Lee, Wei Yi (Centre of Subsurface Seismic Imaging, CSI, Universiti Teknologi PETRONAS) | Hamidi, Rosita (Centre of Subsurface Seismic Imaging, CSI, Universiti Teknologi PETRONAS) | Ghosh, Deva (Centre of Subsurface Seismic Imaging, CSI, Universiti Teknologi PETRONAS) | Musa, Mohd Hafiz (Centre of Subsurface Seismic Imaging, CSI, Universiti Teknologi PETRONAS)
Noise is the unwanted energy in a seismic trace opposed to the signals corresponding to reflected energy from the subsurface features. Since it can overlap with the main signals' energy and conceal the geological information, noise attenuation is one of the most important steps in seismic data processing. The most common method is frequency filtering. However, due to its limitations on separating the noise from signals, this method usually results in hurting the signal. Hence, it is important to develop an alternative method that can attenuate the noise without affecting the signal. Filters based on time-frequency analysis of the data can have a better separation of the noise from signal as they maintain the time localization of events while presenting their frequency content simultaneously. One of the recent approaches to time-frequency analysis of signals is the Empirical Wavelet Transform (EWT) which provides adaptive wavelet filter bank for signal analysis. In this paper, a filter is designed based on EWT for random noise attenuation and is applied on both synthetic and real data.
The present paper is concerned with an experimental study of the acoustic signature of phase inversion in an oil-water mixture system. The system studied was used to correlate the process of phase inversion with the acoustic field generated during the two fluid mixing. The experimental results revealed that the relation between the acoustic fields produced by a water continuous dispersion and the phase inversion has a clear and different signature from an oil-continuous system using a batch mixing system. This dynamical characteristic of the phase inversion phenomenon could be of use in practical systems to detect phase inversion when it occurs based on the acoustic field measured in the subject process.
In this paper we focus on electrical-submersible-pump (ESP) failure caused by scale buildup. Weak fluctuations recorded in the motor current signals several weeks before a failure indicate a change in the motor load. Advanced signal analysis of the motor current data reveals the presence of a dynamic characteristic in the ESP signal during rapid scale buildup in the pump stages. On the basis of the raw data from the motor current draw, a dynamic cascade can be identified in the current marked with the superimposition of several characteristic frequencies added over time that develop into a chaotic trend. Our analysis was conducted with different signal-processing tools, such as Fourier transform, wavelet transform, and chaotic attractors, which described the nature of the scale signature in the current logs. This analysis was the first step toward developing a real-time diagnostic tool for predicting ESP failures.
Due to the shift from conventional reservoirs towards unconventional, ultra-low permeability reservoirs in the last decade, Diagnostic Fracture Injection Test (DFIT) has become one of the dominant and economically practical pressure transient tests. It is crucial to analyze and interpret DFIT data correctly to obtain essential fracture design and reservoir parameters. This study presents the application of wavelet analysis to DFIT falloff pressure data to determine fracture closure pressure and time, to ultimately improve the overall efficiency of hydraulic fracturing designs.
In this study, DFIT pressure is treated as a non-stationary signal and analyzed by one of the signal processing techniques which is wavelet transformation. The purpose of signal analysis is to extract relevant information from a signal by transforming it. Firstly, the signal is transformed into wavelet domain by Discrete Wavelet Transformation (DWT) to calculate high-frequency wavelet coefficients (details), then change-point detection technique is applied to distinguish major changes within the coefficients trend to determine fracture closure pressure and time.
DFIT pressure decline data from different wells were analyzed by wavelet transformation. Detail coefficient demonstrates different patterns depending on the formation analyzed and near wellbore activities. This is expected because wavelet analysis is sensitive to any physical changes within the system. From the amplitude changes of the coefficients, wavelet tool demonstrates the fracture closure as a continuing process.
Because wavelet is sensitive to changes in the system, it detects the fracture closure unambiguously by amplitude change, as compared to slope changes in other conventional methodologies. A comparison with some of the most commonly used diagnostic techniques, conventional log-log diagnostic plot, square root time, G-function and its derivative analysis are also provided in this study.
There have been several publications discussing various techniques analyzing DFIT pressure decline in unconventional formations and yet there is relatively high uncertainty in before-closure-analysis. However, this methodology is more sensitive to fundamental changes in the system, so application in detecting closure pressure and time decreases the uncertainty compared to other conventional tangential methodologies.
Wei Chen, Yu Zhou, and Weigang Yu, Soochow University, and Leilei Yang, China University of Petroleum, Beijing Summary In this study, shale samples were heated under inert and noninert environments to increase the permeability of the shale. It was found that pore diameters increased under all the gas environments. Pore diameters increased more significantly under air environment compared with other gas conditions. However, the diameters of the shale particles remained almost constant during combustion. Moreover, gases emitted from the shale during the combustion and pyrolysis process were investigated using thermogravimetric analysis coupled to Fourier-transform infrared spectroscopy (TGA-FTIR). Finally, scanning electron microscopy (SEM) images showed larger pores on the surfaces of the combusted and pyrolyzed shale samples.
