Thin Sand Bodies Research Articles

Seismic sedimentology analysis of meter-scale thin sand bodies in the Jurassic Qigu Formation, Yongjin area, Junggar Basin

Seismic sedimentology is an interdisciplinary field that integrates sedimentary geology and geophysics to accurately characterize the spatial and temporal distributions of sedimentary systems. This paper focuses on the Qigu Formation in the Yongjin area of the Junggar Basin, China. The objectives are to establish a high-resolution sequence stratigraphic framework and to clarify the types of sedimentary systems present. Various technical methods, including 90° phase adjustment, attribute clustering, red-green-blue attribute fusion, stratal slicing, and seismic phase-controlled waveform indication inversion, are employed to restore the vertical evolution history of the sedimentary system and quantitatively characterize the spatial-temporal distribution of the thin sand bodies in the Qigu Formation. The results revealed that the Qigu Formation is divided into a third-order sequence, consisting of a lowstand systems tract and a lacustrine transgressive systems tract. During the lowstand systems tract, a thick channel sand body developed in the delta front, exhibiting a non-muddy, intermittent normal grading structure. The lacustrine transgressive systems tract features thin, discontinuous channel sand bodies with mud layers, also forming an intermittent normal grading structure. Two distinct types of delta fronts are identified: the first, formed during the lowstand systems tract, is characterized by branching subaqueous distributary channels in a shallow-water environment. The second, associated with the lacustrine transgressive systems tract, displays a network-like distribution of subaqueous distributary channels in a relatively deeper-water environment.

Seismic Prediction Technology for Channel Sand Body of Fuyu Oil Layer in Xinmin Area, Southern Songliao Basin

The Fuyu reservoir in Xinmin area is a delta plane-front facies deposit, and the channel sand body in this area is the main reservoir of oil and gas. Due to the complex sedimentary environment, the sand body shows great variation in thickness and distribution. In this study, the method of combining well vibration, model forward modeling and stratum slicing are used to predict the sandstone bodies of different thickness successfully. Especially for the thin sand body with a thickness of less than 5 meters, this study found that the GR curve can effectively distinguish sandstone and mudstone through the intersection analysis of logging curves, and applied the GR curve co-simulation inversion technology to perform fine characterization. In addition, the study also reveals that the northeastward twisting fault zone in Xinmin area is a favorable accumulation area of the reservoir, which provides a new direction for oil and gas exploration. This study not only improves the accuracy of sandstone prediction, but also provides a valuable reference for oil and gas exploration under similar complex geological conditions.

Optimization Method for Water-Flooded Beach-Bar Sand Bodies: A Case Study of the Fourth Member Red Beds of the Paleogene Shahejie Formation in the Dongying Depression

As water flooding continues to advance in mature oil fields, conventional well logging curve responses exhibit anomalies, particularly in deep-seated beach-bar thin-layer sand bodies. These sand bodies exhibit strong vertical and planar heterogeneity, which hinders a clear understanding of their distribution and connectivity. This paper conducts a sensitivity analysis of the lower part of the 4th member of the Shahejie Formation in fault block C26, based on core data analysis and the integration of drilling, logging, recording, and production dynamic data. Natural potential and resistivity curves are selected as the sensitive curves for identifying sand bodies. Preliminary processing of well logging curves is carried out using the “standard layer constraint and multi-standardization method comparison” principle. Employing sedimentological research methods and the principles of wavelet transformation, the well logging curves within the study area undergo extraction of both high and low frequencies. This procedure accentuates details related to thin sand bodies and responses indicative of sedimentary cyclicity. Through a thoughtful amalgamation of multiple curves, the investigation achieves a systematic fusion of natural potential curves via multi-curve frequency division fusion, employing reconstruction optimization. This method adeptly mitigates interference stemming from water-flooded layers, effectively addressing challenges such as excessive calibration and ambiguous identification of sand bodies. As a result, a comprehensive analytical approach is established for assessing the distribution and connectivity of deep-seated, beach-bar thin sand bodies influenced by water-flooded layers, providing clarity on the connectivity relationships among the sand bodies. Additionally, in combination with the results of mercury injection experiments in the water-flooded layer segments, favorable reservoir criteria for the study area are determined, providing a scientific basis for adjusting future development plans.

