Changes

During the mid-2000s through 2009, Eagle Oil & Gas Co., a Texas Independent, made a capital expenditure of approximately $70 MM drilling geologically successful, subeconomic wells in south Texas and the southern West Texas Basin. Eagle’s 40,000–50,000 acres in the West Texas Basin were scattered over Reeves, Pecos, and Ward Counties in the southern Delaware Basin, southern Central Basin Axis, and deep Sheffield Channel ([[:file:M125-WestTexas-Figure1.jpg|Figure 1]]). Their objectives at that time were conventional reservoirs in Pennsylvanian sandstones on the margin of the Central Basin Axis into the Sheffield Channel, Wolfcamp C sandstones sourced from the Diablo Platform filling the western margin of the abruptly subsiding southern Delaware Basin ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B, C]]), and Third Bone Spring sandstones in central Reeves and southern Ward Counties ([[:file:M125-WestTexas-Figure8.jpg|Figure 8]]).

During the mid-2000s through 2009, Eagle Oil & Gas Co., a Texas Independent, made a capital expenditure of approximately $70 MM drilling geologically successful, subeconomic wells in south Texas and the southern West Texas Basin. Eagle’s 40,000–50,000 acres in the West Texas Basin were scattered over Reeves, Pecos, and Ward Counties in the southern Delaware Basin, southern Central Basin Axis, and deep Sheffield Channel ([[:file:M125-WestTexas-Figure1.jpg|Figure 1]]). Their objectives at that time were conventional reservoirs in Pennsylvanian sandstones on the margin of the Central Basin Axis into the Sheffield Channel, Wolfcamp C sandstones sourced from the Diablo Platform filling the western margin of the abruptly subsiding southern Delaware Basin ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B, C]]), and Third Bone Spring sandstones in central Reeves and southern Ward Counties ([[:file:M125-WestTexas-Figure8.jpg|Figure 8]]).

[[file:M125-WestTexas-Figure7.jpg|center|framed|{{figure number|7}}(A) Blakey reconstruction of the West Texas Basin during Middle Permian and cross-section locations in the Delaware Basin. (B) Cross section A-A’, north to south showing the low-stand, stratigraphic interval, Wolfcamp C in blue. A similar geometry from west to east (dashed line) occurs as represented on the southern half of cross section A-A’. (C) Gamma Ray–Density-Neutron log across the Wolfcamp C showing a representative sandstone, 9’ thick, 14% average porosity with good Neutron–Density crossover. Darker horizontal lines indicate 10’ of depth separation; lighter horizontal lines show 2’ depth separation. 7A and 7B modified from Carr<ref name=Carr>Carr, D. L., 2019, Stratigraphic architecture and facies of the Bone Spring Formation (Permian), Delaware Basin, New Mexico and Texas, in W. Fairhurst, ed., Tight Oil Resource Assessment Research Consortium (TORA) Annual Meeting, May 8–9, 2019, p. 1–10.</ref>]].

 

file:M125-WestTexas-Figure7.jpg|{{figure number|7}}(A) Blakey reconstruction of the West Texas Basin during Middle Permian and cross-section locations in the Delaware Basin. (B) Cross section A-A’, north to south showing the low-stand, stratigraphic interval, Wolfcamp C in blue. A similar geometry from west to east (dashed line) occurs as represented on the southern half of cross section A-A’. (C) Gamma Ray–Density-Neutron log across the Wolfcamp C showing a representative sandstone, 9’ thick, 14% average porosity with good Neutron–Density crossover. Darker horizontal lines indicate 10’ of depth separation; lighter horizontal lines show 2’ depth separation. 7A and 7B modified from Carr<ref name=Carr>Carr, D. L., 2019, Stratigraphic architecture and facies of the Bone Spring Formation (Permian), Delaware Basin, New Mexico and Texas, in W. Fairhurst, ed., Tight Oil Resource Assessment Research Consortium (TORA) Annual Meeting, May 8–9, 2019, p. 1–10.</ref>.

