Characteristics and Genetic Mechanism of Near-Source Accumulated Accumulation for Continuous-Type Tight-Sand Gas
Guo Yingchun
Song Yan
Pang Xiongqi
Jiang Zhenxue
Fu Jinhua
Du Jianjun
Abstract：Among the unconventional gas supply sources,tight-sand gas constitutes a significant percentage,which is the most available part under current technology.It can be divided into two types,continuous-type and trap-type.Geological and geo-chemical differences in characteristics on migration,accumulation,and distribution between trap-type and continuous-type tight-sand gas were compared systematically.Through physical simulation experiments,the dynamic genetic mechanism of near-source accumulation of continuous-type tight-sand gas was revealed.Trap-type tight-sand gas is the result of natural gas accumulation for a long migration distance with a good conducting system,causing an obvious fractionation on gas composition and carbon isotope and resulting in the following characteristics-“convergence in conventional traps,with edge and bottom wa-ter,high-quality sealing”.Continuous-type tight-sand gas is the result of near-source cumulative accumulation.Consequently, the gas composition and carbon isotope fractionation effect is unconspicuous,and discreteness exists among carbon isotopes in the same area.Different from trap-type,the continuous-type tight-sand gas exhibits the following characteristics such as “con-tinuous distribution,near-source aggregation,complex or inverted gas/water distribution”.The near-source accumulation of continuous-type tight-sand gas is consequence of counterbalance between force and resistance when gas migrates in nanoscale pore-throats developed in tight sandstone reservoirs.Before the natural gas migrates to the critical gas-water interface,it is separated into gas system and water system by the inversed gas-water interface.The gas migration force is abnormal gas pres-sure,while the need to generate buoyancy cannot be met.The gas migration resistances include overburden formation water pressure and capillary pressure.The magic trap of continuous-type tight-sand gas can be considered unconventional dynamic trap which core contents can be summarized as “(almost)nanoscale pore-throat,gas migrate follows the piston principle,buoy-ancy does not work,balance between force and resistance determines gas-water interface”.
Keywords：tight-sand gasnear-source accumulationcontinuous-typetrap-typepetroleum geology
Publication Date：2016-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：8( 433-440 )