Effect of Sand Body Enrichment Under the Restriction of a Tectonic Transfer Zone: A Case Study on the Pinghu Formation in the Kongqueting Region on the Pinghu Slope

Results of long-term explorations in the Kongqueting region,located in an East China Sea depression,suggest that the strong fault activity during the sedimentary period of the Pinghu formation significantly influenced the development of the sedimentary system.However,the aggregation and enrichment of the sand body under a tectonic background has become a problem that requires an immediate solution.Considering research outcomes of previous studies,this study used three-dimensional seismic and logging data to identify Y-or H-type and the en echelon distribution patterns of the fault plane,as well as identify the locations wherein the fault growth index value is greater than 1 in the study region,indicating the tectonic background of the fault transfer zone in the region.Second,the development type of the fault transfer zone was studied,and the sand body enrichment site was identified based on seismic inversion data and the development position of the fault transfer point.This helps clarify the evolution of sedimentary facies of the Pinghu formation combined with the sedimentary environment of the braided-river delta.Finally,after summarizing the coupling relationship between the synsedimentary fault systems and the sand body enrichment patterns,three sand-control models were determined,namely,the flexural-parallel,the en echelon collinear,and the torsional-reformed superimposed transfer zones.The findings of this study lay a foundation for the subsequent search of tectonic lithologic oil and gas reservoirs.

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 9sand 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.

Quantitative prediction of channel sand bodies based on seismic peak attributes in the frequency domain and its application

The boundary identification and quantitative thickness prediction of channel sand bodies are always difficult in seismic exploration.We present a new method for boundary identification and quantitative thickness prediction of channel sand bodies based on seismic peak attributes in the frequency domain.Using seismic forward modeling of a typical thin channel sand body,a new seismic attribute-the ratio of peak frequency to amplitude was constructed.Theoretical study demonstrated that seismic peak frequency is sensitive to the thickness of the channel sand bodies,while the amplitude attribute is sensitive to the strata lithology.The ratio of the two attributes can highlight the boundaries of the channel sand body.Moreover,the thickness of the thin channel sand bodies can be determined using the relationship between seismic peak frequency and thin layer thickness.Practical applications have demonstrated that the seismic peak frequency attribute can depict the horizontal distribution characteristics of channels very well.The ratio of peak frequency to amplitude attribute can improve the identification ability of channel sand body boundaries.Quantitative prediction and boundary identification of channel sand bodies with seismic peak attributes in the frequency domain are feasible.

Potential evaluation of saline aquifers for the geological storage of carbon dioxide: A case study of saline aquifers in the Qian-5 member in northeastern Ordos Basin

The well-developed coal electricity generation and coal chemical industries have led to huge carbon dioxide(CO_(2))emissions in the northeastern Ordos Basin.The geological storage of CO_(2) in saline aquifers is an effective backup way to achieve carbon neutrality.In this case,the potential of saline aquifers for CO_(2) storage serves as a critical basis for subsequent geological storage project.This study calculated the technical control capacities of CO_(2) of the saline aquifers in the fifth member of the Shiqianfeng Formation(the Qian-5 member)based on the statistical analysis of the logging and the drilling and core data from more than 200 wells in the northeastern Ordos Basin,as well as the sedimentary facies,formation lithology,and saline aquifer development patterns of the Qian-5 member.The results show that(1)the reservoirs of saline aquifers in the Qian-5 member,which comprise distributary channel sand bodies of deltaic plains,feature low porosities and permeabilities;(2)The study area hosts three NNE-directed saline aquifer zones,where saline aquifers generally have a single-layer thickness of 3‒8 m and a cumulative thickness of 8‒24 m;(3)The saline aquifers of the Qian-5 member have a total technical control capacity of CO_(2) of 119.25×10^(6) t.With the largest scale and the highest technical control capacity(accounting for 61%of the total technical control capacity),the Jinjie-Yulin saline aquifer zone is an important prospect area for the geological storage of CO_(2) in the saline aquifers of the Qian-5 member in the study area.

Composite Sand Bodies Architecture of Deep-Water Turbidite Channels in the Niger Delta Basin

Deep-water turbidite channels have attracted much attention as a focused issue in petroleum exploration and development. Extensive studies have been performed on the architecture of turbidite channels, and most researches have focused on their geometric shapes, sedimentary processes and controlling factors. However, little attention has been paid to the distribution patterns, distribution laws and quantitative studies of composite sand bodies of turbidite channels. Taken one slope area of the Niger Delta Basin as an example, this study conducted a semi-quantitative to quantitative analysis on architecture of composite sand bodies of turbidite channels based on cores, well logging and seismic surveys. It is shown that turbidite channel systems can be classified as confined and unconfined channel systems. For confined channel systems, the vertical evolution process involves four stages. The sinuosity of a channel system is controlled by slope, with a negative power function relationship between them. When slope gradient reaches four degrees, the channel system is nearly straight. Based on the migration direction and migration amount of single channels within channel complexes, channel composite patterns can be divided into four classes（the lateral composite, en-echelon composite, swing composite and vertical composite） and several subclasses. Various channel composite patterns show specific distribution laws spatially. For meandering channel complexes at the middle-late evolution stage of confined channel systems, the lateral migration amongst single channels shows the features of integrity and succession. The sinuosity of single channels in the late period is greater than that in the early period, and cut-offs may occur locally when the sinuosity is larger than five degrees. This study provides a better understanding for the geological theory of deep-water sedimentary, and also improves exploitation benefits of this type of reservoirs.

