Stratigraphic Characterization and Depositional History of the Barnett Shale within the Fort Worth Basin in Denton County, Texas.

摘要

The Barnett shale, located in the Fort Worth Basin, is a geologic unit that has undergone extensive study and currently holds great economic importance. It contains well-known stratigraphy, but still holds questions with regard to the specific stratigraphic variation over much of its area. Denton County contains a large geographic area of the Barnett shale, and holds many answers to the varying stratigraphy of the Barnett shale, as well as an explanation into its depositional history. The investigation involved the use of two cross sections utilizing 32 and 26 wells respectively in the western region of Denton County, Texas. From the cross sections produced, the variation in stratigraphy and structure with the Barnett and related lithologies across a large area was compared with known stratigraphy of the Barnett shale. The variation in structure and stratigraphy agrees with the previous work examined in this study. All of the gamma ray signatures observed within the Barnett shale and related lithologies matched well with the type log used for comparison with all the wells included in the study. The cross sections confirmed the variation expected for the stratigraphy and structure in the region of Denton County along with the location of the area in relation to the Fort Worth basin as well. The Barnett shale shows two individual members, upper and lower, as expected. The presence of the Forestburg limestone dividing the Barnett shale into upper and lower members is also confirmed with the cross sections.;Multiple stratigraphic cross sections were produced along the same south to north and southwest to northeast directions as the in situ cross sections covering the entire study area in Denton County, Texas. This allowed definitive variations of both the individual stratigraphic thickness and change in structural depth to be observed. The overall trends from the stratigraphic cross sections indicate a general deepening to the north and northeast from the south and southwest seen in every section. An increase in stratigraphic thickness is also seen with all of the lithologic units, with the general increase found toward the northeast from the south and southwest. The Marble Falls limestone showed increase from the north to the south, while the Forestburg limestone showing an increase from the south to the northwest.;Isopach and structure maps produced from each lithologic unit confirmed and defined structural and stratigraphic trends seen across the study area. The structural trend includes a deepening from the southwest toward the northeast seen with each of the lithologic units on each of the structural maps. The stratigraphic trend with regard to stratigraphic thickness increase seen was varied with each of the lithologic units. The Marble Falls limestone's increase in stratigraphic thickness occurs from the north to the south edge of the study area. The Upper Barnett shale's increase in stratigraphic thickness occurs along a zone around the center of the study area from the western edge of the area to the northeast. The Upper Barnett shale's stratigraphic thickness increases from the south to the center zone and from the northwest to the center zone as well. The Forestburg limestone's increase in stratigraphic thickness occurs from the south edge of the study area toward the northwest edge of the area. The Lower Barnett shale's increase in stratigraphic thickness occurs from the south edge of the study area toward the northeast edge of the study area.