Pre-Leonardian geology of Midland Farms Field area, Andrews County, Texas

The Midland Farms (Ellenburger) oil field was discovered on September 16, 1952, with the completion of Anderson-Pritchard's 1 Fasken-24 well, drilled on an indicated single-fold seismic structure. The field produces from vuggy, fractured Ellenburger dolomite with up to 310 ft (94 m) of gross and net pay. The Midland Farms (Ellenburger) field is part of a larger structure which incorporates not only Midland Farms field, but Midland Farms, West (Devonian), Inez (Ellenburger), and parts of the Fasken (Penn) and Block 41 (Wolfcamp) fields. The structure is a complex, uplifted block composed of two doubly plunging, asymmetric anticlines bisected by at least one wrench-type fault and several normal faults. This block has undergone at least three periods of structural compression and uplift. Middle Ordovician folding and faulting of Ellenburger dolomite created initial fracture porosity and permeability. Fractures and vugs were enlarged by meteoric water circulating through the emergent Ellenburger carbonates prior to the deposition of the overlying Simpson rocks. A post-Fusselman period of exposure developed vuggy and cavernous porosity in the Fusselman limestones, and beveled existing fault scarps. Late Mississippian to Early Pennsylvanian compression, related to the uplift of the Central Basin platform, folded the Paleozoic rocks and reactivated conjugate shears trending N10 degrees to 30 degrees E. Ellenburger fracture porosity was enhanced during this period of structural movement. No significant fracture-controlled reservoirs developed in any of the younger rocks, probably due to ductile deformation of the interbedded limestones and shales. Oolite limestone banks developed on a shallow platform over the Midland Farms area during the early Wolfcampian. Penecontemporaneous leaching produced oomoldic porosity in the limestones. Ellenburger oil production was established in the Midland Farms area in September 1952, and has amounted to 61.6 million bbl oil and 28.5 bcf of gas from 91 wells to January 1983. Major Fusselman and Wolfcamp oil accumulations were discovered during development of the Ellenburger field. Fusselman oil was first produced in June 1953, and has totaled 10.1 million bbl of oil and 5 bcf of gas from 33 wells to January 1983. Wolfcamp production was established in January 1954 and totals 10.7 million bbl of oil and 1 bcf of gas from 39 wells. Less significant deep production has been established in several other pre-Leonard reservoirs in the Midland Farms area, including the Thirtyone Formation (Devonian) (751,624 bbl of oil and 1.8 mmcf gas from 31 wells); Atoka (368,000 bbl of oil and 0.2 mmcf gas from 8 wells); and Strawn (420,000 bbl of oil and 1.1 mmcf of gas from 9 wells). Total production from all zones including post-Leonard beds in the Midland Farms field area to date has been 210 million bbl of oil and 84 bcf of gas.