Stratum Thickness Research Articles

Multiscale Characterization of Fractures and Analysis of Key Controlling Factors for Fracture Development in Tight Sandstone Reservoirs of the Yanchang Formation, SW Ordos Basin, China

Tight sandstone reservoirs, despite their low porosity and permeability, present considerable exploration potential as unconventional hydrocarbon resources. Natural fractures play a crucial role in hydrocarbon migration, accumulation, and present engineering challenges such as late-stage reformation in these reservoirs. This study examines fractures in the seventh member of the Triassic Yanchang Formation’s tight sandstone within the Ordos Basin using a range of methods, including field outcrops, core samples, imaging and conventional logging, thin sections, and scanning electron microscopy. The study clarifies the characteristics of fracture development and evaluates the relationship between dynamic and static rock mechanics parameters, including the calculation of the brittleness index. Primary factors influencing fracture development were quantitatively assessed through a combination of outcrop, core, and mechanical test data. Findings reveal that high-angle structural fractures are predominant, with some bedding and diagenetic fractures also present. Acoustic, spontaneous potential, and caliper logging, in conjunction with imaging data, enabled the development of a comprehensive probabilistic index for fracture identification, which produced favorable results. The analysis identifies four key factors influencing fracture development: stratum thickness, brittleness index, lithology, and rock mechanical stratigraphy. Among these factors, stratum thickness is negatively correlated with fracture development. Conversely, the brittleness index positively correlates with fracture development and significantly influences fracture length, aperture, and linear density. Fractures are most prevalent in siltstone and fine sandstone, with minimal development in mudstone. Different rock mechanics layer types also impact fracture development. These insights into fracture characteristics and controlling factors are anticipated to enhance exploration efforts and contribute to the study of similar unconventional reservoirs.

Sequence Stratigraphic Analysis of the Volcanic Rock–Evaporite–Clastic Rock Symbiotic Zone in the Fourth Member of the Shahejie Formation in the South of Laizhou Bay

Laizhou Bay Sag is a typical continental rift lake basin, which is affected by strike–slip activity, salt rock activity, volcanic activity, and paleoclimate change in the Tanlu fault zone, where three major lithologies—volcanic rock, clastic rock, and evaporite—mainly develop. In order to determine the sequence correspondence between the different lithologies in the study area based on drilling, logging data, and seismic data, it is determined that the fourth member of the Shahejie Formation in the southern Laizhou Bay mainly develops three types of sequences: clastic rock type sequences, salt lake type sequences, and volcanic rock/clastic rock type sequences. Two second-order sequence boundaries (SBs3L, SBs4L) and one third-order sequence boundary (SBs4U) were identified, and the principle of three divisions of system tracts (LST, TST, HST) and sedimentary processes in different types of sequences were determined by analyzing the stacking patterns of different sequences. Compared with the previous research results, this study provides a more detailed analysis of the sequence boundary definition of different blocks and different lithologic strata, and it improves the previous general sequence stratigraphic division method. Based on the study of distinct types of sequences, a unified stratigraphic framework is established in the whole zone, and the stratum thickness distribution of the fourth member of Shahejie Formation is smaller in the southwest and larger in the northeast. The study area is generally filled with pyroclastic rocks–evaporite–clastic rocks, changing from fan delta–saline lake filling to braided river delta–freshwater lake–fan delta filling from bottom to top. A sequence stratigraphic model for the comparison of steep slope–gentle slope differences is established to provide guidance for future oil and gas field exploration and development.

Study of a high-precision complex 3D geological modelling method based on a fine KNN and kriging coupling algorithm: a case study for Jiangsu, China

A high-precision, complex, three-dimensional (3D) geological model can directly express the attributes of stratum thickness, geological structure, lithology and spatial form, which can provide a reliable basis for the development and utilization of underground space and planning decisions. However, it is difficult to perform accurate modelling due to the lack of basic data. As such, this paper proposes coupling a machine learning algorithm (K-nearest neighbour (KNN)) with the kriging algorithm to construct the topological relationship between the Delaunay triangle and the Thiessen polygon in order to perform the simulation and prediction of virtual drilling. Based on KNN, support vector machine (SVM) and neural network algorithms as well as the virtual borehole encryption data, data standardization processing and analysis are carried out. Through model verification, algorithm optimization is realized, and the optimal modelling method is explored. The results show that the fine KNN algorithm improved by Bayesian optimization can effectively improve the modelling accuracy through 0.1-m encryption, standardization processing and 5-fold cross-validation. Stratum modelling combined with the fine KNN and kriging algorithms can obtain a more accurate modelling without adding virtual boreholes. The improved levels of upper and lower hybrid modelling with an appropriate number of profile boreholes can also effectively optimize model accuracy. Both modelling accuracy and efficiency can be significantly improved by using Delaunay triangles and Thiessen polygons with virtual boreholes. Stratum modelling can effectively express the geological pinch-out in areas with adequate degrees of stratification, and hybrid modelling performs well in irregular geological bodies such as karsts and lenses.

