Effects of water level fluctuation on sedimentary characteristics and reservoir architecture of a lake, river dominated delta

The hydrodynamic conditions present in a river delta's formation are a highly important factor in the variation between its sedimentary regulation and characteristics. In the case of the lacustrine basin river-dominated delta, water level fluctuations and fluviation, are both important controlling factors of the sedimentary characteristics and reservoir architecture. To discuss the effects of water level fluctuation on sediment characteristics and reservoir architecture of this delta, the Fangniugou section in the east of the Songliao Basin was selected for study. Based on an outcrop investigation of the lacustrine basin river-dominated delta, combining with an analysis of the major and trace chemical elements in the sediments to determine the relative water depth, through architecture bounding surfaces and lithofacies division, sedimentary microfacies recognition and architectural element research, this work illustrated the effects of water level fluctuation on the reservoir architecture and established sedimentary models for the lacustrine basin river-dominated delta under various water level conditions. The results show that there are 8 lithofacies in the Fangniugou section. The fan delta front, which is the main object of this study, develops four sedimentary microfacies that include the underwater distributary channel, river mouth bar, sheet sand and interdistributary bay. The effects of water level fluctuation on different orders geographic architecture elements are respectively reflected in the vertical combination of the composite sand bodies, the plane combination of the single sand bodies, the particle size changes in the vertical of hyperplasia in the single sand body, the coset and lamina. In the case of the sand body development of the petroliferous basin, varying water level conditions and research locations resulted in significant variation in the distribution and combination of the sand bodies in the lacustrine basin.

Fine anatomy of reservoir architecture of point bar in meandering river: a case study of Minghuazhen Formation in northern block of Q oilfield,Bohai Sea

In order to solve dynamic Problems caused by the internal structure of fluvial reservoir,it is necessa-ry to study the fine anatomy of Point bar. Taking Minghuazhen Formation in the northern block of Q oilfield, Bohai Sea as an examPle,the authors studied identification marks,distribution Pattern and scale of Point bar based on coring,logging and dynamic data. The results show that the length of Point bar and the width of lateral accretion body are 713-911 m and 71-111m,resPectively;the diP angle and the thickness of lateral accretion bedding are 3. 5o-5. 9o and 0. 1-0. 5 m. The lateral accretion beddings are the key factor affecting the seePage velocity of the tracer.

The Anatomy of Shallow Water Sandy Braided River Reservoir Architecture

1 Introduction Reservoir architecture refers to pattern,scale,direction and overlapping relationship of different levels of architecture units.The research of architecture in fluvial phase began in the 1980s(Miall,1985).The braided river

Distribution Patterns of Remaining Hydrocarbons Controlled by Reservoir Architecture of Distributary Channel with Different Channel Style: S2 Formation of Songliao Basin, China

1 Introduction Reservoir architecture analysis of distributary channel of Daqing oilfield has drawn consistent interest among development geologists and petroleum engineers over the last decade(Lv et al.,1999;Zhou et al.,2008;Zhang et

Sedimentary and reservoir architectures of MB1-2 sub-member of Middle Cretaceous Mishrif Formation of Halfaya Oilfield in Iraq

Based on comprehensive analysis of core,cast thin section,logging and seismic data,the sedimentary and reservoir architectures of the MB 1-2 sub-member of Mishrif Formation in Halfaya Oilfield,Iraq,are studied.The MB 1-2 sub-member of Mishrif Formation has three types of microfacies,lagoon,bioclastic shoal,and tidal channel,and facies architecture controlled by sequence stratigraphy.In the 4th-order sequence,the lagoon facies aggradated vertically,and the bioclastic shoals in lenticular shape embed in the background of lagoon,the end of the sequence is incised by the"meandering river"shape tide channel,which represents the depositional discontinuity.Three types of reservoirs including tidal channel grainstone to packstone reservoirs,bioclastic shoal grainstone to packstone reservoirs and dissolved lagoon wackestone reservoirs are developed.The reservoir architectures within tidal channel and bioclastic shoal are strickly controlled by grainy facies,whereas the dissolved lagoon reservoirs controlled by both facies and dissolution are related to the sequence boundary.The reservoir sections occur mainly in the 4 th sequence highstand systems tract(HST)and are separated by barriers formed in the transgressive systems tract(TST).Complicated facies architecture and dissolution modification resulted in strong heterogeneity within the reservoir,which showed the characteristics of"attic type"architecture.The results of this study can guide the development of similar reservoirs in the Middle East.

The rudist buildup depositional model,reservoir architecture and development strategy of the cretaceous Sarvak formation of Southwest Iran

This paper studies the lithofacies,sedimentary facies,depositional models and reservoir architecture of the rudist-bearing Sar-3 zone of Cretaceous Sarvak in the Southwest of Iran by utilizing coring,thin section,XRD data of five coring wells and 3D seismic data.Research results include the following:According to lithofacies features and their association,the rudist-mound and tidal flat are the main microfacies in the Sar-3 depositional time.By investigating the regional tectonic setting and seismic interpretation,a depositional model was built for the Sar-3 zone,which highlights four key points:1)The distribution of the rudist-buildup is controlled by the paleo-high.2)The build-up outside of the wide colonize stage but reached the wave-base level in a short time by regression and formation uplift,and was destroyed by the high energy current,then forming the moundy allochthonous deposition after being dispersed and redeposited.3)The tidal flat develops widely in the upper Sar-3,and the deposition thickness depends on the paleo-structure.The tidal channel develops in the valley and fringe of the Paleo-structure.4)The exposure within the leaching effect by the meteoric water of the top of Sar-3 is the main controlling factor of the reservoir vertical architecture.The Sar-3 zone featured as the dualistic architecture consists of two regions:the lower is the rudist reef limestone reservoir and the upper is the tidal condense limestone interlayer.The thickness of each is controlled by the paleo-structure.The Paleo-high zone is the preferential development zone.Based on reservoir characteristics of the different zones,a targeted development strategy has been proposed.Keeping the trajectory in the middle of the oillayer in the paleo-high,and in the paleo-low,make the trajectory crossing the oil-zone and then keep it in the lower.

Reservoir architecture patterns of sandy gravel braided distributary channel A case study of Triassic Upper Karamay Formation,Xinjiang oilfield

The purpose of this study was to discuss shape,scale and superimposed types of sandy gravel bodies in sandy-gravel braided distributary channel.Lithofacies analysis,hierarchy bounding surface analysis and subsurface dense well pattern combining with outcrops method were used to examine reservoir architecture patterns of sandy gravel braided distributary channel based on cores,well logging,and outcrops data,and the reservoir architecture patterns of sandy gravel braided distributary channels in different grades have been established.The study shows:(1)The main reservoir architecture elements for sandy gravel braided channel delta are distributary channel and overbank sand,while reservoir flow barrier elements are interchannel and lacustrine mudstone.(2)The compound sand bodies in the sandy gravel braided delta distributary channel take on three shapes:sheet-like distributary channel sand body,interweave strip distributary channel sand body,single strip distributary channel sand body.(3)Identification marks of single distributary channel include:elevation of sand body top,lateral overlaying,“thick-thin-thick”feature of sand bodies,interchannel mudstone and overbank sand between distributary channels and the differences in well log curve shape of sand bodies.(4)Nine lithofacies types were distinguished in distributary channel unit interior,different channel units have different lithofacies association sequence.

Architecture mode, sedimentary evolution and controlling factors of deepwater turbidity channels： A case study of the M Oilfield in West Africa

Turbidity channels have been considered as one of the important types of deepwater reservoir, and the study of their architecture plays a key role in efficient development of an oil field. To better understand the reservoir architecture of the lower Congo Basin M oilfield, semiquantitative–quantitative study on turbidity channel depositional architecture patterns in the middle to lower slopes was conducted with the aid of abundant high quality materials（core, outcrop, logging and seismic data）,employing seismic stratigraphy, seismic sedimentology and sedimentary petrography methods. Then, its sedimentary evolution was analyzed accordingly. The results indicated that in the study area, grade 3 to grade 5 architecture units were single channel, complex channel and channel systems, respectively. Single channel sinuosity is negatively correlated with the slope, as internal grains became finer and thickness became thinner from bottom to top, axis to edge. The migration type of a single channel within one complex channel can be lateral migration and along paleocurrent migration horizontally, and lateral,indented and swing stacking in section view. Based on external morphological characteristics and boundaries,channel systems are comprised of a weakly confining type and a non-confining type. The O73 channel system can be divided into four complex channels named S1–S4, from bottom to top, with gradually less incision and more accretion. The study in this article will promote deeper understanding of turbidity channel theory, guide 3D geological modeling in reservoir development and contribute to efficient development of such reservoirs.

