Numerical modeling for identification of closure pressure from diagnostic fracture injection tests

textDiagnostic fracture injection tests (DFIT) are used to estimate the magnitude of the minimum principal stress, which is assumed to be equal to fluid pressure at the moment of fracture closure. A small volume of water is injected into formation to create a fracture, the well is shut in, and eventually the fracture closes. The pressure during shut-in can be analyzed by several pressure transient methods to pick the time of fracture closure. Pressure at that time is taken to be the fracture closure pressure. In this study, DFIT simulations are performed with a fully numerical hydraulic fracturing simulator. Sensitivity analysis is done to investigate how reservoir parameters such as fracture toughness, permeability, fracture stiffness, and the magnitude of the minimum principal stress impact the DFIT pressure transient. Based on these insights, we use the simulator to match a DFIT pressure transient from a low permeability formation. We analyze the field data with conventional methods for picking closure. The simulation matches suggest that the conventional methods can underestimate the closure pressure in low permeability formations. Based on our results, we propose a new method for picking fracture closure based on the evolution of fracture compliance during closure. Our simulations provide insight into how the fracture compliance impacts to pressure transient. Assuming the closure pressure from our simulations matches to the data are correct, our proposed method picks the correct closure point. This study includes simulation matches to the field data with simulations that use complicated fracture geometry, which may be realistic in some formations. The multiple fractures cases have similar pressure transients and similar reservoir parameters as the single hydraulic fracture simulations, indicating that network complexity will not necessarily be evident from the pressure transient. In the future, DFIT simulations with more complex fracture geometries will be conducted to understand how fracture geometry affects the DFIT pressure transient.Petroleum and Geosystems Engineerin

Investigation of coupled thermo-chemo-mechanical processes for safe carbon geological storage

Safe and permanent CO₂ storage in geological formations requires reservoir geomechanical stability. Injection of CO₂ into the subsurface changes the local pore pressure and, further, alters the effective stresses due to poro-thermo-chemo-mechanical coupled responses. Changes of pore pressure and effective stress may disrupt the host formation mechanical equilibrium. This alteration may result in geomechanical failure events such as fault reactivation and hydraulic fracturing. Such events can favor fluid migration paths for injected CO₂, induce seismic activity, and cause surface uplift. Examples of field observations during CO₂ injection include: (1) surface uplift at the In Salah project in Algeria, (2) absence if bottom-hole pressure (BHP) increase during injection in Cranfield, Mississippi, and (3) induced seismicity with magnitude M>1 in Decatur, Illinois. In this context, accurate estimations of pore pressure build up and local stress alteration induced by CO₂ injection are critical to avoid geomechanical perturbations. However, current models and predictions often assume relatively homogeneous reservoirs without taking into account compositional behavior. Further, the effects of temperature and chemical reactions have not been rigorously incorporated into the interpretation of local stress alteration and the well response to CO₂ injection. This dissertation shows geomechanical analyses of CO₂ geological sequestrations by three field case studies: Frio CO₂ sequestration pilot test in Texas, Cranfield CO₂ sequestration in Mississippi, and Crystal Geyser in Utah. Both Frio and Cranfield case studies are studied with the help of reservoir simulation and history matching of field data including assimilation of vertical heterogeneity from well-logging analysis and calibration with laboratory experiments. The Frio case study focuses on examination of reservoir capacity of a compartmentalized volume to avert fault reactivation. The Cranfield case study analyzes the influence of thermo-chemo-elastic processes on wellbore fracturing induced by CO₂ injection. The Crystal Geyser case study investigates the long-term chemical effects of CO₂-charged brine on rock mechanical properties through analyses and measurements on rock samples from the field, where a natural CO₂ leakage analog exists. The following conclusions are a result of this dissertation. CO₂ dissolution into brine reduces pore pressure build up significantly in small and compartmentalized reservoirs. Thermo-elastic and chemo-elastic effects alter local stresses and may trigger injector fracturing at bottom-hole pressures lower than expected. Capturing phase behavior, coupled thermo-chemo-mechanical processes, and reservoir heterogeneity are important factors to estimate reservoir capacity and prevent geomechanical perturbations.Petroleum and Geosystems Engineerin

Indoor place categorization using co-occurrences of LBPs in gray and depth images from RGB-D sensors

Indoor place categorization is an important capability for service robots working and interacting in human environments. This paper presents a new place categorization method which uses information about the spatial correlation between the different image modalities provided by RGB-D sensors. Our approach applies co-occurrence histograms of local binary patterns (LBPs) from gray and depth images that correspond to the same indoor scene. The resulting histograms are used as feature vectors in a supervised classifier. Our experimental results show the effectiveness of our method to categorize indoor places using RGB-D cameras