Development technologies for Triassic Chang 7 shale oil in Ordos Basin: A case study of Qingcheng Oilfield, NW China

The reservoirs in the seventh member of the Triassic Yanchang Formation (Chang 7 Member) in the Qingcheng Oilfield of the Ordos Basin are characterized by thin sandbody, tight rocks, high heterogeneity, low formation pressure coefficient, and complex geomorphology. Through the efforts in the stages of exploration, appraisal, pilot testing and development, a series of key technologies have been formed, including “sweet spot” optimization, differentiated three-dimensional well deployment, fast drilling and completion of large-cluster horizontal well, intensively-staged volume fracturing in long horizontal well, and optimization of rational production system. Furthermore, a production organization mode represented by factory-like operations on loess platform has been implemented. Application of these technologies has enabled to significantly improve the single-well production of the Qingcheng Oilfield, reduce the investment cost, and realize a large-scale and beneficial development at a full cost below $55 per barrel. In 2022, the annual production of Chang 7 shale oil in the Ordos Basin reached 221×104 t, accounting for 70% of the annual shale oil production of China. The practice of development technologies in the Qingcheng Oilfield provides valuable references for efficient development of continental shale oil.

Seismic Response Variance of Depositional Sequences: Implications for Reservoir Prediction in Lacustrine Basin

In recent years, lithologic oil and gas reservoirs have become an important target in continental hydrocarbon-bearing basins. Geophysical prospecting technology using seismic data is an indispensable tool for oil and gas exploration. However, while previous work has paid much attention to the seismic responses of reservoirs (sandstones), the seismic responses of depositional sequences composed of sandstone–mudstone cycles are not well understood in reservoir prediction. This problem seriously restricts efficient oil–gas exploration and development. The Cretaceous Baxigai Formation in the Yingmaili area, west of the Tabei Uplift, is an important exploration target for lithologic oil and gas reservoirs in the Tarim Basin. The Baxigai Formation is deeply buried with thin thickness. The Baxigai Formation in the study area is divided into a lower sandstone section and an upper mudstone section. Braided river delta sand bodies are developed in the lower sandstone section, and braided river delta sand bodies and beach bar sand bodies are developed in the upper mudstone section. According to the difference in the depositional sequences in different zones, five types of the vertical combination style of sandstone and mudstone were identified. Through seismic forward modeling, the seismic response variance of the five kinds of sequence models was established. Then, the amplitude attributes were extracted via wavelet decomposition to reflect the distribution of sandstone–mudstone in different zones. This could help predict the vertical and horizontal distributions of different depositional sequences and the sandstones in these sequences. During the sedimentary period of the upper mudstone section of the Baxigai Formation, the beach bar sand bodies were distributed along the northeast coast. The thin sand bodies pinched out along the up-dip direction to form favorable lithologic traps, which has important significance for lithologic reservoir exploration.

The conditions and modelling of hydrocarbon accumulation in tight sandstone reservoirs: A case study from the Jurassic Shaximiao formation of western Sichuan Basin, China

