天然气二次运移组分变化机理研究

天然气的烃类组成并不单一,但成藏天然气一般以甲烷为主,除了与烃源岩母质类型及其演化有关以外,二次运移也是一个重要的作用因素。通过天然气二次运移物理模拟实验,研究了天然气二次运移特征,注意到天然气二次运移是一种断续流运移,主要包括2种基本运移方式——活塞流和优势流,两者交替就形成了天然气的断续流运移;结合有机质热演化生烃过程以及气、水、岩的相互关系分析,探讨了天然气二次运移过程中组分变化的机理,认为二次运移会导致成藏天然气组分中甲烷含量增高,其主要原因包括二次运移过程中的组分分异作用,断续流运移导致重组分在岩石孔隙中的封闭滞留作用,以及二次运移路径上残留原油的溶解作用。

STUDY ON SECONDARY MIGRATION MECHANISM OF NATURAL GAS

Natural gas is composed of some kind of low molecular hydrocarbon, but the accumulated natural gas in reservoir is mainly composed of methane generally. This paper studied the secondary migration characteristics of natural gas by the physical simulation experiment, and discovered that the secondary migration of natural gas is a kind of Intermittent Flow which developed from the alternation of Plug Flow and Preferential Flow.The Intermittent Flow of natural gas can cause heavier hydrocarbon captured and sealed off into rock pores with formation water. And then this paper discussed composition alternation mechanism of natural gas during secondary migration based on the analysis of hydrocarbon formation and the relationship of gas, water and rock. It is resulted that the composition differentiation in the secondary migration of natural gas, heavier hydrocarbons captured and sealed off into rock pores caused the Intermittent Flow of natural gas and the dissolution of oil preserved in the secondary migration path are main reasons why the accumulated natural gas is composed of much more methane.