低效气藏地质特点和成因探讨

低效天然气藏特指储量丰度低、气井产能低的一类气藏,其储量约占全国天然气总储量的70%。在中国的这类气藏储层普遍为陆相河流相和三角洲相沉积,而且埋藏深度较大。这类储层具有连续性差,孔隙度和渗透率低及非均质性强等特点,因此,勘探和开发的难度较大。为了有效利用这类资源,在对国内外低效气藏的地质特征进行系统对比的基础上,分析了陆相碎屑岩储层低效气藏的特点,认为沉积相类型和成岩作用是导致储层低效的两大地质因素。沉积相类型决定了储集层的物性和连续性;成岩过程中的压实作用和胶结作用是破坏原生孔隙、造成砂岩致密的主要原因。

A discussion on geologic features and genesis of low-efficiency gas reservoirs

Low-efficiency gas reservoirs refer in particular to those with low abundance of reserves and low well productivity.The reserves of such reservoirs in China account for about 70% of our total gas reserves.In China, reservoir rocks of such gas reservoirs are commonly of fluvial and delta facies with relatively large burial depth,which are characterized by poor continuity,low porosity and permeability,as well as strong heterogeneity.As a result,exploration and development of these reservoirs are quite difficult.For the sake of effectively utilizing these gas resources,the characteristics of low-efficiency gas reservoirs in continental clastic rocks have been analyzed,based on systematic correlating the geological features of low-efficiency gas reservoirs both in China and abroad.It is believed that the types of sedimentary facies and diagenesis are two major geologic factors leading to low efficiency of reservoirs.Sedimentary facies control the poroperm characteristics and continuity of reservoirs,while compaction and cementation are the main factors that destroy primary pores and lead to the formation of tight sandstones.