Tightening the well spacing for unconventional tight reservoirs is an efficient technique to enhance oil and gas recoveries.Infill well-caused fracture connection between wells is widely reported in the field with sma...Tightening the well spacing for unconventional tight reservoirs is an efficient technique to enhance oil and gas recoveries.Infill well-caused fracture connection between wells is widely reported in the field with small well spacing.This will make it difficult to make formation evaluation and fracture characterization between wells compared to single well cases.In this paper,a novel production data analysis(PDA)method is proposed for fracture characterization with the consideration of interwell fracture connections after the hydraulic fracturing of the infill.The PDA method is based on a semianalytical model,in which the small-scaled fractures are treated with the concept of stimulated reservoir volume(SRV).Thus,the fracture connections between wells are classified into three types,including SRV,fractures,and both SRV and fractures.The physical model is discretized into several linear flow regions,so the mathematical model can be solved semianalytically.An integrated workflow is proposed to analyze the production data for the wellpad,and three steps are mainly included in the workflow,including PDA for the parent well before infill,PDA for the parent well after infill,and PDA for the infill well.In each step,the production performance in the early linear and bilinear flow regimes are analyzed with approximate solutions in the square and fourth root-of-time plots.Because only the relationship between unknown model parameters can be obtained with the approximate solutions,history matching to the production data in log-log plots is further used to determine each unknown parameter.The PDA method is benchmarked with a synthetic case generated by the numerical simulator tNavigator and a field case from Southwestern China.The results show that both good matches and precise parameters can be obtained with the proposed PDA method.The connected fracture number will not be sensitive in PDA when the wells are connected with high-conductive dSRV.The innovation of this paper is that a practical method is provided for PDA analysis of well groups with fracture connection,and it will be a good technique for fracture characterization and well-interference analysis for tight formations.展开更多
Severe well interference through complex fracture networks(CFNs)can be observed among multi-well pads in low permeability reservoirs.The well interference analysis between multi-fractured horizontal wells(MFHWs)is vit...Severe well interference through complex fracture networks(CFNs)can be observed among multi-well pads in low permeability reservoirs.The well interference analysis between multi-fractured horizontal wells(MFHWs)is vitally important for reservoir effective development.Well interference has been historically investigated by pressure transient analysis,while it has shown that rate transient analysis has great potential in well interference diagnosis.However,the impact of complex fracture networks(CFNs)on rate transient behavior of parent well and child well in unconventional reservoirs is still not clear.To further investigate,this paper develops an integrated approach combining pressure and rate transient analysis for well interference diagnosis considering CFNs.To perform multi-well simulation considering CFNs,non-intrusive embedded discrete fracture model approach was applied for coupling fracture with reservoir models.The impact of CFN including natural fractures and frac-hits on pressure and rate transient behavior in multi-well system was investigated.On a logelog plot,interference flow and compound linear flow are two new flow regimes caused by nearby producers.When both NFs and frac-hits are present in the reservoir,frac-hits have a greater impact on well#1 which contains frac-hits,and NFs have greater impact on well#3 which does not have frac-hits.For all well producing circumstances,it might be challenging to see divergence during pseudosteady state flow brought on by frac-hits on the logelog plot.Besides,when NFs occur,reservoir depletion becomes noticeable in comparison to frac-hits in pressure distribution.Application of this integrated approach demonstrates that it works well to characterize the well interference among different multi-fractured horizontal wells in a well pad.Better reservoir evaluation can be acquired based on the new features observed in the novel model,demonstrating the practicability of the proposed approach.The findings of this study can help for better evaluating well interference degree in multi-well systems combing PTA and RTA,which can reduce the uncertainty and improve the accuracy of the well interference analysis based on both field pressure and rate data.展开更多
Well interference has become a common phenomenon with the increasing scale of horizontal well fracturing.Recent studies on well interference in horizontal wells do not properly reflect the physical model of the postfr...Well interference has become a common phenomenon with the increasing scale of horizontal well fracturing.Recent studies on well interference in horizontal wells do not properly reflect the physical model of the postfracturing well groups and the realistic fracturing process of infill wells.Establishing the correspondence between well interference causative factors and manifestations is of great significance for infill well deployment and secondary oil recovery.In this work,we develop a numerical model that considers low velocity non-Darcy seepage inshale reservoirs to study the inter-well interferencephenomenon that occurs in theSantanghufield,andconstruct an explicit hydraulic fracture and complex natural fracture network model with an embedded discrete fracture model,focusing on the effect of fracture network morphology on well interactions.The model also considers a multi-segment wellbore model to accommodate the effect of inter-well crossflow on wellbore tubular flow.The changes in formation pressure and water saturation during fracturing are performed by controlling the injection pressure and water injection rate.The result shows that the shape of the fracture network generated by the infill well with the old well determines the subsequent fluid and oil-increasing performance of the disturbed well.The synergistic production or competitive relationship formed by fractures with different connectivity between the two wells determines the positive and negative effects of the interference.The paper also investigates the adaptation study of water injection huff and puff schemes for well groups with different connectivity,and demonstrated a potential yield increase of up to 10.85%under adaptation injection.This method of identifying well interference based on the production dynamics of affected wells and the subsequent corresponding water injection method provides valuable references for the selection of secondary oil recovery measures.展开更多