Goraya, Yassar (Adnoc Offshore) | Nair, Rajeev Nair (Fugro) | AL-Neaimi, Ahmed Khalifa (Adnoc Offshore) | AL-Felasi, Ali (Adnoc Offshore) | Kleef, Franciscus Johannes (Adnoc Offshore) | Al-Dhafari, Bader (Adnoc Offshore) | El-Sayed, Mohamed Abdul-Khalek (Adnoc Offshore) | Akram, Fazeel (Adnoc Offshore) | AL-Hosani, Ibrahim Ali (Adnoc Offshore)
During a routine tower maintenance visit, gas bubbles were observed at sea bed. The challenge now was to identify the source of the gas leak and identify areas where gas had accumulated. The observed gas seep, escaped from the seabed to the water column and was in the vicinity of the TWR-2 platform as confirmed during a diving survey. A geophysical survey was initiated to understand if gas had accumulated in the subsurface and whether it was safe to approach the site with a rig to kill the well.
This paper presents a novel/cost-effective hydrophobic material based 9-octadecenoic acid grafted graphene (POG) for oil/water separation. Graphene derived from graphite was modified with 9-octadecenoic acid to obtain 9-octadecenoic acid grafted graphene (OG). Then, emulsion polymerization of styrene was performed on OG to produce polystyrene branches on 9-octadecenoic acid grafted graphene (POG). Three different composites were prepared by varying the amount of 9-octadecenoic acid grafted graphene used as follows: POG25, POG50, and POG75. The three materials were characterized by using N2-physisorption and Fourier transform Infra-red (FTIR). The BET surface area of POG75 was 288 m2/g while POG50 was 225 m2/g and POG25 was 79 m2/g. These materials were evaluated for their oil/water separation efficiency using model mixture. The results showed that the higher the ratio of the 9-octadecenoic acid grafted graphene, the higher the oil removal efficiency of the material and the faster the rate of the adsorption. The materials showed not only high efficiency but also fast uptake of the certain quantity of the oil just within 1 minute. This can be explained by the high hydrophobicity nature of the materials which repel the water as confirmed by the contact angle of approximately 150°. POG75 showed promising results to be a good candidate adsorbent materials for oil removal from produced water where it displays the highest adsorption capability to organic compounds and the highest BET surface area. POG75 was regenerated and its performance was tested again. This material showed a slightly reduced adsorption rate in the first cycle compared to the fresh material. However, the adsorption rate was constant for the next several cycles. POG75 has the potential to be utilized to remove oil contaminants from produced water.
Long, Yifu (Missouri University of Science and Technology) | Yu, Bowen (Missouri University of Science and Technology) | Zhu, Changqian (Research Institute of Petroleum Exploration and Development, PetroChina)
Conformance improvement for ultra-high-temperature (130 °C) reservoirs is challenging due to the poor thermostability of conventional preformed particle gel (CPPG). To overcome the defect of thermal degradation, a novel hydrostable PPG (HT-PPG) was developed using the high-temperature tolerant crosslinker. In this work, a comparative study between the HT-PPG and CPPG has been presented in respects of their swelling behaviors, rheology properties and thermal stabilities. Particle swelling behaviors and viscoelasticities were firstly assessed in ambient. Using the swollen particles, a long-term aging at 130 °C underwent during which the physical status was monitored through high pressure vials (HPV). Furthermore, characterizations involved Scanning Electron Microscope (SEM) and Fourier Transform-Infrared Spectroscopy (FT-IR) were performed for both virgin and aged specimen. Thereby, an observation of gel microstructures and elucidation upon bonds or functional groups were provided. In addition to aging tests, we deployed the Differential Scanning Calorimetry (DSC) to investigate the inflection temperature as another indicator of particle thermostability. Attributed to the hydrostable crosslinker, the HT-PPG withstood 130 °C for at least 90 d. It was found that the HT-PPG effectively maintained its particulate shape, whereas, the CPPG completely degraded after 3-d aging. The HT-PPG maintained 28.8% of its initial storage modulus (G′). On the contrary, the normalized elasticity (G′/G0‘) of CPPG was only 0.43%. The SEM morphologies illustrated HT-PPG kept its rigid microstructure even after 90-d aging, while indicated destruction within CPPG network. According to FT-IR characterization, the decomposition of pristine crosslinker, N,N′-Methylenebisacrylamide in CPPG may account for its instability. DSC measurements furtherly demonstrated the favorability of HT-PPG in which HT-PPG exhibited a higher inflection temperature of 133.1 °C, however, CPPG only had an inflection temperature of 127.7 °C. This work turned out the novel HT-PPG could withstand ultra-high-temperature (130 °C) for more than 90 d, maintaining its particulate shape and viscoelasticity. This a durable plugging agent was notably superior to the CPPG, offering a candidate material for the conformance improvement in ultra-high-temperature reservoirs.