Complex tight sandstone reservoirs from the Jurassic Shaximiao Formation on the eastern slope of western Sichuan Basin of China, have the characteristics of narrow channels, thin sandbodies with poor physical properties, strong reservoir heterogeneity, high water saturation, and low productivity of individual wells. The exploration and development of these complex tight sandstone gas reservoirs from the Jurassic Shaximiao Formation of the study area are faced with a huge challenge. The key factors controlling natural gas enrichment is unclear, and it is especially difficult to predict high-yield enrichment zones. Based on the data of drilling wells, cores, logs, and experiments, the methods of organic geochemistry analysis, carbon and oxygen isotope analysis and homogeneous temperature analysis of fluid inclusions are applied, to conduct the conditions and modelling of hydrocarbon accumulation in tight sandstone reservoirs from the Jurassic Shaximiao Formation of the study area. The gas source in the Jurassic Shaximiao Formation of the study area has been analysed based on the previous works. The reservoir characteristics and transportation system have been determined, high porosity and permeability of sandstones from the Js3 sand group, with an average porosity of 9.52%, and an average permeability of 0.376 × 10−3 μm2. Five evolution types of the assembly of the faults and sandbodies can be divided in the study area. The timing of hydrocarbon accumulation from the Jurassic Shaximiao Formation of the study area is determined as three periods on the basis of experienced tectonic movements. It is revealed that the hydrocarbon accumulation of the Jurassic Shaximiao Formation of the study area is mainly controlled by the high-quality reservoir, structure characteristics, fault system and evolution of the assembly of faults and sandbodies, and the pathways of channel sandbodies. The sandstones of high porosity and permeability contacted with listric faults and ramp-flat faults of low dip angle or some minor faults, located in the high point of structure, with the evolution of the assembly of faults and sandbodies of type #i and type #ii, leading to the formation of multiple traps in reservoirs laterally and an amount of natural gas in these sandstones. The channel sandbodies going through the high-potential area (i.e., syncline area) is effectively configured with the source rock faults, it is difficulty for a long-distance hydrocarbon accumulation. Based on the petroleum geological conditions and the main controlling factors of hydrocarbon accumulation, the dynamic hydrocarbon accumulation model from the Jurassic Shaximiao Formation of the study area has been established. These research conclusions can provide the theoretical foundation for predicting the high-yield enrichment zones of the study area.

Characterization of fractures in low‐permeability thin tight sandstones: A case study of Chang 6 Member, Yanchang Formation, western Ordos Basin

Structural fractures are formed when the underground rock mass deforms and exceeds its own strength limit, so they represent the complex geomechanical properties of rock. Small or core‐scale fractures usually extend less than 10 m in length, which affects the productivity of tight sandstone. Therefore, core‐scale fracture is the core factor for the prediction of reservoir sweet spots. In this paper, the research on the evolution and prediction of natural fractures in tight sandstone is investigated using the core, thin section, logging materials and numerical simulation methods. The results show that a large number of vertical and horizontal sliding fractures with shearing properties are developed in the tight sandstones of the Yanchang Formation. The particle size affects the compactible space inside the reservoir, which then affects the fracture development degree. Since the superimposed thin sand bodies are formed by the frequent lateral migration of the underwater distributary channels in the study area, therefore, the natural fractures in the thin sand bodies at the edge of river channels are relatively developed. According to statistics, the vertical extension distance of fractures is usually less than 2 m. Meanwhile, the fractured zones are mainly located in the cumulative sand body thickness range of 3 ~ 10 m. Moreover, the fractured zones are generally located in the high part of the structure and its wings. Regional structure and thin sand body distribution jointly affect the evolution of fractures in tight sandstones. Through this study, we found that fractures are more developed in thin sand bodies, and the controlling factors include lithology, sedimentary microfacies, sand thickness and local structure. The comprehensive evaluation of fractures in tight sandstones with high accuracy from 1D to 3D was achieved using core observation, logging interpretation, and three‐dimensional (3D) fracture modelling.