In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature...In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature of a sectorial well-factory is the deviation of the well from the minimum horizontal principal stress, resulting in hydraulic fracture deflection after the initiation, along with possible well interference (i.e., fracture hit) and fracture coalescence in the oblique wells. Four indexes describing well deflection are then proposed according to fracture morphology. Several fracturing designs, including stage arrangement, fracturing sequences, and fracturing techniques are applied to study the feasibility of the sectorial well-factory design. The results show that the “gradual” or “sparse” stage arrangement, large injection rate, and simultaneous multifracture treatment can help to optimize the fracture morphology and stimulation design. However, the subsequent stress shadowing effect usually adversely affects the fracturing of adjacent wells. With a small initial horizontal stress difference, large injection rate and staggered stage arrangement can achieve ideal stimulation performance. Our results can provide a guidance for optimizing stimulation design in unconventional well-factory while taking into account environmental protection.展开更多
Horizontal well-stimulation is the key to unconventional resource exploration and development.The development mode of the well plant helps increase the stimulated reservoir volume.Nevertheless,fracture interference be...Horizontal well-stimulation is the key to unconventional resource exploration and development.The development mode of the well plant helps increase the stimulated reservoir volume.Nevertheless,fracture interference between wells reduces the fracturing effect.Here,a 2D hydro-mechanical coupling model describing hydraulic fracture(HF)propagation is established with the extended finite element method,and the effects of several factors on HF propagation during multiple wells fracturing are analyzed.The results show that with an increase in elastic modulus,horizontal principal stress difference and injection fluid displacement,the total fracture area and the reservoir stimulation efficiency are both improved in all three fracturing technologies.After a comparison of the three technologies,the method of improved zipper fracturing is proposed,which avoids mutual interference between HFs,and the reservoir stimulation effect is improved significantly.The study provides guidance for optimizing the fracturing technology of multiple horizontal wells.展开更多
Epoxy-based nano-composites can be ideal electromagnetic interference(EMI)-shielding materials owing to their lightness,chemical inertness,and mechanical durability.However,poor conductivity and brittleness of the epo...Epoxy-based nano-composites can be ideal electromagnetic interference(EMI)-shielding materials owing to their lightness,chemical inertness,and mechanical durability.However,poor conductivity and brittleness of the epoxy resin are challenges for fast-growing portable and flexible EMI-shielding applications,such as smart wristband,medical cloth,aerospace,and military equipment.In this study,we explored hybrid nanofillers of single-walled carbon nanotubes(SWCNT)/reduced graphene oxide(rGO)as conductive inks and polyester fabrics(PFs)as a substrate for flexible EMI-shielding composites.The highest electrical conductivity and fracture toughness of the SWCNT/rGO/PF/epoxy composites were 30.2 S m^(−1)and 38.5 MPa m^(1/2),which are~270 and 65%enhancement over those of the composites without SWCNTs,respectively.Excellent mechanical durability was demonstrated by stable electrical conductivity retention during 1000 cycles of bending test.An EMI-shielding effectiveness of~41 dB in the X-band frequency of 8.2-12.4 GHz with a thickness of 0.6 mm was obtained with an EM absorption-dominant behavior over a 0.7 absorption coefficient.These results are attributed to the hierarchical architecture of the macroscale PF skeleton and nanoscale SWCNT/rGO networks,leading to superior EMI-shielding performance.We believe that this approach provides highly flexible and robust EMI-shielding composites for next-generation wearable electronic devices.展开更多
Co-primary spectrum sharing for multiple operators has been utilized to fully explore the spectrum resources and thus improve the spectrum efficiency. The inter-operator interference(IOI) problem should be seriously c...Co-primary spectrum sharing for multiple operators has been utilized to fully explore the spectrum resources and thus improve the spectrum efficiency. The inter-operator interference(IOI) problem should be seriously considered in order to achieve the mentioned target, especially under the scenario of the ultradense network(UDN) in the fifth generation(5G) wireless systems. To solve this problem, we propose an asymmetrical power levels based soft IOI coordination mechanism. The shared spectrum pool is consisted of three separated parts, where each part can be dynamically adjusted according to the minimal spectrum demand from each operator. Furthermore, different power masks are configured to different parts for each operator. The simulation results show that the proposed mechanism can improve the network spectrum efficiency significantly.展开更多