Optimizing Layer Thickness and Width for Fused Filament Fabrication of Polyvinyl Alcohol in Three-Dimensional Printing and Support Structures

Polyvinyl Alcohol (PVA) is frequently applied as a support material in 3D printing, especially in the crafting of intricate designs and projecting elements. It functions as a water-soluble filament, often paired with materials like ABS or PLA. PVA serves as a momentary scaffold, supporting the jutting segments of a 3D model throughout the printing process. Subsequent to printing, the primary component can be effortlessly isolated by dissolving the PVA support using water. PVA, being a pliable and eco-friendly polymer, is susceptible to moisture. Its aqueous solubility renders it a prime selection for bolstering 3D print structures. In this investigation, equivalent-sized samples were 3D printed utilizing an Ultimaker 3D printer to assess the potency of PVA-generated specimens. Tensile examinations were executed on each sample employing a testing apparatus. The durability of the specimens was notably impacted by the input parameters, specifically the stratum width and stratum thickness. Strength dwindled as stratum width increased, whereas it rose with augmented stratum thickness. A few specimens with heightened stratum width and compromised quality displayed subpar performance during the tensile assessment. The findings unveiled a peak tensile strength of 17.515 MPa and a maximum load of 1600 N. Attaining an optimal degree of material utilization led to a decrease in filament consumption by 8.87 g, all the while upholding a MTS (maximum tensile strength) of 10.078 MPa.

Sedimentary Facies Types and Their Control of Reservoirs in the Lower Jurassic Lacustrine Facies Shale of the Lianggaoshan Formation, Northeastern Sichuan Basin, China

In recent years, new breakthroughs have been made in the field of shale oil and gas exploration in the Lower Jurassic Lianggaoshan Formation in Sichuan Basin. At present, there is a lack of systematic studies on reservoir properties and sedimentary facies of the Lianggaoshan Formation shale. Therefore, in this study, taking the Lianggaoshan Formation in Sichuan Basin as an example, the sedimentary facies types of shale reservoirs and their control over shale oil and gas are systematically studied, based on a large number of outcrops, experimental testing, logging, and seismic interpretation methods. The results show that five sedimentary microfacies are developed in the Lianggaoshan Formation in the study area, namely, semi-deep lake mud, shallow lake mud, wave-influenced shallow lake mud, delta-influenced shallow lake mud, and underwater interbranch bay microfacies. The stratum thickness of the Lianggaoshan Formation is in the range of 26–315 m, and mainly distributed in the eastern region, but rapidly thinned in the northwestern region. The sedimentary sequence framework of the Lianggaoshan Formation has been constructed. Moreover, the lithology of the Lianggaoshan Formation shale has been divided into three types, including shale, massive mudstone and silty mudstone. The brittleness index and total organic carbon (TOC) value of three types of shale show a negative correlation. Silty mudstone has the highest brittleness, while that of black shale is the lowest. For porosity and permeability, massive mudstone is better than silty mudstone, and silty mudstone is better than black shale. There are many kinds of matrix pores in the Lianggaoshan Formation shale, and the development degree of inorganic pores is higher than that of organic pores. Finally, based on the analysis of oil-bearing, pore types, physical properties and productivity, it is considered that black shale facies is the most favorable lithofacies type. The deep–semi-deep lacustrine facies belt obviously controls the shale oil enrichment of the Lianggaoshan Formation.

