富CO2流体与砂岩储层水-岩反应实验研究与应用:以黄桥油气藏龙潭组砂岩为例

摘要

The Huangqiao oil and gas field in eastern China is unique at the coexistence of CO2 and hydrocarbon accumulations and the production of oil CO2 and sandstone reservoir quality vary largely between wells.CO2-rich fluid has substantial reformation of the reservoir.Based on these backgrounds,a set of interaction experiments within the CO2-formation water-sandstone system is conducted in closed containers from 60 ℃ to 120 ℃ and from 10MPa to 40 MPa,which correspond to the burial depth from 1500m to 4000 m.The objective is to understand the corrosion of CO2-rich fluid on the sandstone reservoir.Analytical results show that the corrosion is apparent,the corrosion mineral is mainly carbonate,and the corrosion has reached equilibrium in the solution after 72 hours.Then,the ion concentration of Ca in the equilibrium solution is two orders of magnitude higher than the other ions.The corrosion intensity has negative and positive correlations with temperature and pressure,respectively,and the pressure is the primary control.Pressure contols the solubility of CO2 in the solution,and has particular corrosion ability at relatively high temperatures.In contrast,feldspars are corroded only a little because they have not reached equilibrium.Based on the regional geology,we infer that the CO2 is derived mainly from mantle along deep-seated faults.The CO2-rich fluid migrated into the Longtan Formation sandstone along the faults,and was overburdened by extremely thick fine-grained clastics.As a consequence,a relatively closed fluid-rock interaction system with high temperature and pressure was formed.The fluid-rock interaction was strong near faults and thus the reservoir corrosion and reformation was significant,leading to great amounts of secondary pores (e.g.in the Xi 3 well).In contrast,the fluid-rock interaction was relatively weak far from faults and thus the fluid-rock interaction and the development of secondary pores were relatively weak (e.g.in the Xi 2 well).Therefore,we propose a fault-controlled model of CO2-rich fluid-rock interaction as the main mechanism controlling the physical properties of the Longtan sandstone reservoir in the study area.%黄桥油气田是CO2和油气共存的一个特殊油气田,不同井的原油和CO2产量差异很大,且与之相关的储层差异也非常明显,富CO2流体对储层的改造作用十分显著.基于以上背景,通过密闭容器中CO2-地层水-砂岩体系相互作用实验,模拟地层埋深介于1500～4000 m的环境条件下(温度:60～120℃、压力:10～40 MPa),富CO2流体对砂岩储层的溶蚀作用.实验结果表明:富CO2流体对砂岩具有显著的溶蚀作用,溶蚀矿物主要是碳酸盐矿物,72 h即可达到平衡,平衡后的溶液中Ca离子浓度比其他离子高出两个数量级.碳酸盐矿物溶解强度与温度负相关,与压力正相关.综合来看,压力是决定性元素,它控制着CO2在溶液中的溶解度,特别是在较高温度下,压力的溶蚀效应更为显著.长石类矿物也发生一定的溶蚀现象,但是很微弱(本次实验中尚未达到平衡).结合该区地质背景,认为CO2主要来自深部(幔源),受深大断裂控制,沿着断裂进入龙潭组砂岩储层,其上被巨厚的细粒碎屑岩覆盖,构成了相对封闭的高温高压流体作用系统,靠近断裂带部位,流体作用强,储层溶蚀改造显著,次生孔隙发育(如溪3井),离开断裂的部位,流体作用减弱,储层发育较差(如溪2井).因此,断裂控制下的富CO2流体作用模式,是控制龙潭组砂岩储集性能的主要机制.