Diagenesis has profoundly altered the reservoir capacity of some Lower Morrowan sandstones in the Anadarko Basin. Definition of sandstone geometry, depositional environment, etc., comprise only part of the information necessary to intelligently explore for hydrocarbons in these rocks.

Bulk of the Lower Morrow sandstones were deposited in a marine transgressive sea. Two basic types of sandstone are recognized: Type I is a very nearshore, clean, well sorted, nonglauconitic, noncalcareous sandstone deposited in a high energy environment; Type II is a slightly offshore facies of Type I, deposited under lower energy conditions and is normally poorly sorted, "glauconitic", calcareous and sometimes shaley.

Petrographic analyses indicates Type I sandstones have either (1) extreme pressure solution and no permeability, or (2) moderate to minor pressure solution with secondary quartz overgrowth cement. These rocks are generally permeable when medium to coarse grained and impermeable if fine grained. Upper and lower edges of some sand bodies are tightly cemented with CaCO³ apparently through ionic impedence at the sand-shale boundary.

Type II sandstones have been diagenetically altered by minor secondary quartz overgrowths and pressure solution, extensive carbonate cementation, and some authigenic clay. Commercial permeability is associated with secondary leaching of carbonate cements. Such reservoirs have random shapes and are difficult to predict or evaluate.

A qualitative petrographic rock fabric classification based on relative degree of pressure solution, type of grain outlines and contact, amount and type of cement and porosity is useful in mapping their geographic distributions. Integration of this type data in conjunction with normal subsurface exploration methods is beneficial for the Lower Morrow in the area studied.

WILLIAM L. ADAMS

William L. Adams was born May 29, 1929, in Clay Center, Kansas. He was granted the BS degree in geology from the University of Kansas in 1951 and an MA degree in geology from the University of California at Los Angeles in 1956. He served as a Naval Officer during and after the Korean War from 1951 through 1954.

Mr. Adams joined the Pan American Petroleum Corporation in 1956 in their exploration department, Wichita, Kansas. In 1958 he moved with Pan American to Liberal, Kansas, where Anadarko Basin activities were consolidated in one office. Much of his time has been spent studying the Morrowan rocks throughout the Anadarko Basin. He currently is a geological supervisor for Pan American as a project geologist in the Liberal Exploration District.

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