Depositional Models of Deep-Water Gravity-Flow in Lacustrine Basin and Its Petroleum Geological Significance—A Case Study of Chang 6 Oil Group in Heshui Area, Ordos Basin, China

Gravity-flow can carry a large number of sediments and organic matters from shallow water to deep lakes with its strong transporting energy, directly or indirectly facilitating the formation of deep-water tight reservoirs and shale reservoirs. Therefore, studying the genetic types, dynamic mechanisms, and depositional models of gravity-flow deposits is essential in the exploration of unconventional petroleum in large lacustrine basins. This research studied the genetic types, dynamic mechanisms, and sedimentary models of the gravity-flow deposits of the Chang 6 oil group in the Heshui Area, Ordos Basin, China, aiming to reveal its petroleum geological significance. Core observation, microscopic thin section identification, particle size analysis, and determination of rare earth elements were carried out. As a result, three types of gravity-flow deposits are detected, namely, slide-slump, sandy debris flow, and turbidity current. A certain slope gradient in bed form is the necessary geomorphic condition for gravity flow formation, and determines its development level, distribution range, and flow transformation efficiency. Sufficient provenance lays the material foundation and determines its depositional composition and development type. Other factors include earthquakes, volcanoes, and floods, which serve as triggering forces. In addition, fragmentation, liquefaction, and fluid mixing are the main dynamic mechanisms driving flow transformation. Based on the flow type of gravity flow, particle size characteristics, gravity-flow transformation relations, development mechanism, and spatial distribution pattern, we distinguished two depositional gravity-flow models, i.e., slump turbidite body and sublacustrine fan. Re-portrait the spatial distribution of deep-water gravity flow in the study area. From the perspective of sedimentology, explain the genesis of sand bodies in the northeast and southwest. The sandy debris flow in the middle fan braided channel microfacies of the sublacustrine fan sways the development of thick massive sand bodies in the study area. Hybrid event beds formed by the fluid transformation in a slump turbidite are the potential dessert area for deep-water tight oil and gas.

Sedimentary Characteristics Analysis and Sedimentary Facies Prediction of Jurassic Strata in the Northwest Margin of Junggar Basin—Covering the W105 Well Region in the Wuerhe Area

As the northwestern area of the Junggar Basin is a key area for oil and gas exploration, the sedimentary facies of the Jurassic formations in the Wuerhe area has long been a focus of research. The target strata are Jurassic strata, including five formations: the Lower Jurassic Badaowan and Sangonghe, the Middle Jurassic Xishanyao and Toutunhe and the Upper Jurassic Qigu. Disputes over the are sedimentary facies division exist in this area. Considering the W105 well region in this area as an example, the overall sedimentary facies of single-well logging facies is analyzed and then expanded to two cross-sections and characterized. Based on previous studies, a detailed overview of the regional stratigraphy is obtained by well logs and other data. Then, two cross-sections are selected and analyzed. The single-well and continuous-well facies of 10 wells in the sections are analyzed to grasp the sand bodies’ spatial distribution. Finally, a planar contour map of the net to gross ratio is mapped to analyze the sources and the distribution of the sand bodies in each period. The sedimentary facies map is also mapped to predict the sedimentary evolution. The results show that the sedimentary facies of the Badaowan Formation in the study area was an underwater distributary channel of the fan-delta front, and the sand body spread continuously from northwest to southeast. The Sangonghe Formation entered a lake transgression period with a rising water level, at which time shore–shallow lacustrine deposits were widespread throughout the region. The period of the Xishanyao Formation entered a regression period, the northwest region was tectonically uplifted, and the central and southeastern regions facies were dominated by the fan-delta front and shallow lacustrine. During the Toutunhe Formation period, the northwest region continued to uplift and was dominated by delta plain facies. During the period of the Qigu Formation, the thickness of stratigraphic erosion reached its maximum, and the non-erosion area of the study area was mainly deposited by the fan-delta plain. Overall, the Jurassic system in the W105 well area is a fan delta–lacustrine–fan delta sedimentary system.