Wireless Body Area Network(WBAN) is an emerging technology to provide real-time health monitoring and ubiquitous healthcare services. In many applications, multiple wireless body area networks have to coexist in a sma...Wireless Body Area Network(WBAN) is an emerging technology to provide real-time health monitoring and ubiquitous healthcare services. In many applications, multiple wireless body area networks have to coexist in a small area, resulting in serious inter-network interference. This not only reduces network reliability that is especially important in emergency medical applications, but also consumes more power of WBANs. In this paper, an inter-network interference mitigation approach based on a power control algorithm is proposed. Power control is modeled as a non-cooperative game, in which both inter-network interference and energy efficiency of WBANs are considered. The existence and uniqueness of Nash Equilibrium in the game are proved, and an optimal scheme based on best response is proposed to find its Nash Equilibrium. By coordinating the transmission power levels among networks under interference environment, the total system throughput can be increased with minimum power consumed. The effectiveness of the proposed method has been illustrated by simulation results, where the performance of the proposed approach is evaluated in terms of overall utility and power efficiency and convergence speed.展开更多
To mitigate interference on celledge users and improve fairness of the whole system, dynamic inter-cell interference coordination(ICIC) is one of the promising solutions. However, traditional dynamic ICIC is considere...To mitigate interference on celledge users and improve fairness of the whole system, dynamic inter-cell interference coordination(ICIC) is one of the promising solutions. However, traditional dynamic ICIC is considered as an NP-hard problem and power variability further adds another dimension to this joint optimization issue, making it even more difficult to quickly reach a near-optimal solution. Therefore, we theoretically obtain the closed-form expression of the near-optimal power allocation ratio for users in adjacent cells paired in the same resource block and interfere each other, so that the total utility corresponding to α-fairness is maximized. Dynamic ICIC using this closed-form solution could improve user fairness without causing an increment of the computational complexity. Numerical results show that, compared with the schemes using identical power for different users, our method does not obviously degrade the system's average spectral efficiency.展开更多
In Orthogonal Frequency Division Multiple Access (OFDMA) systems, such as Long Term Evolution (LTE) and so on, the resources used by each user are orthogonal, and the OFDMA systems performances are mainly affected by ...In Orthogonal Frequency Division Multiple Access (OFDMA) systems, such as Long Term Evolution (LTE) and so on, the resources used by each user are orthogonal, and the OFDMA systems performances are mainly affected by the inter-cell interference. Therefore, the inter-cell interference mitigation technology becomes a hotspot. The objective of interference mitigation technologies used in OFDMA systems are to increase cell-edge throughput and average cell throughput. In this paper, the Resource Block Planning (BRBP) based scheme is proposed to mitigate the inter-cell interference and improve the cell-edge throughput. Comparison between the simulation results of BRBP and Round Robin (RR) illustrates that the enhanced performance of BRBP.展开更多
With the growing concern on data rates and resource utilization, Device-to-Device (D2D) communication has been raised in 3GPP Long-Term Evolution (LTE) networks. In order to limit severe interference, previous studies...With the growing concern on data rates and resource utilization, Device-to-Device (D2D) communication has been raised in 3GPP Long-Term Evolution (LTE) networks. In order to limit severe interference, previous studies mainly focus on intra-cell interference that between cellular links and local D2D links. In this paper, we consider both intra-cell interference and inter-cell interference between D2D and cellular links. We propose a new resource reuse algorithm that D2D users reuse the minimum interference uplink (UL) Semi-Persistent Scheduling (SPS) resources to reach the highest throughput. The simulation results show that this scheme reduces interference as well as improves throughput.展开更多
In this paper, we propose two joint transmit-receive iterative algorithms without the cooperation between different base stations based on the idea of interference alignment (IA) to improve the throughput of relay bac...In this paper, we propose two joint transmit-receive iterative algorithms without the cooperation between different base stations based on the idea of interference alignment (IA) to improve the throughput of relay backhaul links in cellular networks for the case of imperfect channel knowledge,which can be implemented with small changes to existing TD-LTE standards. Unlike the previous interference alignment algorithms' only reducing the sum interference to the other receivers at the transmitter or the sum received Multi-user interference (MUI) at the receiver, our algorithm shapes the transmission of each data stream at transmitters in order not only to minimize interference to the other users, but also to minimize the interference between different streams objected to the same user, suppressing the MUI and Multi-stream interference (MSI) at receivers. The proposed algorithm I is to maximize the SINR at receivers. But the complexity is relatively high. Algorithm II only needs linear operations and sacrifices a little performance for much lower complexity compared to the Maximize SINR iterative algorithm which needs the inversion operation of matrix. It is also proved that the algorithm converges monotonically. The simulation results show that the techniques have considerable performance gain compared with the previous algorithms. Further research about power allocation is also discussed.展开更多
With promising applications in e-health and entertainment, wireless body area networks (WBANs) have attracted the interest of both academia and industry. If WBANs are densely deployed within a small area, serious pr...With promising applications in e-health and entertainment, wireless body area networks (WBANs) have attracted the interest of both academia and industry. If WBANs are densely deployed within a small area, serious problems may arise between the WBANs. In this paper, we discuss issues related to the coexistence of WBANs and investigate the main factors that cause inter-WBAN interference. We survey inter- WBAN interference mitigation strategies and track recent research developments. We also discuss unresolved issues related to inter-WBAN interference mitigation and propose fu- ture research directions.展开更多
In this paper,we propose a novel iterative scheme for exploiting transmit diversity using parallel independent Inter-Symbol Interference (ISI) channels. In this adaptive iterative scheme,we use EXtrinsic Information T...In this paper,we propose a novel iterative scheme for exploiting transmit diversity using parallel independent Inter-Symbol Interference (ISI) channels. In this adaptive iterative scheme,we use EXtrinsic Information Transfer (EXIT) chart tool to choose appropriate iterative method from Itera-tive Combining (IC),used as parallel concatenation turbo-like scheme,and Turbo Equalization (TE),used as serial concatenation turbo-like scheme. It is show that the proposed iterative scheme provides excellent performance both analytically and through simulations without any compute complexity increase comparable to IC.展开更多
As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing (OFDM) has a high usage rate of spectrum and combats inter-symbol interference (ISI) in mul...As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing (OFDM) has a high usage rate of spectrum and combats inter-symbol interference (ISI) in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference (ICI) is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named SINR (signal-to-interference- and-noise ratio) is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair (OWCP) is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR.展开更多
The orthogonality between the subcarriers of multipleinput multiple-output orthogonal frequency division multiplexing( MIMO-OFDM) systems is destroyed due to the Doppler frequency offset,particularly in the high-speed...The orthogonality between the subcarriers of multipleinput multiple-output orthogonal frequency division multiplexing( MIMO-OFDM) systems is destroyed due to the Doppler frequency offset,particularly in the high-speed train( HST) environment,which leads to severe inter-carrier interference( ICI). Therefore,it is necessary to analyze the mechanism and influence factor of ICI in HST environment. In this paper, by using a non-stationary geometry-based stochastic model( GBSM) for MIMO HST channels, ICI is analyzed through investigating the channel coefficients and the carrier-to-interference power ratio( CIR). It is a fact that most of signal energy spreads on itself and its several neighborhood subcarriers. By investigating the amplitude of subcarriers, CIR is used to evaluate the ICI power level. The simulation results show that the biggest impact factor for the CIR is the multipath number L and the minimum impact factor K; when the train speed υR> 400 km / h,the normalized Doppler frequency offset ε > 0. 35,the CIR tends to zero,and the communication quality will be very poor at this condition. Finally,bit error rate( BER) is investigated by simulating a specific channel environment.展开更多
A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net...A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net pressure in hydraulic fracture, stage spacing, perforation parameter, horizontal stress bias and well cementation quality on the propagation geometry of multiple fractures in a tight sandstone formation were studied in detail. The specimen splitting and analogy analysis of fracturing curve patterns reveals: Multiple fractures tend to merge under the condition of high horizontal stress bias and short stage spacing with pre-existing hydraulic fractures under critical closure situation, and the propagation of subsequent fractures is possibly suppressed because of high net pressure in pre-created fractures and asymmetric distribution of fracture width. And the subsequently created fractures are situated in the induced stress decreasing zone due to long stage spacing, leading to weak stress interference, and perforation with intense density and deep penetration facilitates the decrease of initiation fracture pressure. The deflection angle of subsequent fracture and horizontal stress variation tend to be amplified under low horizontal bias with constant net pressure in fractures. The longitudinal fracture is likely to be initiated at the interface of wellbore and concrete sample with poor cementation quality. The initiation fracture pressure of the different stages increases in turn, with the largest increase of 30%. Pressure quickly declines after initiation with low propagation pressure when the transverse hydraulic fracture is formed. The pressure reduces with fluctuation after the initiation of fracture when the fracture deflects, the extension pressure is high, and the fracture formed is tortuous and narrow. There is a violently fluctuant rise of pressure with multiple peak values when longitudinal fracture created, and it is hard to distinguish the features between the initiation stage and propagation stage.展开更多
AIM:To develop a new internal fixation device for comminuted, unstable fractures of the distal femur,and to offer a guide for management of these injuries based on biomechanical studies.METHODS:Ten fresh adult femurs ...AIM:To develop a new internal fixation device for comminuted, unstable fractures of the distal femur,and to offer a guide for management of these injuries based on biomechanical studies.METHODS:Ten fresh adult femurs of cadavers.All femurs were similarly made of the models of supracondylar intercondylar fractures,then double plating with a plate in combination with a polythene plate,and the conventional sigle plating was served as the control.The biomechanic tests (compression,bending,torsion) were performed.RESULTS:The bending and torsion tests demonstrated that the double plating groups were much stronger (P< 0.01) than the single plating groups in anti bending and anti torsion.During the tests loading to failure, the double plating groups failed at a mean peak load of 11 540 N in axial compression,700 N in anterior bending 1 082 N in posterior bending,593 N in medial bending,1 010 N in lateral bending.CONCLUSION: Double plating with a plate in combination with a polythene plate is an excellent technique and design modification for severely comminuted fractures of the distal femur,which may provide a high stability and solidness so that early mobilization and weight bearing are allowed.展开更多
基金supported by the Jiangsu Province Carbon Peak Carbon Neutral Technology Innovation Project in China(BE2022034-2)the foundation of the National Natural Science Foundation of China(51974328)+2 种基金the Fundamental Research Funds for the Central Universities(2021QN1005)the Natural Science Foundation of Jiangsu Province(BK20210520)China Postdoctoral Science Foundation(2022M713372).
