Historic Oil Field
The Eunice and Monument fields of Lea County, New Mexico are usually spoken of together: adjoining Grayburg and San Andres accumulations on the Permian Basin’s Central Basin Platform and shelf margin that were discovered in 1929 and developed into one of the state’s biggest oil producing areas. State records date the discovery to March 1929, with the completion of the Continental Lockhart B-31 well. Today the area is worked through large unitized waterfloods — the Eunice Monument South Unit chief among them — that have carried production far past what primary depletion could have delivered.
Lea County’s oil era opened in June 1928 at Hobbs. Within a year the play had spread south and west, and in March 1929 the Continental Lockhart B-31 well opened what became the Monument accumulation. Drilling followed quickly across the Eunice and Monument areas, and the towns took on the character of oil towns: tank batteries, gas plants, and rail loading facilities. The producing horizons were the same Permian shelf carbonates that made the rest of southeast New Mexico — Grayburg and San Andres dolomite at a few thousand feet, prolific at first and then steadily declining.
For decades the field produced under primary drive, and by the late twentieth century much of it was heavily depleted. Unitization was the answer. The Eunice Monument South Unit was formed in February 1985 to convert the area to secondary recovery, and the resulting waterflood — a large-scale project involving several hundred wells — became a documented case study in reviving a badly depleted Grayburg reservoir. Engineering papers from the period describe the challenge plainly: pressure had to be rebuilt before oil would move again toward the producing wells.
Since then the Eunice-Monument area has followed the pattern of mature Permian shelf fields. Injection patterns have been reworked, infill wells drilled, and packages of leases traded among operators as larger companies rotated capital toward unconventional plays and smaller specialists took over the flood. Production continues at a modest but durable rate, supported by continued water injection, and the field remains a significant piece of Lea County’s output nearly a century after the discovery well. Owners should verify current operatorship from their own check detail rather than assume it has stayed constant.
Production comes from the Grayburg and San Andres formations, Permian carbonates laid down along the shelf and platform margins of the Permian Basin. The Grayburg in particular is a cyclic sequence of dolomite and interbedded finer material, and sequence-stratigraphic studies of the Eunice Monument South Unit have been used to map how those cycles control fluid flow. The practical consequence is that the reservoir is layered: some intervals take water readily and others resist it, so sweep efficiency depends on correlating cycles across the unit rather than treating the pay as a single tank.
Waterflooding defines the modern field. The Eunice Monument South Unit was unitized in February 1985 specifically to implement secondary recovery in a reservoir that primary production had already drained hard, and the project has been written up as an example of flooding a highly depleted Grayburg. Injection here does two jobs: it restores reservoir pressure and it physically displaces oil toward producers. Because the response depends on which cycles the water enters, operators continually adjust injection profiles, convert wells, and target bypassed intervals. Sustained production in this field is a direct product of that ongoing work.
Most Eunice-Monument royalty and mineral interests are unit interests, so a check reflects a tract participation factor applied to unit production rather than one well’s decline. That structure rewards careful valuation: unit performance, injection spending, and remaining flood life matter more than the last six months of revenue. Because New Mexico’s Oil Conservation Division reports by pool, your documents may name a pool or unit rather than the field. We buy minerals and royalties in Lea County and provide free written offers.
County-level well data, production charts, and selling guides for the counties this field spans:
In a unit, many separate tracts are operated as one reservoir and revenue is allocated by a participation formula rather than by which well happens to sit on your acreage. It smooths out well-by-well variation, but it also means your check depends on unit-wide performance and on the operator continuing to invest in the flood.
Waterflooded Permian shelf fields have repeatedly outlasted predictions. Eunice-Monument has produced since 1929 and was substantially re-energized by unitization in the mid-1980s. Remaining life is governed less by geology than by the economics of continued injection and workovers, which is exactly what a careful buyer models.
Send us a recent check stub or division order and, if you have it, your deed. We will identify the unit and pool, look at production and injection history for that area, and provide a free written offer that explains the assumptions behind the number. There is no obligation and no cost.