新生代辉绿岩侵入对围岩物性的影响:以苏北盆地洋心次凹为例

传统观念认为岩浆活动区是油气勘探的禁区,但现今理论研究与实践勘探发现岩浆侵入作用能够显著改造围岩物性。目前岩浆侵入对围岩具体的影响认识不清,查明岩浆侵入影响围岩物性的机理对油气勘探具有重要意义。以苏北盆地洋心次凹的丰页1井为例,结合测井、地震及岩心等资料重点分析辉绿岩侵入对围岩储层物性与储集空间的改造,深入讨论其影响机制。苏北地区丰页1井的辉绿岩在吴堡运动期(约59 Ma)开始顺层侵入,侵入体中心相为辉长岩,侵入体边缘相为辉绿岩,变质相为板岩,上变质带厚度大于下变质带厚度。围岩由非渗透性泥岩转变为油气储层,储集空间为辉绿岩侵入和泥岩变质过程中产生的裂缝与孔隙。辉绿岩的侵入显著提高围岩储层物性,主要的机制有变质固结、热液破裂、冷凝收缩和溶蚀作用4种,其中热液破裂和溶蚀作用对储层的形成最为关键。

Influence of Cenozoic Diabase Intrusion on Reservoir Properties of Mudstone Wallrocks in the Yangxin Sub-depression,Subei Basin

Traditional view holds that magmatic active area is non-permissive for oil and gas exploration, but theoretical study and exploration practices reveal that magmatism may greatly improve their reservoir properties. Up until recently, the magmatic influence on sedimentary wallrocks is unclear, and thus it is important to investigate such influence (e.g., for diabase intrusion) for oil and gas exploration. This study took well Fengye 1 of Yangxin sub-depression in the Subei Basin as an example, with the aim to investigate the influence of diabase intrusion on reservoir properties of the mudstone wallrock. Based on the core, seismic and logging data, we carried out detailed investigations on the reservoir open-space and reservoir physical properties of diabase and its contact metamorphic zone, and discussed the lithofacies, physical properties and influence on the wallrock reservoirs. Diabase intrusion in northern Jiangsu began during the Wubao Movement (ca.59 Ma). The diabase intrusive-metamorphic complex comprises four layers: central gabbro, marginal diabase, slate wallrock, and unmetamorphosed mudstone wallrock. In the slate, the im-permeable mudstones has been transformed into oil and gas reservoir. The reservoir open-space includes all kinds of pores and fractures formed by intrusion and metamorphism, as well as dissolution (dominant). The upper contact zone is thicker than the lower contact zone. Formation of the contact metamorphic mudstone reservoir was mainly controlled by the diabase intrusion, and its influence includes metamorphic consolidation, hydrothermal fracturing, condensation shrinkage and dissolution, among which dissolution may have played a key role.