一种砂岩缓速酸酸岩反应模型的建立

An acid-rock reaction model established for the retarded acid fracturing of sandstone reservoirs

砂岩酸压增产改造工艺技术在复杂岩性、低渗透、特低渗透、非常规及特殊油气藏的勘探开发中,得到了越来越广泛的应用。砂岩储层酸压的关键在于形成较高导流能力的酸蚀裂缝,为了有效改造储层和减轻二次伤害,常采用缓速酸液体系进行砂岩酸压。为了完善砂岩缓速酸的酸压理论,科学指导砂岩酸压设计和现场施工,基于酸液缓速机理和酸岩反应机理,建立了砂岩缓速酸酸压中裂缝内和滤失区的酸液浓度分布和矿物浓度分布模型,并用于计算酸蚀裂缝导流能力、酸液滤失区孔隙度和渗透率的改善程度。实例模拟结果表明:缓速酸酸压可保证酸蚀裂缝和滤失区具有较高的HF浓度,有利于增加酸液有效作用距离和改善基岩孔隙度和渗透率,但过高的HF浓度则会产生硅胶沉淀,对储层造成二次伤害,从而降低酸压效果;单一氟硼酸和氢氟酸的复合缓速酸液体系产生的导流能力随裂缝长度的增加呈现出先增加后降低的趋势,因而应考虑采用多种酸液多级交替注入酸压。

Acid fracturing stimulation technology is used more widely in the exploration and development of unconventional and special oil and gas reservoirs, as well as the reservoirs with complex lithology, low permeability and ultra-low permeability. The critical action of acid fracturing for sandstone reservoirs is to form acid etching fractures with relatively high flow conductivity. In order to stimulate the reservoir and mitigate the secondary damage, the retarded acid fluid system is adopted to perform the acid fracturing for the sandstone reservoirs. For the purpose of scientifically guiding the acid fracturing design and site construction and completing the acid fracturing theory of the retarded acid for sandstones, a concentration distribution model of acid liquids and minerals in the frac- tures and filtration areas is established on the basis of acid retarding mechanism and acid rock reaction mechanism. This model is es tablished to calculate the flow conductivity of the acid etching fracture, the porosity of the acid filtration area and the improvement degree of the permeability. The simulation results in a case show that the acid fracturing with retarded acids is capable of ensuring a high HF concentration in acid etching fractures and filtration areas; the high HF concentration facilitates the increment of the acid＇s effective action distance and the improvement of the bedroek＇s porosity and permeability. However, over-high HF concentration will result in silica gel precipitation, causing the secondary damage to the reservoir and adverse effects on the acid fracturing result. The flow conductivity generated by the composite retarded acid fluid system （composed of fluoroboric acid and hydrofluoric acid） first be- comes stronger then weaker with the increase of the fracture length. Therefore, a multi-stage acid fracturing with various acid fluids is recommended for sandstone acid fracturing.