Architectural Units and Groundwater Resource Quantity Evaluation of Cretaceous Sandstones in the Ordos Basin,China

Sandstone is a common lithology in a number of groundwater reservoirs. Studying the skeleton sandstone architectural units, therefore, lays the basis for characterizing aquifer systems, groundwater quality, and resource evaluation. This comprehensive analysis of Cretaceous aquiferous sandstones in the Ordos basin, China, shows that there exists a basin-scale skeleton sandstone in the Luohe Formation which contains 11 isolated barrier beds, 12 small skeleton sandstone bodies in Huanhe Formation, and 3 in the Luohandong Formation. The spatial structure and superimposed relationship as well as the medium properties of these skeleton sandstones and isolated barrier beds can be shown by 3D visualization models. Simultaneously, resource quantity can be evaluated with the 3D inquiry functions. The comparison between property models and structural models indicates that the salinity of groundwater of the Luohe Formation has a close connection with the locations of isolated barrier beds that contain abundant gypsum. Through quantitative calculation, groundwater resource of the Cretaceous Luohe and Luohandong formations is estimated to be 1.6×10-（12） m-3, and the total groundwater resource of the Cretaceous system in the Ordos basin is more than 2×10-（12） m-3.

Seismic Sedimentology Interpretation Method of Meandering Fluvial Reservoir:From Model to Real Data

Reservoir architecture of meandering river deposition is complex and traditional seismic facies interpretation method cannot characterize it when layer thickness is under seismic vertical reso- lution. In this study, a seismic sedimentology interpretation method and workflow for point bar char- acterization is built. Firstly, the influences of seismic frequency and sandstone thickness on seismic re- flection are analyzed by outcrop detection with ground penetrating radar （GPR） and seismic forward modeling. It is found that （1） sandstone thickness can influence seismic reflection of point bar architecture. With the increasing of sandstone thickness from 1/4 wavelength （λ） to λ/2, seismic reflection geometries various from ambiguous reflection, ＂V＂ type reflection to ＂X＂ type reflection; （2） seismic frequency can influence reservoirs＇ seismic reflection geometry. Seismic events follow inclined lateral aggradation surfaces, which is isochronic depositional boundaries, in high frequency seismic data while the events extend along lithologic surfaces, which are level, in low frequency data. Secondly, strata slice interpretation method for thin layer depositional characterization is discussed with seismic forward modeling. Lastly, a method and workflow based on the above study is built which includes seismic frequency analysis, 90° phasing, stratal slicing and integrated interpretation of slice and seismic profile. This method is used in real data study in Tiger shoal, the Gulf of Mexico. Two episodes of meandering fluvial deposition is recognized in the study layer. Sandstone of the lower unit, which is formed in low base level stage, distributes limited. Sandstone distribution dimension and channel sinuosity become larger in the upper layer, which is high base level deposition.

Sedimentary characteristics of turbidite fan and its implication for hydrocarbon exploration in Lower Congo Basin

The turbidite is favorable for accumulation of oil and gas and it is the most important reservoir in the deepwater area of West Africa.Currently,some commercial discoveries in such the deepwater area generally belong to turbidite sandstone reservoirs.Based on comprehensive analysis of lithology,lithofacies and configuration of the turbidite,and combined with changes of seismic attributes and sedimentary cycle,the turbidite in the deepwater area of West Africa can be classified into by-pass channel(including the constructive by-pass channel and the erosive by-pass channel),confined channel complex,weakly confined channel complex,and lobe.Different types of turbidite reservoirs have different physical property,so there are differences in hydrocarbon exploration potential;the sandstone in the weakly confined channel complex is the key exploration target in the deepwater area of the Angola Sea.