Evaluation of direct hydrocarbon indicators through comparison of compressional‐ and shear‐wave seismic data: a case study of the Myrnam gas field, Alberta

Geophysics ◽  
1985 ◽  
Vol 50 (1) ◽  
pp. 37-48 ◽  
Author(s):  
Ross Alan Ensley

Shear waves differ from compressional waves in that their velocity is not significantly affected by changes in the fluid content of a rock. Because of this relationship, a gas‐related compressional‐wave “bright spot” or direct hydrocarbon indicator will have no comparable shear‐wave anomaly. In contrast, a lithology‐related compressional‐wave anomaly will have a corresponding shear‐wave anomaly. Thus, it is possible to use shear‐wave seismic data to evaluate compressional‐wave direct hydrocarbon indicators. This case study presents data from Myrnam, Alberta which exhibit the relationship between compressional‐ and shear‐wave seismic data over a gas reservoir and a low‐velocity coal.

Geophysics ◽  
1984 ◽  
Vol 49 (9) ◽  
pp. 1420-1431 ◽  
Author(s):  
Ross Alan Ensley

Compressional waves are sensitive to the type of pore fluid within rocks, but shear waves are only slightly affected by changes in fluid type. This suggests that a comparison of compressional‐ and shear‐wave seismic data recorded over a prospect may allow an interpreter to discriminate between gas‐related anomalies and those related to lithology. This case study documents that where a compressional‐wave “bright spot” or other direct hydrocarbon indicator is present, such a comparison can be used to verify the presence of gas. In practice, the technique can only be used for a qualitative evaluation. However, future improvement of shear‐wave data quality may enable the use of more quantitative methods as well.


Geophysics ◽  
1985 ◽  
Vol 50 (4) ◽  
pp. 530-538 ◽  
Author(s):  
P. M. Carrion ◽  
S. Hassanzadeh

Conventional velocity analysis of seismic data is based on normal moveout of common‐depth‐point (CDP) traveltime curves. Analysis is done in a hyperbolic framework and, therefore, is limited to using the small‐angle reflections only (muted data). Hence, it can estimate the interval velocities of compressional waves only, since mode conversion is negligible when small‐angle arrivals are concerned. We propose a new method which can estimate the interval velocities of compressional and mode‐converted waves separately. The method is based on slant stacking or plane‐wave decomposition (PWD) of the observed data (seismogram), which transforms the data from the conventional T-X domain into the intercept time‐ray parameter domain. Since PWD places most of the compressional energy into the precritical region of the slant‐stacked seismogram, the compressional‐wave interval velocities can be estimated using the “best ellipse” approximation on the assumption that the elliptic array velocity (stacking velocity) is approximately equal to the root‐mean‐square (rms) velocity. Similarly, shear‐wave interval velocities can be estimated by inverting the traveltime curves in the region of the PWD seismogram, where compressional waves decay exponentially (postcritical region). The method is illustrated by examples using synthetic and real data.


Geophysics ◽  
1984 ◽  
Vol 49 (5) ◽  
pp. 509-520 ◽  
Author(s):  
M. D. McCormack ◽  
J. A. Dunbar ◽  
W. W. Sharp

This paper describes the use of surface recorded compressional and horizontal shear wave seismic data to detect lateral changes in the physical properties of a clastic unit. Shear and compressional wave transit times were measured across a selected interval from CDP stacked sections derived from data collected along coincident shear and compressional seismic lines. At each surface position the ratio of the shear to compressional transit time across the target horizon is calculated. It is shown that lateral variations in this ratio, coupled with the behavior of the individual transit time curves, can be used to infer changes in the physical properties of a formation. The horizon selected for this case study was the lower Pennsylvanian Morrow formation which produces gas from channel sand bodies at the Empire Abo field, New Mexico. A detailed geologic section of the producing horizon was mapped along a seismic line oriented so that it crossed productive and nonproductive regions of the field. Shear and compressional Vibroseis® surveys were conducted along this surface profile using data acquisition parameters designed to produce comparable signal‐to‐noise ratios and resolution in both sets of field data. After processing, the shear and compressional interval transit times through the Morrow formation decreased in going from nonproductive to productive thicknesses of sand. Furthermore there is a proportionately greater decrease in the shear wave transit time than in the compressional transit time resulting in an overall decrease in the ratio of shear to compressional transit times. While several possible physical changes in the lateral properties of the reservoir could explain these observations, it is concluded that the primary mechanism causing these ratio changes is variation in the sand‐shale ratio within the Morrow formation.