文摘Tightening the well spacing for unconventional tight reservoirs is an efficient technique to enhance oil and gas recoveries.Infill well-caused fracture connection between wells is widely reported in the field with small well spacing.This will make it difficult to make formation evaluation and fracture characterization between wells compared to single well cases.In this paper,a novel production data analysis(PDA)method is proposed for fracture characterization with the consideration of interwell fracture connections after the hydraulic fracturing of the infill.The PDA method is based on a semianalytical model,in which the small-scaled fractures are treated with the concept of stimulated reservoir volume(SRV).Thus,the fracture connections between wells are classified into three types,including SRV,fractures,and both SRV and fractures.The physical model is discretized into several linear flow regions,so the mathematical model can be solved semianalytically.An integrated workflow is proposed to analyze the production data for the wellpad,and three steps are mainly included in the workflow,including PDA for the parent well before infill,PDA for the parent well after infill,and PDA for the infill well.In each step,the production performance in the early linear and bilinear flow regimes are analyzed with approximate solutions in the square and fourth root-of-time plots.Because only the relationship between unknown model parameters can be obtained with the approximate solutions,history matching to the production data in log-log plots is further used to determine each unknown parameter.The PDA method is benchmarked with a synthetic case generated by the numerical simulator tNavigator and a field case from Southwestern China.The results show that both good matches and precise parameters can be obtained with the proposed PDA method.The connected fracture number will not be sensitive in PDA when the wells are connected with high-conductive dSRV.The innovation of this paper is that a practical method is provided for PDA analysis of well groups with fracture connection,and it will be a good technique for fracture characterization and well-interference analysis for tight formations.
基金The authors are grateful to the financial support from China Postdoctoral Science Foundation(2022M712645)Opening Fund of Key Laboratory of Enhanced Oil Recovery(Northeast Petroleum University),Ministry of Education(NEPU-EOR-2021-03).
文摘Severe well interference through complex fracture networks(CFNs)can be observed among multi-well pads in low permeability reservoirs.The well interference analysis between multi-fractured horizontal wells(MFHWs)is vitally important for reservoir effective development.Well interference has been historically investigated by pressure transient analysis,while it has shown that rate transient analysis has great potential in well interference diagnosis.However,the impact of complex fracture networks(CFNs)on rate transient behavior of parent well and child well in unconventional reservoirs is still not clear.To further investigate,this paper develops an integrated approach combining pressure and rate transient analysis for well interference diagnosis considering CFNs.To perform multi-well simulation considering CFNs,non-intrusive embedded discrete fracture model approach was applied for coupling fracture with reservoir models.The impact of CFN including natural fractures and frac-hits on pressure and rate transient behavior in multi-well system was investigated.On a logelog plot,interference flow and compound linear flow are two new flow regimes caused by nearby producers.When both NFs and frac-hits are present in the reservoir,frac-hits have a greater impact on well#1 which contains frac-hits,and NFs have greater impact on well#3 which does not have frac-hits.For all well producing circumstances,it might be challenging to see divergence during pseudosteady state flow brought on by frac-hits on the logelog plot.Besides,when NFs occur,reservoir depletion becomes noticeable in comparison to frac-hits in pressure distribution.Application of this integrated approach demonstrates that it works well to characterize the well interference among different multi-fractured horizontal wells in a well pad.Better reservoir evaluation can be acquired based on the new features observed in the novel model,demonstrating the practicability of the proposed approach.The findings of this study can help for better evaluating well interference degree in multi-well systems combing PTA and RTA,which can reduce the uncertainty and improve the accuracy of the well interference analysis based on both field pressure and rate data.
基金This work is supported by Open Fund Project“Study on Multiphase Flow Semi-Analytical Method for Horizontal Wells of Continental Shale Condensate Gas”of Sinopec Key Laboratory of Shale Oil/Gas Exploration and Production Technology.
文摘Well interference has become a common phenomenon with the increasing scale of horizontal well fracturing.Recent studies on well interference in horizontal wells do not properly reflect the physical model of the postfracturing well groups and the realistic fracturing process of infill wells.Establishing the correspondence between well interference causative factors and manifestations is of great significance for infill well deployment and secondary oil recovery.In this work,we develop a numerical model that considers low velocity non-Darcy seepage inshale reservoirs to study the inter-well interferencephenomenon that occurs in theSantanghufield,andconstruct an explicit hydraulic fracture and complex natural fracture network model with an embedded discrete fracture model,focusing on the effect of fracture network morphology on well interactions.The model also considers a multi-segment wellbore model to accommodate the effect of inter-well crossflow on wellbore tubular flow.The changes in formation pressure and water saturation during fracturing are performed by controlling the injection pressure and water injection rate.The result shows that the shape of the fracture network generated by the infill well with the old well determines the subsequent fluid and oil-increasing performance of the disturbed well.The synergistic production or competitive relationship formed by fractures with different connectivity between the two wells determines the positive and negative effects of the interference.The paper also investigates the adaptation study of water injection huff and puff schemes for well groups with different connectivity,and demonstrated a potential yield increase of up to 10.85%under adaptation injection.This method of identifying well interference based on the production dynamics of affected wells and the subsequent corresponding water injection method provides valuable references for the selection of secondary oil recovery measures.
基金funded by the National Natural Science Foundation of China(42077247,52104029)the Fundamental Research Funds for the Central Universities.
