Contact: Dave Harris
Five ASCII files are included on the diskette. They contain the header data (BIGLPROJ.DAT), tops data (BIGLPROJ.TOP), and three explanatory files (AAAREAD.ME, TOPS.TXT, WELLDATA.TXT) for the 7,713 wells included in the study. A total of 62,709 individual tops were collected during the project. The header and tops data files are in standard ASCII data format (one line per record). These file types are fully explained in TOPS.TXT, WELLDATA.TXT, and AAAREAD.ME. The header data include a rig type field, which was collected as part of this project in order to evaluate the relative quality of drillers' log tops (based on the perception that drillers' tops from cable tool rigs are of higher quality than those from air rotary rigs). Additional information on some of the fields in the tops data set follows:
Formation name: coded using American Association of Petroleum Geologists stratigraphic codes
Datum: height above ground elevation from which log was measured. Datum + elevation = KB
Type of top: can be "S" or "I." "S" tops are true stratigraphic formation tops. "I" tops are interval tops, either zones within formations, or informally recognized tops. In this study all tops are "S" type except for 332PCCV (Pencil Cave shale), and 332BIGL1–333BIGL4 (Big Lime subzones).
Top and base: measured depth to formation top and base, picked from a geophysical log when possible, otherwise from a driller's log.
Lithology: primary and secondary lithology of interval. Default values were used for most of this study; we did not attempt to interpret lithologies for each unit.
Source of pick: an important field collected for each top. It records the data source used to pick the top. DL indicates drillers' log, SDR indicates sample description, and all other abbreviations are geophysical logs (see WELLDATA.TXT and TOPS.TXT for translation). This field allows separation of geophysical log tops from drillers' log tops. Of the wells in the study, 4,380 had at least one geophysical log top; 3,333 wells have only drillers' log tops available.
Fault sequence: we have added a new field to allow identification of repeated tops for the same formation in wells that cut the Pine Mountain Thrust Fault. This field has a numeric value from 0 to 2. Fault sequence 0 indicates the formation is autochthonous (in place), and is the value for all picks north of the Pine Mountain Thrust Fault. Values greater than 0 indicate the formation is within a thrust slice. South of the Pine Mountain fault some picks have fault sequence values of 1 or 2, indicating progressively shallower thrust sheets. Only four wells in the data set have thrust-repeated section, with multiple picks for the same formation. Many others in Harlan, Bell, and Whitley Counties penetrate only the upper thrust sheet, and are coded as fault sequence 1 even though they do not cut the fault.
Comments: any comments that pertain to the top are recorded in this field.
Some of our criteria for picking tops in this project are discussed below, for each formation. See the type log for an example. The AAPG formation codes used in the project are shown in italics.
Pennington Formation (332PNGT): the most difficult pick, and probably most variable. We used the base of the last thick, massive Pennsylvanian sandstone (Lee) on geophysical logs as the top of the Pennington (Mississippian). On drillers' logs we used the first occurrence of red rock, or the base of a thick probable Lee sandstone.
Little Lime (332LTLM): 10- to 30-foot-thick limestone above Pencil Cave.
Pencil Cave Shale (332PCCV): 2- to 15-foot-thick shale between Little Lime and Big Lime.
Big Lime (332BIGL): thick carbonate unit, obvious on geophysical logs and commonly noted on driller's logs.
Big Lime subzones (332BIGL1–333BIGL4): these zones within the Big Lime were picked only in downdip wells with a gamma-ray log available. They were defined on regional cross sections at the start of the project. They were picked on the basis of thin shale markers. As the Big Lime thins updip, it becomes difficult to reliably correlate these zones.
Fort Payne Formation (337FTPN): carbonate unit below the Big Lime in the southwestern part of the study area.
Borden Formation (337BRDN): easily defined silty shale below Big Lime and above the Sunbury shale with its high gamma-ray log response.
Sunbury Shale (339SNBR): thin (2–30 feet) shale below Borden with a high gamma-ray log response.
Berea Sandstone (339BREA): the Berea Sandstone and Bedford Shale were combined in this study. This zone lies between the Sunbury and Ohio black shales in part of the study area.
Ohio/Chattanooga Shale (341OHIO/341CHAT): obvious black shale with high gamma-ray log response. Top and base of the Ohio/Chattanooga were picked where possible. This was the deepest formation picked in the study.