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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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    Numerical study on the law of fracture propagation in supercritical carbon dioxide fracturing

    Tiankui GuoYuelong ZhangLin Shen
    17页
    查看更多>>摘要：Compared with conventional hydrofracturing fluid, SC-CO2 has the merits of no water sensitivity and effective carbon dioxide storage. At present, the research on the fracture initiation mechanism of SC-CO2 fracturing is still at the exploring phase. This paper conducts a detailed study on the fracture initiation mechanism of SC-CO2 fracturing, and establishes a fracture initiation and propagation model of flow-stress-damage coupling according to damage mechanics. A series of numerical simulation studies have been carried out on the rock physical parameters, fracturing construction parameters, natural fracture distribution and other factors that affect the fracture propagation of the reservoir to provide a reference for the SC-CO2 fracturing construction design. The findings suggest;; the lower formation permeability, the less SC-CO2 filtration loss, and the larger total fracture length and width;; SC-CO2 is easier to improve the reservoir continuity and result in a complex fracture network;; The lower the viscosity of SC-CO2, the larger total length of fractures, and the more complex the fracture network;; As the delivery of pump increases, the width of fracture continues to increase, and the total fracture length decreases;; SC-CO2 has a better effect on communicating natural fractures and porous media, and the fracture network is more complex.
      原文链接:
    • NSTL

    Influence of top water on SAGD steam chamber growth in heavy oil reservoirs: An experimental study

    Huiqing LiuJi TianXiaocong Lyu
    11页
    查看更多>>摘要：Steam-assisted gravity drainage (SAGD) is one efficient and mature technology for recovering heavy oil and bitumen resources. The key underlying mechanism is the growth of the steam chamber after injecting steam. However, due to the complex geological environment, the thief zones exist and have a prejudicial effect on the development of the steam chamber, thus impacting the ultimate heavy-oil recovery. In this work, our objective is to investigate the effect of a top-water thief zone (i.e., water zone overlies the oil sand) on SAGD performance and further to understand the crucial mechanisms that control the heat loss during steam injection. A large-scale three-dimensional experimental apparatus is used to carry out the SAGD process with a top aquifer. Based on the similarity criterion, the field-scale model is transformed into a laboratory elemental model. To evaluate the SAGD performance quantitatively, the dynamic growth of the steam chamber is measured using the thermal detectors and the production data is recorded. The results show that the steam chamber exhibits three distinguished stages, that is, upward spread, lateral extension, and downward development in the presence of top-water zone. The bottom-water zone has less impact on the steam-chamber growth. The existence of a confined top-water zone, however, significantly affects SAGD performance, especially the lateral expansion of the steam chamber. The lateral propagation of the steam front is hindered by the top thief zone due to the heat exchange with the top water. Once the steam chamber reaches the boundary, the accumulation of energy in the water thief zone, in turn, can reduce the remaining oil saturation along the topwater-oil interface. This study provides us some key insights into the development of heavy oil resources with top thief zones when implementing SAGD technology.
      原文链接:
    • NSTL

    Channel boundary detection using partial area effect with sub-pixel resolution

    Masoume LotfiAbdolrahim JavaherianSaeid Rezakhah Varnousfaderani
    21页
    查看更多>>摘要：Channel facies, of the most prevalent stratigraphic features, are essential from the perspective of hydrocarbon exploration. However, measuring edge features using the gradient vector's calculation in an individual pixel mainly produces edge borders with pixel resolution even in images with low noise levels. This paper introduces a novel seismic attribute based on the partial area effect algorithm assuming a particular discontinuity in the edge location to extract the buried channel boundaries. First, the Sobel-based edge detector extracts the pixels' partial derivatives as probable channel boundaries. Then, the direction and the dimension of the postulated partial area effect mask in the local maxima points are deliberated to elicit the edge curve coefficients as the perfect edge positions. The proposed algorithm was implemented on a synthetic time slice comprising two-channel events with varying thicknesses and sinuosity. The procedure was also investigated on two high-cut frequency filtered datasets from the Penobscot prospect in the Nova Scotia Basin accommodating canyon-channel events. The proposed algorithm was then compared to the prominent gradient-based edge detectors (Canny, Prewitt, and Sobel) and some conventional seismic attributes (apparent dip, most negative curvature, and similarity). The results showed that applying the nominated algorithm could provide an improved map of buried channels less affected by the coherent noise and acquisition footprints. The partial area effect algorithm also successfully localized more true-positive edge points and fewer false-positive ones in the synthetic and field seismic data examples.
      原文链接:
    • NSTL

