The Fairway field, Anderson and Henderson Counties, Texas, is a major oil field in a reef and reef-associated facies of the Lower Cretaceous James Limestone Member of the Pearsall Formation. The present productive limits are controlled largely by structure. The location of the reef also was influenced by a contemporaneously growing structure, so the reservoir can be considered to have a combination structural-stratigraphic trap, both physically and genetically.
The James Limestone Member consists of several limestone types, differentiated on the basis of texture and fossil content in cores. Maps of the distribution of these rock types during successive stages of reef growth show that the main core of the reef, dominated by frame-building organisms, was in the northwest part of the field. The frame-builders were a closely associated suite of corals, stromatoporoids, algae, and rudistids. By about the middle of the time of development of the James reef, the center of growth was at its maximum, and smaller satellite reefs appeared in the southeast and southwest. A facies dominated by large bivalves occupied much of the area between centers of growth of the main frame-builders. The south-central part of the field was an area of persistent accumulation of carbonate sands and gravels. Carbonate muds and muddy sands were the dominant facies elsewhere.
Porosity and permeability are present in all of the limestone types but are higher on the average in the associated limestones than in the reef proper. The porosity is largely secondary, although it is in part the result of enlargement of primary pores.