Geologic Properties that Affect Waterflooding in the Big Injun Sand of West Virginia

Abstract

Abstract This study was made to determine the petrography, mineralogy, porosity, and petrography, mineralogy, porosity, and permeability of the sandstone, and their permeability of the sandstone, and their relationship to waterflooding in Big Injun reservoirs. Rotary cores, geophysical well logs, petrographic thin sections, and results of chemical analyses of sandstone samples from several Big Injun oil reservoirs were used to determine these parameters. The results show a great range of reservoir characteristics within area of study. The petrography of the sandstones ranges from lithic graywackes (very shaly), to protoquartzites (clean), with varying mineral protoquartzites (clean), with varying mineral constituents. Porosities and permeabilities also vary greatly due to the petrography and mineralogy of the sandstone. Interstitial clay minerals constitute from less than 5 to more than 25 percent of the reservoir rock. Other important interstitial constituents of the Big Injun sand are secondary precipitated carbonates and quartz. The framework of the Pocono Big Injun sand is composed mainly of Pocono Big Injun sand is composed mainly of quartz grains with minor amounts of rock fragments, heavy minerals, and feldspar. The interstitial clays and cements in the Big Injun sand have greatly reduced the original porosity and permeability of many of the porosity and permeability of many of the reservoirs studied, and will dictate water-flooding techniques that must be used for successful operations. Laboratory results show that the permeabilities of most Big Injun sands are reduced more than 50 percent by flooding with fresh water as compared with results after flooding with saline water. Several Big Injun sand pilot waterfloods in which fresh surface water was used have been unsuccessful, partly due to low injection rates caused by reduced permeability and pore plugging of the formation. permeability and pore plugging of the formation. Any future Big Injun waterflood projects should use saline formation water in a closed system to reduce interaction between flood waters and the interstitial constituents of the formation. Introduction Reserves of premium quality Pennsylvania grade crude oils are steadily being depleted. The refining capacity for Penn grade crudes is increasing and will soon place additional demands on the supply. Much of this additional crude must be produced by secondary-recovery techniques such as waterflooding. The Bradford area oilfields in Pennsylvania and New York have been successfully waterflooded since 1920.