Newly developed high-speed, synchrotron-based X-ray computed microtomography enabled us to directly image pore-scale displacement events in porous rock in real time. Common approaches to modeling macroscopic fluid behavior are phenomenological, have many shortcomings, and lack consistent links to elementary porescale displacement processes, such as Haines jumps and snap-off. Unlike the common singular pore jump paradigm based on observations of restricted artificial capillaries, we found that Haines jumps typically cascade through 10-20 geometrically defined pores per event, accounting for 64% of the energy dissipation. Real-time imaging provided a more detailed fundamental understanding of the elementary processes in porous media, such as hysteresis, snapoff, and nonwetting phase entrapment, and it opens the way for a rigorous process for upscaling based on thermodynamic models.hydrology | oil recovery | multiphase flow
During imbibition, initially connected oil is displaced until it is trapped as immobile clusters. While initial and final states have been well described before, here we image the dynamic transient process in a sandstone rock using fast synchrotron‐based X‐ray computed microtomography. Wetting film swelling and subsequent snap off, at unusually high saturation, decreases nonwetting phase connectivity, which leads to nonwetting phase fragmentation into mobile ganglia, i.e., ganglion dynamics regime. We find that in addition to pressure‐driven connected pathway flow, mass transfer in the oil phase also occurs by a sequence of correlated breakup and coalescence processes. For example, meniscus oscillations caused by snap‐off events trigger coalescence of adjacent clusters. The ganglion dynamics occurs at the length scale of oil clusters and thus represents an intermediate flow regime between pore and Darcy scale that is so far dismissed in most upscaling attempts.
With recent advances at X-ray microcomputed tomography (μCT) synchrotron beam lines, it is now possible to study pore-scale flow in porous rock under dynamic flow conditions. The collection of four-dimensional data allows for the direct 3-D visualization of fluid-fluid displacement in porous rock as a function of time. However, even state-of-the-art fast-μCT scans require between one and a few seconds to complete and the much faster fluid movement occurring during that time interval is manifested as imaging artifacts in the reconstructed 3-D volume. We present an approach to analyze the 2-D radiograph data collected during fast-μCT to study the pore-scale displacement dynamics on the time scale of 40 ms which is near the intrinsic time scale of individual Haines jumps. We present a methodology to identify the time intervals at which pore-scale displacement events in the observed field of view occur and hence, how reconstruction intervals can be chosen to avoid fluid-movement-induced reconstruction artifacts. We further quantify the size, order, frequency, and location of fluid-fluid displacement at the millisecond time scale. We observe that after a displacement event, the pore-scale fluid distribution relaxes to (quasi-) equilibrium in cascades of pore-scale fluid rearrangements with an average relaxation time for the whole cascade between 0.5 and 2.0 s. These findings help to identify the flow regimes and intrinsic time and length scales relevant to fractional flow. While the focus of the work is in the context of multiphase flow, the approach could be applied to many different μCT applications where morphological changes occur at a time scale less than that required for collecting a μCT scan.
Textual cues are essential for everyday tasks like buying groceries and using public transport. To develop this assistive technology, we study the TextVQA task, i.e., reasoning about text in images to answer a question. Existing approaches are limited in their use of spatial relations and rely on fully-connected transformer-based architectures to implicitly learn the spatial structure of a scene. In contrast, we propose a novel spatially aware self-attention layer such that each visual entity only looks at neighboring entities defined by a spatial graph. Further, each head in our multi-head self-attention layer focuses on a different subset of relations. Our approach has two advantages: (1) each head considers local context instead of dispersing the attention amongst all visual entities; (2) we avoid learning redundant features. We show that our model improves the absolute accuracy of current state-of-the-art methods on TextVQA by 2.2% overall over an improved baseline, and 4.62% on questions that involve spatial reasoning and can be answered correctly using OCR tokens. Similarly on ST-VQA, we improve the absolute accuracy by 4.2%. We further show that spatially aware self-attention improves visual grounding.
