Geofluids最新文献

This paper is aimed at introducing a method for the division of development units of thick carbonate reservoirs. This method consists of eight steps, ranked according to impact weight, each of which is independent but intrinsically linked. When there is a conflict between studies in different steps, the results of the previous step take precedence. (1) Pressure is the most important and reliable data. When the wells with an abnormal pressure gradient in the same interval account for more than 60%, further division of the reservoir is appropriate. (2) Baffles are the second most important and reliable basis. When there are continuous baffles or poor reservoirs that encounter more than 80% wells, it is appropriate to further divide reservoirs. (3) Without the two mentioned above, but with an unconformity surface or discontinuity surface between two sequences, it is appropriate to treat these two sequences as two development units. (4) Without the three mentioned above, if the permeability above and below the sequence boundary differs by 10 or more times, reservoirs above and below the sequence boundary are appropriate as distinct development units. (5) When the thickness, continuity, distribution pattern, and microstructure of two adjacent sequences are significantly different, it is appropriate to treat these two sequences as two development units. (6) If the development units are based on sequences, check for homogeneity within the stratigraphy. If depositional facies or physical property discontinuities are present, the sequence would be reconsidered for subdivision. (7) The reserves in each development unit should account for more than 20% of that of the whole reservoir. (8) When the division of the development units is complete, it needs to be examined to ensure that there is a consistent structure, fluid property, and free water level. If inconsistencies exist, then subdivision is considered. The method was successfully applied to A oilfield, Central Arabian Basin, in combination with the cores, cast thin sections, regular or special core analysis, wireline logging data from 450 wells, formation pressure from 63 wells, and more than 100 wells with a production logging test. The Mishrif reservoir was divided into four development units, in which different well patterns and well types were deployed. The improved development effect proves that the division of development units for thick bioclastic limestone reservoir is reasonable.

Hydraulic fracturing has been a common treatment to enhance well productivity, especially in tight oil and gas reservoirs. Studying the pressure response characteristics of fractured reservoir has been a hot topic due to the significant contribution of fractures to conductivity enhancement. Because of the difficulty in describing the flow problems in vertical fractured well and the lack of related literatures, a novel method to determine the bottom-hole pressure of a vertical well with multiple fractures based on Newman product method is proposed in this paper. First, the physical model and corresponding mathematical model are established. Then, the solution of bottom-hole pressure can be obtained through Laplace transformation. Sequentially, the validations of computational method and computational codes contain are presented. From the view of curve fitting and interpretation results, the calculations in this paper are in good agreement with the previous numerical results and our computation method is reliable. Next, a group of typical curves are generated to analyze the flow regimes. And a series of curves are generated to demonstrate effects of key parameters on curve shape. The results indicate that increasing the fracture wings, fracture intersection angle, and fracture length uniformity can enhance the well productivity. Lastly, a case study is exhibited to show the application of the proposed method.

Aiming at the problems of safety production cost caused by the increase of mining face width and pressure mining in Xizhuo Coal Mine in Chenghe Mining area, a mechanical model of floor plastic slip failure is established based on the theory of plastic slip line, and the difference between it and the traditional floor failure model is analyzed. The damaged contour line of the support stress and lateral support stress on the bottom plate through the advancing direction of the working face is the intersection line of a straight line and an arc line. The failure of the floor caused by lateral supporting stress is the failure of the floor again on the basis of the failure of the floor in the advancing direction of the working face, and there is a superimposed failure area. The analysis of the failure form of the stope floor by this mechanical model is closer to the engineering practice. By using “ultrasonic detection method + stress monitoring inverse analysis method,” the measured data such as disturbance failure depth and distribution law of large mining width working face were obtained. The test method used in this paper is relatively rare in the monitoring of the depth of floor disturbance failure at home and abroad. Considering that the traditional pressure water test method has disadvantages such as easy collapse hole, long period, and large error in monitoring the failure rule of deep floor rock mass, the embedded stress monitoring and reverse analysis method and ultrasonic detection method are used to successfully collect and real-time monitor the data of rock floor before, during and after mining in the lower part of wide mining face of Xizhuo Coal Mine for the first time, and several effective data are obtained, which solves the three-part “spatial-time” all-round floor disturbance and failure law field measurement which cannot be realized by traditional testing technology. By comparing the results of theoretical analysis, field measurement, and numerical simulation, the law and depth of floor disturbance failure of a 240-m wide mining face in the Chenghe mining area are obtained for the first time, which provides scientific guidance for floor water disaster induced by coal seam mining under similar conditions in the future and has an important reference role for the prevention and control of Ordovician ash water disaster in coal mining. It provides important technical parameters for the safe setting of the effective water barrier layer and the selection and timing of the grouting layer of the floor, which can bring considerable economic and social benefits. The research results have important popularization value.