Sedimentary characteristics and sand body distributions in the Lower Permian He 8 member, Ordos Basin, China

The Lower Permian He 8 Member (P1h8) in the Ordos Basin is a typical producing zone of tight lithologic gas reservoirs. Analyses of sedimentary characteristics, electrofacies, and sand-body distributions of P1h8, conducted on modern fluvial deposits, outcrops, cores, and well logs, revealed that braided rivers that developed in the Lower P1h8 and Upper P1h8 are characterized by meandering river. Within these fluvial deposits, the procedure consists of analyzing high-resolution sequence stratigraphy and sedimentary dynamics defined from calibrated logging curve signatures and depositional studies. According to modern and ancient fluvial deposits, we have developed a process-based sedimentary conceptual model for interpreting and predicting the distribution and geometries of sand bodies in braided and meandering deposits. The main sand body of the braided river system was bars and channel fill deposits. The braided river sand bodies are distributed over multiple vertical superimpositions and overlapping horizontal connections. The meandering river sand bodies are mainly point-bar deposits, which are bead-shaped and exhibit scattered development in the vertical direction. This comparison indicates that there were significant differences between braided and meandering deposystems. The sand bodies in the Lower P1h8 were multidirectionally connected and primarily distributed in a stacked pattern. In contrast, the sand bodies in the Upper P1h8 were distributed in an isolated manner, and fine grains (mud and silt) were deposited between the sand bodies with poor connectivity. We interpreted the fluvial deposits that control the distributions of the sand body of the He8 Member in the eastern Sulige gas field and constructed a corresponding prediction model of a braided-meandering reservoir. This model will promote understanding of the extent of fluvial deposits and sand-body distribution of P1h8, thus elucidating hydrocarbon-bearing sand units of the Ordos Basin for future exploration.

Study on Stability of Tunnel Surrounding Rock and Precipitation Disaster Mitigation in Flowing Sand Body

Flowing sand is a special surrounding rock encountered by tunnel construction. Due to the looseness and low viscosity of the flowing sand, after excavation, the sand body is easy to flow along the open surface. In addition, the water seepage also causes tunnel instability. Considering the characteristics of water seepage, how to improve the stability of flowing sand bodies and prevent the instability of surrounding rocks has become a difficult problem. In this paper, a parametric experiment on the surrounding rock taken from the project site was carried out, and then, a numerical simulation of the flowing sand body was conducted to study the precipitation construction method and stability of the flowing sand body. Other than that, the tunnel face vacuum dewatering, vertical vacuum dewatering at the top of the tunnel, and the vacuum dewatering technology of the gravity well in poor geological section were systematically analyzed in our research. A radial vacuum enclosed precipitation process for the face of the tunnel was proposed, which effectively solved the problem concerning continuous seepage of water in the front. Through numerical simulation and field experiments, the basis for determining the precipitation parameters of the tunnel face was obtained, while aiming at the top position of the tunnel, a vertical vacuum negative pressure precipitation method of intercepting the top seepage water and the water supply behind the top of the tunnel was proposed. For the bottom of the tunnel, setting gravity wells on the side walls for the purpose of preventing seepage at the bottom was put forward. The application of these methods in the project ensured the safety of construction and improved the construction schedule. After the completion of the dewatering construction, the method of inserting plywood into the small pipe was adopted to avoid the collapse of the dry sand. Then, to solve the problem of borehole collapse in flowing sand bodies, pipe feeding was introduced, thus further enhancing the precipitation effect. Furthermore, in view of the problem that the dewatering hole in the flowing sand body is easy to collapse, resulting in the failure of 60% of the dewatering hole and the sand body is extracted from the dewatering pipe, causing the risk of the cavity at the top of the tunnel, a method of pipe following is presented to avoid the damage of geotextile caused by directly inserting the dewatering pipe and further improve the dewatering effect. All the above processes together form an omnidirectional three-dimensional negative pressure precipitation method that considers the special sand body flow and water seepage of unfavorable geology and that has been proved to enhance the stability of surrounding rock in practice.