Side lobes of wavelets impact identification of thin sand bodies

Recently, we found that side lobes of wavelets have a large impact on the identification of thin sand reservoirs when studying some gas fields in a basin in Northwest China. Reflections from the top of the H Formation, in which there are gas-bearing thin sand bodies, have the main wavelet lobe between two weak peak side lobes. The lower one always mixes with another peak reflected from the top of a thin sand reservoir. That makes it difficult to identify the sand reservoir. In order to solve this, many forward models were set up using typical well logs. 2D synthetic profiles were produced using Ricker wavelets to study the relationships between the effects of wavelet side lobes and thin sand position and frequency and between amplitude and the thin sand body. We developed the following conclusions： First, it is easier to identify thin sands in a shallower position. Second, a good way to tell sand body reflections from side lobes is by comparing profiles with different frequency windows. Third, it is helpful and effective to describe sand extent using amplitude attributes.

Braided river and distribution patterns of sand bodies of Jurassic Badaowan formation in Block T13 of Junggar basin

In order to determine the planar and volume distribution of sand bodies of the Jurassic Badaowan formation in Block T13 of Junggar basin,we used analysis of field outcrop and 3D seismic data,which play an essential role in areas of sparse well coverage.We describe sedimentary facies characteristics,sand body planforms,width and connectivity patterns of sand bodies,and vertical associations and successions by acoustic impedance inversion technology and sedimentological theory.Results of our study show braided fluvial strata deposits in the Jurassic Badaowan formation.Each sand body is approximately lenticular in shape.The width of each sand body falls in the range 100～800 m,with most between 200 and 400 m.The sand bodies vary in thickness from 4 to 13 m,with most below 9 m.The width/thickness ratios lie in the range 20～55.The connectivity of braided fluvial channel sand bodies is controlled by changes of accommodation space.One fining-upward sedimentary cycle of base-level rise is recognized in Badaowan formation,representing an upward rise of base level.The connectivity of sand bodies was found to be greatest in the early stage of base-level rise,becoming progressively worse with increasing base-level rise.

Distribution of shallow water delta sand bodies and the genesis of thick layer sand bodies of the Triassic Yanchang Formation, Longdong Area, Ordos Basin

Based on the cores from 47 wells and logging data of 130 wells,the main types of sand bodies in the shallow water delta of the Chang 8_(2) sub-member in the Triassic Yanchang Formation,Longdong Area,Ordos Basin were comprehensively analyzed,the distribution characteristics of sand bodies more than 20 m thick were identified,and the genetic types of the thick sand bodies were sorted out.In this region,thick-bed sand bodies can be divided into two types according to the shape and position:type 1 is the sand body in wide strip and is distributed between the average high water mark and the average low water mark;type 2 is distributed on both sides of the average low water mark and is in irregular lump shape.Based on the principle of the volume distribution of sediments and the change rule of accommodation space,the genetic models of two types of thick-bed sand bodies in the Chang 8_(2) sub-member are superimposed distributary channel sand bodies in high accommodation space and superimposed composite sand bodies in low accommodation space.

Oil／Gas Accumulation Characteristics and Exploration Methods of the Deltaic Lithologic Reservoirs in Northern Shaanxi Area

There are large deltaic systems in the Triassic Yanchang Formation in the northern Shaanxi area of the Ordos Basin, and developed two sets of good source-reservoir-caprock assemblages and many sets of oil-bearing beds. Exploration experience demonstrates that the formation and distribution of the reservoir were controlled by the generative depression of the Yanchang Formation, and deltaic reservoir sand body is the material basis for large-scale oilfields. In addition, secondary laumontite in a low permeable area was dissolved and then a high permeable area was formed. The updip lithologic variety of reservoir sand bodies is favorable to the formation of subtle lithologic traps, and the deltaic reservoirs are characterized by large multi-beds of oil-generation and abundant hydrocarbon resources. In this paper, the petroleum geologic settings of the studied area are analyzed, and the accumulation characteristics and exploration methods of lithologic reservoirs are summarized. It is of theoretical significance for the study of the exploration theories of lithologic reservoirs, and also expedites the exploration steps of deltaic reservoirs in the northern Shaanxi area.