Triangulated irregular network-based probabilistic 3D geological modelling using Markov Chain and Monte Carlo simulation

Three-dimensional geological modelling based on triangulated irregular networks (TINs) often results in deterministic models that do not capture the uncertainty of stratigraphic attributes. This study presents a method for building a 3D TIN geological model that incorporates probability analysis and random simulation to account for this uncertainty. First, we generated the Markov chain sequence of the stratum and combined it with the correlation of boreholes to obtain the transition probability matrix of the virtual borehole. This matrix was then used to describe the probability of changes in the stratum. Second, we constructed a probabilistic model of stratum thickness and generated the stratum state of virtual boreholes through Monte Carlo simulation. Using the TIN algorithm, we built an overall probabilistic model and added validation boreholes to adjust the virtual boreholes and obtain the maximum probabilistic model of the study area. Finally, we performed a case analysis in South China to verify the modelling method, including visualisation, probability analysis and comparative analysis. Our results demonstrate that the proposed modelling method effectively visualises the stratigraphic configuration and quantifies the stratigraphic uncertainty, providing a reference for 3D geological modelling.

Impact of Underground Coal Seam Mining on Stability and Slippage of the Loess Slope

How to quantitatively characterise the impact of underground coal mining on the stability and slippage of loess slopes is a key problem in the evaluation of mining damage under loess slopes, but it is more difficult to study this problem under the impact of the particular mechanical properties and topographical features of loess slopes. In order to clarify the impact of underground coal seam mining on the stability and slippage of the loess slope, theoretical analysis, numerical simulation and physical similarity simulation experiments are used to address the problem based on the theory of slope stability and strata movement. The results show that the stability coefficient of a mining slope (Kms) is introduced to quantitatively characterise the stability of a mining loess slope, and to measure the degree of landslide risk. Due to the superposition of slope movement caused by mining subsidence and slope sliding tendency, the slope is more unstable when mining along the slope than when mining against the slope. The slope angle and slope height are the most important factors influencing the Kms. The ratio of rock stratum thickness to mining height and the ratio of rock stratum thickness to soil stratum thickness are positively correlated with Kms, and the correlation is relatively strong. The range of variation of the volume weight, internal friction angle and cohesion of the loess is small, and the influence on Kms is relatively weak. Probability integral theory is used to construct the relationship between stability and slippage of mining loess slopes. Taking the mining of a working face under the loess slope of Ningtiaota Coal Mine (China) as an example, the predicted results of the slope movement and deformation theory are in good agreement with the similar simulation test results, reaching 93.57~97.97%.

High-quality sandstone reservoir evaluation and prediction in a half-graben rift sag under the influence of igneous intrusions, Songliao Basin, Northeast China

Tight sandstone reservoirs of continental lake basins are one of the most important types of unconventional hydrocarbon resources. The first member of the Yingcheng Formation (k1y1) in Baojia Sag, Songliao basin, is an important tight sandstone reservoir and also a region rich in hydrocarbon. However, volcanic rock intrusions increase the stratum thickness and change the characteristics of the reservoirs, thus making the distribution of high-quality reservoirs more difficult to predict. Therefore, according to the identification of sequence boundaries, the five 4th-order sequences of k1y1 in Baojia sag are divided, into SQ1–SQ5, which are mainly dominated by lacustrine and fan-delta depositional systems. The stratigraphic characteristics in the study area were affected by two stages of volcanic activity. In the first stage, a large area of tuff was developed in SQ5. In the second stage, sheets of intrusive rocks were formed in SQ1–SQ4. Through the identification of cast thin sections and Scanning Electron Microscopy (SEM) data, the types of reservoir micro-pores mainly develop primary pores, microfractures, intergranular, and intragranular dissolved pores. Given the complex strata under the interference of volcanic rocks, it is considered that sandstone with a 10–40% argillaceous content is a high-quality reservoir. The results showed that under the background of episodic tectonic activities, humid paleoclimate, and sufficient paleoprovenance, large-area fan-deltas of SQ2 and SQ4 are developed in both steep slope and gentle slope zones. Compared with SQ1 and SQ3, small-scale fan-deltas are formed under the background of a stable structure and arid paleoclimate. The reservoir quality gradually improved from SQ1 to SQ4, this is mainly due to the progressive reduction of reservoir argillaceous content, the gradual reduction of compaction, and the gradual enhancement of dissolution, resulting in the expansion of pore throats to improve pore connectivity. Geostatistical inversion based on argillaceous content was proven to be more effective than wave impedance inversion as it distinguishes lithology and predicts high-quality reservoirs disturbed by volcanic rocks. Comprehensive analyses show that the sandstone of SQ3 and SQ4 with a 10–40% argillaceous content is the highest quality of reservoirs, which interact with lacustrine source rocks and easily form “self-generated and self-stored” and “the lower-generation and upper-storage” patterns of hydrocarbon reservoirs. The prediction method and distribution law of high-quality reservoirs under the influence of volcanoes can provide guidance for hydrocarbon exploration and development.

