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Journal of Petroleum Science & Engineering
Elsevier Science B.V.
Journal of Petroleum Science & Engineering

Elsevier Science B.V.

0920-4105

Journal of Petroleum Science & Engineering/Journal Journal of Petroleum Science & Engineering
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    Experimental study on physicochemical structure of different rank coals under acid solvent treatments and its effects on heat of gas adsorption

    Zhang, ShuoWang, ZhimingZhang, XiaodongChen, Fengjie...
    15页
    查看更多>>摘要：Physicochemical structure characteristics and its effects on the heat of gas adsorption are the foundation for coalbed methane (CBM) development. Herein, this paper selected different rank coals before and after acid treatments to analyze the relationship among nanopore structure, chemical functional groups and the heat of gas adsorption through low-temperature N-2 adsorption, Fourier transform infrared spectroscopy (FTIR) and calorimetric tests. This enabled us to explore the effect of acid solvents on nanopore structure and functional groups, and finally reveal a coupling mechanism between physicochemical structure and gas adsorption. Results showed that the specific surface area of Brunauer-Emmett-Teller model (BET-SSA) and pore volume of Barret-JoynerHalenda model (BJH-PV) decrease first and subsequently increase with increasing coal evolution before and after acid treatments. However, both pore structure parameters and fractal dimension show a decrease or an increase at different degrees under pore expansion and increase effects. On the other hand, after acid treatments, aliphatic structures evidently decrease and aromatic structures relatively increase. For oxygen-containing functional groups affected by ester hydrolysis and Fourier reaction, more carboxyl and hydroxyl groups appear but ether groups reduce. This suggests that acid treatment is actually accompanied by more physicochemical changes. Then, according to its physicochemical response, less aliphatic structures and more aromatic structures significantly contribute to appear more micropores. However, a non-significant effect of aliphatic structure on gas adsorption is observed, while micropores, aromatic structure and oxygen-containing groups give a positive effect on gas adsorption.
      原文链接:
    • NSTL
    • Elsevier

    Mechanical properties of marine shale and its roof and floor considering reservoir preservation and stimulation

    Wang, LeiGuo, YintongZhou, XiaoguiYang, Guangguo...
    14页
    查看更多>>摘要：The mechanical differences between reservoir rock and its overlying (roof) and underlying (floor) rocks have significant influence on oil/gas preservation and hydraulic fracture propagation, which is still lack of adequate research in marine shale gas formation. In this work, homogeneous intact specimens of roof siltstone, reservoir shale and floor limestone were prepared from representative outcrops, and the corresponding siltstone-shalelimestone composite samples were also fabricated with strong/weak interface cementation properties. Mechanical parameters, fracture morphology, brittleness, and failure mechanism of marine shale and its roof and floor in tri-axial compressive state were comparatively investigated. Results show that reservoir shale had relatively low compressive strength, Young's modulus, internal frictional angle, and cohesive strength, making it more susceptible to rupture, compared with the roof and floor. The floor limestone had relatively high strength and low brittleness, which were beneficial for maintaining its integrity and the preservation of shale gas during tectonic movement. Considering the high brittleness of roof siltstone, more attention should be given to the integrity of the roof, where fractures induced by tectonic movement could provide as a pathway of gas escape. Interface cementation property played a key role in the fracture propagation behavior at lithologic boundaries. Interfaces with weak cementation tended to arrest extending fractures, which was advantageous to gas preservation or fracture height control in reservoir stimulation. Whereas fracture would probably cross over strong cementation interfaces, leading to the threat of oil/gas leakage or incontrollable hydraulic fracture propagation in vertical direction.
      原文链接:
    • NSTL
    • Elsevier

    Mechanism study of spontaneous imbibition with lower-phase nano-emulsion in tight reservoirs