[[file:M125-WestTexas-Figure8.jpg|center|framed|{{figure number|8}}Third Bone Spring sandstone. (A) Third Bone Spring sandstone Type Log showing Hoban, A, and C sandstones (B sandstone is not developed at this type log location; D/E not illustrated). (B) Cross section B-B’ is located from central Reeves County on the south to southern Ward County on the north (see location on the map, ([[:file:M125-WestTexas-Figure7.jpg|Figure 7A]]). The Hoban, A, and C sandstones are well developed on the south end of cross section B-B’ in central Reeves County, and there are no lower sandstones D/E to the south. The upper sandstones pinch out to the north in southern Ward County, but the lower sandstones D/E are present immediately above the Wolfcamp Shale (stratigraphic cross section B-B’ is hung on the red line, Bone Spring–Wolfcamp contact). Cross section B-B’ modified after Masterson<ref>Masterson, R., 2010, North-South geologic cross section of the 3rd bone spring sandstones: Reeves and Ward Counties, Eagle Oil & Gas, 1 plate.</ref>.]]

file:M125-WestTexas-Figure8.jpg|{{figure number|8}}Third Bone Spring sandstone. (A) Third Bone Spring sandstone Type Log showing Hoban, A, and C sandstones (B sandstone is not developed at this type log location; D/E not illustrated). (B) Cross section B-B’ is located from central Reeves County on the south to southern Ward County on the north (see location on the map, ([[:file:M125-WestTexas-Figure7.jpg|Figure 7A]]). The Hoban, A, and C sandstones are well developed on the south end of cross section B-B’ in central Reeves County, and there are no lower sandstones D/E to the south. The upper sandstones pinch out to the north in southern Ward County, but the lower sandstones D/E are present immediately above the Wolfcamp Shale (stratigraphic cross section B-B’ is hung on the red line, Bone Spring–Wolfcamp contact). Cross section B-B’ modified after Masterson<ref>Masterson, R., 2010, North-South geologic cross section of the 3rd bone spring sandstones: Reeves and Ward Counties, Eagle Oil & Gas, 1 plate.</ref>.

Cross section A-A’ ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B]]) is north–south through the center of the Delaware Basin. It is hung on the top of the Bone Spring formation showing the Bone Spring and Wolfcamp filling the abruptly subsiding Delaware Basin. The Wolfcamp C (blue) is the thickest, onlapping basin-filling, low-stand stratigraphic interval. In southern Reeves County, the Wolfcamp C thins dramatically onto the Diablo Platform ([[:file:M125-WestTexas-Figure1.jpg|Figure 1]], [[:file:M125-WestTexas-Figure7.jpg|Figure 7A]]), and a dashed cross section (A-A’) is illustrated, showing a similar geometry as displayed on the southern part of cross section A-A’. Wells that penetrate the Wolfcamp C closer to the Diablo Platform are up to 75% sandstone with high resistivity and typically have 5–10 ft flairs while drilling ([[:file:M125-WestTexas-Figure7.jpg|Figure 7C]]). To the east into the basin, farther from the source, the sandstone percentages decrease, but the reservoir quality, resistivity, and 5–10 ft flairs are consistent, with an increased or uniform thickness of the entire interval. Where productive, these sandstone reservoirs and older, Pennsylvanian sandstone reservoirs produce 1 BCFG per foot from conventional reservoir porosity.

Cross section A-A’ ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B]]) is north–south through the center of the Delaware Basin. It is hung on the top of the Bone Spring formation showing the Bone Spring and Wolfcamp filling the abruptly subsiding Delaware Basin. The Wolfcamp C (blue) is the thickest, onlapping basin-filling, low-stand stratigraphic interval. In southern Reeves County, the Wolfcamp C thins dramatically onto the Diablo Platform ([[:file:M125-WestTexas-Figure1.jpg|Figure 1]], [[:file:M125-WestTexas-Figure7.jpg|Figure 7A]]), and a dashed cross section (A-A’) is illustrated, showing a similar geometry as displayed on the southern part of cross section A-A’. Wells that penetrate the Wolfcamp C closer to the Diablo Platform are up to 75% sandstone with high resistivity and typically have 5–10 ft flairs while drilling ([[:file:M125-WestTexas-Figure7.jpg|Figure 7C]]). To the east into the basin, farther from the source, the sandstone percentages decrease, but the reservoir quality, resistivity, and 5–10 ft flairs are consistent, with an increased or uniform thickness of the entire interval. Where productive, these sandstone reservoirs and older, Pennsylvanian sandstone reservoirs produce 1 BCFG per foot from conventional reservoir porosity.