文摘In the Changqing Oilfield in northwest China, when traditional petroleum exploitation encounters forestry reserves or water source protection areas, sectorial well-factory design is proposed. The most distinct feature of a sectorial well-factory is the deviation of the well from the minimum horizontal principal stress, resulting in hydraulic fracture deflection after the initiation, along with possible well interference (i.e., fracture hit) and fracture coalescence in the oblique wells. Four indexes describing well deflection are then proposed according to fracture morphology. Several fracturing designs, including stage arrangement, fracturing sequences, and fracturing techniques are applied to study the feasibility of the sectorial well-factory design. The results show that the “gradual” or “sparse” stage arrangement, large injection rate, and simultaneous multifracture treatment can help to optimize the fracture morphology and stimulation design. However, the subsequent stress shadowing effect usually adversely affects the fracturing of adjacent wells. With a small initial horizontal stress difference, large injection rate and staggered stage arrangement can achieve ideal stimulation performance. Our results can provide a guidance for optimizing stimulation design in unconventional well-factory while taking into account environmental protection.
基金funded by Shaanxi Natural Science Basic Research Program Project Study on Liquid Propellant High Energy Gas Fracturing Mechanism in Radial Well Based on Phase Field Method(No.2019JQ-824)NSFC Projects Evolution Mechanism and Effectiveness Evaluation of Fracture Network Produced by Volume Fracturing with Tighter Clusters in Continental Shale Oil Reservoir(No.52274040)+1 种基金Study on Thermal Secondary Pore Evolution and Salt Precipitation Regulation Mechanism in Fire Flooding Reservoirs Based on Multi-field Coupling of Thermal-Flow-Solid-Chemical(No.52274039)Xi’an Shiyou University Youth Scientific Research and Innovation Team Operation Funds in 2018 Flow Mechanism of Complex Reservoirs and High Efficiency Development and Oil Production Technology(No.115080020).
文摘Horizontal well-stimulation is the key to unconventional resource exploration and development.The development mode of the well plant helps increase the stimulated reservoir volume.Nevertheless,fracture interference between wells reduces the fracturing effect.Here,a 2D hydro-mechanical coupling model describing hydraulic fracture(HF)propagation is established with the extended finite element method,and the effects of several factors on HF propagation during multiple wells fracturing are analyzed.The results show that with an increase in elastic modulus,horizontal principal stress difference and injection fluid displacement,the total fracture area and the reservoir stimulation efficiency are both improved in all three fracturing technologies.After a comparison of the three technologies,the method of improved zipper fracturing is proposed,which avoids mutual interference between HFs,and the reservoir stimulation effect is improved significantly.The study provides guidance for optimizing the fracturing technology of multiple horizontal wells.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korea government(MSIT)(No.2022M3J7A1062940).
文摘Epoxy-based nano-composites can be ideal electromagnetic interference(EMI)-shielding materials owing to their lightness,chemical inertness,and mechanical durability.However,poor conductivity and brittleness of the epoxy resin are challenges for fast-growing portable and flexible EMI-shielding applications,such as smart wristband,medical cloth,aerospace,and military equipment.In this study,we explored hybrid nanofillers of single-walled carbon nanotubes(SWCNT)/reduced graphene oxide(rGO)as conductive inks and polyester fabrics(PFs)as a substrate for flexible EMI-shielding composites.The highest electrical conductivity and fracture toughness of the SWCNT/rGO/PF/epoxy composites were 30.2 S m^(−1)and 38.5 MPa m^(1/2),which are~270 and 65%enhancement over those of the composites without SWCNTs,respectively.Excellent mechanical durability was demonstrated by stable electrical conductivity retention during 1000 cycles of bending test.An EMI-shielding effectiveness of~41 dB in the X-band frequency of 8.2-12.4 GHz with a thickness of 0.6 mm was obtained with an EM absorption-dominant behavior over a 0.7 absorption coefficient.These results are attributed to the hierarchical architecture of the macroscale PF skeleton and nanoscale SWCNT/rGO networks,leading to superior EMI-shielding performance.We believe that this approach provides highly flexible and robust EMI-shielding composites for next-generation wearable electronic devices.
基金supported by National High Technology Research and Development Program of China under Grants No.2014AA01A701major project of Ministry of Industry and Information Technology of China under Grant No.2015ZX03001032+1 种基金major project of Shanghai under Grant No.,14511101501National Natural Science Foundation of China under Grant No.61471347
文摘Co-primary spectrum sharing for multiple operators has been utilized to fully explore the spectrum resources and thus improve the spectrum efficiency. The inter-operator interference(IOI) problem should be seriously considered in order to achieve the mentioned target, especially under the scenario of the ultradense network(UDN) in the fifth generation(5G) wireless systems. To solve this problem, we propose an asymmetrical power levels based soft IOI coordination mechanism. The shared spectrum pool is consisted of three separated parts, where each part can be dynamically adjusted according to the minimal spectrum demand from each operator. Furthermore, different power masks are configured to different parts for each operator. The simulation results show that the proposed mechanism can improve the network spectrum efficiency significantly.
