A COMPARISON OF WELL VELOCITY METHODS IN SOUTH TEXAS

Geophysics ◽  
1959 ◽  
Vol 24 (3) ◽  
pp. 443-450 ◽  
Author(s):  
A. B. Wood
Keyword(s):  
Seismic Data ◽  
Short Interval ◽  
Present Form ◽  
South Texas ◽  
Basic Data ◽  
Sonic Velocity ◽  
Velocity Data ◽  
Interval Velocity ◽  
Delay Times

This velocity study is limited to data from one well in South Texas. Two short‐interval velocity logging methods compared with conventional seismic geophone data show large discrepancies. The Shell short‐interval velocity log agrees within close limits to the conventional seismic data except for the lower 4,000 ft. The indicated delay times for the upper 2,000 ft of this 4,000‐ft interval are short by 6.5 percent, and indicated delay times for the lower 2,000 ft are short by 4.0 percent. The Schlumberger Sonic Velocity Log, limited in this survey to the bottom 4,200 ft of hole, indicated delay times larger than the seismic time by more than 5 percent. There is a difference of approximately 9 percent between the two velocity logs, even though the tools were of similar dimensions. The spacing between detectors was three feet, and the distance from transmitter to near receiver was four feet for the Shell tool and three feet for the Schlumberger tool. An analysis of the basic data is necessary to resolve these discrepancies. There is no check on the Sonic data in its present form, but a thorough study of the Shell Oscillogram log and conventional seismic data for errors fails to explain the 6.5‐percent and 4‐percent discrepancies in the Shell short‐interval velocity data. The conclusion must be drawn that these discrepancies are real. This survey demonstrates the necessity to check short‐interval velocity logging with conventional seismic shots to maintain acceptable seismic well velocity standards.

Implementation Of Interval Velocity Data In The Analysis Of Vertical Fluid Migration Routes And Charging Offshore Qatar

2014 ◽  
Author(s):  
K. J. Andresen ◽  
A. Uldall ◽  
M. Hertle ◽  
L. Madsen ◽  
C. Perrin ◽  
...  
Keyword(s):  
Fluid Migration ◽  
Velocity Data ◽  
Migration Routes ◽  
Interval Velocity

Automatic, geologic layer-constrained well-seismic tie through blocked dynamic warping

2017 ◽  
Vol 5 (3) ◽  
pp. SJ81-SJ90 ◽  
Author(s):  
Kainan Wang ◽  
Jesse Lomask ◽  
Felix Segovia
Keyword(s):  
Seismic Data ◽  
Oil And Gas ◽  
Synthetic Data ◽  
Optimal Solution ◽  
Velocity Model ◽  
Data Set ◽  
Oil And Gas Exploration ◽  
Interval Velocity ◽  
Velocity Changes ◽  
Dynamic Warping

Well-log-to-seismic tying is a key step in many interpretation workflows for oil and gas exploration. Synthetic seismic traces from the wells are often manually tied to seismic data; this process can be very time consuming and, in some cases, inaccurate. Automatic methods, such as dynamic time warping (DTW), can match synthetic traces to seismic data. Although these methods are extremely fast, they tend to create interval velocities that are not geologically realistic. We have described the modification of DTW to create a blocked dynamic warping (BDW) method. BDW generates an automatic, optimal well tie that honors geologically consistent velocity constraints. Consequently, it results in updated velocities that are more realistic than other methods. BDW constrains the updated velocity to be constant or linearly variable inside each geologic layer. With an optimal correlation between synthetic seismograms and surface seismic data, this algorithm returns an automatically updated time-depth curve and an updated interval velocity model that still retains the original geologic velocity boundaries. In other words, the algorithm finds the optimal solution for tying the synthetic to the seismic data while restricting the interval velocity changes to coincide with the initial input blocking. We have determined the application of the BDW technique on a synthetic data example and field data set.

Diapiric shale and coast-perpendicular, fault-related subbasins, south Texas Gulf Coast

2015 ◽  
Vol 3 (2) ◽  
pp. T43-T56 ◽  
Author(s):  
Osareni C. Ogiesoba ◽  
Rodolfo Hernandez
Keyword(s):  
Seismic Data ◽  
Gulf Coast ◽  
Structural Features ◽  
South Texas ◽  
3D Seismic ◽  
Texas Gulf Coast ◽  
Vertical Loading ◽  
The North ◽  
Visualization Tools ◽  
3D Seismic Data

Coast-perpendicular shale ridges are rare structural features worldwide, and their origin remains a subject of debate. We studied some coast-perpendicular shale ridges and faults within a minibasin located onshore in Refugio County in the Texas Gulf Coast. We used 3D seismic data, visualization tools, and seismic attributes to examine the geometry of coast-perpendicular diapiric structures associated subbasins (SBs) and faults, and coast-parallel listric faults. Our results indicated that the minibasin is subdivided into four SBs by five diapiric shale ridges that intrude through the fault heaves of down-to-the-basin (synthetic) and coast-perpendicular faults. Three of the SBs are oriented perpendicular to the coast, whereas the fourth has a curvilinear form trending northeast–southwest–southeast. Of the five diapiric shale ridges, three are coast-perpendicular. The other two are curvilinear to the coast. All five diapiric shale ridges are associated with coast-perpendicular faults that bound the flanks of the ridges. On the basis of our mapping results, we deduced that the origin of the coast-perpendicular faults in the study area are related to the coalescing of en echelon synthetic faults, as well as the coalition of synthetic and antithetic fault planes. We inferred that the origin of the shale diapirs is related to vertical loading and, possibly, local southwest–northeast lateral compression of interbedded, overpressured, shale-prone intervals. The coast-perpendicular faults within the Frio formed as a result of reactivation of the Eocene-Vicksburg coast-perpendicular faults. Synthetic faults dominate the pattern within the SB in the north where shale ridges are broad, whereas antithetic faults dominate the pattern in the south where shale ridges are narrow.

Calculation of the Free Volume and the Internal Pressure of Liquids from Sonic Velocity Data

1956 ◽  
Vol 25 (3) ◽  
pp. 581-581 ◽  
Author(s):  
F. C. Collins ◽  
W. W. Brandt ◽  
M. H. Navidi
Keyword(s):  
Internal Pressure ◽  
Free Volume ◽  
Sonic Velocity ◽  
Velocity Data

Estimating the amount of gas hydrate and free gas from marine seismic data

Geophysics ◽  
2000 ◽  
Vol 65 (2) ◽  
pp. 565-573 ◽  
Author(s):  
Christine Ecker ◽  
Jack Dvorkin ◽  
Amos M. Nur
Keyword(s):  
Gas Hydrate ◽  
Seismic Data ◽  
Rock Physics ◽  
Free Gas ◽  
Interval Velocity ◽  
Blake Ridge ◽  
Hydrate Saturation ◽  
Physics Model ◽  
Rock Physics Model ◽  
Marine Seismic

Marine seismic data and well‐log measurements at the Blake Ridge offshore South Carolina show that prominent seismic bottom‐simulating reflectors (BSRs) are caused by sediment layers with gas hydrate overlying sediments with free gas. We apply a theoretical rock‐physics model to 2-D Blake Ridge marine seismic data to determine gas‐hydrate and free‐gas saturation. High‐porosity marine sediment is modeled as a granular system where the elastic wave velocities are linked to porosity; effective pressure; mineralogy; elastic properties of the pore‐filling material; and water, gas, and gas‐hydrate saturation of the pore space. To apply this model to seismic data, we first obtain interval velocity using stacking velocity analysis. Next, all input parameters to the rock‐physics model, except porosity and water, gas, and gas hydrate saturation, are estimated from geologic information. To estimate porosity and saturation from interval velocity, we first assume that the entire sediment does not contain gas hydrate or free gas. Then we use the rock‐physics model to calculate porosity directly from the interval velocity. Such porosity profiles appear to have anomalies where gas hydrate and free gas are present (as compared to typical profiles expected and obtained in sediment without gas hydrate or gas). Porosity is underestimated in the hydrate region and is overestimated in the free‐gas region. We calculate the porosity residuals by subtracting a typical porosity profile (without gas hydrate and gas) from that with anomalies. Next we use the rock‐physics model to eliminate these anomalies by introducing gas‐hydrate or gas saturation. As a result, we obtain the desired 2-D saturation map. The maximum gas‐hydrate saturation thus obtained is between 13% and 18% of the pore space (depending on the version of the model used). These saturation values are consistent with those measured in the Blake Ridge wells (away from the seismic line), which are about 12%. Free‐gas saturation varies between 1% and 2%. The saturation estimates are extremely sensitive to the input velocity values. Therefore, accurate velocity determination is crucial for correct reservoir characterization.

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