Evaluation Method of Reservoir Heterogeneity Based on Neural Network Technology

Reservoir is the underground storage and accumulation place of oil and natural gas. The accuracy of reservoir heterogeneity evaluation has great economic value for correctly guiding the production and development of oil and natural gas. The high-order neural network method is used to comprehensively evaluate the heterogeneity of the reservoir. This method was applied to the evaluation of reservoir heterogeneity in the PK area. The results show that the heterogeneity of sandy clastic flow sand bodies is the weakest, the sandy landslide sand bodies are medium, and the turbidity current sand bodies are strongest. The evaluation method of reservoir heterogeneity based on high-order neural network technology effectively solves the problem of inconsistent conclusions of single-parameter evaluation of heterogeneity in conventional methods, and can quantitatively characterize the degree of reservoir heterogeneity.

Applied seismic attribte to study the distribution of sandstone reservoirs of D sequence, upper Oligocene sediments, CT field, Cuu Long basin

In this paper, the seismic attribute analysis methods in combination with well data were used to predict the distribution of the D sequence. A seismic attribute is any measurement of seismic data that enhances the visibility or quantification of geological elements or rock properties to determine the structure or depositional environment of sediment. The authors have selected the basic attributes, which are related to amplitude and frequency such as RAI, RMS, ARC length, Specdecom, Sweetness attribute. The attributes reflect quite accurately the changes in lithology, sedimentary facies, etc. from which will be possible to predict the distribution of the sand bodies. There are 02 large reservoirs discovered in the D sequence: the main reservoirs (D0 -D3) sands and minor reservoirs (D4 - D10). The study results show that the main reservoirs from D0 to D3 are widely distributed in the study area, especially in the western block and near the Con Son swell (except A well due to erosion process). Meanwhile, the reservoirs from D4 to D10 are of discontinuous distributions. Zones of high amplitude anomalies that are likely related to volcanic sediments in the study area are also delineated. The seismic attribute analysis reveals the possible distribution of high potential sand bodies (D2-D3) in the south-western and north-eastern parts that need further study.

Petrophysical Analysis of ‘Bright’ Field, Onshore Niger Delta

Petrophysical analysis is key to the success of any oil exploration and exploitation work and this task requires evaluation of the reservoir parameters in order to enhance accurate estimation of the volume of oil in place. This research work involves the use of suite of well logs from 4-wells to carry out the petrophysical analysis of ‘Bright’ Field Niger Delta. The approach used includes lithology identification, reservoir delineation and estimation of reservoir parameters. Two sand bodies were mapped across the entire field showing their geometry and lateral continuity, gamma ray and resistivity logs were used to delineate the reservoirs prior to correlation and relevant equations were used to estimate the reservoir parameters. The result of the petrophysical analysis showed variations in the reservoir parameters within the two correlated sand bodies with high hydrocabon saturation in sand 1 well 1 while the remaining wells within the correlated wells are water bearing. The porosity values range from 0.19 to 0.32, volume of shale from 0.15 to 0.40, water saturation from 0.20 to 0.92 for the sand bodies.

Comprehensive Analysis of the Geological and Geophysical Data in the Study of the Upper Miocene Turbidite Systems of the Nam Con Son Basin, Vietnam

The article considers the approaches to the G&G data interpretation used in the Branch Office of Gazprom International in Saint Petersburg (hereinafter referred to as "GPEPI") when studying the geology aspects of turbidite deposits. This approach is showcased on one of the Upper Miocene deposits of the Nam Con Son Basin in Vietnam, and a conclusion is drawn about the possibility of using this complex technique in the study of sand bodies of any genesis.