基金supported by the National Natural Science Foundation of China (No.61074165 and No.61273064)Jilin Provincial Science & Technology Department Key Scientific and Technological Project (No.20140204034GX)Jilin Province Development and Reform Commission Project (No.2015Y043)
文摘Wireless Body Area Network(WBAN) is an emerging technology to provide real-time health monitoring and ubiquitous healthcare services. In many applications, multiple wireless body area networks have to coexist in a small area, resulting in serious inter-network interference. This not only reduces network reliability that is especially important in emergency medical applications, but also consumes more power of WBANs. In this paper, an inter-network interference mitigation approach based on a power control algorithm is proposed. Power control is modeled as a non-cooperative game, in which both inter-network interference and energy efficiency of WBANs are considered. The existence and uniqueness of Nash Equilibrium in the game are proved, and an optimal scheme based on best response is proposed to find its Nash Equilibrium. By coordinating the transmission power levels among networks under interference environment, the total system throughput can be increased with minimum power consumed. The effectiveness of the proposed method has been illustrated by simulation results, where the performance of the proposed approach is evaluated in terms of overall utility and power efficiency and convergence speed.
基金supported by the National Natural Science Foundation of China under Grant No. 61501160supported by the Fundamental Research Funds for the Central Universities of China under Grant No. 2015HGCH0013
文摘To mitigate interference on celledge users and improve fairness of the whole system, dynamic inter-cell interference coordination(ICIC) is one of the promising solutions. However, traditional dynamic ICIC is considered as an NP-hard problem and power variability further adds another dimension to this joint optimization issue, making it even more difficult to quickly reach a near-optimal solution. Therefore, we theoretically obtain the closed-form expression of the near-optimal power allocation ratio for users in adjacent cells paired in the same resource block and interfere each other, so that the total utility corresponding to α-fairness is maximized. Dynamic ICIC using this closed-form solution could improve user fairness without causing an increment of the computational complexity. Numerical results show that, compared with the schemes using identical power for different users, our method does not obviously degrade the system's average spectral efficiency.
文摘In Orthogonal Frequency Division Multiple Access (OFDMA) systems, such as Long Term Evolution (LTE) and so on, the resources used by each user are orthogonal, and the OFDMA systems performances are mainly affected by the inter-cell interference. Therefore, the inter-cell interference mitigation technology becomes a hotspot. The objective of interference mitigation technologies used in OFDMA systems are to increase cell-edge throughput and average cell throughput. In this paper, the Resource Block Planning (BRBP) based scheme is proposed to mitigate the inter-cell interference and improve the cell-edge throughput. Comparison between the simulation results of BRBP and Round Robin (RR) illustrates that the enhanced performance of BRBP.
文摘With the growing concern on data rates and resource utilization, Device-to-Device (D2D) communication has been raised in 3GPP Long-Term Evolution (LTE) networks. In order to limit severe interference, previous studies mainly focus on intra-cell interference that between cellular links and local D2D links. In this paper, we consider both intra-cell interference and inter-cell interference between D2D and cellular links. We propose a new resource reuse algorithm that D2D users reuse the minimum interference uplink (UL) Semi-Persistent Scheduling (SPS) resources to reach the highest throughput. The simulation results show that this scheme reduces interference as well as improves throughput.
基金Sponsored by the Important National Science & Technology Specific Projects of China (Grant No. 2009ZX03004-001)the Cooperation Project with Huawei Technologies Company (Grant No. YBWL2010242)
文摘In this paper, we propose two joint transmit-receive iterative algorithms without the cooperation between different base stations based on the idea of interference alignment (IA) to improve the throughput of relay backhaul links in cellular networks for the case of imperfect channel knowledge,which can be implemented with small changes to existing TD-LTE standards. Unlike the previous interference alignment algorithms' only reducing the sum interference to the other receivers at the transmitter or the sum received Multi-user interference (MUI) at the receiver, our algorithm shapes the transmission of each data stream at transmitters in order not only to minimize interference to the other users, but also to minimize the interference between different streams objected to the same user, suppressing the MUI and Multi-stream interference (MSI) at receivers. The proposed algorithm I is to maximize the SINR at receivers. But the complexity is relatively high. Algorithm II only needs linear operations and sacrifices a little performance for much lower complexity compared to the Maximize SINR iterative algorithm which needs the inversion operation of matrix. It is also proved that the algorithm converges monotonically. The simulation results show that the techniques have considerable performance gain compared with the previous algorithms. Further research about power allocation is also discussed.
基金supported by the National Natural Science Foundation of China under Grant No.61202406the USTC Grand Master Professor Funds under Grant No.ZC9850290097
文摘With promising applications in e-health and entertainment, wireless body area networks (WBANs) have attracted the interest of both academia and industry. If WBANs are densely deployed within a small area, serious problems may arise between the WBANs. In this paper, we discuss issues related to the coexistence of WBANs and investigate the main factors that cause inter-WBAN interference. We survey inter- WBAN interference mitigation strategies and track recent research developments. We also discuss unresolved issues related to inter-WBAN interference mitigation and propose fu- ture research directions.
基金Supported by the National Natural Science Foundation of China (No.60372030)China Ministry of Education Foundation for Visiting Scholar (No.[2003]406)Key Project of Provincial Scientific Foundation of Shandong (No.Z2003G02).
文摘In this paper,we propose a novel iterative scheme for exploiting transmit diversity using parallel independent Inter-Symbol Interference (ISI) channels. In this adaptive iterative scheme,we use EXtrinsic Information Transfer (EXIT) chart tool to choose appropriate iterative method from Itera-tive Combining (IC),used as parallel concatenation turbo-like scheme,and Turbo Equalization (TE),used as serial concatenation turbo-like scheme. It is show that the proposed iterative scheme provides excellent performance both analytically and through simulations without any compute complexity increase comparable to IC.