    Reservoir performance analysis through the material balance equation;; An integrated review based on field examples

    Gorgonio Fuentes-CruzMario A. Vasquez-Cruz
    22页
    查看更多>>摘要：The Material Balance Equation (MBE) has proved its versatility over a century because it has been adapted to include several production mechanisms identified in homogeneous, naturally fractured, and unconventional reservoirs. Thus, numerous field cases regarding the practical use of the MBE are found in the Petroleum Engineering literature. However, those cases have been analyzed by using diverse approaches introduced at different times, leading to a wide variety of analysis methods. Several field examples are revisited in this work through an integrated review that properly uses analysis techniques focused on diagnostics, straight-line analysis, and pressure-production history matching. This review provides additional insights about the reservoir performance compared to the results presented in the original papers. Thus, the conceptual model of the reservoir-aquifer system is consistently characterized by using several graphs along the process of analysis. The reasons related to the complementary role between the conventional straight-line analysis and the history matching technique are provided;; the latter should confirm the results from the straight-line analysis, while this one should guide the history matching technique. Also, based on the observation that a good history match does not guarantee the correct characterization of the reservoir-aquifer model, the relevance of integrating the Material Balance analysis with other disciplines is discussed. The significance of the multidisciplinary approach to mitigate the non-uniqueness inverse problem is illustrated through the study of complex examples, such as a naturally fractured reservoir connected to an aquifer. Furthermore, scrutiny on the concept of total effective formation-water compressibility is provided to emphasize the similarities and differences in the analysis of homogeneous and naturally fractured reservoirs through the MBE.
      原文链接:
    • NSTL

    Long-term effect of desorption-induced matrix shrinkage on the evolution of coal permeability during coalbed methane production

    Mingyao WeiChun LiuYingke Liu
    8页
    查看更多>>摘要：In a coal reservoir, matrix shrinkage caused by gas desorption is regarded as a significant factor that can influence natural fracture permeability. It is considered to be a constant and lasting effect throughout coalbed methane (CBM) production based on previous investigations. However, experimental measurements of long-term permeability change have demonstrated that adsorption-induced strain has a time-dependent effect on permeability evolution. This study presents long-term investigations on permeability evolution of coal reservoir during CBM production. A fully coupled two-phase flow model for gas-water is specially proposed. Furthermore, the independent impacts of the matrix swelling during gas adsorption are characterized by a strain-rate-based permeability model. The competing effect between pressure depletion and desorption shrinkage on the permeability change is evaluated during the process of long-term production. The calculations of the proposed model are respectively consistent with experimental and field data and the findings show that matrix shrinkage is the most important factor in permeability evolution towards the wellbore. The effect of matrix shrinkage on permeability enhancement is significant in the primary stage and vanishes with uniform depressurization in the matrix. As a result, matrix shrinkage dominates permeability first, followed by effective stress. A sensitivity analysis of mechanical properties and flow properties on permeability evolution was performed and has demonstrated that the larger the matrix shrinkage-induced strain is, the higher the permeability enhancement is, which can be also enhanced with greater initial permeability and a lower diffusion coefficient of the matrix and the impact of the negative strain induced by decreasing pore pressure is solely related to the bulk modulus. The range of permeability variation is narrowed when porosity is high, which implies that the influence of matrix shrinkage and effective stress on permeability is suppressed. This research will advance the understanding of the permeability change during long-term CBM production.
      原文链接:
    • NSTL

    Methane adsorption on shales and application of temperature-related composite models based on dual adsorption modes