Three-dimensional modeling of loose layers based on stratum development law

Abstract Loose layers are the locus of human activities. The high-quality 3D modeling of loose layers has essential research significance and applicability in engineering geology, hydraulic and hydroelectric engineering, and urban underground space design. To address the shortcomings of traditional 3D loose-layer modeling based on borehole data, such as the lack of bedrock surface constraints, simple strata pinch-out processing, and the higher fitting error of the strata surface, a 3D loose-layer modeling method based on the stratum development law is proposed. The method mainly uses three different virtual boreholes, bedrock-boundary virtual boreholes, pinch-out virtual boreholes, and densified virtual boreholes, to control the stratigraphic distribution. Case studies demonstrate the effectiveness of this 3D loose-layer modeling method in the Qinhuai District of Nanjing and Hangkonggang District of Zhengzhou. Compared to the previous methods that interpolated stratigraphic surfaces with elevation information, the method proposed in this article interpolates the stratum thickness based on stacking, which could improve the interpolation accuracy. In the area where the loose layers and exposed bedrock are alternately distributed, stratigraphic thickness errors’ mean and standard deviation decreased by 2.11 and 2.13 m. In the pure loose-layer area, they dropped by 0.96 and 0.33 m. In addition, the proposed approach allows us to infer the different stratigraphic distribution patterns accurately and complete 3D loose-layer model construction with higher accuracy and a good visualization effect.

Intelligent Generation of Cross Sections Using a Conditional Generative Adversarial Network and Application to Regional 3D Geological Modeling

The cross section is the basic data for building 3D geological models. It is inefficient to draw a large number of cross sections to build an accurate model. This paper reports the use of multi-source and heterogeneous geological data, such as geological maps, gravity and aeromagnetic data, by a conditional generative adversarial network (CGAN) and implements an intelligent generation method of cross sections to overcome the problem of inefficient modeling data based on CGAN. Intelligent generation of cross sections and 3D geological modeling are carried out in three different areas in Liaoning Province. The results show that: (a) the accuracy of the proposed method is higher than the GAN and Variational AutoEncoder (VAE) models, achieving 87%, 45% and 68%, respectively; (b) the 3D geological model constructed by the generated cross sections in our study is consistent with manual creation in terms of stratum continuity and thickness. This study suggests that the proposed method is significant for surmounting the difficulty in data processing involved in regional 3D geological modeling.

Geochemistry and heterogeneous accumulation of organic matter in lacustrine basins: A case study of the Eocene Liushagang Formation in the Fushan Depression, South China Sea

Determining the spatial distributions of organic-rich mudstones in hydrocarbon-bearing lacustrine basins is crucial for targeting exploration wells and discovering commercially viable petroleum accumulations. However, the strong heterogeneity of sedimentary systems and organic matter (OM) input and accumulations make it difficult to identify OM-rich mudstones in lacustrine deposits. This paper takes the Eocene Liushagang Formation, in the Fushan Depression, South China Sea, as an example to clarify the relationship between the geochemical characteristics of OM and sedimentary facies. A practical approach is proposed for predicting the spatial distribution of good-quality source rocks with high OM contents. The method used is a combination of logging-based surface fitting and the mudstone to stratum thickness ratio (M/S ratio) of different depositional systems. It was found that this approach improved TOC content prediction both vertically and laterally. The results suggest that semi-deep lacustrine mudstones with predominantly aquatic organism input, deposited in suboxic-anoxic saline stratified water, contain more preserved OM than other mudstones. Using this method, limited areas on the southern slope of the lower Liushagang sequence (SQls3), the central part of the Huangtong Sag in the middle Liushagang sequence (SQls2), and the northern part of the Huangtong Sag in the upper Liushagang sequence (SQls1) are determined to be the best-quality source rocks in the development area.