Research on infill adjustment method for XX narrow and thin sand body oilfield

The sedimentation of XX oilfield is mainly composed of underwater distributary channel sedimentation, and the sand body has the characteristics of “narrow, thin, and scattered”. Although basic well network development, primary and local secondary infill, edge expansion adjustment, and corresponding injection production relationship adjustments have been carried out, there are still problems in current development, such as poor well network adaptability, low utilization degree of thin and poor layers, fast production decline rate, long shut-in wells, and many inefficient wells. In order to explore the potential of infill adjustment in narrow and thin sand body oilfields and further improve oilfield recovery efficiency, well pattern infill adjustment work has been carried out, achieving good results. A supporting infill adjustment technology has been formed, which includes “well seismic joint fine reservoir prediction, multi-disciplinary research on remaining oil quantification, multi-parameter evaluation of infill well location optimization, and multi information fusion perforation layer optimization”, effectively improving the development effect.

Frequency information extraction based on time-frequency ridges for characterizing thin sand bodies

Abstract Time-frequency analysis (TFA) is a widely used reservoir prediction technology. During the identification of sand bodies using TFA, abnormally high values in the high-frequency portion of the spectrum usually indicate the presence of thin sand bodies. However, owing to the complexity of the depositional environment, the spatial distribution of thin sand bodies is often variable, and multiple phases of sand bodies—superimposed on each other—can occur with uneven thicknesses. A frequency information extraction technique based on time-frequency ridges (TFRs) is proposed in this study to identify stable TFRs in the time-frequency spectrum of a rearranged smooth pseudo-Wigner–Ville distribution with high energy aggregation, as well as to extract the main- and high-frequency energy contents relative to them. To enhance the ability of these energy components to detect thin sand bodies, a frequency-energy weighting factor is computed. By performing the aforementioned steps, information about each frequency band can be obtained and a comprehensive depiction of sand bodies with different thicknesses achieved. It is concluded that by using the proposed method thin sand bodies such as small riverbeds can be effectively characterized using seismic data.

Seismic-Geological Integrated Study on Sedimentary Evolution and Peat Accumulation Regularity of the Shanxi Formation in Xinjing Mining Area, Qinshui Basin

Accurate identification of the lithofacies and sedimentary facies of coal-bearing series is significant in the study of peat accumulation, coal thickness variation and coal-measured unconventional gas. This research integrated core, logging and 3D seismic data to conduct a comprehensive seismic–geological study on the sedimentary evolution characteristics and peat accumulation regularity of the Shanxi Formation in the Xinjing mining area of the Qinshui Basin. Firstly, the high-resolution sequence interface was identified, and the isochronous stratigraphic framework of the coal-bearing series was constructed. Then, the temporal and spatial evolution of sedimentary filling and sedimentary facies was dynamically analyzed using waveform clustering, phase rotation, stratal slice and frequency–division amplitude fusion methods. The results show that the Shanxi Formation in the study area can be divided into one third-order sequence and two fourth-order sequences. It developed a river-dominated deltaic system, mainly with delta plain deposits, and underwent a constructive–abandoned–constructive development stage. The locally distributed No. 6 coal seam was formed in a backswamp environment with distribution constrained by the distributary channels. The delta was abandoned at the later stage of the SS1 sequence, and the peat accumulation rate was balanced with the growth rate of the accommodation, forming a large-area distributed No. 3 thick coal seam. During the formation of the SS2 sequence, the No. 3 coal seam was locally thinned by epigenetic erosion of the river, and the thin coal belt caused by erosion is controlled by the location of the distributary channels and their extension direction. This study can provide a reference for the research on the distribution of thin sand bodies, sedimentary evolution and peat accumulation regularity in the coal-bearing series under the marine–continental transitional environment.

Fine Logging Evaluation of Fractures in Continental Tight Oil Sandstone Reservoirs of Yanchang Formation in the Ordos Basin

