--> The Formation of Diagenetic Trap in the Squirrel Sandstone

AAPG Eastern Section Meeting

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The Formation of Diagenetic Trap in the Squirrel Sandstone

Abstract

Samples of Pennsylvanian Squirrel Sandstone from one producing well in Kansas are examined on their petrography in order to determine the diagenetic history of the sandstone and the nature of petroleum trap. The sandstone is made of fine size (< 1 mm in diameter), angular monocrystalline quartz and euhedral feldspars. The degree of quartz overgrowth is minor and partial. The feldspars, include both K-feldspar and Na-plagioclase, show features of extensive dissolution. The clay matrix is dominated by kaolinite, in both detrital and authigenic morphology. There existed two layers of recrystallized coquinas, free of quartz and feldspars. Pore space in the reservoir quality sandstone is sporadically filled by authigenic kaolinite and siderite. In between the reservoir layers, pores of the sandstone are partially, or totally filled up with kaolinite.

Based on the observations, the depositional and diagenetic history of the Squirrel Sandstone is suggested as the following: immature sediments was provided by the nearby cratonic rocks to the low energy basin. The reservoir quality sand were deposited with little or no clay matrix. Detrital kaolinitic clay was episodically deposited in other sand layers to form much less impermeable layers. Feldspars dissolution continued to take place in shallow burial, and provided material for the authigenic kaolinite precipitated, Before the feldspars were totally dissolved, the emplacement of petroleum into layers that are still porous, and arrested all diagenetic reactions.