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Title: Facies, faults and potential sweet spots in a tight gas reservoir: Almond Formation, Wyoming

Abstract

The Almond Formation is a major producer of gas in southwestern Wyoming. Although exploration generally is aimed at finding conventional reservoirs in upper Almond marine sandstones, the majority of Almond gas is contained in the underlying main Almond, a succession of dominantly non-marine, interbedded tight sandstones, siltstones, carbonaceous shales and coals. Production data indicate that some of the best gas wells completed in upper Almond sands show little production decline and have already produced more gas than calculations indicate they contain. This implies that these wells have somehow successfully tapped into the vast supply of gas contained in the main Almond. We believe that the more permeable reservoirs, in addition to providing [open quotes]sweet spots[close quotes] for exploration, also serve as lateral conduits capable of draining gas over a broad area from the main Almond. The [open quotes]sweet spots[close quotes] themselves do not need to be volumetrically large, only permeable and laterally continuous. Previously unrecognized marine sands, similar to those in the upper Almond, are favorably located in the middle of the main Almond succession and may provide additional lateral conduits. Studies also show that syndepositional faults significantly influenced deposition and may also be important in terms of fluid flow.more » At least some syndepositional faults are associated with anomalously high gas and/or water production within fields, and may be vertical conduits for fluid flow.« less

Authors:
; ;  [1]
  1. (Univ. of Wyoming, Laramie, WY (United States))
Publication Date:
OSTI Identifier:
6582715
Report Number(s):
CONF-960527--
Journal ID: ISSN 0149-1423; CODEN: AABUD2
Resource Type:
Conference
Resource Relation:
Journal Name: AAPG Bulletin; Journal Volume: 5; Conference: Annual convention of the American Association of Petroleum Geologists, Inc. and the Society for Sedimentary Geology: global exploration and geotechnology, San Diego, CA (United States), 19-22 May 1996
Country of Publication:
United States
Language:
English
Subject:
03 NATURAL GAS; NATURAL GAS; PRODUCTION; RESERVOIR ROCK; FLUID FLOW; PERMEABILITY; WYOMING; NATURAL GAS DEPOSITS; STRATIGRAPHY; GEOLOGIC FAULTS; DEVELOPED COUNTRIES; ENERGY SOURCES; FLUIDS; FOSSIL FUELS; FUEL GAS; FUELS; GAS FUELS; GASES; GEOLOGIC DEPOSITS; GEOLOGIC FRACTURES; GEOLOGIC STRUCTURES; GEOLOGY; MINERAL RESOURCES; NORTH AMERICA; RESOURCES; USA 030200* -- Natural Gas-- Reserves, Geology, & Exploration

Citation Formats

Martinsen, R., Iverson, W., and Surdam, R. Facies, faults and potential sweet spots in a tight gas reservoir: Almond Formation, Wyoming. United States: N. p., 1996. Web.
Martinsen, R., Iverson, W., & Surdam, R. Facies, faults and potential sweet spots in a tight gas reservoir: Almond Formation, Wyoming. United States.
Martinsen, R., Iverson, W., and Surdam, R. 1996. "Facies, faults and potential sweet spots in a tight gas reservoir: Almond Formation, Wyoming". United States. doi:.
@article{osti_6582715,
title = {Facies, faults and potential sweet spots in a tight gas reservoir: Almond Formation, Wyoming},
author = {Martinsen, R. and Iverson, W. and Surdam, R.},
abstractNote = {The Almond Formation is a major producer of gas in southwestern Wyoming. Although exploration generally is aimed at finding conventional reservoirs in upper Almond marine sandstones, the majority of Almond gas is contained in the underlying main Almond, a succession of dominantly non-marine, interbedded tight sandstones, siltstones, carbonaceous shales and coals. Production data indicate that some of the best gas wells completed in upper Almond sands show little production decline and have already produced more gas than calculations indicate they contain. This implies that these wells have somehow successfully tapped into the vast supply of gas contained in the main Almond. We believe that the more permeable reservoirs, in addition to providing [open quotes]sweet spots[close quotes] for exploration, also serve as lateral conduits capable of draining gas over a broad area from the main Almond. The [open quotes]sweet spots[close quotes] themselves do not need to be volumetrically large, only permeable and laterally continuous. Previously unrecognized marine sands, similar to those in the upper Almond, are favorably located in the middle of the main Almond succession and may provide additional lateral conduits. Studies also show that syndepositional faults significantly influenced deposition and may also be important in terms of fluid flow. At least some syndepositional faults are associated with anomalously high gas and/or water production within fields, and may be vertical conduits for fluid flow.},
doi = {},
journal = {AAPG Bulletin},
number = ,
volume = 5,
place = {United States},
year = 1996,
month = 1
}

