statistical analyses of means value appeared that there was statistically significant difference in stresses means value around implant of the second group with that’s values around mesial and distal implant supporting first group of model . Regarding the result of both ball and bar system, it has been demonstrated that stress was greater with ball attachment and MIR-OD supported by the use of four dental implants and anchored by bar attachments with distal extension gives the minimum values of stresses than the rest models. Also the results show that higher stresses value was appeared at the cortical bone ring surrounding dental implant especially the distal implant nearest to the free end extension area. Also it was appeared that the best model was Mandible implant- retained overdenture that’s anchored by bar with distal extension and support by four dental implant. Conclusions: Bar-clips with distal extension mode of attachment considered the best type in producing the least stresses around dental implant regardless number of dental implant used.

Facies Architecture and Stratigraphic Evolution of A River-Dominated Delta Front, Turonian Ferron Sandstone, Utah, U.S.A

Abstract Facies architectural analysis of a river-dominated deltaic parasequence in the Turonian Ferron Sandstone Member, near Factory Butte, Utah, was conducted to determine the hierarchical spatial arrangement of mouth bars and their role in constructing the delta. Five architectural elements were identified using 21 measured sections, paleocurrent measurements, and bedding diagrams. They are: (1) prodelta (PF), (2) frontal splay (FS), (3) detached distal bars (DBs), (4) distributary mouth bars (DMBs), and (5) terminal distributary channels (TDCs). Lower in the parasequence, detached bars consist of proximally located cross-bedded and quasi-parallel laminated subaqueous bars that onlap the delta-front slope and grade distally into finer-grained distal delta front splays. These bars translate downstream in a progradational–aggradational–degradational trajectory and are overlapped by adjacent bars, forming a bar assemblage. These bars are interpreted to have been deposited by descending hyperpycnal flows as a decelerating axial jet. Deposition of these bars occurs at the delta-front to prodelta chokepoint, presumably due to flow deceleration. The distal bar assemblage is capped by an extensive but discontinuous shale drape, suggesting local abandonment. Upper facies assemblages show a distinct switch to predominantly cross-bedded distributary mouth bars, corresponding to a decrease in water depth, an increase in friction, and a likely transition into planar versus axial jets. This is indicated by aggrading cross-bedded distributary mouth bars that overlie the distal bars. Laterally, the mouth-bar deposits are interstratified with terminal distributary-channel deposits with prominent scour surfaces at the base. Separate distributary channels and their bars coalesce, ultimately to build the entire delta lobe. The detached distal bars prograde locally west to northwest and lack fair-weather wave-formed sedimentary structures, suggesting a local embayment along the regionally northeast prograding shoreline. Low levels of ichnofaunal diversity indicate a stressed, river-dominated setting. At the base of the section, frontal splays and detached bars, dominated by storm-driven river-flood deposits, are deposited over muddy prodelta facies. Detached bars are likely initiated about 500 meters distal of the distributary channel, in water depths of ∼ 10–30 meters, based on the thickness of the parasequence. Once this subaqueous platform is constructed by the distal bar assemblage, more proximal distributary mouth bars fill the remaining shallow-water accommodation. As the system continues to shallow, distributary channels override and scour the bars, reflecting reduced accommodation.

Non-linear 3D finite element analysis of full-arch implant-supported fixed dentures

Despite the necessity for faster clinical protocols for immediate loading of implant-supported dentures, there is a lack of biomechanical studies to confirm the rigid splinting effectiveness. We compared the stress in mandibular full-arch implant-supported fixed dentures under immediate loading through three-dimensional finite element analysis. Edentulous human mandible models were restored with a 4-implant fixed denture. Implants were splinted with a metallic framework and submitted to conventional loading (group A—control), with acrylic resin and submitted to immediate loading (group B), with a metallic framework and submitted to immediate loading (group C), and with acrylic resin and a prefabricated distal bar and submitted to immediate loading (group D). Models were supported by masticatory muscles. A 100-N oblique load was applied on the first molar. Group A presented the lowest stress and implant displacement values, whereas group D showed the highest values. In bone, groups under immediate loading exhibited the highest stress, whereas the group experiencing conventional loading showed an approximately 50% reduction. All groups submitted to immediate loading presented similar stress values in peri-implant bone. The loading protocol influenced the stress and implant displacement, but the design of the fixed denture did not affect the stress in the peri-implant bone. Rigid splinting of implants submitted to immediate loading is not essential for treatment success.

