Penwell is the field that named a town. J. H. Penn, a veteran West Texas operator, drilled the well that put Penwell on the map in October 1929, and the townsite was platted the following month. The field produces from shallow San Andres dolomite on the east flank of the Central Basin Platform anticline, around 3,400 to 3,800 feet, and has made roughly 100 million barrels from that zone alone. Beneath it lies one of the more heavily stacked reservoir columns in Ector County.
Source: Texas Railroad Commission production filings, aggregated across RRC field designations 70537001, 70537198, 70537066, 70537462, 70537264. Reported volumes lag the calendar by several months.
Dating Penwell depends on which well you count. Ector County’s first producer came in on December 28, 1926 on the W. E. Connell ranch southwest of Odessa at twenty barrels a day, which is very likely why Railroad Commission records carry a 1926 discovery year for the field. The town-founding well, the R. R. Penn Kloh-Rumsey No. 1 drilled by J. H. Penn, came in October 1929 — the date used by the Texas State Historical Association and the Texas Almanac. Bureau of Economic Geology work on the East Penwell unit splits the difference at 1927.
Whatever the starting date, development ran downward for decades. Operators added the Penwell (4500) reservoir in 1948, Penwell Ellenburger at 8,888 feet in 1946, and Penwell Glorieta, Penwell Clear Fork and Penwell Fusselman all in 1953. Each carries its own Railroad Commission designation, discovery year and depth. Counting every Penwell-named reservoir together brings cumulative production to roughly 128 million barrels, against about 100 million from the shallow San Andres field alone.
The shallow field was later consolidated into waterflood units, including the East Penwell San Andres Unit on University Lands and the North Penwell (San Andres) Unit, the latter the subject of a published reservoir-management study in the 1990s. Bureau of Economic Geology work on the East Penwell unit found it had produced 43 million barrels of an estimated 164 million barrels originally in place, leaving roughly 30 million barrels of mobile oil unrecovered — an unusually explicit public estimate of what a mature unit still holds.
Penwell produces from San Andres dolomite on the east flank of the Central Basin Platform anticline, with pay tops near 3,400 to 3,800 feet. The reservoir is subtidal pellet grainstone and packstone in which much of the porosity is secondary, created by dissolution of anhydrite. That anhydrite and gypsum content is a practical headache: it degrades conventional log and core analysis so badly that the acoustic log is the only dependable porosity tool here, and cores must be cleaned at low temperature or bound water is driven off and porosity is overstated.
The shallow San Andres has been waterflooded through unit operations for decades, and the Bureau of Economic Geology study of the East Penwell San Andres Unit quantified what that leaves behind: 43 million barrels produced from 164 million barrels originally in place, with about 30 million barrels of mobile oil still unrecovered. That is the case for continued infill and injection management rather than abandonment. No CO2 project has been documented at Penwell, and reports of horizontal San Andres redevelopment in this field are not supported by available public records.
Penwell interests are frequently deeper than owners realize. Seven or more separately designated reservoirs sit under the same surface, from the shallow San Andres through the Clear Fork, Glorieta, Fusselman and Ellenburger, each with its own field name and potentially its own lease. A check that shows one field name does not mean one field is all you own. University Lands acreage in the area adds another layer worth reading. We buy minerals and royalties in Ector County and provide free written offers.
County-level well data, production charts, and selling guides for the counties this field spans:
Because they are counting different wells. Ector County’s first producer came in December 1926, the well that founded the town of Penwell came in October 1929, and Railroad Commission and academic sources land on 1926, 1927 and 1929 respectively. None is wrong; they are answering slightly different questions. For an owner it makes no practical difference, since your rights come from your deed and lease, not the field vintage.
It is a reservoir estimate of oil that could still move to a wellbore in one unit, not a promise that it will be produced or that it would be economic to chase. It does explain why operators keep investing in mature units instead of plugging them. For valuation it supports a longer production tail, which is a reason to look carefully at the discount rate rather than a reason to expect a windfall.
If your tract adjoins or overlaps state university lands, the leasing terms and unit participation on those tracts follow a different framework than ordinary private leases. It does not affect what you own on your own tract, but it can affect unit boundaries and the operator’s development sequence. We check the record so you know which regime your acreage sits under.