    Zhongqi MuZhengfu NingChunyu Ren
    11页
    查看更多>>摘要：There are some controversies in shale gas about adsorption mechanisms and thermodynamics. This paper studied the adsorption of methane on two shale samples at pressures up to 20 MPa and temperatures in the range of 40-80 °C. Two composite models based on monolayer adsorption and filling of micropores were proposed and used for the fitting of the experimental isotherms under multiple temperatures. The fitting results show that the composite models lead to better fitting effects for isotherms and under low pressure compared to the Langmuir models thus being appropriate models for fitting. Using the composite models, the competition of two adsorption modes was investigated that the filling of micropores hardly appear until pressure rises to approximately 2 MPa. The isosteric heat and entropy change were determined by the Clapeyron equation and weighted average method, showing their dependence on the competition of two adsorption modes at different adsorbed amounts. These findings not only determine two novel models for describing shale gas adsorption but also reveal the adsorption process and associated thermodynamics.
      原文链接:
    • NSTL

    Shale gas production from reservoirs with hierarchical multiscale structural heterogeneities

    Jianwei TianJishan LiuDerek Elsworth
    16页
    查看更多>>摘要：Hydrofractured shale reservoirs exhibit a complex hierarchy of heterogeneous structures. Although the importance of hierarchical structures has long been recognised, the full control of scale-dependent heterogeneities on gas production remains ill-defined. We characterize reservoir structural heterogeneity at four hierarchical levels;; (1) heterogeneous nanopore structure of the OM (Organic Matrix/Kerogen);; (2) heterogeneous micro-structure of the IOM (Inorganic Matrix);; (3) discrete structure of the NFNs (Natural Fracture Networks);; and (4) discrete structure of the HFs (Hydraulic Fractures). A fractal approach is applied to characterize these internal structural heterogeneities for both the OM and IOM. These characterisations are incorporated into the constitutive relations defining transport within the OM and IOM. NFNs are generated by the Monte Carlo method while HFs are represented by a fractal tree-like network. A constitutive law for flow within a fracture is applied to both NFNs and HFs. Overall mechanical equilibrium and continuity of deformations are applied across these hierarchical systems comprising the shale reservoir while separate field equations for transport are derived for each structural system. The mass exchange between the individual structural systems is satisfied through source/sink terms compatibility of deformation enforced through boundary conditions and internal controls. The resulting multi-scale heterogeneous model is verified against the analysis of an idealised shale reservoir. Simulation results honor the ultimate recovery fractions and demonstrate the significant impacts of both hydraulic fracture and natural fracture heterogeneities on the evolution of recovery. The verified model is applied to a field case. The modelled gas production rate curve agrees well with field data for a reservoir in Barnett shale. Sensitivity studies confirm that heterogeneities at all scales are important but that their respective roles evolve separately during the history of gas production.
      原文链接:
    • NSTL

    Effect of interlayer mechanical properties on initiation and propagation of hydraulic fracturing in laminated coal reservoirs

    Yulong LiuDazhen TangHao Xu
    16页
    查看更多>>摘要：Coal macrolitho types control the heterogeneity of coal physical properties in coalbed methane (CBM) reservoirs and have a significant effect on the success of hydraulic fracturing stimulation. However, only a few studies have focused on this heterogeneity, and the propagation mechanism of hydraulic fractures related to the coal macrolithotype is not well understood. In this study, we considered the Hancheng area, Ordos Basin, China, as an example to understand macrolithotype differences, establish finite element numerical models of the cohesive zone, and evaluated the hydraulic fracture initiation and vertical propagation behavior of laminated coal reservoirs. We used physical experiments, such as direct shear test and Digital Image Correlation (DIC), along with finite element simulation and a finite element model;; the results show that the tensile strength of bright coal is the lowest and that of dull coal is the greatest;; the average cohesion and shear strength of the bright-dull coal interface are 0.418 MPa and 1.3778 MPa (o = 3 MPa), respectively. Notably, behavioral differences are likely to impact the geometric evolution of hydraulic fractures. In the numerical models of hydraulic fracturing for a laminated coal reservoir, the hydraulic fracture propagates predominantly vertically as the interlayer has a lower elastic modulus and higher tensile strength. Because the interfacial shear strength is weak, the fractures can easily penetrate and propagate into the bedded interface between layers, and often, the distance of lateral slip increases into the interlayer interface. Thus, when dull coal is fractured, the geometry of the hydraulic fracture is often characterized as an isolated fracture distribution. The fracture then, rapidly propagates into the interlayer, activating the natural fractures in the bright coal reservoir, thus improving the fracture scale in the interlayers (model 2). However, as bright coal is a productive strata, the geometry of the hydraulic fracture is also dominated by crisscross network structures, and the fractures preferentially propagate along the interface (model 1).
      原文链接:
    • NSTL

