渤南洼陷北带沙四上亚段储层成岩流体演化

摘要

With multi-period of acid-alkaline fluid evolution as well as multi-period of hydrocarbon charging during the burial,the reservoir physical property went through a complex evolution in the upper part of the fourth member of the Shahejie Formation (Ess4 )in the north zone of the Bonan sag.With the comprehensive analysis of burial history,the thermal evolution of organic matter and dehydration of gypsum-salt bed,combined with characteristics of different hydrocarbon inclusions and salt-water inclusions,the diagenetic sequence of Ess4 in the north zone of the Bonan sag is studied.During the deposition of Ess4,the original formation-water is of weak alkalescence because of the dry climate;from the beginning of the deposition of Ess4 to 42.5 Ma,the for-mation fluid keeps weak alkaline with immaturate organics,and the main type of diagenesis is compaction,and early spherulitic pyrites are formed.From 42.5 Ma to 30 Ma,the formation fluid becomes acid for the existence of organic acid,and feldspar dissolution and quartz overgrowth take place.From 30 Ma to 24.6 Ma,the dehy-dration with alkaline water of gypsum-salt bed in the top of Ess4 occurs as well as decarboxylation of organic acid, thus the formation water becomes alkaline,and carbonate cementation and quartz dissolution simultaneously take place.During this period the first phase of hydrocarbon filling takes place from 28.8 Ma to 24.6 Ma,and from 24.6 Ma to 6 Ma,the organic acid is generated for the second time resulting from the uplifting stratum,and the formation water becomes acid,so the second phase of acid dissolution and quartz overgrowth begins,and the second phase of hydrocarbon filling take place in the period of 1 0 Ma to 6 Ma.From 6 Ma till now,the dehydra-tion occurs again in gypsum-salt beds of Ess4 and the formation fluid becomes alkaline once more,so a few of lat-er pyrite cementation can be found.%渤南洼陷北带沙四上亚段在埋藏过程中经历了多期酸碱流体演化，同时经历了多期油气充注作用，导致储层物性经历了复杂的演化过程。对渤南洼陷北带沙四上亚段埋藏演化史、有机质热演化、膏盐层脱水等综合研究，结合各种烃类和盐水包裹体特征分析，确定了渤南洼陷北带沙四上亚段成岩流体演化序列：（1）沙四上亚段沉积时期气候干旱，原始地层水呈弱碱性。（2）开始沉积至距今42.5 Ma，有机质尚未成熟，地层流体仍保持弱碱性，成岩作用主要为压实排水作用，形成早期球粒状黄铁矿胶结物。（3）距今42.5～30 Ma，为有机酸控制下的酸性环境，发生长石溶解、石英加大。（4）距今30～24.6 Ma，有机酸发生脱羧，同时沙四上亚段顶部膏盐层脱出大量碱性水，使地层水pH值呈碱性，发生碳酸盐胶结和石英溶解，其中距今28.8～24.6 Ma，发生第一期油气充注；距今24.6～6 Ma，地层经历抬升及再沉降，在抬升过程中有机质再次生成有机酸，使地层水pH值呈酸性，发生第二期酸性溶解、石英加大，其中距今10～6 Ma，发生第二期油气充注。（5）距今6 Ma至现今，沙四上亚段膏盐层发生脱水，地层流体呈碱性，发育少量晚期黄铁矿胶结等。