Formation conditions of Neogene large-scale high-abundance lithologic reservoir in the Laibei low uplift,Bohai Sea,East China

By using drilling,high-precision 3 D seismic data,data of geochemistry,logging and testing,the reservoir characteristics and accumulation conditions of the KL6-1 lithologic oilfield in the Laibei Low Uplift in the Bohai Sea are examined comprehensively.The study shows that:KL6-1 oilfield is a monolithic,high-quality,large-scale Neogene lithologic oilfield featuring shallow reservoir depth,high productivity,concentrated oil-bearing intervals,large oil-bearing area,and high reserve abundance;hydrocarbon source supply from two directions provides a sufficient material basis for the formation of large oil field;two types of"inherited structural ridge"developed under the effect of block rotation,late active faults formed by Neotectonic movement,and widely distributed contiguous sand bodies provide an efficient oil and gas transportation system for the large-scale accumulation of oil and gas;contiguous channel and lacustrine lowstand system sand bodies developed in low accommodation condition provide the basic condition for the formation of large-scale lithologic traps;deep formations structural ridge,faults(dominant migration pathways)and large-scale superimposed contiguous sand bodies constitute a"vine type"oil and gas migration and accumulation system in the Laibei Low Uplift,which is conducive to the formation of large-scale and high-abundance lithologic reservoir in this area.The successful discovery of KL6-1,100 million ton reserve order lithologic oil field,has revealed the exploration potential of Neogene large lithologic reservoirs in Bohai Sea,expanded the exploration field,and also has certain reference significance for the exploration of large lithologic reservoirs in similar areas.

Research and Application of Joint Interpretation Using P-Wave and PS-Wave in Tight Gas Exploration

The exploration and development of tight sandstone gas reservoirs are controlled by high-quality river channel sand bodies on a large scale in Sichuan Basin.In order to improve the accu-racy of sand body prediction and characterization,Multi-component exploration technology research has been carried out in Northwest Sichuan Basin.First,based on the array acoustic logging data,a for-ward modeling has been established to analyze the seismic response characteristics of the PS-wave data and P-wave data.The result shows that the response characteristics of the P-wave and PS-wave to the sand bodies with different impedance are different.And then through the analysis of logging data,the effectiveness of the forward modeling has been proved.When the sandstone velocity is close to the sur-rounding rocks,the P-wave performs as a weak reflection,which may lead to reduce the identification range of the sand bodies.However,the PS-wave exhibits strong reflection,which can identify this type of sand bodies.Finally,by comparing and explaining the PS-wave data and P-wave data,and integrat-ing their attributes,the prediction accuracy of sand bodies is improved.Compared with the interpreta-tion of a single P-wave,the results can significantly expand the distribution range of sand bodies,lay-ing a foundation for improving the production capacity of single wells and reserve submission.

Control of Anticline Crest Zone on Depositional System and Its Geological Significance for Petroleum in Changshaling,Ying- er Sag,Eastern Jiuquan Basin

ABSTRACT： Yinger sag is the main petroleum and only the Changshaling oil resource has shaling anticline crest zone was formed above the generative sag in eastern Jiuquau Basin, been found after 60 years prospecting. Chang- regional uplift, and was slightly affected by crest was identified as a structural transposition zone. Based on analysis of seismic facies, logging facies and seismic inversion technique, it has been demonstrated that anticline crest zone conducts drainage entering basin and dominates sedimentary detritus further dispersing, and the anticline crest zone controls the distribution of sand bodies and the development of sedimentary system consequently. The sequence stratigraphic patterns of multi-step fault belt in Member 3 of Xiagou Formation in Lower Cretaceous in the anticline crest zone is composed of the development of sedimentary facies in plan and distribution of multi-step fault belt sand bodies in spa- tial. This research investigates the sand-control models and sequence patterns, and finally a model of reservoirs in anticline crest zone is identified.

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 reser- voir characteristics show that the development of the slope and its sand bodies＇ depositional genesis de- termined 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.

Stratigraphic Framework and Microfacies of the Triassic Lower Karamay Formation in Districts Ⅰ,Ⅲ, NW Junggar, China

The Triassic Lower Karamay Formation（T2k1） is one of the main oil-bearing stratigraphic units in the northwestern margin of Junggar Basin（NW Junggar）, China. Based on an integrated investigation of outcrops, well logs and seismic data of NW Junggar, the Lower Karamay Formation is subdivided into 2 sets, 6 beds and 13 layers. Also, it is considered that the alluvial fan, the braided river, the meandering river and the shore-shallow lacustrine were developed during the early period of Middle Triassic in Karamay districts Ⅰ, Ⅲ. The Lower Karamay Formation deposits the following 9 sedimentary subfacies： the lower fan, the middle fan, the upper fan, the braided channel, the overflow bank, the river flood of braided river, the meandering channel, the river flood of meandering river, the shore-shallow lacustrine. Seventeen microfacies such as the braided stream channel, the alluvial sand floodplain, the alluvial glutenite floodplain, the water channel, the channel bar etc. have been identified in subfacies as well. The thickness of strata is firstly up-thinning and then thickening upward to the top, it is a process from large-scale lacustrine transgression to partly lacustrine regression. Furthermore, the microfacies planar distributing law proves that the remaining oil may enrich along the margin of microfacies because of the planar microfacies changes. Therefore, this research is beneficial for searching remaining oil in NW Junggar and providing information to the project ＂The Secondary Exploration＂ of PetroChina.