The Guadalupe Formation, a prolific hydrocarbon producing shallow marine sandstone, has a complex diagenetic history resulting in reservoirs which are characterized by abundant secondary porosity. The development of the secondary pore system is controlled by the pore water chemistry and depositional environment. A study of the Palogrande, Tello, and Cebu Fields shows significant variations in the type and amount of secondary pores, secondary cements, and authigenic clay in all three fields. Illite and chlorite occur in variable amounts in each field, but are less common in the Cebu Field. Distinct stratigraphic intervals containing chlorite have been identified, suggesting that depositional environment controls its occurrence. In environments where original sediments had the highest porosity, diagenetic processes have resulted in the greatest reduction in porosity and permeability.

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