    Geochemical characteristics and the organic matter enrichment of the Upper Ordovician Tanjianshan Group, Qaidam Basin, China

    Yuping WuChenglin LiuYongjun Liu
    14页
    查看更多>>摘要：Organic matter enrichment and preservation are significant in the formation of source rocks. The Lower Paleozoic source rocks of the Qaidam Basin have not been extensively studied. We collected outcrop samples in order to examine the sedimentary environment, evolution, and abundance of the organic matter in the "a" member of the Upper Ordovician Tanjianshan Group from the northern margin of the Qaidam Basin. We applied detailed geochemical and mineralogical techniques (including X-ray diffraction, X-ray fluorescence spectrometry, Rock-Eval pyrolysis and gas chromatography-mass spectrometry) to assess its source rock potential, paleoenvironmental setting, analyze the main controlling factors associated with enrichment of organic matter and present an organic matter enrichment model. The results show that the total organic carbon content in the "a" member is elevated, with an average value of 1.75 wt%. Additionally, the organic matter has reached a mature-overmature stage (ReqU>1.8%), and the kerogen was mainly type 111. The ratios of Sr/Cu, Rb/Sr, Cvaiue and CIA reflect hot-arid paleoclimatic conditions during the deposition of the mudstone. Paleoredox indicators V/(V + Ni), 8U, Ceanomaiy, and Ce/La reveal the mudstones formed in an anoxic environment. Paleowater depth indicators Mn/Fe and Mn/Ti show that the depth of the sedimentary water was shallower than 250 m. Meanwhile, the Mo/TOC value and the U-Mo co-variation model indicate that it was deposited under strongly restricted conditions. The apparent hot-arid climatic conditions were not conducive for the reproduction of algae, which limited paleoproductivity. The formation of strong restricted water conditions and a stratified water column were caused by the change of paleowater depth that positively affected the organic matter accumulation. The TOC content has a good correlation with paleoredox conditions, but does not correlate with the paleo-bioproductivity index P/Ti and Ba/Al. Therefore, the present research suggests the formation of these rocks was mainly based on preservation conditions, resulting from the restricted water setting, and paleoredox conditions, which played a significant role in the organic matter enrichment.
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    • NSTL

    Mechanism and geological significance of anomalous negative δ~(13) C_(kerogen) in the Lower Cambrian, NW Tarim Basin, China

    Taohua HeWenhao LiShuangfang Lu
    11页
    查看更多>>摘要：The Lower Cambrian black strata with an anomalous negative excursion of carbon isotope in organic carbon are widely developed in many continents, contracting few attentions from scholars around the world. Based on the detailed investigations for the strata from the Xiaoerbulake and Shiairike outcrop sections located in the Aksu area, northwest Tarim Basin, multiple test and analysis methods including the total organic carbon (TOC), carbon isotope of kerogen (δ~(13)C_(Kerogen)), aryl isoprenoids and major/trace elements were systematically performed to reveal the mechanism and developmental model for the anomalous negative δ~(13)C_(kerogen). This anomalous negative excursion was caused by the coupling of paleoweathering and hydrothermal activities. Euxinic bottom water created by hydrothermal activities made the organic carbon (CO2 or HCO3") from the decomposing organisms as the additional carbon source of phytoplankton photosynthesis, resulting in the development of ~(13)C-depleted original organisms. Insufficient availability of essential nutrient (particularly Fe) caused by paleoweathering enhanced the low growth rate, resulting in the development of more ~(13)C-depleted original organisms during the deposition of the organic-poor siliceous shales compared to that of the organic-rich shales. Besides, TOC was mainly affected by the dilution of high concentrations of hydrothermal SiO2, resulting in the organic-rich shales under weak hydrothermal conditions, while the organic-poor siliceous shales under strongly hydrothermal condition. Importantly, the production of anomalous negative δ~(13)C_(Kerogen) triggered the occurrence of diagnostic biomarkers, aryl isoprenoids, indicating the photic zone euxinia. These contributes allow for potential application for deep petroleum exploration in the Lower Paleozoic in the Tarim Basin and insights for biological evolution.
      原文链接:
    • NSTL