Fractures are the main seepage channels in tight reservoirs, and they affect the distribution of high-quality reservoirs and the enrichment of hydrocarbons. Fine logging identification of fractures in the strongly heterogeneous continental tight oil reservoirs of the Upper Triassic Yanchang Formation in the Ordos Basin is a hot and difficult point in the field of petroleum geology. In this paper, taking the Yanchang Formation as an example, a fractal model was constructed to identify fractures in tight oil reservoirs using a large number of cores, conventional and micro-resistivity imaging logging data. The results show that high-angle, vertical and bedding fractures are mainly developed in the Yanchang Formation tight sandstones. There is a negative correlation between sand body thickness and fracture development degree. The fracture sensitivity parameters were used to construct a coupled fractal fracture index. The fractal model incorporates logging information from natural gamma, acoustic wave time difference, rock density, and shallow lateral resistivity. In addition, the constructed fracture fractal index realizes the functions of multi-conventional logging information fusion, which can effectively identify fracture development segments in sandstone. According to the statistics, the fracture identification rate is 83.3%. The study also found that with the increase of sandstone brittleness index, the fracture index has a “S” shape increasing trend. Therefore, the content of brittle mineral components in sandstone is an important factor affecting the development degree of natural fractures, and fractures are more likely to occur in high brittle, thin sand bodies. The highly brittle framework minerals have strong stress-supporting capacity, which can keep fractures open by resisting high overlying loads.

Use of Seismic Spectral Decomposition, Phase, and Relative Geologic Age as Attributes to Improve Quantitative Porosity Prediction in the Daqing Field, China

The high production potential of the Daqing oilfield in China is recognized for seismically thin sand bodies that usually are not resolved with conventional seismic data. The present study assesses the usefulness of applying seismic multi-attribute analysis to bandwidth extended data in resolving and making inferences about these thin layers. In thin layers, tuning can obscure relationships between seismic amplitude and rock properties. In such cases, the seismic phase varies with the layer impedance and may hence aid in reservoir characterization. A seismically derived relative geologic age may also be a useful attribute in predicting rock properties because it helps define the stratigraphic position of a layer. When utilized in multi-attribute analysis in the Daqing field, spectral decomposition amplitude, phase, and a relative geological age attribute to improved prediction of well log effective porosity from seismic data and are preferentially selected by stepwise regression. The study follows standard methodology by implementing seismic multi-attribute analysis and discusses the improvement of applying it to bandwidth extended data. This will include a combination of attributes such as relative geologic age, phase, amplitude, and the magnitude components of spectrally decomposed data.

High-resolution seismic processing technique with broadband, wide-azimuth, and high-density seismic data — A case study of thin-sand reservoirs in eastern China

Seismic processing and interpretation techniques provide important tools for oil and gas exploration in the Songliao Basin in eastern China, which is dominated by terrestrial facies. In the Songliao Basin, a large number of thin-sand reservoirs are widely distributed and they are the primary targets of potential oil and gas exploration and exploitation. An important part of exploration in the Songliao Basin is to accurately describe the distribution of these thin-sand belts and the sand-body shapes. However, the thickness of these thin-sand reservoirs is generally below the resolution of conventional seismic processing. Most reservoirs are thin interbeds of sand and mudstones with strong vertical and lateral variations. This makes it difficult to accurately predict the vertical and horizontal distribution of the thin-sand bodies using conventional seismic processing and interpretation methods. In addition, these lithologic traps are difficult to identify due to the complex controlling factors and distribution characteristics and the strong concealment. These challenges motivate us to improve the seismic data quality to help delineate thin-sand reservoirs. We have used the broadband, wide-azimuth, and high-density integrated seismic exploration technique to help delineate thin reservoirs. We first use field single-point excitation and single-point receiver acquisition to obtain seismic data with wide frequency bands, wide azimuth angles, and high folds, which contain rich geologic information. Next, we perform near-surface Q compensation, viscoelastic prestack time migration, seismic attributes, and seismic waveform indication inversion on the newly acquired seismic data. The 3D case study indicates the benefits of improving the imaging of thin-sand body and the accuracy of inversion and reservoir characterization using our method.