    Qu, MingLiang, TuoXiao, LixiaoHou, Jirui...
    11页
    查看更多>>摘要：Spontaneous imbibition has been proved to be a promising enhanced oil recovery method for tight reservoirs, but the mechanisms of spontaneous imbibition oil recovery (SIOR) are still unclear. Here, we use the self-prepared novel lower-phase nano-emulsion (LWPNE) to reveal the mechanisms. In LWPNE solution, nano-scale oil drops (NODPs) in 6 nm diameter are formed and dispersed with co-presence of micelle solubilizing N-hexane. The effects of LWPNE on both interfacial tension (IFT) and contact angle were studied at 0-10,000 mg/L salinity condition, and spontaneous imbibition efficiency was determined from imbibition experiments in Amott cells at 60 degrees C. Electron Microscope and Transmission Electron Microscope were used to analyze the emulsification and solubilization mechanisms of LWPNE. Experimental results show that the original 135 degrees (oil-wet) contact angle can be reduced to 32.7 degrees (water-wet); the IFT is decreased to 0.0038 mN/m, and electrolyte has no contribution to either IFT reduction or wettability alteration. The average oil recovery from spontaneous imbibition testing using 0.3 wt% LWPNE is 44.1%, which is 20.5% higher than that from systems at similar conditions but using brine only. The LWPNE can solubilize oil by increasing NODPs' sizes to average 36 nm in diameter, which is the dominant mechanism to improve SIOR for LWPNE. The solubility of LWPNE is evaluated by the diameter growth rate of NODPs, and once it reaches 350%, a self-driving force drives oil drops to move forward. Moreover, the transformation mechanisms of spontaneous imbibition modes from imbibition to drainage are revealed by using the imbibition discriminant parameter (Nxe213; 1
      原文链接:
    • NSTL
    • Elsevier

    The influence of depositional and diagenetic processes on rock electrical properties: A case study of the Longmaxi shale in the Sichuan Basin

    Zhang, BingWen, HuaguoQing, HairuoYang, Kai...
    21页
    查看更多>>摘要：Primary depositional and diagenetic processes exert very important influences on shale gas reservoirs. Rock electrical properties are an important basis for making reservoir prediction using the electromagnetic method (EM). However, there is still a lack of understanding about the impact of the sedimentary diagenesis process on shale electrical properties, this study focuses on the impact of diagenesis on rock properties. In this study, rock electrical properties are studied based on electromagnetic experiments. We systematically studied the lithofacies of different depositional paleoenvironments and diagenetic processes, and the influence of diagenetic evolution on the rock electrical properties was discussed, by means of X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FE-SEM), low-temperature nitrogen adsorption (LTNA), and trace element (TE) geochemical analysis. Based on the study of mineral composition, grain assemblages and pore systems, we identified four lithofacies in the Longmaxi Formation: siliceous shale, siliceous-argillaceous mixed shale, silty shale and argillaceous shale. Redox proxies (U/Th, V/Cr, and Ni/Co) indicate that the siliceous shale was deposited in a relatively anoxic and reducing environment, indicating a deep-water shelf depositional paleo-environment. The siliceous-argillaceous shale, silty shale and argillaceous shale were deposited under a relatively dysoxic-oxic environment, indicating a shallow-water shelf depositional paleoenvironment. The order of re-sistivity values of the lithofacies within the Longmaxi Formation is 36.78 omega m (siliceous shale), 66.81 omega m (siliceous-argillaceous mixed shale), 79.54 omega m (silty shale), and 107.00 omega m (argillaceous shale), and the re-sistivity decreases with an increase in porosity. The siliceous shale has the most abundant authigenic quartz, which filled the primary pores forming a rigid framework during the gas window, inhibited compaction, increased the distribution of organic matter (OM), and enhanced the development of OM pores. The high TOC content and high maturity of siliceous shale at the bottom of Longmaxi Formation make the OM pores more developed. Pyrite, conductive fluid and pore network under the main control of OM pores in shale form a conductive circuit when AC voltage is input, which increases the exchange capacity of cations and leads to the phenomenon of low resistivity. The interconnected OM pore network, both depositionally and diagenetically derived, affects the electrical properties of the Longmaxi shale. This study reveals that electrical properties of shale rocks and its variations can be impacted by the depositional environment and diagenetic processes. This work provides resistivity parameters for the electromagnetic exploration of shale gas under complex terrain conditions and provides a theoretical basis for later interpretation.
      原文链接:
    • NSTL
    • Elsevier

    The evolution of lost circulation prevention and mitigation based on wellbore strengthening theory: A review on experimental issues

    Mirabbasi, Seyed MortezaAmeri, Mohammad JavadAlsaba, MortadhaKarami, Mohsen...
    16页
    查看更多>>摘要：One of the most challenging issues during drilling operations is lost circulation, which can cause several problems that could lead to increasing the non-productive time (NPT) and drilling cost. Wellbore strengthening techniques have been applied as a well-known approach to increase the mud weight window by improving mud cake properties or adding lost circulation materials (LCMs) to the drilling fluid. The success-to-failure ratio of remedial or preventive solutions during the field operation is highly dependent on the appropriate selection of wellbore strengthening strategy. Initial studies, which have often focused on trial and error and operational practices, have not provided a clear understanding of fundamental mechanisms and performance of LCMs in strengthening of a formation. Hence, in the last decades, several analytical and numerical studies, as well as experimental evaluations have been performed by numerous researchers to simulate the fluid loss process and LCM effectiveness. Conducting a comprehensive and well-designed experimental investigation can be a more applicable and cost-effective approach to select proper wellbore strengthening method and recommend the best drilling fluid formulation to treat the loss zone. The aim of this paper is to present an overall review on the various published experimental investigations, to assess the different aspects of lost circulation and wellbore strengthening theory. This extensive literature review collects limitations, advances, and differing opinions from experts. It also broadens the scope for future work and helps in solving industrial problems from an operational point of view.
      原文链接:
    • NSTL
    • Elsevier