The following difference between Wolfcamp A and B were identified and defined in [[:file:M125-WestTexas-Figure15.jpg|Figures 15]], [[:file:M125-WestTexas-Figure16.jpg|16]], [[:file:M125-WestTexas-Figure17.jpg|17]] and [[:file:M125-WestTexas-Table1.jpg|Table 1]]<ref name=FairhrstHamln />.

The following difference between Wolfcamp A and B were identified and defined in [[:file:M125-WestTexas-Figure15.jpg|Figures 15]], [[:file:M125-WestTexas-Figure16.jpg|16]], [[:file:M125-WestTexas-Figure17.jpg|17]] and [[:file:M125-WestTexas-Table1.jpg|Table 1]]<ref name=FairhrstHamln />.

[[file:M125-WestTexas-Figure16.jpg|center|framed|{{figure number|16}}Stratigraphic column Upper Pennsylvanian to Lower Permian from Fu et al.<ref> Fu, Q., R. W. Baumgardner Jr., and H. S. Hamlin, 2020, Early Permian (Wolfcampian) succession in the Permian Basin: Icehouse platform, slope carbonates, and basinal mudrocks, in S. C. Ruppel, ed., Anatomy of a Paleozoic Basin: The Permian Basin, USA: Bureau of Economic Geology Report of Investigations 285 and AAPG Memoir 118, p. 185–225.

</ref> (reprinted with permission). The Wolfcamp A is 50% thicker in the Delaware Basin than in the Midland Basin, the Wolfcamp B in the Delaware and Midland Basins are similar thickness, and the Wolfcamp C thicknesses vary considerably by locality ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B]]), typically reaching maximum thickness in the southern parts of both basins. The Wolfcamp D (Cline) is the Missourian–Virgilian stage; Canyon–Cisco stratigraphic equivalents in the West Texas Basin. Canyon–Cisco stratigraphic terminology is used on the basin margins; Wolfcamp D (Cline) terminology is used for the deep-basin, basin-floor facies.]]

file:M125-WestTexas-Figure16.jpg|{{figure number|16}}Stratigraphic column Upper Pennsylvanian to Lower Permian from Fu et al.<ref> Fu, Q., R. W. Baumgardner Jr., and H. S. Hamlin, 2020, Early Permian (Wolfcampian) succession in the Permian Basin: Icehouse platform, slope carbonates, and basinal mudrocks, in S. C. Ruppel, ed., Anatomy of a Paleozoic Basin: The Permian Basin, USA: Bureau of Economic Geology Report of Investigations 285 and AAPG Memoir 118, p. 185–225.

 

</ref> (reprinted with permission). The Wolfcamp A is 50% thicker in the Delaware Basin than in the Midland Basin, the Wolfcamp B in the Delaware and Midland Basins are similar thickness, and the Wolfcamp C thicknesses vary considerably by locality ([[:file:M125-WestTexas-Figure7.jpg|Figure 7B]]), typically reaching maximum thickness in the southern parts of both basins. The Wolfcamp D (Cline) is the Missourian–Virgilian stage; Canyon–Cisco stratigraphic equivalents in the West Texas Basin. Canyon–Cisco stratigraphic terminology is used on the basin margins; Wolfcamp D (Cline) terminology is used for the deep-basin, basin-floor facies.

