How to effectively identify the oil and water layer has been a difficult problem in the hydrocarbon indicator (HCI). It is generally believed that the oil layer has the characteristics of low frequency enhancement and high frequency attenuation on the frequency spectrum. But in the actual application, the amplitude and frequency characteristics of the thicker water layer are very similar to that of the oil layer, which makes it hard to distinguish one from the other. In this paper, in order to identify the oil and water layer, a new method basis on matching pursuit decomposition (MPD) is proposed. Firstly, the time-frequency analysis of seismic data is carried out though high precision MPD method. Through analyzing the instantaneous amplitude at different frequencies, we consider that the main difference of the oil and water layer in the frequency spectrum is at the high frequency band where the oil layer shows relatively strong amplitude characteristics. Secondly, base on the high frequency resonance (HFR), the high frequency bright spot attribute is calculated from the frequency division data in the high frequency range. In this new attribute, the water layer is suppressed by the strong amplitude of the oil layer. Finally, the results of the HCI are obtained by multiplying the new attribute with the −90 degree phase shift of the seismic data. The forward modeling test and actual application in Bohai oilfield show that the high frequency bright spot method is more effective in suppressing the water layer and identifying thinner oil layers compared with the conventional low frequency and high frequency attenuation methods of HCI.
The Kirchhoff Q PSDM technique is studied in this paper in order to compensate the amplitude and correct the distortion of phase due to seismic attenuation in the earth, during the seismic waves traveling through the earth, especially through the the gas cloud region, to improve the resolution of the imaging results, and to satisfy the requirements of industrial production. In order to improve the calculation efficiency of the QPSDM, a time domain interpolation strategy is also proposed. This strategy avoids the compensation in frequency doamin at each imaging point, which is time-consuming. The computation efficiency of Q migration has been greatly improved with our method, making the Kirchhoff QPSDM able to meet the needs of industrial production. By analyzing the sources of the high frequency noise, the time-variant gain-limits are used to suppress the high frequency noise in the compensation procedure. The numerical results show that the compensation method using the time-variant gain-limits can effectively compensate the energy of the severe attenuation region while suppressing the high-frequency noise. Finally, we test the QPSDM approach on synthetic data and field data. These examples demonstratethat the QPSDM approach could produce higer resolution images with imporoved amplitude and correct phase compared to the convetional PSDM. The Kirchhoff QPSDM technology realized in this paper has produced desirable seismic images while it is applied in many exploration areas such as Dagang, Daqing, Malaysia, Nanhai, etc.
This paper presents an alternative solution for gas cloud imaging using full wavefield migration (FWM). The application of FWM method have been applied on both synthetic dataset with gas cloud event and existing field with gas cloud issue. The full wavefield migration is an inversion-based imaging algorithm that utilizes the complete reflection measurements: primaries as well as all multiples, both surface and internal to obtain the total reflections measurement. It combines the primary and higher order scattering reflection from the gas cloud to estimate the true amplitude response below the gas cloud. Successful applications to both synthetic and field data examples demonstrate that FWM improves the imaging illumination and resolution below gas cloud as compared to conventional migration.
Least-squares migration (LSM) has become an increasingly important imaging tool in the seismic industry. It can successfully address imaging issues related to insufficient illumination and mitigate both migration artifacts and noise. More recently, a number of case studies from around the world have shown that LSM provides greatly improved seismic imaging. However, only a few examples reveal its advantages in both imaging and amplitude-versus-offset (AVO) inversion. For the amplitude aspect, compensating the effect of anelastic absorption and elastic scattering during propagation inside the earth has become increasingly popular over the past few years. The anelastic absorption and elastic scattering causes frequency-dependent amplitude decay, phase distortion, and resolution reduction. This is often quantified by the quality factor commonly called Q model. This effect can be largely compensated through Q prestack depth migration (QPSDM). Therefore, QPSDM has become an effective solution for seismic imaging in areas where strong absorption anomalies exist in the overburden. However, the excessive noise often resulting from QPSDM poses a big challenge to its application. In this paper, we propose a least-squares Q migration (LSQM) method that combines the benefits of both LSM and QPSDM to improve the amplitude fidelity and image resolution of seismic data. We also demonstrate that both seismic imaging and AVO inversions at wells can be significantly enhanced through image-domain single-iteration least-squares QPSDM Kirchhoff migration.
Bao, Yi (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Wang, Cheng (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Chen, Shu-min (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Wang, Jian-min (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Chen, Zhi-de (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Pei, Jiang-yun (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.) | Wu, Jia-yi (Exploration and Development Research Institute of Daqing Oilfield Company Ltd. CNPC.)