Micro-seismic and acoustic emission (AE) activities resulting from rock failure are among the main parameters used for understanding the rock burst phenomenon in tunnel excavation. To evaluate the mechanism of AE behavior with rock failure, AE is measured by conducting a rock triaxial compression test. The test results are then used to evaluate the characteristics of AE behavior resulting from rock failure. The laboratory test results are subsequently compared to simulate the AE occurrence behaviors due to rock failure by using the particle flow code (PFC) method. The AE event, AE amplitude, AE frequency, and b-value that are measured by using PFC are able to simulate the actual rock failure. The simulated rock burst signals are closely related to the AE measurements obtained from the rock triaxial compression test.
Rock burst is a type of rock failure that occurs when strain energy is rapidly released by an unstable rock mass, which is usually triggered by deep underground excavation (Hoek and Brown, 1997; Rudajev et al., 2000; Beck and Brady, 2002; Weng et al., 2017). Acoustic emission (AE) is measured by conducting a rock triaxial compression test to predict and evaluate the mechanism and progress of rock burst. The AE occurrence behaviors resulting from rock failure are also simulated by using the particle flow code (PFC) method. The number of AE occurrences, waveform frequency, amplitude value, and b-value obtained from the PFC analysis are then modelled, and the analysis results are subsequently compared with the AE measurements obtained from the rock triaxial compression test. The AE occurrence behaviors obtained from the PFC simulation are discussed below along with the results of the rock triaxial compression test.
2. AE measurements obtained from the rock triaxial compression test
2.1 Testing method and equipment
As shown in Table 1, the rock specimen used for this study was hard granite. The test pieces were prepared by using a boring core with a diameter of 50 mm and height of 100 mm. Figure 1 shows the apparatus for the rock triaxial compression test and AE measurement. AE sensors were placed on the top and bottom pedestals of the stress chamber. The loading pattern was recorded by using the strain control method, and the triaxial compression test was performed at confining pressures of 0.5, 10, 20, 30, and 40 MPa. AE was measured throughout the rock triaxial compression test by using several parameters, including the number of AE events, the frequency of the AE signal wave as obtained by conducting a fast Fourier transform (FFT) analysis and by using the AE signal waveform, the amplitude value of the AE signal waveform, and b-value. All these parameters were obtained by performing calculations based on the amplitude value of the waveform (Mori et al., 2003).
Corredor, Laura (Department of Chemical and Petroleum Engineering, University of Calgary) | Maini, Brij (Department of Chemical and Petroleum Engineering, University of Calgary) | Husein, Maen (Department of Chemical and Petroleum Engineering, University of Calgary)
The objective of this study was to examine the feasibility of improving the performance of EOR polymers by adding surface modified silica nanoparticles (NP). The nano-polymer sols were prepared by mixing different types of surface modified silica NP and hydrolyzed polyacrylamide (HPAM) or xanthan gum (XG) solutions. It is well known that the compatibility between organic polymer-inorganic oxide filler increases when the surface of the inorganic filler is chemically modified. To generate different interfacial interactions, the silica NP were treated by chemical grafting with carboxylic acids and silanes. The properties of the modified silica NP were characterized using Fourier transform infrared spectroscopy (FTIR) and the properties of the nano-polymer sols were investigated with viscometry and ζ-potential measurements. The non-Newtonian behavior of the nano-polymer sols was represented by Oswald-de Waele model.
Areal sweep efficiency of viscous oil displacements by nano-polymer sols was measured at 25°C in a Hele-Shaw cell representing one-quarter of a five-spot pattern. The fingering patterns of all XG samples were characterized by the formation of branched structures (at earlier growth stage) which by merging and coalescing formed stable interfaces. It was the expected behavior considering the high shear-thinning strength of the XG polymer and nano-polymer sols (n values between 0.17 and 0.27). However, the HPAM solutions and nano-polymer sols exhibited different fingering patterns with tip-splitting or suppressed tip-splitting and side-branching. This difference was attributed to different interactions between the modified NP and the polymeric chains of the two polymers.
The areal sweep efficiency of the HPAM polymer solutions did not improve by the addition of any type of NP because of the reduction of the viscosity of the polymer solution and the reduction of the interfacial tension between the injection fluid and oil. However, the XG polymer solutions, modified with the addition of 1.0 and 2.0 wt.% NP provided considerably improved sweep efficiency. The results are promising and show good potential for improving the performance of polymer flooding with Xanthan gum by addition of silica NP.