摘要： 水驱波及效率提升可以显著增强碳酸盐岩油藏开发效果.本文在考虑地层水离子组成基础上,借助体视显微镜和激光粒度仪配制了一种离子匹配悬浮液,其中悬浮的硫酸钙颗粒处于临界饱和状态,大部分颗粒粒径在10 μm左右,静置后由于絮凝和聚集作用最大可到 50 μm.悬浮液的静态性质实验表明,由于硫酸钙"逆溶解度"特征和水合物的变化,其微粒会在小于 45℃范围缓慢消失,并在 90℃时迅速析出;矿化度和离子组成改变会使硫酸钙微粒浓度和粒径显著增大.在渗透率级差为 4.7的岩心并联实验中,离子匹配悬浮液可使较低渗岩心的分流率最大提高约9.8%,最终采收率提高约4.3%.温度、压力和盐度的影响,以及注入水与地层水离子交换,使悬浮液中的饱和硫酸钙周期性溶解和沉淀,导致压力波动.压力波动使硫酸钙的溶解/沉淀特征复杂化,最终显著改变了水驱后期并联模型中的分流率.含有饱和硫酸钙的不稳定离子匹配悬浮液是从材料领域借鉴到石油领域的新尝试,具有一定提高波及效率作用.它比常规欠饱和离子匹配水驱过程中产生的不可控原位微粒更有效、更可靠、更环保.

关键词: 碳酸盐岩油藏, 提高采收率, 波及效率, 悬浮液, 硫酸钙

Abstract: Improvement of water flooding sweep efficiency can significantly enhance the development of carbonate reservoirs.In this paper,an ion-matched suspension was obtained and studied with stereoscopic microscopy and a laser particle size analyzer,based on considering the ion composition of formation water.The suspended calcium sulfate particles are in a critical saturation state,most of which are approximately 10 μm in size,and the maximum size can reach 50 μm after standing due to flocculation and aggregation.Experiments on static properties of suspension show that,due to the"retrograde solubility"of calcium sulfate and the change of hydrate,its particles disappear slowly when the temperature is less than 45℃ and precipitate rapidly when the temperature is 90℃.The concentration and particle size of calcium sulfate particles increased significantly with a change of salinity and ion composition.In the parallel core experiment with a permeability ratio of 4.7,the ion-matched suspension increased the flow distribution ratio of the lower permeability core by up to 9.8％and the ultimate recovery factor by approximately 4.3％of original oil-in-place(OOIP).The influence of temperature,pressure,and salinity,as well as the ion ex-change between the injected water and the formation water,causes the saturated calcium sulfate in the suspension to periodically dissolve and precipitate,resulting in pressure fluctuations.Pressure fluctuations complicate the dissolution/precipitation charac-teristics of calcium sulfate and eventually lead to altering the flow distribution ratio in parallel models in the late stage of water flooding.The unstable ion-matched suspension containing saturated calcium sulfate is a new attempt based on material science to the field of petroleum production and has promising potential.It is more effective,reliable,and environmentally friendly than the uncontrolled in-situ particles produced in conventional under-saturated ion-matched water flooding.

Key words: carbonate reservoir, EOR, smart water, suspension, calcium sulfate