[[file:M125-WestTexas-Figure17.jpg|center|framed|{{figure number|17}}Scott Hamlin’s<ref name=FairhrstHamln /> (reprinted with permission) quick-look open-hole log mineral facies identification for the Wolfcamp confirmed with XRF from whole core. Note the siliceous and calcareous mudrock dominance and higher total TOC in the Wolfcamp A versus argillaceous mudrock and lower TOC in the Wolfcamp B. Also shown are the thicker, amalgamated debrites, carbonate facies in the Wolfcamp B and thin to very thinly bedded turbidite, carbonates facies in the Wolfcamp A. A type log showing the typical oil industry division of the Wolfcamp A and B in the Delaware Basin. The Wolfcamp A1 is present in northern Reeves, Loving, Winkler, and Ward Counties and not present in southern Reeves and Pecos Counties (from Gherabati et al.,<ref name=Gherbtietal2019>Gherabati, A., K. Smye, G. McDaid, and S. Hamlin, 2019, Developing a depletion score to study well spacing and the parent–child effect, in E. Goodman, ed., Tight Oil Resource Assessment Research Consortium Annual Meeting: Bureau of Economic Geology, November 20–21, p. 37–44.</ref> reprinted with permission).]]

file:M125-WestTexas-Figure17.jpg|{{figure number|17}}Scott Hamlin’s<ref name=FairhrstHamln /> (reprinted with permission) quick-look open-hole log mineral facies identification for the Wolfcamp confirmed with XRF from whole core. Note the siliceous and calcareous mudrock dominance and higher total TOC in the Wolfcamp A versus argillaceous mudrock and lower TOC in the Wolfcamp B. Also shown are the thicker, amalgamated debrites, carbonate facies in the Wolfcamp B and thin to very thinly bedded turbidite, carbonates facies in the Wolfcamp A. A type log showing the typical oil industry division of the Wolfcamp A and B in the Delaware Basin. The Wolfcamp A1 is present in northern Reeves, Loving, Winkler, and Ward Counties and not present in southern Reeves and Pecos Counties (from Gherabati et al.,<ref name=Gherbtietal2019>Gherabati, A., K. Smye, G. McDaid, and S. Hamlin, 2019, Developing a depletion score to study well spacing and the parent–child effect, in E. Goodman, ed., Tight Oil Resource Assessment Research Consortium Annual Meeting: Bureau of Economic Geology, November 20–21, p. 37–44.</ref> reprinted with permission).

 

file:M125-WestTexas-Table1.jpg|'''Table 1''' Total Organic Carbon, Mineral Facies, Clay, and Open-Hole Log Differences Noted in the Wolfcamp A and B (Fairhurst and Hamlin<ref name=FairhrstHamln /> reprinted with permission).

[[file:M125-WestTexas-Table1.jpg|center|framed|’’’Table 1’’’Total Organic Carbon, Mineral Facies, Clay, and Open-Hole Log Differences Noted in the Wolfcamp A and B (Fairhurst and Hamlin<ref name=FairhrstHamln /> reprinted with permission).]]

Drilling vertical wells, running complete log suites, obtaining core, and testing completion techniques in various intervals provided data and information to solve rock property, completion techniques, and productivity of multiple horizons and facies. During that process, Eagle drilled and completed 26 vertical wells and participated in another half dozen outside operated vertical wells before drilling the first horizontal well in the Wolfcamp unconventional reservoirs in the southern Delaware Basin. By 2012, the Midland Basin zonal definitions of the Wolfcamp ([[:file:M125-WestTexas-Figure16.jpg|Figure 16]]) were being identified and used by the industry in the Delaware Basin.

Drilling vertical wells, running complete log suites, obtaining core, and testing completion techniques in various intervals provided data and information to solve rock property, completion techniques, and productivity of multiple horizons and facies. During that process, Eagle drilled and completed 26 vertical wells and participated in another half dozen outside operated vertical wells before drilling the first horizontal well in the Wolfcamp unconventional reservoirs in the southern Delaware Basin. By 2012, the Midland Basin zonal definitions of the Wolfcamp ([[:file:M125-WestTexas-Figure16.jpg|Figure 16]]) were being identified and used by the industry in the Delaware Basin.