Unconventional Resources最新文献

Hydraulic fracturing plays a crucial role in the development of unconventional resources, and assessing fracture geometry is a fundamental aspect of hydraulic fracturing analysis. Among the various technologies for evaluating fracture geometry, the water percussion signal-based method has gained popularity due to its cost-effectiveness, convenience, and real-time capabilities. In this study, we present a methodology for analyzing fracture data that utilizes the water percussion effect. By leveraging the impact of fractures on water percussion pressure attenuation, we propose an inverse calculation approach to determine fracture geometry. Firstly, we introduce the RCI (Reservoir-Completion-Interaction) circuit model, which effectively addresses the bottom hole fracture boundary and simulates the variation of water percussion pressure in the wellbore. Secondly, the simulation results are utilized in an iterative process to determine the RCI values, which are then utilized for the inversion calculation of fracture geometry. Finally, we apply this method to a field case and compare the simulation results with microseismic monitoring data. A larger resistance (R) value indicates a smaller fracture volume, while the (C) value can be used to monitor any poorly performing stages of the fracturing simulation process. The (I) value primarily affects the parameter calculation of the fracture size, especially the fracture width. The results of the field application show that the accuracy rate exceeding 80%, validating the reliability of the model and providing a valuable reference for field fracturing data analysis.

The investigation of seismic wave propagation across discontinuous rock masses is of great importance for solving earthquake engineering problems. Although the parameters affecting the propagation of wave on the structural surface have been known to some extent, the influence of cohesion, inclination, and stiffness on the propagation of wave when passing through structural plane still needs further study. In the study of the incident wave simulation, we implemented FLAC^3D to build the model with interface to measure the energy loss due to different parameters in the interface. The effect of cohesion, normal and shear stiffness, and dipping angle on characteristics of energy dissipation were investigated. Numerical results indicated that the cohesion as the adhesion of the material is playing an important role in energy dissipation. The normal and shear stiffness is not as obvious as what cohesion does, especially when they are at very low value. In addition, an increase in angle will bring about a decrease in the transmission coefficient and a decrease followed by an increase in the reflection coefficient.

Hot Dry Rock (HDR) is a renewable energy source that has garnered attention due to its abundant reserves, widespread distribution, and consistent energy supply. However, the injection of cold water during the drilling and production process of HDR can alter the temperature of the rock in the HDR reservoir, leading to variations in its physical and mechanical properties near the wellbore. These changes can impact the stability and safety of the HDR wellbore. This study investigated the alterations in the physical and mechanical properties of HDR under different temperature conditions. The results revealed that there were negligible changes in the physical and mechanical properties when the temperature rose from 25 °C to 400 °C. However, noticeable changes occurred as the temperature increased from 400 °C to 800 °C, establishing 400 °C as the threshold for physical and mechanical property variations in the granite. Building upon these experimental findings, a segmented wellbore instability model was developed and validated. The model demonstrated that an increased temperature difference between the drilling fluid and the borehole corresponded to an expanded range of borehole failure. Furthermore, higher wellbore temperatures led to more pronounced disparities between the maximum and minimum principal stress of the borehole, rendering it more susceptible to instability. The research also uncovered that the optimal drilling position was influenced by temperature.

These research outcomes hold significant importance for understanding the mechanisms of wellbore instability in HDR with high-temperature.

H₂ is clean energy and an important component of natural gas. Moreover, it plays an irreplaceable role in improving the hydrocarbon generation rate of organic matter and activating ancient source rocks to generate hydrocarbon in Fischer-Tropsch (FT) synthesis and catalytic hydrogenation. Compared with hydrocarbon reservoir system, a complete hydrogen (H₂) accumulation system consists of H₂ source，reservoirs and seal. In nature, the four main sources of H₂ are hydrolysis, organic matter degradation, the decomposition of substances such as methane and ammonia, and deep mantle degassing. Because the complex tectonic activities, the H₂ produced in a geological environment is generally a mixture of various sources. Compared with the genetic mechanisms of H₂, the migration and preservation of H₂, especially the H₂ trapping, are rarely studied. A necessary condition for large-scale H₂ accumulation is that the speed of H₂ charge is much faster than diffusion loss. Dense cap rock and continuous H₂ supply are favorable for H₂ accumulation. Moreover, H₂O in the cap rock pores may provide favorable conditions for short-term H₂ accumulation.

Complex lithofacies of Lucaogou Formation in Jimusar Sag promote strong heterogeneity of oil distribution in fine grained sedimentary rocks. It is of great significance to define the formation mechanism of fine-grained sedimentary rocks for favorable reservoir prediction and exploration target selection in Jimusar Sag. Based on detailed petrographic characterization, in-situ geochemical parameter testing, and high-resolution cycle analysis, sedimentary cycles on the micron to meter scales were successfully identified in Lucaogou Formation from Jimusar Sag. Precession-forced paleo-environmental evolution mainly induces the deposition of meter-scale sedimentary cycles. In the period of low precession, the paleo-environment is cold and dry, the lake level falls. Silt-grained particles advance toward the center of the lake basin carried by gravity current, thus siliciclastic sediments are mainly deposited. In the period of high precession, the climate is warm and humid, the lake level rises. The inputs of siliciclastic sediments are limited and the temperature increases, which are conductive to the carbonate deposition. On this basis, high-frequency paleo-environmental evolution caused by solar activity (70–110yr cycle) further induces the formation of sedimentary cycles on micron-centimeter scale. When the precession is low, the rise and fall of lake level controlled by solar activity is contribute to the deposition of tuff-rich lamina and silt-grained felsic lamina, respectively. The period of high precession is under the background of overall high lake-level, the rise and fall of lake level, along with fall and rise of temperature, controlled by solar activity finally induce the deposition of tuff-rich lamina and carbonate lamina, respectively. The development of multi-scale sedimentary cycles controlled by Milankovitch cycle and solar activity cycle have important implications for shale oil enrichment. The fine-grained sediments deposited during the period of low precession and intense solar activity dominate feldspar dissolution pores and intergranular pores, which are favorable for shale oil enrichment.

