Material Balance Equation of Overmature Organic-Rich Gas Shale

Abstract

Abstract. Gas shale was treated as a quintuple porosity system. When the source rock matures, a portion of kerogen or bitumen will be transformed into hydrocarbon, and move to displace the water out from inorganic matrix. When the kerogen is recrystallized to graphite, there will be less dissolved gas left in solid kerogen, which was assumed to be substantial in immature source rock. A series of resistivity tests showed the resistivity of shale decreases with higher vitrinite reflectance value, and proved the graphite do exist in overmature shale. With the role of natural fracture in shale analyzed, the water and hydrocarbon stored in overmature shale was summarized, and the overmature organic-rich gas shale should be treated as two porosity system. To find out which kind of pore may accommodate most of the free gas, a generalized material balance equation was presented, and the volume change with pressure drop in organic matrix and inorganic matrix can be calculated simultaneously. The field case herein proved that new material balance equation can be applied to calculate original free gas and adsorbed gas in shale or sandstone, and it was suggested that while in overmature gas shale there is free gas in inorganic pore, free gas in organic pore and adsorbed gas in kerogen, most of the free gas is in the organic pores.

Computer modeling and simulation for undersaturated primary drive recovery mechanism

“…The Schilthuis material balance equation has long been regarded as one of the basic tools for reservoir engineers for interpreting and predicting reservoir performance. The application of material balance has been acknowledged by several researchers for analyzing petroleum reservoirs with simplifying assumptions especially in the works of Yang et al 13 , Xu et al 14…”

“…The Schilthuis material balance equation has long been regarded as one of the basic tools for reservoir engineers for interpreting and predicting reservoir performance. The application of material balance has been acknowledged by several researchers for analyzing petroleum reservoirs with simplifying assumptions especially in the works of Yang et al 13 , Xu et al 14 , and Habibi et al 15 Adeloye et al 16 described material balance as zero-dimensional simulator since there are no changes in any direction within the reservoir system being seen as a serious drawback. Buduka et al 17 in their work also used graphical material balance as an equation of a straight line to estimate reservoir fluids in place but with some drawbacks.…”