The existing seismic data in the deep layer of Songliao Basin have low vertical resolution, poor imaging accuracy and weak ability to depict anisotropy of seismic data, so the seismic data can not meet the geological requirements of fine target characterization. In order to identify thinner reservoirs and smaller faults in deep and complex structural areas, to complete sequence subdivision on volcanic rocks of Yingcheng formation and the dense sand of Shahezi formation, BWH seismic data acquisition is deployed in Anda sag. Aiming at the characteristics of clear description of BWH wave field but low SNR. A Full-frequency Fidelity and Amplitude preserving processing Technology (Flow) supported by surface consistent time-varying pulse deconvolution and viscoelastic medium prestack time migration and depth migration techniques is formed. Compared with the old data, the target band width of the BWH data has been widened by 15 Hz, the imaging quality of the complex structural area is improved obviously, and the prediction coincidence rate of the thin sand body over 8m is increased by more than 10 percentage points. The thin interbed is developed in continental sedimentary basin, and the horizontal heterogeneity is serious. The BWH acquisition and full frequency amplitude preserving processing technology will bring a new solution for fine target exploration in deep and complex structural area of Continental Sedimentary basin.
Cementing forms an essential part of well construction as it supports the casing and provides hydraulic sealing. Wireline (WL) sonic tools have been providing the cement evaluation (CBL/VDL) for more than 50 years. Quantitative cement evaluation is becoming increasingly important in the industry to verify well integrity and zonal isolation. There has been a growing interest in providing cement bond quality quantitatively with LWD sonic tools owing to its plethora of benefits over wireline logging, such as rig time saving, tool conveyance, less tool eccentering effect and timelapse evaluation. However, there is also an LWD specific challenge that has for long hindered the ability to measure quantitative bond index i.e. drill collar contamination which limits the range of cement bond evaluation with the conventional amplitude-based approach. Deriving a characteristic correlation of attenuation measurement against the bond index was one of the key components to overcoming the limitation of amplitude-based. A new hybrid processing approach combining amplitude and attenuation was established for full-range cement bond evaluation. Schlumberger's LWD multipole sonic Cement Evaluation Service delivers the industry's first quantitative bond index answer product on LWD platform. The quantitative bond index becomes even more critical in offshore and deepwater markets.
This paper discusses, in brief, the technology and associated challenges in delivering industry's first quantitative bond index and showcases the result for one of the deepwater well. A subsequent comparison of LWD multipole sonic cement evaluation results with conventional WL CBL-VDL further corroborates the reliability of the result. The performance of the industry's first LWD bond index derived using LWD multipole sonic from around the globe has demonstrated that it can be expected to show abundant success in expanding the LWD utilization globally
This paper will introduce a new generation wireline Array Noise Tool (ANT). This tool is used to detect downhole acoustic / vibration activities originating from fluid-structure friction flow. One of main applications in Well Integrity (WI) and Plug & Abandonment (P&A) for ANT is to locate leak sources in well completions and tubulars. The innovative sensor matrix and system configuration together with three novel data processing methods are studied and developed to address the following primary challenges; Tiny acoustic leakage signals (-30dB to -60dB), for example, the minor leaks behind pipes or even inside the formation matrix, Strong road-noise acoustic signal contamination from tool motion while dynamic logging, Nonstationary and/or nonlinear signal distortions because of tool flexural vibrations, and Downhole seismic noise.
Tiny acoustic leakage signals (-30dB to -60dB), for example, the minor leaks behind pipes or even inside the formation matrix,
Strong road-noise acoustic signal contamination from tool motion while dynamic logging,
Nonstationary and/or nonlinear signal distortions because of tool flexural vibrations, and
Downhole seismic noise.
The tool can be operated both in stationary logging and in dynamic logging.
The wide-band sensor matrix is designed with a unique configurable technique to form different measurement arrays. As a result, the tool can simultaneously acquire absolute and differential acoustic signals. By using this sensor matrix we are able to improve Signal-to-Noise Ratio (SNR) by up to 20 to 30dB. From the acquired data, we employ a multi-dimensional machine learning (ML) classification module, cascaded with cluster iteration to separate real leak signatures from other unwanted noise signals. After a data conditioning process, the wave velocity-domain decomposition method is utilized to further distinguish the leak signal propagation characteristics against other noise propagations to enhance overall SNR for leak detectability. Lastly we use a Bayesian likelihood analysis to identify the leak depth locations with a confidence index based on the information contained in both signal energy and signal velocity. We are able to achieve 15dB to 20dB SNR improvement from this data processing methodology. The system design goal is to eliminate unwanted acoustic noise that is not associated with leaks, while maintaining sufficient sensitivity to pick up minor leaks.
The tool has been logged commercially in the US, Middle East, East Asia, and Latin America. The tool performance has been validated through simulation, lab tests, and field logs. Field logging examples are demonstrating a leak detection success rate above 95%. Field cases include multi-annulus, low flow rate, and gas well field examples. Field results will be presented in this paper.