The Central Paleo-Uplift is a key target for exploration in the deep layers of the Songliao Basin. Our study focused on the systematic analysis of the forming conditions and accumulation patterns of bedrock reservoirs. We conducted this analysis using data such as gas composition, isotopes, slices, and CT scans, while also considering factors such as source rock, hydrocarbon supply window, and transport channels. By analyzing these factors, we were able to gain insights into the geological processes that led to the formation of these reservoirs. Our findings reveal that the gas in the Central Paleo-Uplift is primarily coal-formed and highly mature. These gases originate from two main sources - the Xujiaweizi Fault Depression as the primary source, and the Gulong Fault Depression as the secondary source. We identified two types of gas reservoirs in the area, namely weathering reservoirs and inside bedrock reservoirs. The weathering reservoirs primarily contain gas trapped in erosion pores and fractures, while the inside bedrock reservoirs mainly contain gas in fractures. The Central Paleo-Uplift area is surrounded by favorable source rocks, with greater hydrocarbon supply windows on the east side compared to the west. The efficient transport channels have facilitated the accumulation of gas, while the presence of a steady mudstone cap has been advantageous for the preservation of gas reservoirs. The region contains various traps that are favorable for gas accumulation, with higher concentrations found at elevated positions. Our study identified three distinct accumulation patterns in the north, middle, and south regions of the Central Paleo-Uplift. The Wangjiatun Bulge, Changde Bulge, and Zhaozhou Bulge are particularly promising areas for exploration in this region.

The lack of seismic data and special log data on the Chang 7 Member of the Yanchang Formation in Block X of the Ordos Basin poses a major challenge to the study of the development characteristics and identification of fractures that greatly influence on-site production. To overcome this obstacle, this study determined the macroscopic characteristics of fractures in the study area based on field outcrop profiles and indoor core observations. The results are as follows: (1) Fractures in the study area are dominated by regional fractures in weakly deformed structural areas, with three sets of fractures mainly occurring. Core observations show that fractures in the study area have high dip angles, small extensions, and small openings; (2) The vertical extended lengths of these fractures are significantly controlled by rock mechanical layers; (3) Fractures show three types of extended morphologies when meeting weak planes. Vertically, there is an exponential correlation between the sand body thickness and the fracture linear density. The argillaceous shale thickness has a logarithmic relationship to the fracture linear density when it is < 1 m and has an exponential relationship to the latter otherwise. The planar distribution of fractures is significantly affected by layer thickness and rock mechanical properties. Given the stable occurrence, high dip angles, and small extensions of regional fractures, this study highlighted the abnormal increase or decrease in log curve values of fracture segments by calculating the extrema of log curves. The purpose is to identify the locations and quantity of fractures using conventional log curves in the case of limited drilling data. This log curve-based extremum method enjoys a high resolution. For both coring and non-coring wells in the study area, there is a positive correlation between their fracture linear density determined based on the production segment thickness of vertical wells and their daily liquid yield in the first week of well test and pilot production. This result indicates that the method for identifying natural fractures proposed in this study is highly reliable. Moreover, this study provides key parameter controls for predicting the three-dimensional distribution of fractures. The understanding of the fracture spatial distribution is also a key external factor that affects the design and construction of horizontal well fracturing.

The study of gas hydrate researched by the ice powder method is helpful for us to understand the storage, separation, transportation and transformation of gas on the solid surface. In this work, the change regulation has been studied that temperature, pressure, hydrate saturation, and conversion rate in the formation process of methane-ethylene mixed hydrate, which exploring the internal action mode of the methane-ethylene mixed hydrate. The experimental results show that under the condition of −4.0 °C and 4 MPa, the conversion rates of methane, methane-ethylene (with mole ratios 2, 1, and 0.5), and ethylene hydrate are 5.30%, 11.95%, 16.57%, 19.93%, and 26.84%, respectively. And more, the conversion efficiencies of hydrate are 0.36, 0.81, 0.96, 1.58, and 6.58, respectively. The above data show that with the increase of ethylene content, the formation of hydrate is easier, which proves that ethylene can promote the formation efficiency of methane hydrate. These results have reference value for understanding the formation of natural gas hydrates, so as to promote the development and application of gas hydrate.

In-situ stress orientation is a key parameter in studying oil and gas migration and accumulation, analyzing the stability of borehole wall during drilling, carrying out horizontal well design, fracturing reconstruction and well pattern layout in water injection development. Accurately predicting the in-situ stress orientation of reservoirs is of utmost importance for oil and gas exploration and development. It is the most effective and commonly used method to evaluate the in-situ orientation by using the induced fracture and breakout fracture of imaging logging data. However, in cases where effective induced fracture or breakout fracture cannot be formed during drilling, the in-situ orientation cannot be evaluated by imaging data alone. Taking the shale reservoir of Longmaxi Formation in Yongchuan area as an example, this paper presents a novel method for evaluating in-situ orientation. Firstly, the in-situ orientation is determined relative to the core sample marker line through the wave velocity anisotropy experiment. Secondly, the core sample is rotated to obtain an unfolded image of the core surface. The orientation of the core marker line in the electrical imaging is then determined by comparing the core image with the electrical imaging logging image. By doing so, the true orientation of the core can be obtained. This method aligns well with the in-situ stress orientation determined through induced fracture evaluation, addressing the limitation of electrical imaging data in evaluating in-situ stress orientation in plastic strata.