Deposition, diagenesis, and porosity history of San Andres Formation, Shafter Lake Field, Andrews County, Texas
In the Shafter Lake field area, the San Andres contains 14 depositional cycles, consisting of upward-shoaling progradational sequences of subtidal, intertidal, and supratidal deposits. The deposits can be correlated between the two cores located 2 mi apart along the depositional strike. Six of the cycles are capped by supratidal deposits and are essentially complete, whereas eight were subjected to erosional truncation, which generally excavated supratidal and intertidal deposits. Thus, the San Andres reflects a complex eustatic history. The San Andres consists entirely of dolostones, the diagenesis of which records the following multicyclic stages: (1) dolomitization; (2) emplacement of anhydrite as cement, replacement, or a combination of cement and replacement; (3) dissolution of anhydrite or its alteration by gypsum, hemihydrate, or calcite. Many intervals record at least two complete diagenetic cycles (six stages). Three types of primary porosity were formed initially: intergranular, intrabiotic, and fenestral voids. Secondary pore types include intercrystalline pores, biomolds, and fractures. Varieties of tertiary pores are anhydrite porphryoblast models and intracrystalline voids. A previously undescribed variety of intracrystalline porosity was observed. A medial area between the dolomite crystal core and the outer rim was dissolved to create a moat-like pore. The principal occluders of all pore types are dolomite and anhydrite cements. The best effective porosity zones are preserved in subtidal facies wherein intercrystalline and intracrystalline pores, biomolds, and anhydrite porphyroblast molds are interconnected.
- Research Organization:
- Texas Tech Univ., Lubbock
- OSTI ID:
- 7013724
- Report Number(s):
- CONF-8604186-
- Journal Information:
- Am. Assoc. Pet. Geol., Bull.; (United States), Vol. 70:3; Conference: American Association of Petroleum Geologists Southwest Section convention, Ruidoso, NM, USA, 27 Apr 1986
- Country of Publication:
- United States
- Language:
- English
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