Anisotropic statics for a 2D line over a mountainous overthrust belt in Bolivia

The Meade thrust, in southeastern Idaho, is a major element of the Western Overthrust Belt. The allochthon is of geo-economic importance both as a potential hydrothermal area and as the principal mining area within the Western Phosphate Field. To assist in the development of these two resources, an understanding of the regional ground-water circulation was sought. Geologic and hydrologic data from boreholes in this area are virtually nonexistent. Waterwell development in the area has not occurred because of the abundance of springs and only a few hydrocarbon exploration boreholes have been drilled. Thus, the problem lends itself to evaluation by isotope hydrologic and geochemical methods. Ten springs from within the thrust block and around its periphery were sampled for major ions, 2H/18O, and 14C/13C analysis. Data from these analyses and from field geologic evidence have identified two distinct flow regimes within the Meade thrust allochthon. Shallow flow systems lie above the impermeable Phosphoria Formation, usually within a few hundred meters of the surface. Most of the spring waters from this system are recent and cool. In all cases, they have mean subsurface residence times of less than a few hundred years. The deeper flow systems which lie below the Phosphoria formation are hydraulically isolated from the shallow system. Warm waters from these springs have 14C contents suggesting mean ground-water residence times on the order of 15,000 years. Although these waters could have circulated to as deep as 1900m, 2H/18O results show that high temperatures were never reached. There is no evidence to suggest that water from beneath the Meade thrust has contributed to the circulation in the allochthon.

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Automatic estimation of large residual statics corrections

Geophysics ◽

10.1190/1.1442092 ◽

1986 ◽

Vol 51 (2) ◽

pp. 332-346 ◽

Cited By ~ 184

Author(s):

Daniel H. Rothman

Keyword(s):

Monte Carlo ◽

Statistical Mechanics ◽

Probability Distributions ◽

Synthetic Data ◽

Linear Inversion ◽

Traveltime Inversion ◽

Automatic Estimation ◽

Crucial Component ◽

Practical Algorithm ◽

Overthrust Belt

Conventional approaches to residual statics estimation obtain solutions by performing linear inversion of observed traveltime deviations. A crucial component of these procedures is picking time delays; gross errors in these picks are known as “cycle skips” or “leg jumps” and are the bane of linear traveltime inversion schemes. This paper augments Rothman (1985), which demonstrated that the estimation of large statics in noise‐contaminated data is posed better as a nonlinear, rather than as a linear, inverse problem. Cycle skips then appear as local (secondary) minima of the resulting nonlinear optimization problem. In the earlier paper, a Monte Carlo technique from statistical mechanics was adapted to perform global optimization, and the technique was applied to synthetic data. Here I present an application of a similar Monte Carlo method to field data from the Wyoming Overthrust belt. Key changes, however, have led to a more efficient and practical algorithm. The new technique performs explicit crosscorrelation of traces. Instead of picking the peaks of these crosscorrelation functions, the method transforms the crosscorrelation functions to probability distributions and then draws random numbers from the distributions. Estimates of statics are now iteratively updated by this procedure until convergence to the optimal stack is achieved. Here I also derive several theoretical properties of the algorithm. The method is expressed as a Markov chain, in which the equilibrium (steady‐state) distribution is the Gibbs distribution of statistical mechanics.

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An Extraordinary Drilling Challenge in the Rocky Mountain Overthrust Belt

SPE Drilling Engineering ◽

10.2118/14425-pa ◽

1987 ◽

Vol 2 (01) ◽

pp. 75-85

Author(s):

J.D. Swanson ◽

I.M. Brandt ◽

R.D. Johnston

Keyword(s):

Rocky Mountain ◽

Overthrust Belt

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EXPLORATION AND EXPLOITATION OF A MATURE BASIN SUCCESSFUL APPLICATION OF A PROCESS-DRIVEN MULTI-DISCIPLINARYTEAM APPROACH

The APPEA Journal ◽

10.1071/aj99036 ◽

2000 ◽

Vol 40 (1) ◽

pp. 562

Author(s):

W. Ringhofer ◽

H. Sperl

Keyword(s):

New Technology ◽

Hydrocarbon Exploration ◽

Vienna Basin ◽

Sequence Stratigraphic ◽

High Pressure High Temperature ◽

Drilling Technology ◽

Integration Of Disciplines ◽

Well Data ◽

Clastic Reservoirs ◽

Overthrust Belt

From the early 1940s until the mid-1980s, hydrocarbon exploration within Austria was focussed upon Tertiary clastic reservoirs within the Vienna Basin. From 1980 to the early 1990s, an increasing number of exploration wells were drilled for carbonate reservoirs within deep thrust anticlines in the Alpine overthrust belt. These were typically high pressure-high temperature wells, and as a result, technically challenging and expensive.In the early 1990s, after little success within the Alpine overthrust belt, the focus of Austrian exploration was switched back to the 'maturely' explored Vienna Basin. During this period, the integration of historical well data, reprocessed 2D seismic and newly acquired 3D seismic data, evaluated within a sequence stratigraphic framework, has facilitated the accurate placement of multi-target wells. Together with the application of new drilling technology, the result has been a dramatic increase in new field discoveries. The reserves size of exploration and appraisal targets, in accordance with the maturity of the basin, have been relatively small, but, as a result of well-developed infrastructure and low drilling costs, highly profitable.The drive for increased drilling success and cost reduction and the application of 'new' technology has demanded an even closer integration of disciplines including exploration, reservoir engineering, drilling and production engineering. This integration in turn has necessitated process driven management. Multi- disciplinary teams, working with key contractors in an incentivised environment, achieved risk reduction, increased exploration success and budget reductions. As a result successful exploration has revived the mature Vienna Basin.

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