This study analyzes the depositional regime and textural properties of the sediments from the Shitalakshya River in Bangladesh, enabling us to comprehend how these sediments evolved in a river environment. For this investigation, 30 representative samples were taken from the Shitalakshya River, and their textures were analyzed. The cumulative frequency curve is obtained by using semilog graph paper to plot particle size (in phi scale) against cumulative percent. The statistical parameters such as median (M_d), mode (M_o), mean (M_Z), standard deviation (σ_i), skewness (SK_i), and kurtosis (K_G) were calculated using the percentile of phi values (1%, 5%, 16%, 25%, 50%, 75%, 84%, and 95%). The cumulative curves show that the sediments are deposited through the traction population (1.90%), saltation population (75.64%), and suspension population (22.46%). The median value varies between 0.7Ø and 4.85Ø, with an average of 2.738Ø indicating coarse sand to coarse silt. The analyzed samples have unimodal, bimodal, and polymodal distribution, which indicates the sediments are carried by different tributaries and distributaries in the Sitalakshya River system. The range of 1.46Ø–4.05Ø represented by the observed mean value suggests sand with medium to extremely fine grains. Most of the sediments indicate moderate sorting, which is shown by the standard deviation (sorting), which ranges from 0.399Ø to 1.48Ø. The skewness value ranges between −0.01Ø and 0.66Ø, suggesting near symmetrical skewed, while the kurtosis value ranges from 0.54Ø to 1.87Ø, indicating the sediments are 20% leptokurtic, 20% mesokurtic, and 60% platykurtic. According to the CM plot, the Shitalakshya River is mostly deposited in the area between the rolling and suspension fields, indicating a transportation regime of saltation. The scatter plots of skewness versus sorting and graphic mean versus sorting indicate that the sediments fall within the river sand zone. The energy process discriminant functions of the sediments show that they were deposited by a fluvial process.

Terrestrial shale oil resources in China are abundant. However, its development in China is still in the early stages. And its scale of transformation and production systems is still being explored. Currently, reservoir numerical simulation on shale oil reservoirs faces two main challenges: (1) multiscale flow of matrix–microfracture–hydraulic fractures in shale oil reservoirs and (2) bidirectional coupling of reservoir–wellbore–nozzle systems. This paper proposes a self-flow model for horizontal shale wells that describes multiscale fractures and production controlled by the nozzle. The model integrates the embedded discrete fracture model (EDFM), pipe flow model, and nozzle flow model. The accuracy of the model has been validated through comparisons with other reference models and field data. Then, this study analyzes the effects of different natural fracture densities, horizontal section lengths, number of fracturing stages, and nozzle diameters on the production capacity during the self-flow period. The results indicate that reservoirs with developed natural fractures can enhance the development efficiency during the self-flow period, and appropriate horizontal section lengths and fracturing stages contribute to achieving maximum economic benefits in development. Additionally, smaller nozzle diameters lead to longer self-flow periods and higher cumulative production. The research findings of this paper can be applied to simulate the production of hydraulic fractured horizontal shale wells.

Rammed earth, a commonly used building material in ancient times, differs from natural sedimentary layers in that it is more compact. Buildings constructed from historical rammed earth sites frequently encounter the issue of rainwater erosion. Microbially induced calcium carbonate precipitation (MICP) is commonly applied to sand soil treatment, yet reports on its use for stabilizing rammed earth are scarce. This study focused on the rammed earth of the Shanhaiguan Great Wall and explored the efficacy of MICP in mitigating rain erosion through permeation tests, splash experiments, and scouring trials. The findings indicate that the forms of rain erosion damage under MICP treatment vary across different operational conditions. In laboratory experiments, as the concentration of the cementation solution increases, the amount of calcium carbonate crystals also increases. However, the permeability, splash resistance, and rain erosion resistance initially increase and then decrease. When the cementation solution concentration is 1.0 mol/L, the penetration rate is the highest, lasting 712.55 s. The splash pit rate is the lowest, at only 1.2 mm, and the soil erosion rate is the lowest, at only 4.13%. The rain erosion resistance in the field test exhibit the same trend, and the optimal concentration is 1.2 mol/L. The optimal concentration mechanism involves the aggregation of calcium carbonate crystals at suitable cementation solution concentrations, which begin to fill the soil particle pores, effectively resisting rainwater erosion. At lower concentrations of the cementation solution, calcium carbonate crystals are merely adsorbed by soil particles without blocking the pores. Due to the high compressibility of rammed earth, which results in lower porosity, a higher concentration of the cementation solution leads to rapid pore clogging by excessive calcium carbonate crystals, which accumulate on the surface to form a white crust layer. The MICP technique can effectively alleviate rainwater erosion in rammed earth, and the optimal concentration needs to be tailored to the porosity of the rammed earth. This mechanism was also validated in field scouring experiments on the Shanhaiguan Great Wall’s rammed earth.

