查看更多>>摘要：A three-dimensional (3D) continuous-discrete seepage mixed model is presented, which considers the fluid exchange and the pore pressure discontinuity at the fracture. In this model, both the fracture seepage and pore seepage are considered simultaneously. Moreover, the node sharing connection of the neighboring elements near the fracture are dynamically updated during fracture propagation. The pore pressure discontinuity and fluid exchange at the fracture can be well considered but the virtual joint element and its very large exchange coefficient do not need to be introduce. The mixed model is coupled with finite discrete element method (FDEM) to create a hydro-mechanical coupling model for simulating hydraulic fracturing. Three examples are given to verify the mixed seepage model and hydro-mechanical coupling model. Finally, a hydraulic fracturing experiment is simulated by using the coupling model. The simulation results demonstrate that the differences in in-situ stress and approach angle are the most important factors controlling the fracture propagation behavior, and the shear strength of natural fractures also affects the intersection mode.
Andre Lucas Batista de LimaTais Freitas da SilvaMarleny Blanco Gonzalez
20页
查看更多>>摘要：The Campos Basin is considered an important Brazilian petroleum province, with the most of its oils consisting in a mixture of biodegraded and non-biodegraded oils, which is related to more than one generation and migration pulse coupled with biodegradation events during successive stages of reservoir filling. Its turbidites reservoirs are also structural controlled through faults generated by halokinesis comprising the main route of oil migration from underlying source rocks. Throughout the biomarkers analyses of free hydrocarbons in oil, adsorbed, and occluded in the asphaltene structures, samples from different oilfields, and distances from the main fault responsible for its reservoirs filling, were comprehensive studied. The gas chromatography coupled mass spectrometer (GC-MS) methodology was applied. The results of biodegradation, source, and thermal maturation parameters reveals that the free and adsorbed saturated hydrocarbons are similarly altered, but differ in biodegradation degrees and pathways between oils, while occluded hydrocarbons and all fractions of aromatic compounds are well preserved. The predominance of biodegradation process over the recharge is suggested for distant samples from the main fault in each area, contributing to the local models of oil migration. The occluded hydrocarbons showed source similarities regardless of oilfield. According to thermal maturity based on unaltered aromatics compounds, the occluded hydrocarbons showed lower mature ratios than those free. This study introduces the application and limitations concerning biodegradation, source, and thermal maturation inferences from occluded hydrocarbons in asphaltenes covering Brazilian oils, in view to improve a concise geochemical tool in petroleum exploration.
查看更多>>摘要：Recent studies show that the shale gas content and storage space are influenced by connate water, while it is unclear how connate water occurs in different nanoscale pores in high and overmature shales, and research concerning the occurrence characteristics and factors controlling connate water in overmature shale gas formations is scarce. In this research, overmature lower Paleozoic shale samples from southeastern Chongqing were selected for connate water distribution and factor analysis. The results show that connate water in the lower Paleozoic shale occurs in organic matter and clay minerals, mainly occurs in clay minerals and tends to form clay-bound water in clay minerals. The effect of the connate water content (C_(IW)) on the inorganic nonmicropore (mesopore + macropore) surface area (SA) is greater than that on the organic nonmicropore SA. The C_(IW) mainly affects the micropore structure parameters of clay minerals, and the total organic carbon (TOC) content is the main factor controlling the shale micropore structure. Connate water occurs in shale micropores and non-micropores, and adsorption and filling states simultaneously exist and are distributed in <10 nm mesopores and 0.4-0.6 nm micropores; this distribution reduces the pore structure parameters of inorganic matter in shale, especially the nonmicropore SA. The effect of the C _(IW) on nonmicropore SA and micropore pore volume (PV) in inorganic minerals is significantly greater than that of organic matter. Connate water mainly occurs in inorganic mineral pores and mainly occupies the mineral nonmicropore SA. Connate water significantly reduces the inorganic pore structure parameters, while its effect on organic pores is limited.
查看更多>>摘要：To improve the pay zone exposure and avoid hazardous interbed, the wellbore trajectory is necessary to be adjusted in real-time according to the geosteering data in a long horizontal wellbore, leading to a special wavy trajectory. At present, there are few pieces of research on hole cleaning and pressure management for the wavy wellbore trajectory. Besides, there is no quantitative definition of the trajectory. In this study, a transient solids-transport model with the modified mass flux is employed to assess the risk of hole cleaning and the feasibility of pressure management of the wavy trajectory. As a new quantitative definition, the wavy wellbore trajectory has the wellbore tortuosity with periodic variations. The wavy wellbore is classified as the up-dip wellbore, the down-dip wellbore, and the complex wellbore to evaluate the influences of wellbore trajectory on the cuttings bed height and the annulus pressure compared with the conventionally horizontal and smooth wellbore. A parametric analysis of build-up rate is conducted to assess its fluence on hole cleaning and pressure management. The result indicates that the wavy wellbore displays higher risks of drilling complicacy than the conventional wellbore. The down-dip wellbore has 1.36 times the volume of cuttings bed and 1.49 times the bottom hole pressure of the horizontal wellbore. The bottom hole pressure of the up-dip wellbore is 0.49 times that of the horizontal wellbore. In comparison to a smooth wellbore, the up-dip wellbore contains 43% hazardous sections. The build-up rate has an optimal value on hole cleaning and the larger build-up rate is beneficial to manage pressure. In the simulation of a field instance in West China, excessing drag and torque, wall instability, and lost circulation exist at the same time, of which inducements are predicted by the model very well. The findings serve as a useful guideline to risk prediction and control in drilling the long horizontal wellbore with wavy intervals.
查看更多>>摘要：Depleted gas reservoir type underground gas storage is the most widely distributed gas storage in the world. Due to the complex geological conditions and frequent gas injection and production operations, it is prone to the wellbore integrity failures leading to hazards such as annular pressure. To protect the wellbore integrity and contain the escape of gas to subterranean formations or surface, a finite element model is developed to study the wellbore integrity change. This model simulates the typical gas injection and production processes of gas storage with complex geological conditions and non-uniform ground stress. A new comprehensive method considering complex well conditions was developed to simulate the wellbore integrity failure process more realistically. This model can predict the wellbore integrity failure and high-risk areas during the gas injection and production processes. The simulation results indicate that the cement shear failure sections are mainly concentrated near the upper and lower boundaries of the formation interlayer during the gas injection process, and the distribution area and ti'end of the shear failure areas are the same as the gas production process. The most common cement tensile failure sections during the gas injection process all occur on the inner side of the cement in the direction of maximum ground stress during the gas injection process. The highest effective (Von Mises) stress area of the casing is mainly concentrated in the upper and lower boundary zone of the formation interlayer during the gas injection process. And the highest Von Mises stress sections are mainly distributed in the direction of the minimum ground stress near the formation interlayer lower boundary inside the casing, which is similar to the distribution in gas production process. The first cohesive failure position and final failure distribution result of cement inner interface both appear in the depth range of the formation interlayer. The cement outer interface's first and final failure areas are all concentrated on the lower boundary of the formation interlayer and consistent with the direction of the maximum ground stress. The cement inner interface failure occurred earlier but not as significant as the outer interface failure, which occurred later but the failure range was large in this case. Practical guidelines and solutions derived from the simulation results can be useful for improved wellbore integrity protection in field applications.
查看更多>>摘要：Sand screens act as the key downhole equipment for sand control in weakly consolidated oil and gas reservoir, but always face the risk of erosion failure in sanding wells with high productivity. To develop an effective methodology to predict erosion performance in actual wells is a pressing demand of high reliability sand control. In this work, we conducted series of erosion experiments to investigate the failure mechanism and influencing factors of typical premium mesh screen with gas and liquid carrying sand. The results show that the protective shroud and the metal mesh medium show similar erosion laws under various sensitive factors. The erosion rate increases nonlinearly with fluid velocity, but increases linearly with sand particle size and concentration, and decreases linearly with erosion distance. In addition, erosion angles within 30°-60° can result in higher erosion rates than other angles. With new proposed screen structure function and eroding condition function, an integrated model for erosion rate prediction of protective shroud and metal mesh medium was developed for gas and liquid carrying sand respectively by experiment data fitting. To make it easy to use the new model to predict the erosion performance of actual wells, an index of partial inflow factor (PIF) was furtherly put forward to describe the highest inflowing velocity in the heterogeneous inflow profile caused by the heterogeneity of reservoir properties. Considering the erosion of sand particles and the protection of the screen by sand accumulation, a systematic method was proposed to simulate the erosion performance of wells with sand control screen. Using this method, the final result of whether screen erosion failure can take place at the end of early stage the well production can be predicted, which depends on the relative speeds of screen erosion and sand accumulation in the wellbore annulus. The proposed methodology of erosion performance simulation takes into account not only the characteristics of screen itself, but also the actual inflow condition of well bottom hole. The models and methods are really very easy for practical application and offer a reliable access for sand control and well completion design, and integrity evaluation of completion string in weakly consolidated reservoirs.
查看更多>>摘要：We construct an innovative static-dynamic integrated workflow capable of bridging the gap between input geological data, inherent to a lacustrine carbonate outcrop containing karst geobodies, and the description of the flow patterns and quantification of the multi-well productivity index (MWPI) for a particular well configuration in the outcrop. The workflow incorporates additional features stemming from the use of Machine Learning-based methods to mitigate lack of data in the locations away from the sections of input signals, along with the construction of new upscaling methods to assess the MWPI matrix. The ML-enhanced geostatic model hinges upon shallow surface geophysical data collected using Ground-Penetrating Radar (GPR) techniques. Furthermore, by discretizing the flow equations and adopting a flow-based upscaling method, we construct correlations between well flow rates and pressure drawdown in a typical five-spot well configuration. In this setting, we analyze the sensitivity of each well productivity with respect to heterogeneity distribution and correlations in the karst system within the outcrop. Computational simulations illustrate the ability of the integrated workflow proposed herein to improve prediction of hydraulic-connectivity between well pairs, which appear manifested in the entries of the MWPI matrix, whose magnitude aims at quantifying the effects of the karst geobodies upon geofluid production.