Quantitative evaluation of morphological characteristics of thin sand body: Taking the deltaic distributary channel sand body as an example in Shengtuo oil field of Dongying sag, east of Bohai Bay Basin

Because of the small scale of distributary channel sand body and the superposition of sand bodies in vertical and lateral direction, drilling data with 150–200 m well spacing is difficult to describe its scale, shape and connectivity characteristics effectively. It has a great restriction on the recovery of these reservoirs. Taking Sheng2 Block of Shengtuo Oilfield as an example, the architectural elements of distributary channel are quantitatively investigated by using dense-drilling well and seismic data. Based on frequency division seismic data, the boundary of distributary channel belts are described vertically and laterally, and then the scale and morphological characteristics of channel bodies in the channel belt are characterized by using local dense well pattern data. The target layer can be divided into six channel belts longitudinally. After seismic frequency demultiplication, 60–75 Hz seismic data was used to describe the distribution of channel belts. From the bottom to the top, the width and distribution range of the channel belts decrease as a whole. Channel belt thickness and its width show linear positive correlation. On the channel-belt cross section, channel stories on the dense drilling-well logging profiles are identified with reference to the profile geometry of the distributary channel. On the channel-belt cross section, the projection distance between wells is fitted to a linear correlation with the thickness variation of channel stories. The ratio of the two parameters decreases from bottom to top of the target layer as a whole. The channel shape parameters predicted by the dense drilling-well logging section are of great significance to the study of paleocurrent deposition and paleohydrological evolution. At the same time, it has guiding significance for the development and adjustment of oil and gas reservoirs.

Case study: Seismic resolution and reservoir characterization of thin sands using multiattribute analysis and bandwidth extension in the Daqing field, China

The Daqing field, located in the Songliao Basin in northeastern China, is the largest oil field in China. Most production in the Daqing field comes from seismically thin sand bodies with thicknesses between 1 and 15 m. Thus, it is not usually possible to resolve Daqing reservoirs using only conventional seismic data. We have evaluated the effectiveness of seismic multiattribute analysis of bandwidth extended data in resolving and making inferences about these thin layers. Multiattribute analysis uses statistical methods or neural networks to find relationships between well data and seismic attributes to predict some physical property of the earth. This multiattribute analysis was applied separately to conventional seismic data and seismic data that were spectrally broadened using sparse-layer inversion because this inversion method usually increases the vertical resolution of the seismic. Porosity volumes were generated using target porosity logs and conventional seismic attributes, and isofrequency volumes were obtained by spectral decomposition. The resulting resolution, statistical significance, and accuracy in the determination of layer properties were higher for the predictions made using the spectrally broadened volume.

Factors controlling the reservoir accumulation of Triassic Chang 6 Member in Jiyuan-Wuqi area, Ordos Basin, NW China

Abstract In the Triassic Yanchang Formation, Jiyuan-Wuqi area, Ordos Basin, the Chang 6 reservoir is contacted to the Chang 7 high-quality source rock, but the oil pools are unevenly distributed, and complex in oil and water distribution. Through cores observation and fracture statistics, combined with comprehensive analyses of physical property, mercury injection, logging and geochemical data, and comparisons of the sandbodies scales, reservoir physical properties, argillaceous laminae and fractures between source and reservoir in the eastern and western oil-bearing areas and in the central water producing area, it is found that the hydrocarbon accumulation patterns are different in the eastern, central and western areas, and the characteristics of hydrocarbon migration under the background of double-provenance were sorted out. The study results show that the crude oil in the eastern area has different Pr/Ph and sterane distribution from that in the western area. The oil and gas primarily migrated vertically. The high-quality source rocks and favorable source-reservoir-cap combinations lay the foundation for large-scale oil and gas accumulations. Vertically, the oil and gas enrichment is controlled by the scale of sandbody and the difference of physical properties, while on the plane, it is controlled by the connectivity of sandbodies, the argillaceous laminae between source rock and reservoir, the reservoir physical property and the fractures. The sandbodies of oil-rich zones in the eastern and western areas have large thickness, low shale content, good physical properties, weak heterogeneity, few argillaceous laminae and abundant fractures, all of which are favorable for the vertical migration and accumulation of oil and gas. In contrast, in the middle area with converging provenances, the reservoirs, composed of thin sandbodies, features rapid variation in lithology and physical properties, strong heterogeneity, poor continuity of sandbodies, abundant argillaceous laminae between source rock and reservoir, and few fractures, makes it difficult for the oil and gas to migrate vertically, and results in low oil enrichment degree ultimately. For the exploration of continental multiple-provenance tight reservoirs, not only the good-property source rocks and reservoirs, but more importantly the source-reservoir contact relationship and the effect of fractures on the hydrocarbon migration and accumulation should be considered.