The coring data in high water-cut oilfields indicates that the reservoir permeability will change continuously with water flooding, while the existing reservoir numerical simulation software cannot consider the time-varying phenomenon of permeability. With the enhancement of reservoir heterogeneity, the near-wellbore profile control fails to stabilize the oil production and control the water cut. The in-depth profile control has been widely used in oilfields as a new technology, and the types of profile control agents are diverse, with a complex mechanism that cannot be effectively described by the existing conventional numerical simulation software. Considering these two phenomena comprehensively, a new three-dimensional, three-phase, six-component mathematical model that can take into account the time-varying phenomenon of reservoir permeability is proposed for a new kind of in-depth profile control system, namely, the core–shell coagulation system, and an integrated numerical simulation software is developed. The mechanism of the in-depth profile control system can be perfectly demonstrated in the simulator with time-variation of permeability. The results of sensitivity analysis show that the effect is influenced by three factors: the mix slug injecting concentration, the coagulant aid slug volume, and the concentration of the suspension dispersing agent.

As an important and universal petrophysics of heavy oil reservoirs, the two-phase flow ability inside porous medium is vital for heavy oil development. Utilizing the laminar flow theory and an ideal pore structure, especially cylinder model, the function of the relative permeability of heavy oil–water with water saturation is derived by incorporating the principles of momentum conservation and the characteristics of Bingham fluids, which was modified by validated experiment. Two-phase relative permeability, considering heavy oil as non-Newtonian fluid, is the function of water saturation, pore size, oil–water viscosity ratio, and yield stress. The results of the validated experiment show that the theoretical values calculated employing the modified equation exhibit better agreement with the experimental values, particularly when the viscosities of two-phase fluid are great. The results of the modified two-phase relative permeability show a decrease in water saturation interval corresponding to the two-phase flow area and a smaller value of permeability at equal two-phase relative permeability. The oil–water viscosity ratio in the hydrophobic pores affects the water-phase relative permeability, although the magnitude of its influence diminishes as the viscosity ratio increases. The behavior of relative permeability in hydrophilic pores is the opposite of that in hydrophobic pores. This work can afford good application prospects for mobility control in multilayered reservoirs through the heterogeneous-phase-composite fluid. The saturations of the remaining oil and irreducible water also play a vital role in the prediction of permeability. The work can afford good application prospects for the flow behavior of Bingham heavy oil in pores with different types of wettability.

In order to understand the resistance loss along the way during multistage high-pressure slurry transportation, the flow state of fly ash slurry in the pipeline was simulated by Fluent software in this paper, and the effects of pipe diameter D, pipe transportation flow rate Q, and fly ash mass concentration C_w on the resistance loss along the pipeline were studied. The fly ash slurry is a non-Newtonian Bingham fluid that moves in a turbulent state in a pipeline. When simulating the flow of fly ash slurry using Fluent software, the mesh type is a mixed mesh of hexahedron and wedge shapes, and the viscous model is selected as realizable k-ε Turbulence Model, with Enhanced-Wall Function (EWF) selected as the wall function, combined with a four-layer boundary layer mesh, which can more accurately capture the details of velocity changes at the wall, thereby improving the accuracy of the model. The inlet of the model is the velocity inlet, and the outlet is the pressure outlet. The coupled algorithm is chosen as the solution method. Under these conditions, the model converges quickly and the calculation accuracy is high. The results show that the resistance loss along the pipeline decreases as a power function with the increase of pipeline diameter, and there is a polynomial relationship between the pipeline flow and the resistance loss along the pipeline, while the mass concentration of fly ash slurry changes linearly with the resistance loss along the pipeline. In addition, three friction coefficient models, namely Blasius formula, Colebrook–White equation, and Wilson–Thomas model, were selected according to the flow characteristics of fly ash slurry. Based on the Blasius formula with the smallest relative calculation error, the Blasius formula was modified by multiple linear regression analysis to improve the accuracy of the frictional resistance coefficient model and to provide help for the design and use of separate layer grouting conveying system.

Hydrothermal geochemical signatures in outcropping rock samples of the super-hot Los Humeros geothermal field were discovered by using an integrated geochemometric study of the mobility of components (major oxides) and trace elements. Chemical component and element mobilities were determined by using the Gresens–Grant equation for mass balances. A spatial distribution of component and element mobility patterns was carried out through the mineral characterization, hydrothermal alteration, and whole-rock elemental analysis. Four alteration assemblages were mainly identified: (i) argillic–silicic; (ii) argillic–sericite; (iii) advance argillic–sulphate acid (alunite or jarosite); and (iv) silicic–carbonate. A clear increasing order of mobility for major oxides such as Fe₂O₃^T, P₂O₅, K₂O, MnO, SiO₂, CaO, Al₂O₃, and MgO and trace elements such as Pb, Th, Sr, Zn, V, Rb, Cr, Cu, and Ba was inferred from hydrothermally altered rocks. The mobility of these components and trace elements showed a geochemical association with a higher contribution of Fe₂O₃^T, CaO, V, Cu, Zn, and Sr and a lower contribution of K₂O, Rb, Th, and Cr. The spatial distribution of hydrothermal signatures obtained by tracking the mobilities of major and trace elements in samples collected in a new sector of Los Humeros geothermal field is aligned with NW-SE and NE-SW fault systems. Three areas characterised by a higher permeability were identified, for the first time, from low-cost analyses of rock samples by using energy-dispersive X-ray fluorescence spectrometry. The successful application results obtained from this study provided a new integrated geochemometric method to track high permeability zones for geothermal prospection tasks.