Untitled Document

This study of the Ordovician sandstones of the Michigan Basin, representing six-man years of geological research, is designed to assist exploration and production geologists in their understanding of factors that control hydrocarbon distribution and production in these reservoirs. The study area covers 54,000 square miles and includes all of Michigan's southern peninsula. The 437 wells incorporated into the study include all of the deep penetrations in the central part of the basin and all of the wells that penetrated more than 100 feet into the Lower Ordovician section in the southern portion of the basin.

Logs for these study wells were correlated to define the distribution of potential reservoir intervals. The delineation of subdivisions in the Ordovician sandstones is based on the correlation of laterally-persistent marker beds. Porosity, net sandstone and interval isopach maps have been created in order to determine and document the distribution and nature of Ordovician sandstone depositional patterns and porosity trends.

Exploration for Ordovician sandstone reservoirs in the Michigan Basin

has been primarily a structural play. Shallow Dundee structures have been used with some success as an indicator of structural closure in Ordovician strata. Most discoveries have been completed from the upper part of the porous Ordovician sandstones. However, recent drilling has shown that numerous other stratigraphic intervals in the Ordovician sandstones are potentially productive.

This report documents the role of depositional and diagenetic systems in defining the distribution of porous reservoir sandstones. By combining information on porosity trends with potential seals and structural styles, exploration analogs can be defined that will aid in the identification of significant reservoir-quality sandstones with favorable trapping characteristics.

Geological, petrophysical, and engineering characteristics for Falmouth, Reed City and Woodville fields are combined into fields studies to document reservoir characteristics, drive systems and producibilities in the Ordovician sandstone reservoirs. These studies provide valuable analogs for future exploration and development of the deep gas reservoirs in the central Michigan Basin.

Database

437	Study Wells	39	Cores Described (12,095')
49	Regional and Subregional Markers	655	Thinsections (from 26 cores)
22	Outcrops Described (Wisc. and Minn.)

Maps

Regional Maps (1:250,000)		Field Study Maps
26 Interval Isopach Maps 3 Structure Contour Maps 1 Study Well Distribution Map		28 Interval Isopach Maps 8 Structure Contour Maps 2 Porosity Maps

Cross Sections		Key Well Panels
5 regional stratigraphic sections (VS 1"=100') 3 regional stratigraphic sections (VS 1"=200') 7 field structural sections (VS 1"=40') 2 regional stratigraphic sections with computed lithologies (VS 1"=20')		Seven key well panels with computed lithologies, porosity and fluid saturations for: Gulf Oil, Robert Umlor 1-3 H.L. Brown, Ruwe Gulf 1-19A H.L. Brown, Snowplow 5-9 Hunt Energy, Martin 1-15 JEM, Doornbos 5-30 Traverse Oil, Frostic 1-30 Wolverine, St. Norwich - Patrick 2-28

Field Studies

Falmouth
Reed City
Woodville

Maps of reservoir interval thickness, porosity-feet and structure
Two cross sections per field
Engineering, petrophysical and production data.

Report Contents

TEXT AND FIGURES-This extensively illustrated report includes discussion, figures, and color photographs on such topics as: Depositional Setting, Stratigraphy and Lithofacies, Depositional History, Petrography, Petrophysics and Engineering, Field Studies (Falmouth, Woodville, Reed City), Exploration Recommendations and Bibliography.

STRATIGRAPHIC DATA-This appendix contains the well information and stratigraphic data for each of the 437 study wells including: the name of the operator and well, API number, location of the well, and 49 stratigraphic tops.

CORES DESCRIPTIONS - This section contains both written and graphic descriptions of 5,961 feet of core from 39 wells. These descriptions provide a basis for defining lithologic facies and depositonal sequences in the Ordovician Sandstones and the adjacent units. Physical, textural, and biogenic features are noted in the descriptions to aid in interpreting the environments in which these rocks were deposited.

EXECUTIVE SUMMARY ATLAS - This section provides a brief review of major findings of the study. It includes small?scale versions of key maps and cross sections.

MAPS, CROSS SECTIONS AND KEY WELL PANELS - These three sections contain a grid of cross sections including: eight regional cross sections (19 files), two computed lithology regional cross sections (6 files), two field cross sections for Falmouth Field (2 files), two field cross sections for Reed City Field (4 files, and three field cross sections for Woodville Field (4 files). Also contained in these sections are 30 regional maps at a scale of 1:250,000 and 38 field maps at a scale of 1:96,000. This includes: structure maps, contour maps, interval isopach maps, distribution maps, and porosity maps. In addition, the sections contain seven key well panels for the seven wells listed above.