New approach to appraise non-structural Tyumen formation traps in the absence of high quality of data

Background. On the one hand, the focus of exploration works changes to the more difficult reserves side, which were basically accumulated in the non-structural traps of Achimov and Tyumen formations. On the other hand, there are two important questions. The first is how the volume of reserves should be estimated correctly and the second is which volume of reserves is enough for economic successfully development. Aim. The main aim is to create a new actual approach of non-structural traps appraisal is considered in the absence of high quality of seismic data which allows identify such types of traps, which allows identify such types of traps. Materials and methods. Presented at the article algorithm enables estimate resources of non-lithological traps as exemplified in Tyumen formation, which was formed during depositional changes from continental to transitional depositional environments. The algorithm consists of some steps. The first step is collection on numbers, sizes and areas potential sand bodies based on different seismic attributes from analogies data. On the next step the coefficient which shows what numbers of geological bodies can be found on the unit of area was defined. Based on these data the probability distribution function which shows what part of studied area could be covered by potential bodies was made. After these steps, the integral resource base without regard to geological chance of success (gCoS) can be estimated. In order to account for geological risks the numbers of potential traps (including also non-structural traps), which were formed by meandering rives, tidal channels and point-bars, have to be defined. As a result, the discrete mathematical distribution of expected numbers of traps was made based on analogies data. If the oil infl ow was obtained from wells which have already drilled on the studied area part of resource base transfer to reserves (without including gCoS). Results. Discussed method was applied for “blind-test” on the new studied block with 3D seismic data. The obtained results of potential sand bodies fraction is correspond to the initial distribution from analogy fields. The method can be used for resource base potential on any block where there are lithological traps, which are controlled by mainly the facies conditions instead of structural plan, and also the 3D seismic data is absent. Conclusions. The appliance of discussed method which based on the available statistical data helps improve the quality estimation of change resource base range and allows to map the new prospective areas containing reserves and resources. One more important thing is this method allows to resolve the problem of base potential estimation and as a result to put a price on asset and risk capital values needed to explore the potential areas by drilling before the key outlays in the exploration program will be invested.

Controlling Factors Analyses of Sediment Dispersal From Source-to-Sink Systems of Lacustrine Rift Basin: A Case Study From Paleogene Shahejie-Dongying Formations of Nanpu Sag, Eastern China

Tectonic activity not only shapes the basic stratigraphic framework of rift basins, but also profoundly affects the sediment dispersal in rift basins. In this study, analyses of heavy mineral assemblages in different periods demonstrate that there are three obvious tectono-sedimentary evolutionary stages (Es3–Es2, Es1–Ed2, and Ed1, respectively) in the Paleogene provenance area of Nanpu Sag, and the volume of sand bodies increases from the bottom of the Paleogene Shahejie (Es) Formation to the top of the Dongying (Ed) Formation in Nanpu Sag. Besides, this study comprehensively utilize the analyses of seismic interpretation, palynology, heavy mineral, and borehole core samples to investigate the controlling factors of sediment dispersal in the rift basin. The assemblages of heavy minerals in different periods reflect the rock composition and catchment area of different provenance areas, and their vertical differences reflect the evolution process of the provenance area and reflect the uplift-denudation process of the provenance area. The results reveal that the synergy of the evolution of tectonic activity and the adjustment of topographical evolution are the main controlling factors of sediment dispersal in Nanpu Sag, while climate change is not the main controlling factor. We conclude that an increased sediment supply rate in the long term reflects the control of tectonic activity on basin topography, rather than climate fluctuations. The differences in morphological modification result in differential sediment dispersal, which is principally related to the differential extrusion of the fault system. The catchment area and provenance distance adjustment is evidenced by the vertical changes of heavy mineral characteristics of single-well and interaction and linkage of boundary faults, and the adjustment of topography evolution. A consideration is that the interaction and linkage of boundary faults and complex subsidence history are multi-directional, and differential evolution of provenance area is universal in lacustrine rift basins, all of this highlights the adjustment of sediment pathways generated by this characteristic of rift basins and emphasizes the importance of controlling factors analyses in understanding differential sediment dispersal that presents in the rift basins. Besides, four sets of sediment dispersal patterns were delineated based on different developmental regions in the rift basin, which are fault segmental point and multi-stage fault terrace, single-stage fault terrace and axial fault valley, axial fault terrace, and paleo-terrace and axial fault valley, respectively. This study has a certain guiding significance for the prediction of the spatial distribution of sand bodies in the rift basin and the exploration of potential oil and gas targets in the rift basin.