东濮地区下古生界牙形石色变指标的研究及其对油气勘探的意义

A STUDY OF COLOUR ALTERATION INDEX OF CONODONTS IN LOWER PALEOZOIC IN DONGPU REGION AND ITS SIGNIFICANCE IN OIL AND GAS EXPLORATION

牙形石色变指标CAI是有机质成熟度的良好标志。东濮凹陷下古生界牙形石CAI的横向分布及其形成历史的分析表明,凹陷北部边缘地区如观城、范县、毛岗一带,有机质已达成熟阶段,具有良好的生油远景;凹陷中部庆祖集、卫城、濮城、白庙一带,有机质已达高成熟阶段,可生成凝析油及湿气,凹陷中央部位,有机质过成熟,仅能保存干气;凹陷南部三春集、马厂一带,有机质基本处于高变质阶段,形成原生油气藏的可能性很小。北部地区,影响牙形石 CAI及有机质成熟度的主要因素是埋藏深度,南部地区则主要是中、新生代的火山喷发及岩浆侵入活动。

As one of the indexes of maturity of organic matter,the colour altera- tion index(CAI)of conodont has been accepted by all palaeontologists and petrogeologists.The CAI value of conodonts in Lower Paleozoic(mainly Ordovician)in Dongpu basin,eastern Henan,ranges from one to six and even to eight.Its distribution mainly depends on the depth of burial in the north part of the basin,and the distribution of the Mesozoic and Cenozoic volcanic rocks in the southern part.The CAI map shows that the organic matter in the Lower Paleozoic is matured and highly-matured in the marginal area of the north of the basin,giving a better oil and gas prospect;over-matured in the central of the basin,indicating gas generation only;while in the south of the basin,the organic matter has metamorphosed on the whole,no oil or gas generation will be expected. The history of the Lower Paleozoic conodonts colour alteration in this area can be divided into three stages as follow. (1)Ordovician to Triassic.CAI=1 or slightly higher; (2)Jurassic to Palaeogene:the CAI value ill the south area had risen to the present standard nearly under the high temperature caused by magm- atism and volcanicity; (3)Paleogene to Quaternary:the steady subsidence of the basin result- ed in the increase of CAI value,which had not been affected by volcani- city and magmatism,exhibited present CAI pattern.