Scott W. Tinker1,
Laura C. Zahm1,
(1) Marathon Oil Company, Littleton, CO
(2) Univ of Texas, Austin, Austin, TX
Abstract: Structural controls on shelf margin evolution and reservoir distribution in Pennsylvanian Icehouse conditions: South Dagger Draw Field, New Mexico and Big Hatchet Mountains, New Mexico
Carbonate reservoirs are highly dependent upon the complex interplay between depositional textures, secondary cementation and dissolution, and jointing related to tectonism and compaction. For example, the initial position and evolving areal geometry of a carbonate ramp or shelf can be highly influenced by structural lineaments that existed during deposition. Likewise, faults and joints often act as conduits for cementing and dissolving fluids, and influence the distribution of permeability and secondary porosity in a reservoir.
South Dagger Draw field, a Pennsylvanian reservoir (Canyon and Cisco Formations) located in southeast New Mexico, provides an excellent example of structural, stratigraphic, and diagenetic interplay. Data used in the study include 135 well-log suites, 35 FMI logs, 7 cored wells, a 3-D seismic inversion, production information, and a depositional model. Structurally, the Huapache fault zone (Marathon-Ouachita orogenic front) located 10 miles SW of South Dagger Draw was active from Pennsylvanian to early Permian time. Stratigraphically, extensive glaciation of Gondwana resulted in high-amplitude eustatic sea-level changes during Pennsylvanian time. The combination of jointing and high-amplitude eustasy influenced the geographic position and areal trends of the prograding, sigmoid-oblique clinoforms that make up South Dagger Draw.
In addition to influencing depositional trends, joints played an important role in reservoir formation at South Dagger Draw. The data indicate that acidic, hydrothermal waters moved upward along joints and faults, and were "dammed" below shales to form dolomitized, "mushroom" shaped, matrix-vug networks. These matrix-vug networks formed preferentially where major joints intersected better initial matrix quality, typically at the ramp margin, and often enhanced the existing matrix quality. Analogous joint-controlled dolomite "mushrooms" have been observed in outcrop in age-equivalent strata in the Big Hatchet Mountains, New Mexico, and provide an analog for 3-D reservoir modeling.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana