二氧化碳对塔河油田裂缝性储层酸岩反应的影响研究

Experiment Research on the Effect of CO_2 on Acid-Rock Reactions in Fractured Reservoirs

为提高塔河油田裂缝性油藏的酸压改造效果,研究了CO_2对裂缝性油藏酸岩反应影响的问题。利用自主研制的裂缝性储层酸岩反应仪,基于网状裂缝模型,对考虑CO_2影响的不同类型、不同黏度和不同浓度酸液的酸岩反应情况进行了试验评价。试验得出:随着回压增大,酸岩反应产生的CO_2转变为超临界态后大量溶于酸液中,酸液流动阻力大幅降低,酸蚀量增大;与胶凝酸及Ⅰ型地面交联酸相比,HCl质量分数为20%的Ⅱ型地面交联酸滤失量小、黏度高,受CO_2影响最大,酸岩反应最慢,有利于实现裂缝性储层深穿透酸压的目的。Ⅱ型地面交联酸在YJY井重复酸压中进行了现场试验,与该井应用胶凝酸的首次酸压效果相比,液体效率大幅提高,酸蚀缝缝长大幅增加,压裂后累计产油1.2×104 t,增油效果显著。研究表明,超临界CO_2有助于降低酸液流动阻力,提高酸液深穿透能力,提高塔河油田裂缝性储层酸压改造效果。

To enhance acid fracturing performance in fractured reservoirs in the Tahe Oilfield,research has been conducted to highlight the impact of CO_2 on acid rock reactions in such reservoirs.By using independently developed acid rock reaction instruments and a fracture network model,tests were conducted to study the impact of CO_2 on acid rock reactions with different acids,viscosity and concentration.Test results showed that flow resistance of acid may decrease sharply as CO_2 generated during acid rock reaction become supercritical,then dissolve in acid massively as back pressure increases.Compared with gelled acid and Type I surface cross-linked acid,Type II surface cross-linked acid with concentration of 20% has less filtering loss,higher viscosity and susceptibility to CO_2 and lower acid rock reaction speed.This kind of acid may facilitate acid fracturing to achieve deep penatration in fractured reservoirs.A pilot test was conducted for Type II surface cross-linked acid in the acid refracturing of the Well YJY.Compared with the primary acid fracturing with gelling acid,both fluid efficiency and fracture length increased dramatically.With cumulative oil production of 1.2×10^4 t after refracturing,productivity enhancement performance has been observed.So research results showed supercritical CO_2 could effectively reduce flow resistance of acid,enhance acid penetration and promote the performance of acid-fracturing of fractured reservoirs in the Tahe Oilfield.