2021 ◽  
pp. 1-67
Author(s):  
Stewart Smith ◽  
Olesya Zimina ◽  
Surender Manral ◽  
Michael Nickel

Seismic fault detection using machine learning techniques, in particular the convolution neural network (CNN), is becoming a widely accepted practice in the field of seismic interpretation. Machine learning algorithms are trained to mimic the capabilities of an experienced interpreter by recognizing patterns within seismic data and classifying them. Regardless of the method of seismic fault detection, interpretation or extraction of 3D fault representations from edge evidence or fault probability volumes is routine. Extracted fault representations are important to the understanding of the subsurface geology and are a critical input to upstream workflows including structural framework definition, static reservoir and petroleum system modeling, and well planning and de-risking activities. Efforts to automate the detection and extraction of geological features from seismic data have evolved in line with advances in computer algorithms, hardware, and machine learning techniques. We have developed an assisted fault interpretation workflow for seismic fault detection and extraction, demonstrated through a case study from the Groningen gas field of the Upper Permian, Dutch Rotliegend; a heavily faulted, subsalt gas field located onshore, NE Netherlands. Supervised using interpreter-led labeling, we apply a 2D multi-CNN to detect faults within a 3D pre-stack depth migrated seismic dataset. After prediction, we apply a geometric evaluation of predicted faults, using a principal component analysis (PCA) to produce geometric attribute representations (strike azimuth and planarity) of the fault prediction. Strike azimuth and planarity attributes are used to validate and automatically extract consistent 3D fault geometries, providing geological context to the interpreter and input to dependent workflows more efficiently.


2019 ◽  
Author(s):  
Zhiwen Deng ◽  
Chengwu Li ◽  
Guowen Chen ◽  
Jing Yang ◽  
Ruizhen Wang ◽  
...  

2013 ◽  
Vol 167 ◽  
pp. 72-83 ◽  
Author(s):  
J.S. L'Heureux ◽  
M. Long ◽  
M. Vanneste ◽  
G. Sauvin ◽  
L. Hansen ◽  
...  

Geophysics ◽  
2010 ◽  
Vol 75 (2) ◽  
pp. B73-B82 ◽  
Author(s):  
Marit Ulvmoen ◽  
Henning Omre ◽  
Arild Buland

We have performed lithology/fluid inversion based on prestack seismic data and well observations from a gas reservoir offshore Norway. The prior profile Markov random field model captures horizontal continuity and vertical sequencing of the lithology/fluid variables. The prior model is also locally adjusted for spatially varying lithology/fluid proportions. The likelihood model is inferred from basic seismic theory and observations in wells. An approximate posterior model is defined, which can be simulated from by an extremely computer-efficient algorithm. The lithology/fluid inversion results are compared to manual interpretations and evaluated by cross validation in one well. Moreover, inversions based on simplified prior models are developed for comparative reasons. Both lithology/fluid realizations and predictions look geologically reasonable. The results seem to reflect general reservoir experience and information provided by the prestack seismic data and well observations. The lithology/fluid proportions appear as geologically plausible and thin elongated lithology/fluid units are identified. The study is made in a 2D cross section, but extension to a full 3D setting is feasible.


2014 ◽  
Vol 1073-1076 ◽  
pp. 592-596
Author(s):  
Pei Luo ◽  
Yu Ming Luo ◽  
Kai Ma ◽  
Biao Zhang ◽  
Sha Sha Song

In the process of high sulfur gas field development, the sulfur will separate out from the mixed gas when the pressure near wellbore area drops to a critical pressure of H2S. This will reduce the reservoir porosity greatly and decrease the gas well productivity as well. This paper discusses the characteristics of pressure transient testing plots when sulfur deposition occurs based on the redial composite reservoir model. And introduce an approach to determine the sulfur deposition radius near the wellbore with pressure transient testing interpretation in high sulfur gas reservoir. The method has been applied in some high sulfur gas field in eastern Sichuan Basin. The result shows that the method is simple and practical.


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