Automated identification of rock boundaries: An application of the Walsh transform to geophysical well‐log analysis

Geophysics ◽  
1983 ◽  
Vol 48 (2) ◽  
pp. 197-205 ◽  
Author(s):  
Eric N. Lanning ◽  
Douglas M. Johnson
Keyword(s):  
Walsh Transform ◽  
Well Log ◽  
Generalized Fourier Transform ◽  
Automated Identification ◽  
Borehole Data ◽  
Orthogonal Functions ◽  
Log Data ◽  
Basic Equations ◽  
Well Log Analysis ◽  
Continental Basalt

A system of orthogonal functions, known as Walsh functions, which assume only the values +1 and −1, are presented as a tool appropriate for the analysis of well‐log data. Many of the characteristics of these rectangular waveforms, such as discrete transitions in signal level, make them ideal for processing borehole data. Using the generalized Fourier transform, the basic equations for the Walsh transform and Walsh power spectrum are developed showing how the energy in a given signal is distributed among these rectangular wave components. As a first application of the Walsh transform to logging data, a method of computeraided rock boundary identification is developed and demonstrated on a set of well logs from a continental basalt sequence. This technique provides a fast, simple yet accurate means of dividing well‐log data into groups of measurements corresponding to different rock units.

On: “Automated identification of rock boundaries: an application of the Walsh transform to geophysical well‐log analysis” by E. N. Lanning and D. M. Johnson (GEOPHYSICS, v. 48, p. 197–205, February, 1983).

Geophysics ◽  
1984 ◽  
Vol 49 (10) ◽  
pp. 1801-1802
Author(s):  
David S. K. Chan
Keyword(s):  
Well Logs ◽  
Walsh Transform ◽  
Log Analysis ◽  
Well Log ◽  
Transform Domain ◽  
Original Signal ◽  
Step Width ◽  
Automated Identification ◽  
Low Pass ◽  
Well Log Analysis

Lanning and Johnson’s paper presents the technique of Walsh transform domain low‐pass filtering as a means of enhancing transitions in well logs prior to boundary picking. They argue that existing fast means of computing the Walsh transform (fast Walsh transform algorithms) make this procedure particularly efficient. In this discussion it is shown that, for all practical cases of interest, the results of their paper can be obtained without any mention of the Walsh transform. In fact, using the Walsh transform unnecessarily increases computational complexity. Specifically, it is shown that the low‐pass sequency filtering described for obtaining a stepped version of the original signal with a given step width is equivalent to segmenting simply the signal into equal length segments and replacing all values in each segment by the segment average.

Identification of Natural Gas Hydrates in Blocks 25a, 25b, 26 and 27 Offshore Trinidad Using Available Well Log Data

2014 ◽  
Author(s):  
M. M. Smith ◽  
L. E. Sobers
Keyword(s):  
Natural Gas ◽  
Deep Water ◽  
Gas Hydrates ◽  
Seismic Data ◽  
East Coast ◽  
Depositional Environments ◽  
Well Log ◽  
Borehole Data ◽  
Log Data ◽  
Natural Gas Hydrates

Abstract Natural gas hydrates can be found in conventional hydrocarbon depositional environments such as clastic marine sediments, siltstones and unconsolidated sands and in oceanic environments for reservoir pressures greater than 663 psi (46 bars) and temperatures less than 20 °C. These conditions are found in the deep water (> 300 m) acreage off the South East coast of Trinidad. Natural gas hydrates have been recovered in this area during drilling and seismic data have shown that there may be deposits in some areas. In this study we reviewed all the available borehole data and employed well log interpretation techniques to identify natural gas hydrates in the deep water acreage blocks 25 a, 25 b, 26 and 27 off the Trinidad South East coast. The analysis of well log data for the given depths did not present evidence to suggest the presence of natural gas hydrates in Blocks 25 a, 25 b, 26 and 27. In this paper we present our analysis of the data available and recommend the formation depths which should be logged in during the deep water exploration drilling to confirm the seismic data and core data which indicate the presence of natural gas hydrates in these blocks.

scholarly journals Wave Propagation Characteristics in Gas Hydrate-Bearing Sediments and Estimation of Hydrate Saturation

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 804
Author(s):  
Lin Liu ◽  
Xiumei Zhang ◽  
Xiuming Wang
Keyword(s):  
Gas Hydrate ◽  
Clay Content ◽  
Clean Energy ◽  
Compressional Wave ◽  
Physical Parameters ◽  
Well Log ◽  
Log Data ◽  
Phase Velocities ◽  
Hydrate Saturation ◽  
Hydrate Bearing Sediments

Natural gas hydrate is a new clean energy source in the 21st century, which has become a research point of the exploration and development technology. Acoustic well logs are one of the most important assets in gas hydrate studies. In this paper, an improved Carcione–Leclaire model is proposed by introducing the expressions of frame bulk modulus, shear modulus and friction coefficient between solid phases. On this basis, the sensitivities of the velocities and attenuations of the first kind of compressional (P1) and shear (S1) waves to relevant physical parameters are explored. In particular, we perform numerical modeling to investigate the effects of frequency, gas hydrate saturation and clay on the phase velocities and attenuations of the above five waves. The analyses demonstrate that, the velocities and attenuations of P1 and S1 are more sensitive to gas hydrate saturation than other parameters. The larger the gas hydrate saturation, the more reliable P1 velocity. Besides, the attenuations of P1 and S1 are more sensitive than velocity to gas hydrate saturation. Further, P1 and S1 are almost nondispersive while their phase velocities increase with the increase of gas hydrate saturation. The second compressional (P2) and shear (S2) waves and the third kind of compressional wave (P3) are dispersive in the seismic band, and the attenuations of them are significant. Moreover, in the case of clay in the solid grain frame, gas hydrate-bearing sediments exhibit lower P1 and S1 velocities. Clay decreases the attenuation of P1, and the attenuations of S1, P2, S2 and P3 exhibit little effect on clay content. We compared the velocity of P1 predicted by the model with the well log data from the Ocean Drilling Program (ODP) Leg 164 Site 995B to verify the applicability of the model. The results of the model agree well with the well log data. Finally, we estimate the hydrate layer at ODP Leg 204 Site 1247B is about 100–130 m below the seafloor, the saturation is between 0–27%, and the average saturation is 7.2%.

Predicting Formation Pore-Pressure from Well-Log Data with Hybrid Machine-Learning Optimization Algorithms

2021 ◽  
Author(s):  
Mohammad Farsi ◽  
Nima Mohamadian ◽  
Hamzeh Ghorbani ◽  
David A. Wood ◽  
Shadfar Davoodi ◽  
...  
Keyword(s):  
Machine Learning ◽  
Pore Pressure ◽  
Optimization Algorithms ◽  
Well Log ◽  
Log Data ◽  
Hybrid Machine ◽  
Formation Pore Pressure
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