ANT instrument technology and the associated advanced processing methods are a new solution for detecting the leak source locations and monitor leak paths, especially, in Well Integrity (WI), Plug and Abandonment (P&A), and many other well applications.
Water hammer shock pulses are generated when the flow in a length of tubing is interrupted in a time that is much shorter than the pulse duration. Water hammer tools used for well intervention incorporate a poppet valve that closes very quickly and a pilot valve that then causes the valve to open so that the flow is stopped periodically. The upstream water hammer shock generates an impulsive mechanical load on the bottom hole assembly (BHA) that can be used for milling or other applications. The intense axial vibration also extends the reach of tubing in long tortuous completions. These tools also generate a significant rarefaction shock downstream of the tool, comprising a sudden drop in pressure that can extend over 100's of meters of wellbore. The rarefaction pulse propagates into the dead volume beneath the tool and upstream into the annulus. The rarefaction shock causes flow to surge into and out of the formation. The extent and duration of these pulses has been observed in surface tests. Case histories of well cleaning and stimulation applications are described. Best practices for operation include squeezing treatment fluids into the formation followed by flow circulation to shock surge the completions.
Zhou, Zhihong (Jianghan Shale Gas Development Technical Service Company) | Zhang, Guofeng (Jianghan Shale Gas Development Technical Service Company) | Yuan, Fayong (Jianghan Shale Gas Development Technical Service Company) | Wang, Tang (Jianghan Shale Gas Development Technical Service Company) | Gao, Yunwei (Jianghan Shale Gas Development Technical Service Company) | Wang, Weijia (Jianghan Shale Gas Development Technical Service Company)
According to literature, most failures of coiled tubing are classified into four kinds of causes, mechanical damage, corrosion, string manufacturing, and human error. Among these, the failures due to mechanical damages take 29% of all failures. Although there are various kinds of mechanical damages, longitudinal plowing marks (LPM) are the major mechanical damages, account for 46%. Understanding the mechanism of LPM damage on coiled tubing surface will help to reduce this kind of damage.
A conjecture is proposed that the running of the CT-gripper block-chain system will produce a period excitation which arouses CT string system resonance, and the vibration of CT string may make slippage between the gripper blocks and CT string at the wave peak and stop slippage at the wave trough, which may form fish scale damage. Because of the mismatch of the diameters between CT with grown diameter and gripper blocks, the first principle stress on the surface of CT will be large enough so that rock debris can carve CT easily when a gripper block is clamping it. FEM is employed to calculate the stress of CT when it is in this situation. The results verify the guess.
To determine the CT string system resonance, we tried to find which gives the system a period excitation and how the system resonates. First a mechanical model of CT-gripper-chain is build, and excitation frequency is found to be related with the velocity of CT string running and length of gripper block. After idealization, a dynamic model for CT string in vertical well is built, and the wave equation is established, then frequency equation is derived and natural frequencies are found. After that, finite difference method is used to conduct numerical calculation. The results show that when system resonates, it must take minutes to reach large stress amplitude of the CT string enough to make damage on it. The field recorded data indicate that there maybe exists resonance actually.
After synthesizing the information above, an image of the process how LPM is formed has been constructed. Finally, the measures to reduce LPM damage are recommended.
Data telemetered in harsh environments are traditionally compressed, filtered, and processed before being transmitted, if telemetered at all. The user then has limited information about the status of monitored systems; however, the user's knowledge can be improved by real-time raw information transmission.
In harsh environments, data are traditionally transmitted over dedicated lines, through variations in a power source, or wirelessly. These methods suffer from signal attenuation and dispersion over long lengths, leading to lower data rates. Optical fiber systems, however, have low attenuation, little dispersion, and can use a variety of communication schemes, such as varying signal amplitudes, phases, or wavelengths. In particular, quadrature amplitude modulation (QAM) or pulse amplitude modulation (PAM) methods common for fiber telemetry backhauls can achieve greater bandwidths in harsh environments to realize real-time data retrieval without the need for processing.
This paper reviews the current state-of-the-art fiber-optic telemetry systems for harsh environments and discusses a proof-of-principle demonstration using higher-order optical modulation techniques to obtain data rates that are orders of magnitude greater than those achieved by electrical telemetry equivalent systems. The demonstration consisted of optical and electrical components that operated at temperatures up to 200°C and transmitted data along 18 km of fiber with over 10 dB of optical margin. The current state of the project and its application to a wide variety of possible field uses are explored.
Additionally, the use of fiber communications is reviewed to help improve data delivery to users in the energy industry, a topic of growing interest. It also highlights the innovative approaches for developing real-time, high-data-rate, bidirectional optical fiber telemetry for harsh environments.