Recently, various companies published sophisticated design methodologies to engineer the ‘cement’ sheath in a oil/gas well completion such that the zonal isolation would remain intact (i.e.pressure tight) during its projected lifetime. Loading within a prescribed design envelope (e.g. pressure and/or thermal cycling or mechanical compaction processes) are the main considerations. Improved performance of a candidate zonal isolation material is achieved by adjusting its material properties, especially the Young's modulus and the compressibility. These earlier studies indicated that apart from a proper mechanical characterisation of the ‘cement sheath’ (preferably described by non-linear material models), the in-situ stresses in the ‘cement’ play a prominent role as well. The latter are influenced by the volumetric behaviour of the slurry during setting and the thermal expansion coefficient of the set ‘cement’. However, often these parameters are not known for ‘real life’ well construction materials. Therefore, Shell International E & P B.V., the Netherlands, decided to design and construct dedicated laboratory equipment to determine those parameters for commercial ‘cement’ formulations at conditions encountered in typical well completions. A first feature of this unique system (which can operate at pressures up to 1500 Bar and temperatures up to 300°C) is to monitorthe progress of the ‘setting’ reaction of Oil Well Cements and or thermosetting resins,their reaction behaviour (from the onset of gelling to the ‘final set’) andthe softening or swelling phenomena encountered in thermoplastic and thermoset materials. The apparatus has inter alia the same functionality as conventional API Cement Consistometers or Ultrasonic Cement Analysers. However, it can also be used in combination with self-vulcanising rubbers, that cannot be used in the conventional API devices. A second aspect of the apparatus is the determination of the volume changes (at constant pressure) or alternatively the pressure changes (at constant volume), during setting of the cement (or resin) system. All measurements can be performed at either isothermal conditions or for prescribed temperature sweeps over time. Either volumetric properties (shrinkage or expansion) or compressibilities of cements / resin systems can be measured in a time frame ranging from the onset of gelling to far beyond ‘final set’. In yet another operational mode, the volume change of set materials as a function of temperature (i.e.their volumetric thermal expansion coefficient) can be quantified. In addition to a review of the principles of this novel apparatus, this paper also presents a typical application of the data in a Plug and Abandonment design (i.e. the Finite Element Engineering design of a thermally pre-stressed ‘rubber’ abandonment plug). Introduction The main purpose of primary cementing and well abandonment operations is to provide effective zonal isolation during the entire life span of the well. To achieve this objective the sealant should meet both the short-term and long-term requirements dictated by the well's operational regime. Traditionally, petroleum engineers have only concentrated on the compressive strength as a quality indicator; long-term properties such as resistance to downhole chemical attack were only occasionally considered. Until recently, no attention has been paid to other mechanical properties such as tensile strength, Young's modulus, etc. The conventional approach was acceptable if the sealant would not be subjected to a "large" change in stress level.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractRecently, various companies published sophisticated design methodologies to engineer the 'cement' sheath in a oil/gas well completion such that the zonal isolation would remain intact (i.e. pressure tight) during its projected lifetime. Loading within a prescribed design envelope (e.g. pressure and/or thermal cycling or mechanical compaction processes) are the main considerations. Improved performance of a candidate zonal isolation material is achieved by adjusting its material properties, especially the Young's modulus and the compressibility. These earlier studies indicated that apart from a proper mechanical characterisation of the 'cement sheath' (preferably described by non-linear material models), the in-situ stresses in the 'cement' play a prominent role as well. The latter are influenced by the volumetric behaviour of the slurry during setting and the thermal expansion coefficient of the set 'cement'. However, often these parameters are not known for 'real life' well construction materials. Therefore, Shell International E & P B.V., the Netherlands, decided to design and construct dedicated laboratory equipment to determine those parameters for commercial 'cement' formulations at conditions encountered in typical well completions. A first feature of this unique system (which can operate at pressures up to 1500 Bar and temperatures up to 300 o C) is to monitor i) the progress of the 'setting' reaction of Oil Well Cements and or thermosetting resins, ii) their reaction behaviour (from the onset of gelling to the 'final set') and iii) the softening or swelling phenomena encountered in thermoplastic and thermoset materials.
One of Shell's deepwater projects has decided to use the cost-saving Single Casing Combo Top-Tension Riser with nitrogen insulation for the Tension Leg Platform (TLP) dry-tree wells to reduce the overall riser cost and TLP payload. However, the thermal performance of such a riser is poorly understood and an accurate prediction model was not available. A conservative thermal-hydraulic design approach would result in redundant requirements for the flow assurance chemicals and unnecessary challenges for the TLP operations. Numerical and experimental work was carried out to better understand and predict the riser thermal performance during startup, normal operation, and shut-in conditions. This paper described the numerical and experimental results. The overall heat transfer coefficients (U-values) from the detailed numerical simulations and experiments were used to derive the effective thermal conductivity (k eff ) of the nitrogen in the annulus, which includes the effect of all three modes of heat transfer (i.e. conduction, radiation and convention). This effective conductivity for the nitrogen gas was used in a one-dimensional model for the riser. The results of that model give the operator confidence in the system design and operability. The main benefit for the project is less chemical storage weight and space required on the TLP. The experimental and numerical model, with some modifications as required, can be used to optimize performance of riser systems in other projects as well.
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