基金Project (No. 2006AA01Z273) supported by the Hi-Tech ResearchDevelopment Program (863) of China
文摘As one of the most important components of the wideband wireless access technique, orthogonal frequency division multiplexing (OFDM) has a high usage rate of spectrum and combats inter-symbol interference (ISI) in multi-path fading channel. However, when there are frequency offsets during the signal transmission, the inter-carrier interference (ICI) is introduced, which significantly degrades the performance. The existing ICI self-cancellation schemes such as PCC-OFDM are not optimum to minimize the interference considering both noise and ICI. In this paper, a new metric named SINR (signal-to-interference- and-noise ratio) is proposed. We discuss the optimization issue when a constant frequency offset exists and in time-varying channels. The optimum weighting-coefficient-pair (OWCP) is obtained, which maximizes SINR theoretically through the alternant iteration algorithm. Simulations show that the performance of OWCP-OFDM is better than that of PCC-OFDM, especially when the frequency offset is large. Although the ICI self-cancellation scheme suffers bandwidth inefficiency, from the simulation results we can also see that the performance of OWCP-OFDM is much better than that of the standard OFDM systems with the same bandwidth efficiency when a frequency offset exists. Moreover, since the redundant modulation provides the capability to suppress ICI as well as a receiving SNR gain, it can be considered as exchanging the bandwidth for SNR.
基金National Natural Science Foundation of China(No.61271213)
文摘The orthogonality between the subcarriers of multipleinput multiple-output orthogonal frequency division multiplexing( MIMO-OFDM) systems is destroyed due to the Doppler frequency offset,particularly in the high-speed train( HST) environment,which leads to severe inter-carrier interference( ICI). Therefore,it is necessary to analyze the mechanism and influence factor of ICI in HST environment. In this paper, by using a non-stationary geometry-based stochastic model( GBSM) for MIMO HST channels, ICI is analyzed through investigating the channel coefficients and the carrier-to-interference power ratio( CIR). It is a fact that most of signal energy spreads on itself and its several neighborhood subcarriers. By investigating the amplitude of subcarriers, CIR is used to evaluate the ICI power level. The simulation results show that the biggest impact factor for the CIR is the multipath number L and the minimum impact factor K; when the train speed υR> 400 km / h,the normalized Doppler frequency offset ε > 0. 35,the CIR tends to zero,and the communication quality will be very poor at this condition. Finally,bit error rate( BER) is investigated by simulating a specific channel environment.
文摘A novel laboratory simulation method for modeling multi-staged fracturing in a horizontal well was established based on a true tri-axial hydraulic fracturing simulation system. Using this method, the influences of net pressure in hydraulic fracture, stage spacing, perforation parameter, horizontal stress bias and well cementation quality on the propagation geometry of multiple fractures in a tight sandstone formation were studied in detail. The specimen splitting and analogy analysis of fracturing curve patterns reveals: Multiple fractures tend to merge under the condition of high horizontal stress bias and short stage spacing with pre-existing hydraulic fractures under critical closure situation, and the propagation of subsequent fractures is possibly suppressed because of high net pressure in pre-created fractures and asymmetric distribution of fracture width. And the subsequently created fractures are situated in the induced stress decreasing zone due to long stage spacing, leading to weak stress interference, and perforation with intense density and deep penetration facilitates the decrease of initiation fracture pressure. The deflection angle of subsequent fracture and horizontal stress variation tend to be amplified under low horizontal bias with constant net pressure in fractures. The longitudinal fracture is likely to be initiated at the interface of wellbore and concrete sample with poor cementation quality. The initiation fracture pressure of the different stages increases in turn, with the largest increase of 30%. Pressure quickly declines after initiation with low propagation pressure when the transverse hydraulic fracture is formed. The pressure reduces with fluctuation after the initiation of fracture when the fracture deflects, the extension pressure is high, and the fracture formed is tortuous and narrow. There is a violently fluctuant rise of pressure with multiple peak values when longitudinal fracture created, and it is hard to distinguish the features between the initiation stage and propagation stage.
文摘AIM:To develop a new internal fixation device for comminuted, unstable fractures of the distal femur,and to offer a guide for management of these injuries based on biomechanical studies.METHODS:Ten fresh adult femurs of cadavers.All femurs were similarly made of the models of supracondylar intercondylar fractures,then double plating with a plate in combination with a polythene plate,and the conventional sigle plating was served as the control.The biomechanic tests (compression,bending,torsion) were performed.RESULTS:The bending and torsion tests demonstrated that the double plating groups were much stronger (P< 0.01) than the single plating groups in anti bending and anti torsion.During the tests loading to failure, the double plating groups failed at a mean peak load of 11 540 N in axial compression,700 N in anterior bending 1 082 N in posterior bending,593 N in medial bending,1 010 N in lateral bending.CONCLUSION: Double plating with a plate in combination with a polythene plate is an excellent technique and design modification for severely comminuted fractures of the distal femur,which may provide a high stability and solidness so that early mobilization and weight bearing are allowed.