Reservoir Heterogeneity and Permeability Barriers in the Vicksburg S Reservoir, McAllen Ranch Gas Field, Hidalgo County, Texas

Langford, Richard P.; Grigsby, Jeff D.; Collins, R.E.; Sippel, Mark A.; Wermund, E. G.

doi:10.23867/ri0222d

Cited by 3 publications

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“…The top and base of the Massive Frio are readily correlated on well logs and can be easily tied to strong, continuous events on the 3D seismic data. This permitted a 3D velocity model to be created involving four simple steps (Figure 7): 1) Using the 3D volume, map the time surfaces bounding the top and base of the three units with distinct velocity differences: 1 Langford et al, 1994). Actual producing depth in the study area is approximately 4250 m (14,000 ft).…”

Section: Mitigationmentioning

confidence: 99%

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Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Bain

2015

Interpretation

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Reliance on prestack time-migrated seismic data to define structural highs without incorporating all subsurface data and without taking into account the regional and local lateral depositional trends may result in dry holes or poorly positioned production wells due to local velocity changes, which are usually caused by some depositional or structural phenomenon. Tying check-shot control to depositional units may reveal those phenomena and permit assumptions to be made about velocities in areas beyond check-shot control points. We discovered a significant gas accumulation in an area surrounded by dry holes and marginal wells in the Vicksburg Formation in McAllen Ranch Field, Hidalgo County, Texas, by treating a seismic velocity anomaly as a geologic problem and by simple application of arithmetic and geometry to a 3D velocity model. Due to the effects of the anomaly, seismic data displayed in time gave no indication of the existence of a 325 ha (800 ac), 150 BCFG anticlinal structure. A subsurface model that accounted for the velocity anomaly was able to predict its extent and severity by readily identifiable thickness changes in the anomalous units. The resulting discovery yielded a sevenfold increase in field production within a two-year time span.

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Section: Mitigationmentioning

confidence: 99%

“…Map of the Texas Gulf Coastal Plain showing the McAllen Ranch Field in Hidalgo County, South Texas (modified afterLangford et al, 1994).…”

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Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Bain

2015

Interpretation

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Origin and Growth Mechanism of Authigenic Chlorite in Sandstones of the Lower Vicksburg Formation, South Texas

Grigsby¹

2001

Journal of Sedimentary Research

105

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Authigenic chlorite, occurring as grain coatings, pore fillings, and rosettes, is common in deltaic sandstones of the lower Vicksburg Formation in South Texas. Chlorite rosettes are isolated and occur late in the diagenetic history, whereas grain-coating and pore-filling chlorite occur early, predating the development of secondary porosity and the precipitation of quartz overgrowths and Fe-poor calcite. Grain-coating and pore-filling chlorite, which are interstratified with approximately 15 percent 7 Å layers, are Fe-rich with a mean Fe/ (Fe؉Mg) ratio of 0.68. Stable-isotope data (␦ 18 O averages 13.5‰ (SMOW)) indicate that the grain-coating and pore-filling chlorite began precipitating between 20؇C to 40؇C within the upper 1.8 km (6000 ft) of burial.Sandstones of the lower Vicksburg Formation were deposited in a relatively shallow deltaic environment as part of a large fluvial system draining the volcanics of Sierra Madre Occidental, Mexico and Trans Pecos, Texas. Weathering of these volcanics brought large amounts of particulate Fe to the river mouth. An increase in salinity in the distributary channel complex caused Fe flocculation and deposition. During periods of high river discharge, or when coastal currents acted to concentrate particulate Fe, large amounts of particulate Fe were deposited in the delta system. This resulted in thick layers of Fe-rich clay (odinite?) around grains. During periods of low river discharge, or when coastal currents caused wide distribution of particulate Fe, less particulate Fe was deposited. It is proposed that the grain-coating and pore-filling chlorite began forming through the transformation of an Fe-rich clay precursor in the formation-water hydropressure zone following Ostwald processes. The presence of this synsedimentary Fe-rich clay, and its recrystallization to Fe-chlorite, strongly influenced fluid flow and played a large role in developing the diagenetic heterogeneity seen in lower Vicksburg sandstones today.

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Effects of Diagenesis on Enhanced-Resolution Bulk Density Logs in Tertiary Gulf Coast Sandstones: An Example from the Lower Vicksburg Formation, McAllen Ranch Field, South Texas

Grigsby

Langford²

1996

Bulletin

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Reservoir Heterogeneity and Permeability Barriers in the Vicksburg S Reservoir, McAllen Ranch Gas Field, Hidalgo County, Texas

Cited by 3 publications

References 0 publications

Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Pitfalls in the seismic interpretation of fault shadow events — Vicksburg formation of south Texas

Origin and Growth Mechanism of Authigenic Chlorite in Sandstones of the Lower Vicksburg Formation, South Texas

Effects of Diagenesis on Enhanced-Resolution Bulk Density Logs in Tertiary Gulf Coast Sandstones: An Example from the Lower Vicksburg Formation, McAllen Ranch Field, South Texas

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