Abstract

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Title:: Discovery of Matrix Pore of High Efficiency Bedrock Gas Reservoir in Saline Basin and Its Significance

Author(s):: WU Li-rong; HUANG Cheng-gang; YUAN Jian-ying; YAN Cun-feng; MA Feng; SUN Xiu-jian; 1. Key Laboratory of Reservoir Description of CNPC, Lanzhou 730020, Gansu, China; 2. Northwest Branch of PetroChina Research Institute of Petroleum Exploration and Development, Lanzhou 730020, Gansu, China

Keywords:: saline basin; bedrock; reservoir characteristic; matrix micropore; intercrystalline pore; two-unit structure; Dongping area; Qaidam Basin

Abstract:: There is a major breakthrough on gas exploration in Dongping area of Qaidam Basin in recently years. The cumulative gas production is more than 2×108 m3. According to the drilling core observation, polarizing microscope identification, physical property analysis and field emission scanning electron microscopy, the bedrock in Dongping area is made up of metamorphic rock and granite with the average porosity of 4.72% and the average permeability of 1.71×10-3 μm2. In addition to crack and a small amount of dissolved pore, matrix micropores widely develop in rocks, including micropore developed in femic mineral from granite and mica sheet intercrystalline pore in gneiss. These pores have tiny radius and poor connectivity, and the sizes are from hundreds of nanometers to several micrometers. They are the important types of gas reservoir space of bedrock in Dongping area. A lot of gypsum fill in the aperture of the upper bedrock, because there are saline fluid infiltration, precipitation and cementation when the overlying Lulehe Formation and Ganchaigou Formation deposit. Plugging effect of saline mineral has an important role on the formation of a great gas field. The first discovery of “two-unit structure” developed in bedrock has an important significance on guiding the petroluem exploration in bedrock of saline basin.