桑托斯盆地R油田辉绿岩对盐下碳酸盐岩储层接触热变质影响

Influence of Diabase Contact Thermal Metamorphism on Pre-Salt Carbonate Reservoir in R-Oilfield of Santos Basin

摘要: 针对岩浆侵入接触热变质作用对超深水环境盐下碳酸盐岩储层的影响问题，以桑托斯盆地R-油田为例，对6口井中不同厚度辉绿岩侵入对盐下灰岩储层的重结晶程度、影响厚度、物性变化等进行统计分析。研究表明，R-油田盐下的灰岩受巨厚层辉绿岩的接触热烘烤变质作用显著，普遍发生大理岩化重结晶，颗粒变粗大，颜色白化，但不均匀性也较强；储层物性急剧降低，一般降低幅度4~8倍，孔隙度越高降低幅度也越大；接触变质带厚度与侵入体厚度具有正相关关系，符合二项式y = 0.001x2 + 0.0801x + 0.2426变化规律，但明显低于塔里木盆地辉绿岩影响灰岩的幅度。研究认为，接触变质带高度重结晶和胶结作用是导致储集空间降低的主要原因；超深水环境较低的围岩温度以及侵入体上覆巨厚导热性好的膏盐岩是造成接触变质影响厚度偏低的主要原因。

Abstract: In view of the influence of magma intrusion contact thermal metamorphism on carbonate reser-voirs in ultra-deep water environment, taking R-oilfield in Santos Basin as an example, the litho-logical changes, influence thickness and physical properties of pre-salt limestone reservoirs caused by diabase with different thickness in six wells are studied. The research shows that the pre-salt limestone in the ultra-deep water environment of R-oilfield is affected significantly by the contact thermal metamorphism of the thick diabase. The recrystallization is common, the minerals become coarse and the rock color changes to white but with obvious heterogeneity. The porosity of the reservoir drastically reduced, generally decreasing by four to eight times. The higher the porosity, the greater the reduction. The thickness of intrusive rocks is positively correlated with that of the carbonate contact metamorphism aureole, which fits the binomial equation y = 0.001x2 + 0.0801x + 0.2426. However, the metamorphism influence thickness of the diabase in R-oilfield on the pre-salt country limestone is significantly lower than that in the Tarim Basin in western China. It believed that the high degree of recrystallization and cementation of the contact metamorphic aureole are the main reasons for the decrease of the reservoir space. The overlying huge gypsum and salt layers with high heat conduction effect and the lower temperature country rocks may probably be responsible for the thinner contact metamorphism aureole in R-oilfield.