The Glorieta formation is oil productive in the northern Midland basin. Production through 1982 totaled over 25 million bbl of oil. Carbonate as well as siliciclastic facies are productive in different locations on the shelf. This production is largely diagenetically controlled, with secondary porosity enhancement prevalent in both clastic and carbonate reservoir types.

The Glorieta formation is composed of cyclicly deposited siliciclastics, carbonate, and carbonate-evaporite units. Environments of deposition range from supratidal sabkha through shallow subtidal to open-marine conditions. The siliciclastics are eolian-derived sediments that prograded onto the shelf of the northern Midland basin. The overall coarsening-upward sequence, the gently seaward dip of the clastics, and the open-marine characteristic of adjacent carbonate sediments suggest a subaqueous deposition similar to that described by Shinn along the leeward, southeast coast of Qatar Peninsula in the Persian Gulf.

Diagenetic features affecting porosity development in the siliciclastic intervals include etching of quartz grains and penecontemporaneous precipitation of pore-filling, poikilotopic anhydrite cement. Subsequent partial dissolution of anhydrite cements increased porosity in clastic reservoir facies. The carbonate units have undergone pervasive dolomitization of mud matrix, leaching of allochems, and extensive anhydrite void filling. Replacement of dolomicrite by anhydrite and later solutioning of replacement fabric anhydrite contributed to secondary porosity in carbonate reservoirs. A better understanding of these diagenetic relationships could aid in predicting porosity trends in these distinctly different reservoir types within the Glorieta formation.

End_of_Article - Last_Page 248------------