    Numerical investigation into hydraulic fracture initiation and breakdown pressures considering wellbore compliance based on the boundary element method

    Chen, MingGuo, TiankuiQu, ZhanqingSheng, Mao...
    14页
    查看更多>>摘要：There is a wealth of experimental evidence that fracture initiation and breakdown pressures differ depending on in-situ stress status, rock properties, and injection conditions. However, the mechanism is not fully understood from a theoretical modeling perspective. In this study, a fully coupled plain-strain fracture model is proposed to interpret the mechanism of fracture initiation and breakdown pressures. The fracture model consists of fracture initiation and propagation governed by linear elastic fracture mechanics. The effects of wellbore compliance (or compressibility), solid-fluid coupling, and fracture multiscale propagation behavior are fully considered. The solid-fluid coupling equations are solved using the Newton-Raphson iterative method. The explicit time marching method is used to capture the fracture initiation process. An implicit time-stepping with the fracture tip asymptotic solution is used to capture fracture propagation fronts. The model is validated against the analytical solutions of the plane-strain model. Sensitivity analysis demonstrates that the initiation pressure mainly depends on rock properties, especially the fracture toughness. The peak pressure (breakdown pressure) is related to rock properties and injection conditions and usually occurs before the peak of the pressurization rate is reached. It increases with the injection rate, fluid viscosity, Young's modulus, and fracture toughness. The dimensionless inlet flux into the fracture can be used to determine the fracture initiation pressure. The pressurization rate during the fracture initiation stage is constant and can be used to assess wellbore compliance. Using a low injection rate and a low-viscosity fluid is beneficial to capturing the fracture initiation pressure. This study can help understand fracture initiation and propagation and interpret hydraulic fracture initiation and breakdown pressures.
      原文链接:
    • NSTL
    • Elsevier

    Discussion on the paper entitled "Estimating elasticity modulus and uniaxial compressive strength of sandstone using indentation test" by E. Mousavi, A. Cheshomi and M. Ashtari [Journal of Petroleum Science and Engineering 169 (2018) 157-166]

    Xie, Wei-Qiang
    5页
    查看更多>>摘要：A discussion on the paper by Mousavi et al. (2018) is presented. The paper is focused on the estimation of elastic modulus (E) and uniaxial compressive strength (UCS) of sandstone using indentation test. The authors concluded that the thickness effect of samples on the indentation indices (critical transition force (CTF) and indentation modulus (IM)) was negligible. They proposed a dimensionless surface parameter (S) to eliminate the size effect on the E and UCS. On the basis of the test results and analysis method presented in the paper by Mousavi et al. (2018), three aspects of indentation test need to be clarified: the methods to prevent the movement of rock specimens, the results obtained from indentation test and the effect of specimen sizes on the CTF and IM. Meanwhile, the present discussion paper proposed some references for the methods to prevent the movement of rock specimens and the methods to eliminate the size effect in indentation test.
      原文链接:
    • NSTL
    • Elsevier

    A novel self-adaptive multi-fidelity surrogate-assisted multi-objective evolutionary algorithm for simulation-based production optimization

    Wang, LianYao, YuedongZhang, TaoZhao, Guoxiang...
    14页
    查看更多>>摘要：Multi-objective production optimization (MOPO) which aims at finding an optimal well control scheme is regarded as a win-win strategy for improving economic and production gains. Generally, the MOPO processes involve computationally expensive numerical simulations and high-dimensional decision variables which limit their application to actual reservoir optimization problems. Surrogate-assisted multi-objective optimization method which uses a simple yet efficient approximation model shows huge potential in solving production optimization problems since it lessens the computational burden by decreasing the use of computationally expensive numerical simulations. In this paper, a novel self-adaptive multi-fidelity surrogate-assisted (SAMFS) multi-objective production optimization algorithm (SAMFS-MOPO) is proposed to reduce the computational burden and enhance the accuracy of the surrogate model. A similar method has been applied to well spacing optimization but the uniqueness of this method is that two fidelity samples are used to establish a multi-fidelity (MF) surrogate model, while i-updating and g-updating strategies are used to renew the MF surrogate model during the optimization process so as to improve its accuracy and reduce the computational burden. To the best of our knowledge, this is the first time a self-adaptive multi-fidelity surrogate model is used for production optimization. Furthermore, three classic multi-objective benchmark problems and two reservoirs with different complexities were applied to illustrate the effectiveness and accuracy of the proposed SAMFS-MOPO method. It was found that the SAMFS-MOPO method had superior performance in convergence, diversity, and efficiency than other conventional methods.
      原文链接:
    • NSTL
    • Elsevier

    Crude oil-water interface partitioning of polyvinylpyrrolidone-coated silica nanoparticles in low-salinity brine

    Tangparitkul, SuparitYu, Kai
    8页
    查看更多>>摘要：Nanoparticles are of interest in recent oil production process due to their potential to wettability alteration, but not interfacially active at the crude oil-water interface. Stability loss in brine environment, where nanoparticles tend to aggregate, is another issue for field implementation. Hence, recent challenge is to functionalize nano particles that are interfacially active and still stabilized in brine. The current study fabricated and characterized the polyvinylpyrrolidone-coated silica composite nanoparticles for their interfacial activity at the crude oil-water interface. Reduction in oil-water interfacial tension was observed and more dramatic with increasing particle concentration, confirming particle adsorption performance. In low-salinity brine (2000 ppm NaCl), the composite particles remained stabilized with weakened electrostatic force between particle and crude oil surfaces, while their size was smaller due to polymer shell dehydration. These led to faster diffusion rate than in Milli-Q water, which affected the rate of change in oil-water/brine interfacial tension, with the early-stage adsorption being a diffusion-controlled in both fluids. At equivalent particle concentration, the oil-water interfacial tensions in brine were lower than those of Milli-Q water (by similar to 2 mN/m), with interfacial coverage of the particles at the interface was found to be higher in the brine. Such difference is attributed to a weaker repulsive force between particle and the interface, induced by surface charge screening that is only present in brine. The study has demonstrated the potential use of polymer-coated nanoparticles as suitable additives for use in oil recovery, which can be used concurrently with low-salinity brine as a combined fluid. While both chemicals are known to construct disjoining pressure for wettability alteration, advantage of using interfacially active nanoparticles is additional mechanism to enhance oil recovery, i.e. reducing the oil-water interfacial tension, which unfunctionalized particles could not contribute.
      原文链接:
    • NSTL
    • Elsevier

    Experimental investigation on plugging performance of CO2 microbubbles in porous media

    Nam Nguyen Hai LeSugai, YuichiVo-Thanh, HungNguele, Ronald...
    14页
    查看更多>>摘要：To further improve carbon dioxide enhanced oil recovery CO2-EOR efficiency in heterogeneous reservoirs, the use of CO2 microbubbles as a temporary blocking agent is attracting widespread interest due to their significant stability. This study aims to investigate the plugging performance of CO2 microbubbles in both homogeneous and heterogeneous porous media through a series of sandpack experiments. First of all, CO2 microbubble fluids were generated by stirring CO2 gas diffused into polymer (Xanthan gum (XG)) and surfactant (Sodium dodecyl sulfate (SDS)) solution with different gas: liquid ratios. Then, CO2 microbubbles fluids were injected into single-core and dual-core sandpack systems. The results show that the rheological behaviors of CO2 microbubble fluids in this study were followed the Power-law model at room temperature. The apparent viscosity of CO2 microbubble fluid increased as the gas: liquid ratio increased. CO2 microbubbles could block pore throat due to the "Jamin effect" and increase the resistance in porous media. The blocking ability of CO2 microbubbles reached an optimal value at the gas:liquid ratio of 20% in the homogeneous porous media. Moreover, the selective pugging ability of CO2 microbubbles in dual-core sandpack tests was significant. CO2 microbubbles exhibited a good flow control profile in the high permeability region and flexibility to flow over the pore constrictions in the low permeability region, leading to an ultimate fractional flow proportion (50%:50%) in the dual-core sandpack model with a permeability differential of 1.0:2.0 darcy. The fractional flow ratio was considerable compared with a polymer injection. At the higher heterogeneity of porous media (0.5:2.0 darcy), CO2 microbubble fluid could still establish a good swept performance. This makes CO2 microbubble fluid injection a promising candidate for heterogeneous reservoirs where conventional CO2 flooding processes have limited ability. This finding would be helpful in developing the utilization of CO2 microbubbles in EOR operation by better understanding their plugging mechanism in porous media.
      原文链接:
    • NSTL
    • Elsevier