Re-examining interpretations of non-ideal behavior during diagnostic fracture injection tests

AbstractDiagnostic fracture injection tests (DFITs) are performed in low permeability formations to estimate the minimum principal stress, formation pressure, permeability, and other parameters. G-function derivative plots are used for diagnosing fracture closure and “non-ideal” reservoir processes. In this study, we use a discrete fracture network hydraulic fracturing simulator to investigate non-ideal DFIT mechanisms. The simulator fully couples fluid flow with the stresses induced by fracture deformation. DFITs are simulated for six different scenarios: a single hydraulic fracture, multiple fracture strands, opening of transverse fractures, near-wellbore complexity, far-field complexity, and height recession. The results indicate that pressure transient behavior commonly ascribed to “fracture height recession,” “closure of transverse fractures,” and “fracture tip extension” are likely to be misinterpreted by conventional techniques. In previous studies, we found that a curving upward G×dP/dG plot is caused by changing fracture stiffness after closure and that the closure pressure is best picked when G×dP/dG begins to deviate upward. In contrast, the commonly used “tangent” method can significantly underestimate the minimum principal stress. The results of this study confirm those prior results. The results suggest that in most cases, it should be possible to use pump-in/flowback tests to confirm estimates of the minimum principal stress. However, if a flow bottleneck occurs at the wellbore due to near-wellbore complexity, the pump-in/flowback test may be uninterpretable

Categorization of indoor places by combining local binary pattern histograms of range and reflectance data from laser range finders

This paper presents an approach to categorize typical places in indoor environments using 3D scans provided by a laser range finder. Examples of such places are offices, laboratories, or kitchens. In our method, we combine the range and reflectance data from the laser scan for the final categorization of places. Range and reflectance images are transformed into histograms of local binary patterns and combined into a single feature vector. This vector is later classified using support vector machines. The results of the presented experiments demonstrate the capability of our technique to categorize indoor places with high accuracy. We also show that the combination of range and reflectance information improves the final categorization results in comparison with a single modality

Indoor Place Categorization using Co-Occurrences of LBPs in Gray and Depth Images from RGB-D Sensors

Abstract-Indoor place categorization is an important capability for service robots working and interacting in human environments. This paper presents a new place categorization method which uses information about the spatial correlation between the different image modalities provided by RGB-D sensors. Our approach applies co-occurrence histograms of local binary patterns (LBPs) from gray and depth images that correspond to the same indoor scene. The resulting histograms are used as feature vectors in a supervised classifier. Our experimental results show the effectiveness of our method to categorize indoor places using RGB-D cameras

Assessment of glomerular filtration rate with dynamic computed tomography in normal Beagle dogs

The objective of our study was to determine individual and global glomerular filtration rates (GFRs) using dynamic renal computed tomography (CT) in Beagle dogs. Twenty-four healthy Beagle dogs were included in the experiment. Anesthesia was induced in all dogs by using propofol and isoflurane prior to CT examination. A single slice of the kidney was sequentially scanned after a bolus intravenous injection of contrast material (iohexol, 1 mL/kg, 300 mgI/mL). Time attenuation curves were created and contrast clearance per unit volume was calculated using a Patlak plot analysis. The CT-GFR was then determined based on the conversion of contrast clearance per unit volume to contrast clearance per body weight. At the renal hilum, CT-GFR values per unit renal volume (mL/min/mL) of the right and left kidneys were 0.69 ± 0.04 and 0.57 ± 0.05, respectively. No significant differences were found between the weight-adjusted CT-GFRs in either kidney at the same renal hilum (p = 0.747). The average global GFR was 4.21 ± 0.25 mL/min/kg and the whole kidney GFR was 33.43 ± 9.20 mL/min. CT-GFR techniques could be a practical way to separately measure GFR in each kidney for clinical and research purposes

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Local N-ary patterns: a local multi-modal descriptor for place categorization

This paper presents an effective integration method of multiple modalities such as depth, color, and reflectance for place categorization. To achieve better performance with integrated multi-modalities, we introduce a novel descriptor, local N-ary patterns (LTP), which can perform robust discrimination of place categorization. In this paper, the LNP descriptor is applied to a combination of two modalities, i.e. depth and reflectance, provided by a laser range finder. However, the LNP descriptor can be easily extended to a larger number of modalities. The proposed LNP describes relationships between the multi-modal values of pixels and their neighboring pixels. Since we consider the multi-modal relationship, our proposed method clearly demonstrates more effective classification results than using individual modalities. We carried out experiments with the Kyushu University Indoor Semantic Place Dataset, which is publicly available. This data-set is composed of five indoor categories: corridors, kitchens, laboratories, study rooms, and offices. We confirmed that our proposed method outperforms previous uni-modal descriptors