Assessing the Stability of Dip Slopes Based on Analyzing the Stress at a Key Point on the Sliding Surface

Dip slopes are often encountered in deep-cut canyons and engineering projects. Such slopes, when they become unstable, commonly undergo bi-planar failure, and this mode of failure tends to produce the widest-ranging effects. In this work, a novel method is proposed for assessing the potential of a slope to undergo bi-planar failure based on a stress analysis at a key point on the sliding surface, namely, the point at which the two sections of the sliding surface are connected. Discrete-element simulations are first carried out to capture the essence of the penetration process of the bi-planar sliding surface based on displacement results, plastic failure, and principal stress development. Then, the key point on the sliding surface is skillfully selected according to the sliding surface penetration process, and the characteristics of the stress changes leading to slope failure are investigated using the stress analysis method. Subsequently, considering the stress states of this key point both in the overlying rock strata and in the intact rock at the toe of the slope, a novel method is proposed for assessing the stability of the dip slope and predicting the bi-planar failure surface formed. The stability of dip slopes was subsequently analyzed using both numerical and theoretical methods. The results obtained are highly consistent, confirming the feasibility and accuracy of the proposed method. The results also show that the bi-planar failure process is progressive and that the range of the failure is mainly located in the stress reduction zone. Moreover, the critical height of the dip slope remains approximately unchanged as the stratum thickness is changed. However, it decreases as the slope angle increases and increases linearly if the strength of either the rock or joints is increased. Additionally, if the joint strength is low, the dip slope undergoes buckling failure—increasing the joint strength, however, increases the likelihood of the occurrence of bi-planar failure. The proposed method offers a novel approach to assessing and designing dip slopes.

Main Factors of Mesozoic Tectonic Deformation in the Erlian Basin, Inner Mongolia, China: Insights from Physical Modelling

Erlian Basin is a Mesozoic oil and gas-bearing basin in northeast of China. The extension rate, extension direction, and stratum thickness of this rift basin have a clear control on its shape and extension. In this study, we design three sandbox models of the Erlian Basin to represent the effects of changing these three factors. The extension rate controls the timing of secondary fault formation inside the rift basin; a high extension rate promotes faster deformation inside the rift. The extension direction controls the strike of the fault inside the rift; a greater angle between the extension direction and the normal direction of the strike of the rift favors rapid evolution of internal secondary faults. The stratum thickness represents the control of sedimentation on the rift basin; the thinner the brittle layer, the wider the rift. The simulation results also show that the extension direction is the major factor controlling tectonic deformation in the basin. Stratum thickness and extension rate are secondary controlling factors. Additionally, according to geometric and kinematic similarities between typical Mesozoic rift basins in eastern and adjacent areas of China, we suggest that southeastward extension is a possible kinematic mechanism for basin formation.

Effects of heated block comprised porous stratum and micropolar hybrid nanofluid on convective heat transfer and entropy generation in a square enclosure

AbstractA numerical study is performed to explore the effects on heat convection and entropy gthe eneration due to porous stratum and heated block in an enclosure saturated with micropolar hybrid nanofluid. Constant heat flux through half of the length of the square enclosure is centrally placed at the bottom wall and the top wall is isothermally cooled while vertical walls are insulated. The Cu‐Al2O3/water hybrid nanofluid is considered a micropolar fluid (MF) with constant physical properties. The Boussinesq approximation is implemented on the density variation and convection within the porous layer is regulated with the Darcy–Brinkman model. The governing nondimensional equations are solved with the finite difference method (FDM). Effects of various key parameters on isotherms, streamlines, local Nusselt number, and average Nusselt number are discussed numerically and analyzed through graphs. The entropy generation analysis (EGA) has been done with local and average Bejan numbers, local entropy generation, and entropy generation numbers. The heat convection from the heat flux enhances with the increase in the volume fraction of the hybrid nanoparticles (), Rayleigh number (Ra), and Darcy's number (Da) while attenuating by increasing the vortex viscosity K0. The domination of the heat transfer irreversibility over the frictional irreversibility upraises with K0 and . With an increase in the porous stratum's thickness, the average value of the Bejan's number enhances, and a decline in the entropy generation number Ns.