Fusing multiple frequency-decomposed seismic attributes with machine learning for thickness prediction and sedimentary facies interpretation in fluvial reservoirs

Abstract Defining the boundaries, thicknesses and sedimentary facies of fluvial reservoirs (sand bodies) is critical for predicting hydrocarbon volumes, designing schemes for petroleum exploration and development and improving oil recovery. Most reservoirs contain thick and thin sand bodies at the same intervals, while the amplitude values of seismic data usually highlight sand bodies near the 1/4 wavelength for the tuning phenomena. Hence, the application of spectral decomposition to seismic attributes and the combination of multiple frequency-decomposed (spectral-decomposed) seismic attributes have gained increasing attention for the readjustment of tuning thickness to predict sand bodies of various thicknesses. However, the popular method of red-green-blue blending is a simple linear combination of three frequency-decomposed seismic attributes that qualitatively analyzes the sand thickness without well-log interpretation. This research proposes machine learning fusion as a new nonlinear method for fusing high-, middle-, and low-frequency seismic attributes. This method uses machine learning to link well-log interpretation and multiple-frequency seismic attributes for the quantitative prediction of sand thickness, which is important for development work in a mature field. Test results of the conceptual model and the real case indicate that the predicted sand thickness after fusing multiple frequency-decomposed seismic attributes is approximately in line with the actual thickness (correlations between 80 and 90%). Combined with the coherence attribute and the red-green-blue blending results, the distributions and histories of sedimentary facies are analyzed based on the predicted sand thickness and well data. The results suggest that the proposed method can effectively readjust the tuning thickness and improve the resolution of seismic interpretation. This method is a potentially effective technique to characterize the sand thickness and sedimentary facies in other fields using a similar geological setting and dataset.

A new method for clastic reservoir prediction based on numerical simulation of diagenesis: A case study of Ed1 sandstones in Bozhong depression, Bohai Bay Basin, China

The use of seismic exploration technique to provide reliable reservoir information is a conventional method. However, due to its quality and resolution reasons, it cannot satisfy the detailed research and characterization of reservoirs, especially the clastic reservoir with thin sand body. Diagenesis is a fundamental process in the development and formation of all petroleum reservoirs and is a major contributor to their ultimate physical properties. Based on numerical simulation of diagenesis, a new prediction method called geology prediction techniques is presented to simulate the evolution of the diagenetic stages, diagenetic facies and porosity of clastic reservoirs and ultimately for favorable reservoir prediction. It emphasizes the idea of dynamic quantitative research dominated by process recovery, the most important of which is the establishment of mathematical models, including mineral dissolution models, mineral cementation models and sediment compaction models using the experimental data in study area and the results of previous studies. The essence of this method is illustrated, and its effectiveness is proved using Ed1 clastic sandstones in the Bozhong depression, Bohai Bay Basin, China. At present, the reservoir is in the early diagenetic stage B (IB) and the middle diagenetic stage A1 (IIA1). The major diagenetic processes that influence the porosity of the sandstones in study area are mechanical compaction, carbonate cementation, quartz cementation, clay cementation, feldspar dissolution and carbonate dissolution. There are three types of sandstones including fine sandstone, siltstone, and argillaceous siltstone, and the variation range of primary porosity of these sandstones is from 26% to 38%. Compaction and carbonate cementation are the main reasons for porosity reduction, with porosity loss percentage by compaction (P-Com) and porosity loss percentage by cementation of carbonate (P-C-Car) being 53.1% ~ 7.8% (av. 41.9%) and 53.1% ~ 7.8% (av. 18%), respectively, while carbonate dissolution and feldspar dissolution can greatly improve reservoir physical property, with porosity increase percentage by dissolution of carbonate (P-D-Car) and porosity increase percentage by dissolution of feldspar (P-D-Fel) being 0 ~ 9.9% (av. 8.9%) and 0 ~ 27.8% (av. 9.4%), respectively. The predicted porosities match the measured porosities well. Cited as : Qian, W., Yin, T., Hou, G. A new method for clastic reservoir prediction based on numerical simulation of diagenesis: A case study of the Ed1 clastic sandstones in the Bozhong depression, Bohai Bay Basin, China. Advances in Geo-Energy Research, 2019, 3(1): 82-93, doi: 10.26804/ager.2019.01.07