柴达木盆地油砂山油田上干柴沟组沉积微相特征

以岩芯观察和测井分析为基础，通过对柴达木盆地油砂山油田上干柴沟组的沉积背景、物源方向、沉积构造、粒度分析的研究，确定其为一套以陆源碎屑的辫状河三角洲逐渐向浅湖过渡的沉积。区内以浅水三角洲前缘亚相沉积为主体，主要包括辫状分流河道微相、分流河道间微相、水下分流河道微相、水下分流河道间微相、河口坝微相、远砂坝微相、席状砂微相、砂坝微相、砂滩微相、颗粒滩微相、浅滩微相、浅湖泥微相等11种沉积微相类型。此外，以单井微相分析为基础，结合大量的地球物理测井及录井资料，研究了区块内上干柴沟组6个油层组的沉积微相平面分布规律，最有利砂体主要发育在三角洲前缘的水下分流河道、河口坝及浅湖砂坝中。沉积微相的精细研究为推测有利相带为良好的岩性油气藏的发育、主力层剩余油挖潜以及油田的下一步勘探开发奠定了基础。 Based on core observation and logging analysis, the upper Ganchaigou formation of Youshashan in Qaidam Basin is determined to deposit in the terrigenous clastic transitional environment from the braided delta to the shallow river, through the research on its sedimentary background, source direction, sedimentary structure and analysis of grain sizes. The region is dominated by shallow- water delta front, including the braided distributary channels, interdistributary areas, sub- aqueous distributary channels, sub-aqueous interdistributary areas, mouth bars, distal bars, sheet sands, sand bars, sand beaches, grain banks, shallow-lake sheet sands and mudflats. What’s more, on the basis of single-well facies analysis, integrated with a great mass of geophysical logging and well logging data, a study has been made on the microfacies areal distribution patterns of the six oil layer groups in upper Ganchaigou formation in the region, and it has been found out that the most favorable sand bodies were deposited in the sub-aqueous distributary channels and mouth bars in the delta front and sand bars in the shallow lake. The fine studies of microfacies lay a foundation for the speculation of the favourable facies belts, the potential tapping of remaining oil in the main layers and the future exploration and development of the oil field.

The Characteristics of Sedimentary Facies of Tanzhuang Formation of Upper Triassic of Luoyi District

Based on the observation and description of single well and outcrops and the analysis of reservoir compositions, petrology, clastic structure and sedimentary structure,this paper determines the sedimentaty facies characteristics of Tanzhuang formation. The types of sedimentary facies in late Triassic epoch are delta front,shallow lake and semi-deep lake. The delta front develops subaqueous distributary channel, mouth bar and distal bar. Lacustrine facies develops shallow lake mud, shallow lake sand bar, turbidite sand and semi-deep lake mud.The reservoir rock formations in this area are lithic sandstone,feldspathic lithic sandstone with high content of feldspar and debris.The sedimentary structures include ripple, scour surface and cross-bedding are identified.

Complications with Computer‐Aided Designed/Computer‐Assisted Manufactured Titanium and Soldered Gold Bars for Mandibular Implant‐Overdentures: Short‐Term Observations

Implant-overdentures supported by rigid bars provide stability in the edentulous atrophic mandible. However, fractures of solder joints and matrices, and loosening of screws and matrices were observed with soldered gold bars (G-bars). Computer-aided designed/computer-assisted manufactured (CAD/CAM) titanium bars (Ti-bars) may reduce technical complications due to enhanced material quality. To compare prosthetic-technical maintenance service of mandibular implant-overdentures supported by CAD/CAM Ti-bar and soldered G-bar. Edentulous patients were consecutively admitted for implant-prosthodontic treatment with a maxillary complete denture and a mandibular implant-overdenture connected to a rigid G-bar or Ti-bar. Maintenance service and problems with the implant-retention device complex and the prosthesis were recorded during minimally 3-4 years. Annual peri-implant crestal bone level changes (ΔBIC) were radiographically assessed. Data of 213 edentulous patients (mean age 68 ± 10 years), who had received a total of 477 tapered implants, were available. Ti-bar and G-bar comprised 101 and 112 patients with 231 and 246 implants, respectively. Ti-bar mostly exhibited distal bar extensions (96%) compared to 34% of G-bar (p < .001). Fracture rate of bars extensions (4.7% vs 14.8%, p < .001) and matrices (1% vs 13%, p < .001) was lower for Ti-bar. Matrices activation was required 2.4× less often in Ti-bar. ΔBIC remained stable for both groups. Implant overdentures supported by soldered gold bars or milled CAD/CAM Ti-bars are a successful treatment modality but require regular maintenance service. These short-term observations support the hypothesis that CAD/CAM Ti-bars reduce technical complications. Fracture location indicated that the titanium thickness around the screw-access hole should be increased.