从已发现的油气田看中国海相油气勘探

中国海相油气勘探的主要目标是古生界碳酸盐岩,在漫长的演化历程中它的主要成藏类型是准原生型。对形成保存至今的工业油气藏来说,碳酸盐岩中有效烃源岩的总有机碳含量下限应≥0.5%,滨海相或海陆交互相煤系可对生烃作出重大贡献。碳酸盐岩中的储集体受裂缝—岩溶发育程度的控制而分为三种基本类型:(1)以孤立的缝洞储集体为主者称纳溪型,各储集体内的流体性质、压力均可有不同;(2)各储集体间相互连通从而有统一的压力和气、油、水界面,若其似块状者称任丘型,若其似层状者则称威远型;(3)居于这两个端元间的过渡类型为塔河型,其各部分之间的流体性质和压力可有一定差别,无统一油水界面。应注意对似层状储集体的勘探研究,保存条件的好坏对海相油气田有决定性的意义。在分析复杂的多期成藏史中,要注意古隆起和晚期成藏的辩证关系。我国的海相油气勘探有难度,要重新评价有效和高效烃源岩,从较浅部和次生油气蒇入手逼近油气源,寻找主力油气藏,要重视岩性圈闭和各构造(形变)层间的不吻合性。中国的海相油气勘探方向可分为优先勘探、立争突破、劣中选优三个层次。

An Appraisal of the Ways of Marine Strata Petroleum Exploration in China Given by Discovered Oil and Gas Fields

The main object for petroleum exploration in marine strata in China focuses on Paleozoic carbonate rock.The dominant type of the carbonate rock reservoirs was pene-primary during the long evolution history.As for the well-preserved commercial reservoirs,the lower limit of TOC in effective carbonate source rocks should be ≥0.5% in value and littoral marsh facies or marine/continental transition facies coal meassures should have a significant contribution to hydrocarbon generation.Con- trolled by different extents of fracture-karst development, reservoir bodies in carbonate rock can be divided into Naxi, Renqiu or Weiyuan and Tahe types.Naxi type is predominated by isolated fracture and/or cave reservoir bodies but each of them has different fluid property and pressure.Renqiu type (blocklike bodies)or Weiyuan type(bedlike bodies)is char- acterized by connecting reservoir bodies from each other with uniform pressure as well as gas,oil and water interfaces. Tahe type is a traditional one between the both types that characterized by some different fluid property and pressure but no uniform oil and water interfaces for every body.It is neces- sary to pay a concern to the research and exploration of bedlike reservoir bodies,and to the dialectic relationship between pa- leouplifts and late hydrocarbon accumulation under the back- ground of complicated multi-phase hydrocarbon accumulation. The extent of preservation condition is decisively significant to marine origin fields.It is suggested that exploration for marine strata in China can take three steps:preferential exploration for the fault areas overlain by wide-distributing continental de- pressions,doing best to make exploration breakthrough for the marine strata areas overlain by Mesozoic-Cenozoic continental rift system,and choiceness among low mature exploration for the areas of widely-exposed marine strata series.