Quantitative characterization of fracture-pore distribution and effects on production capacity of weathered volcanic crust reservoirs: Insights from volcanic gas reservoirs of the Dixi area, Junggar Basin, Western China

Igneous hydrocarbon reservoirs worldwide are of significant importance to the petroleum industry for oil and gas exploration. The Carboniferous weathered volcanic crust reservoirs of the Dinan salient in the northern Junggar Basin are major exploration targets of PetroChina. The present study analyzes the geological, well logging, and production data to formulate development and distribution methods for quantitative characterization of weathered volcanic crust fractures and examine their fracture-pore distributions. The effects of the fracture-pore distribution on the productivity of various lithologies of weathered volcanic crust reservoirs were investigated. Various volcanic lithofacies demonstrate the lithological differences in their physical properties, fracture development, and distributions due to the conspicuous variations in weathering resistance among different volcanic rock types. The present study revealed the level of physical properties of volcanic rocks, which are ranked as follows: volcanic breccia > mafic lava > tuff > felsic intrusive rock. However, the degree of fracture development ranked differently from most developed to least developed as follows: felsic intrusive rock > mafic lava > volcanic breccia > tuff. The fracture distribution was primarily controlled by lithology, rock stratum thickness, degree of weathering and leaching, along with tectonism. Compared to other rock types, felsic intrusive rock and mafic lava were more prone to fracturing owing to different petrophysical properties. Additionally, fractures typically developed in single lithological bodies with a thickness of less than 15 m and were characterized by the “single-section” developing mode. For lithological bodies of thickness greater than 15 m, fracture development was more limited, primarily concentrated at the top and bottom of the lithological body and characterized by the “bi-section” or “tri-section” developing modes. These differences can be quantitatively characterized by the fracture development thickness, fracture layer density, and fracture development thickness ratio. Moreover, the influence of the degree of fracture development on the productivity of mafic lava and felsic intrusive gas reservoirs was higher than that of the porosity; however, volcanic breccia and tuff exhibited the opposite effect. The production capacity of weathered volcanic crust reservoirs is affected by the following factors in the order of degree of fracture development > porosity > lithology > thickness of a single lithological body > distance from the top surface of the weathered crust. These quantitative characterization methods can provide valuable technical support for optimizing favorable exploration targets.

Synchrosqueezing Optimal Basic Wavelet Transform and Its Application on Sedimentary Cycle Division

Sedimentary cycle division is an important step for sequence stratigraphy analysis. For the division of sedimentary cycle using seismic data, a key issue is characterizing the changes of dominant frequencies caused by the changes of stratum thickness with high accuracy and high resolution. The synchrosqueezing transform (SST) can provide a time–frequency (TF) representation with high resolution by synchrosqueezing the TF spectrum, which helps the sedimentary cycle identification. Unfortunately, it is a hard task to choose an appropriate basic wavelet, which influences the accuracy of the SST to characterize the sedimentary cycle. To solve this issue, we construct a synchrosqueezing optimal basic wavelet transform (SOBWT) to optimally characterize the sedimentary cycle. We first propose a criterion to construct the basic wavelet of SST by deriving the dominant frequency location condition and defining the similarity coefficient condition of the basic wavelet. Then, we introduce the optimal basic wavelet (OBW) to construct the basic wavelet that satisfies the dominant frequency location condition and the similarity coefficient condition. Note that we term the SST with a basic wavelet that satisfies the dominant frequency location condition and the similarity coefficient condition as the SOBWT. Finally, we apply the proposed SOBWT to synthetic and field data to testify its validity and effectiveness and compare it with conventional SST-based methods. The application results illustrate that it is much more convenient and easier for the sedimentary cycle division based on the SOBWT results.

The Multisynchrosqueezing Optimal Basic Wavelet Transform and Applications to Sedimentary Cycle Division

The time-frequency (TF) analysis (TFA) tools are usually used to analyze the seismic reflection signals to assist the sedimentary cycle division. The high-resolution TFA results are beneficial to characterize the dominant frequency changes caused by the variations of the stratum thickness. The multisynchrosqueezing transform (MSST) is an iterative version of the synchrosqueezing transform (SST), which provides a more concentrated TF representation than the SST. So, the MSST is suitable for the sedimentary cycle characterization. However, it is a hard task to construct an appropriate basic wavelet. In this study, by combining the MSST and optimal basic wavelet (OBW), we proposed a multisynchrosqueezing OBW transform (MSOBWT) to help the sedimentary cycle division. The proposed method first defines the dominant frequency location condition (DFLC) that ensures the MSST to reassign the TF spectrum to the dominant frequencies position. Further, the OBW is introduced to construct the basic wavelet that satisfies the DFLC. Finally, the synthetic traces and field data are used to testify its effectiveness for the sedimentary cycle division.