Conference:
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  • The Almond Formation is a major producer of gas in southwestern Wyoming. Although exploration generally is aimed at finding conventional reservoirs in upper Almond marine sandstones, the majority of Almond gas is contained in the underlying main Almond, a succession of dominantly non-marine, interbedded tight sandstones, siltstones, carbonaceous shales and coals. Production data indicate that some of the best gas wells completed in upper Almond sands show little production decline and have already produced more gas than calculations indicate they contain. This implies that these wells have somehow successfully tapped into the vast supply of gas contained in the mainmore » Almond. We believe that the more permeable reservoirs, in addition to providing {open_quotes}sweet spots{close_quotes} for exploration, also serve as lateral conduits capable of draining gas over a broad area from the main Almond. The {open_quotes}sweet spots{close_quotes} themselves do not need to be volumetrically large, only permeable and laterally continuous. Previously unrecognized marine sands, similar to those in the upper Almond, are favorably located in the middle of the main Almond succession and may provide additional lateral conduits. Studies also show that syndepositional faults significantly influenced deposition and may also be important in terms of fluid flow. At least some syndepositional faults are associated with anomalously high gas and/or water production within fields, and may be vertical conduits for fluid flow.« less
  • In order to accurately predict fluid flow within a reservoir, variability in the rock properties at all scales relevant to the specific depositional environment needs to be taken into account. The present work describes rock variability at scales from hundreds of meters (facies level) to millimeters (laminae) based on outcrop studies of the Almond Formation. Tidal channel, tidal delta and foreshore facies were sampled on the eastern flank of the Rock Springs uplift, southeast of Rock Springs, Wyoming. The Almond Fm. was deposited as part of a mesotidal Upper Cretaceous transgressive systems tract within the greater Green River Basin. Beddingmore » style, lithology, lateral extent of beds of bedsets, bed thickness, amount and distribution of depositional clay matrix, bioturbation and grain sorting provide controls on sandstone properties that may vary more than an order of magnitude within and between depositional facies in outcrops of the Almond Formation. These features can be mapped on the scale of an outcrop. The products of diagenesis such as the relative timing of carbonate cement, scale of cemented zones, continuity of cemented zones, selectively leached framework grains, lateral variability of compaction of sedimentary rock fragments, and the resultant pore structure play an equally important, although less predictable role in determining rock property heterogeneity. A knowledge of the spatial distribution of the products of diagenesis such as calcite cement or compaction is critical to modeling variation even within a single facies in the Almond Fin. because diagenesis can enhance or reduce primary (depositional) rock property heterogeneity. Application of outcrop heterogeneity models to the subsurface is greatly hindered by differences in diagenesis between the two settings. The measurements upon which this study is based were performed both on drilled outcrop plugs and on blocks.« less
  • Gas production from the Almond Formation in the Standard Draw trend can only be accounted for by draining numerous layers of tight gas sands via the permeable upper bar sand. Discovery of this field originally focused upon production from this bar sand. But continued development cannot be explained simply by considering depletion of a 30 foot sand. Gas volumetrics verify the need to include lower sands in reservoir analysis. Core obtained from the Almond bar sand confirm petrophysical constants used in the authors` models. Their results imply that economic levels of gas production should be possible wherever a similar horizontalmore » conduit can be tied into gas saturated layers through massive hydraulic fracturing.« less
  • The Campanian upper Almond Formation in Southwestern Wyoming contains at least 15 aggradational to backstepping microtidal to low mesotidal barrier/shoreline complexes laid down during a period of net transgression from 72 to 70.5 million years ago. Reservoir compartmentalization in the upper Almond occurs at several scales, including an aggradational to retrogradations sequence set composed of 3 retrogradational parasequence sets; numerous parasequences, and diverse barrier sub-facies units. The lowstand shorelines of these sequence sets stack aggradationally prior to transgression by a really extensive, marine mudstone horizons which separate the sequences. Highstand systems tracts are poorly preserved, often completely removed below fourthmore » of fifth order sequence boundaries which cause seaward jumps of facies in excess of 30 Km and place fluvial sediment, coal and lagoonal deposits abruptly over marine mudstone. Each sequence in the upper Almond is composed of several parasequences (sanding-upward, storm-dominated barrier shorefaces) which intercalate with marine mudstone to the east and grade into oyster-bearing, organic-rich lagoonal mudstone to the west. Compartmentalization in the barrier complexes occurs at most parasequence boundaries and in association with major sub-facies; boundaries (barrier margins, tidal inlets, flood-tidal deltas, washover fans). Further reservoir compartmentalization is induced by synsedimentary faulting and subsidence which locally preserve isolated reservoir-quality barrier/shoreline sandstone bodies by dropping them below the depth of ravinement (5-30 m). The recognition of synsedimentary faulting and subsequent ravinement is critical to accurate sequence stratigraphic analysis and for prediction of reservoir compartments.« less
  • The Campanian upper Almond Formation in Southwestern Wyoming contains at least 15 aggradational to backstepping microtidal to low mesotidal barrier/shoreline complexes laid down during a period of net transgression from 72 to 70.5 million years ago. Reservoir compartmentalization in the upper Almond occurs at several scales, including an aggradational to retrogradations sequence set composed of 3 retrogradational parasequence sets; numerous parasequences, and diverse barrier sub-facies units. The lowstand shorelines of these sequence sets stack aggradationally prior to transgression by a really extensive, marine mudstone horizons which separate the sequences. Highstand systems tracts are poorly preserved, often completely removed below fourthmore » of fifth order sequence boundaries which cause seaward jumps of facies in excess of 30 Km and place fluvial sediment, coal and lagoonal deposits abruptly over marine mudstone. Each sequence in the upper Almond is composed of several parasequences (sanding-upward, storm-dominated barrier shorefaces) which intercalate with marine mudstone to the east and grade into oyster-bearing, organic-rich lagoonal mudstone to the west. Compartmentalization in the barrier complexes occurs at most parasequence boundaries and in association with major sub-facies; boundaries (barrier margins, tidal inlets, flood-tidal deltas, washover fans). Further reservoir compartmentalization is induced by synsedimentary faulting and subsidence which locally preserve isolated reservoir-quality barrier/shoreline sandstone bodies by dropping them below the depth of ravinement (5-30 m). The recognition of synsedimentary faulting and subsequent ravinement is critical to accurate sequence stratigraphic analysis and for prediction of reservoir compartments.« less