查看更多>>摘要：One of the procedures to measure the surface and interfacial tension (ST and IFT) is pendant drop tensiometry which has distinguished drawbacks to determine the ultra-low interfacial tension. The main drawbacks of previous pendant drop procedures were incapacitation for the drop formation at ultra-low IFT values, inability to provide a suitable photo for small needles, and drop formation with non-uniform discharges. Refer to the lack of a comprehensive method for measuring all ranges of IFT and ST from ultra-low to high values felt by considering the porous media limitation in many unique studies, such as enhanced oil recovery (EOR), and carbon capture and storage (CCS), to cover the fluid-fluid and gas-fluid interactions, improving the pendant drop method is to be crucial. In this study, a new procedure was introduced to measure the ultra-low IFT in order of 10~(-3) mN m~(-1) using different needles with an outer diameter (OD) of 31G (0.46 mm) to 34G. The needles were used in this study had OD from 34G (0.16 mm) to 14G (2.11 mm) to provide a wide range of IFT and ST values from ultra-low to high values. At last, a comprehensive table was made based on more than 450 IFT and ST results to assist the researchers in selecting the best type of needle for performing the pendant drop test according to the range of IFT and ST values by considering varied applications.
查看更多>>摘要：Background and objective: Entropy generation is a novel prospective in many thermodynamic processes and presents dynamic applications in heat polymer processing optimization. The significance of entropy generation is observed in heat exchangers, combustion, thermal systems, nuclear reactions, turbine systems, porous media and many others. In view of such thermal applications, the main objective of recent analysis is to analyze the entropy optimized analysis for dissipative flow of Darcy-Forchheimer nanofluid over a permeable medium. Flow is generated by stretching of surface. Thermal radiation and viscous dissipation are incorporated in heat expression. Boehmite (AlOOH) and silica (SiO2) are considered as nanoparticles. Here propylene glycol (C3H8O2) is considered as continuous phase fluid. Entropy features is discussed through thermodynamics second law. Methodology: Nonlinear ordinary dimensionless form is obtained through suitable dimensionless variables. The obtained dimensionless expressions are numerically solved by implementation of ND-solve method. Results: Graphical feature of entropy rate, temperature, Bejan number and velocity profile against flow variables for both Boehmite (AlOOH) and silica (SiO2) nanoparticles are discussed. Computational results of thermal transport rate and drag force versus sundry variables for Boehmite and silica nanoparticles are studied. An increment in velocity profile is seen through volume fraction. Conclusions: A reverse trend hold for entropy rate and velocity with rising values of porosity variable. An amplification in radiation correspond to augments thermal field and Bejan number. A decrement occurs in Bejan number with increasing values of Brinkman number. An improvement in drag force is noticed through volume fraction. An improvement in radiation improves the thermal transport rate. Higher estimation of radiation boosts up entropy generation.
查看更多>>摘要：Recent field reports show the uplift in oil production rate (q_o), after the shut-in period, referred to as 'flush production'. The conventional hypotheses for explaining this phenomenon are based on water-oil-rock interactions such as counter-current oil production and water-blockage reduction due to imbibition of fracturing water. Here, we hypothesize other drive mechanisms responsible for the uplift in q_o: 1) pressure buildup near matrix-fracture interface during the shut-in period, 2) increasing oil saturation (S_o) and compressibility (c_o) due to an increase in solution-gas content at higher pressures, and 3) gas expansion (solution-gas drive) during pressure drawdown after restarting the well. We analyzed the production data of two unconventional wells which were shut-in for 194 and 20 days after the primary-production period. Analysis of production data indicates that pressure buildup is the primary mechanism responsible for higher post-shut-in q_o, followed by an increase in oil relative permeability (k_(ro)). The results of our compositional simulations show that by increasing the pressure near the fracture face during the shut-in period, a fraction of the free gas is dissolved in the oil phase, leading to an increase in S_o which is considered as the primary factor for k_(ro) enhancement. Increasing cG because of increasing solution-gas content is the secondary factor that improves post-shut-in k_(ro). However, gas relative permeability (k_(rg)) drops after the shut-in period while k_(ro)increases. The reduction of gas saturation because of pressure buildup during the shut-in period and trapping of the gas phase due to hysteresis effect are the two reasons that explain k_(rg) reduction.
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