Genetic Types and Main Control Factors of Microfractures in Tight Oil Reservoirs of Jimsar Sag

Microfractures are key for migrating and aggregating hydrocarbon source rocks and fracturing oil-gas exploitation in tight reservoirs. In this study, rock samples from the Lucaogou Formation tight reservoirs in Xinjiang, China, were studied using multidisciplinary techniques to investigate the genetic types and main control factors of microfractures. Results indicated that the Lucaogou Formation mainly developed diagenetic microfractures followed by tectonic microfractures, with slight formations of granular microfractures. These observations were used to clarify the relationship between the development of microfractures and the pore fluid content, lithology, mineral composition, and stratum thickness. A higher pore fluid content corresponded to a lower compressive strength of the rocks and a larger ring count, resulting in a higher probability of failure and microfracture formation. Tight reservoirs containing more quartz and carbonate minerals were found to develop more microfractures. Quartz grains showed fractures at the margins under stress, which increased the pore permeability of rocks. Carbonate minerals tended to form microfractures owing to corrosion. Microfracture formation mechanisms differed depending on lithology, and microfractures were found to develop most in dolomite and dolomitic siltstones and least in mudstone. Muddy rocks developed fewer tectonic fractures because they can easily absorb stress and undergo plastic deformation. Within a certain stratum thickness range, the average single-well fracture space and stratum thickness showed positive correlations. Moreover, the fracture space increased and the fracture density decreased as the stratum thickness increased. When the stratum thickness was less than 2.5 m, the fracture space increased linearly with the stratum thickness, and when the stratum thickness was greater than 2.5 m, the fracture space remained constant. This study will provide an essential scientific basis for enhancing tight oil recovery.

Tectonic development of subtle faults and exploration in mature areas in Bohai Sea, East China

Based on the theory of structural analysis, the characteristics and structural patterns of subtle faults are studied using 3D seismic data of the Bohai Sea to analyze the development process and origin of the subtle faults. A method of identifying subtle faults is proposed, forming a complete system for analyzing origins of subtle faults in the Bohai Sea. The complex strike-slip fault patterns under the strike-slip and extension stress background, diverse formation rocks, and strong neotectonic movement are the reasons for the development of subtle faults. According to the tectonic origin and development location, the subtle faults in Bohai Sea can be divided into 12 types in the three categories of strike slip dominant, extension dominant and strike slip and extension composite, and the different types of subtle faults occur in different regions of the Bohai Sea. Unreasonable variation of sedimentary stratum thickness, inherited distortion or even abrupt change of stratum occurrence, zonation of plane fault combination and the variation of oil-water system in the same structure with no-lithologic change are the important signs for identifying subtle faults in Bohai Sea. The subtle faults greatly enlarge the size of the structural trap groups, and areas with dense subtle faults are often active area of hydrocarbon migration and accumulation and favorable exploration zones, which have strong control on the hydrocarbon accumulation. The identification method for subtle faults has guided the exploration in the mature areas of Bohai Sea effectively, with a number of large and medium oil and gas fields discovered, such as Bozhong 29-6 and Penglai 20-2.

Catastrophic mechanism analysis of deformation and instability of the layered rock slope

This paper is based on engineering background in the phosphate mine called Jianlinshan belonging to the Yunnan Phosphate Chemical Group limited company. In terms of the deformation and instability characteristics of stratified steep dip rock slope, the slope instability process and intrinsic controlling factor have been analyzed by using the cusp catastrophe model. The excavation open-pit slope stability has been researched with respect to the stress state of the stratified rock slope. The results show the following conclusions. (1) The increase of strata thickness can improve the flexural rigidity of rock mass, and can effectively control the occurrence of slope collapse and buckling. The risk of destabilization of the slope can be reduced by using rock-soil anchorage technology or grading bedding. (2) When the slope rock thickness is fixed, the critical slope length decreases with the increase of the dip angle, and the higher the thickness, the more obvious the decreasing trend; When the dip angle of strata is certain, the critical slope length of the slope increases with the increase of the stratum thickness, and the increasing amplitude decreases. Meanwhile, when the dip of strata is greater than 40°, critical slope length increasing amplitude caused by the thicker thickness of strata tends to coincide. The relevant research results can provide theoretical and technical guidance and advice for the open pit transportation technology of this mining area or mining area with similar conditions.