特低渗油藏注CO_(2)吞吐适应性评价及规律模拟

Adaptability evaluation and regular simulation of CO_(2) injection huff and puff in ultra-low permeability reservoirs

CO_(2)驱油是常规油藏提高采收率有效方法。为了分析研究在特低渗储层注CO_(2)的适应性及作用规律,分析研究了注入CO_(2)后原油体系相态变化特征,通过建立岩心尺度的基质裂缝基本渗流单元模型,研究不同吞吐介质CO_(2),N_(2)和H_(2)O在单簇缝中的渗流规律,定性表征CO_(2)在扩散效应、降黏作用、改善流动性以及抽提富集作用中区别于其他2种介质的优越性。研究结果表明:考虑CO_(2)扩散效应作用体现在基质网格中摩尔分数分布差别,最大相差约10%;CO_(2)降黏和改善油相渗透率作用明显,在相同注入压力下CO_(2)注入性弱于N_(2)优于H_(2)O;经过5轮次吞吐后注CO_(2)采出程度为23%,注H_(2)O为20%,注N_(2)约为18%,这为特低渗油藏注CO_(2)提高采收率提供了依据。

CO_(2) flooding is an effective method for enhancing oil recovery in conventional oil reservoirs.In order to analyze and study the adaptability and action law of CO_(2) injection in ultra-low permeability reservoirs,the phase behavior change characteristics of the crude oil system after CO_(2) injection were analyzed and studied.By establishing a core-scale matrix fracture basic seepage unit model,the CO_(2) and N_(2) huffing and puffing media were studied.The percolation law of H_(2)O in a single cluster crack qualitatively characterizes the superiority of CO_(2) in the diffusion effect,viscosity reduction effect,fluidity improvement,extraction and enrichment effect that distinguishes CO_(2) from the other two media.The result of research shows that considering the CO_(2) diffusion effect is reflected in the difference in the distribution of mole fractions in the matrix grid,the maximum difference is about 10%;CO_(2) has obvious effects in reducing viscosity and improving oil phase permeability,and from the effect evaluation,the CO_(2) injection performance is weaker than that under the same injection pressure.N_(2) is better than H_(2)O.After 5 rounds of huff and puff,the CO_(2) injection recovery rate is 23%,H_(2)O is 20%,and N_(2) is about 18%.This provides a basis for CO_(2) injection to increase recovery in ultra-low permeability reservoirs.