Facies and porosity 3D models constrained by stochastic seismic inversion to delineate Paleocene fluvial/lacustrine reservoirs in Melut Rift Basin, Sudan

Abstract The Paleocene sandstones of the Yabus and Samma formations are the main oil reservoirs in the Melut Rift Basin of interior Sudan. In our study area, we implemented a multi-modeling approach to reveal heterogeneity and reservoir characteristics of this sandstone. It estimates acoustic impedance from seismic data using deterministic and stochastic inversion algorithms. We integrated petrophysical and geostatistical analyses of the well logs to produce facies and porosity 3D models. The study populated and evaluated three different porosity models; one from well logs only, a second from well logs constrained by inversion results, and a third from well logs constrained by inversion results and facies. Stochastic inversion reveals a significant vertical facies heterogeneity as less as two meters in Yabus Sandstone. This heterogeneity is a lithology dependent and facies distribution is structurally controlled by major faults that developed during the third rift phase. The geostatistical integration of seismic inversion, sedimentologic and stratigraphic analyses reveal lateral facies distribution in the study area. The significant correlation between facies distribution and porosity allows reliable mapping of thin sandbodies. The facies and porosity 3D models indicate vertically-stacked channels with isolated sandbodies in Yabus Sandstone. This strongly suggests a meandering origin for this sandstone. However, the thick sandbodies observed in Samma Formation might indicate a braided channel setting. The dominant claystone and mudstone facies deposited in Melut Formation indicate a shallow lacustrine setting. The reservoir quality decreases with depth from the Paleocene Yabus and Samma formations at the top towards the Cretaceous Melut Formation at the bottom. The porosity estimates support this conclusion as detected low porosity (as less as 5%) in Melut Formation with respect to higher porosity (as high as 25%) in Yabus and Samma formations. The facies and porosity 3D models enhanced our understanding in predicting the reservoir heterogeneity, quality and architecture of this sandstone.

Water Injection Study in a Block Cycle

Block reservoir sand body main front deposition within the channel sand is given priority to, less layers, the thickness of thin sand body development, small scale, more is given priority to with narrow channel sand, water cut rising too fast in the process of oilfield development, plane, small interlayer adjustment scope, difficult to control the production decline and water cut rising speed, oil use degree is high, poor development effect. Under the condition of steady water injection, it is very difficult to expand the affected volume, and most of the water in the water channel is produced by the water channelling to the ground, making the injected water use less and less. It can improve the effect of oilfield development by adopting periodic water injection and preliminary exploration of stable yield path. Cyclic water flooding is the use of the existing well pattern, through the adjustment of the pressure field, the remaining oil used up state, improve the utilization rate of injected water and controlling water cut rising speed, delay of water breakthrough time, enlarge the swept volume of injected water, improve water drive recovery factor. It is an effective way to explore the effect of water flooding in high water content period.