缝洞型碳酸盐岩凝析气藏压力衰竭过程中凝析油微观赋存状态

凝析气藏衰竭开采过程中,不同缝洞类型会影响凝析油的析出过程和赋存形态。为了研究缝洞型碳酸盐岩凝析气藏压力衰竭过程中凝析油的形成机理和微观赋存状态,对单缝洞型、多缝洞垂向叠置型和多缝洞横向叠置型三种缝洞类型的碳酸盐储层开展凝析气压力衰竭实验协同微米电子计算机断层扫描技术(computed tomography, CT)扫描,并对不同压力下扫描得到的图像采用人工智能算法进行油、气、岩石骨架分割,得到真实岩心三维孔隙网络模型,通过图像处理和计算分析,实现模拟不同缝洞类型凝析气藏在不同开发阶段凝析油赋存状态的定量和定位置表征。研究表明:碳酸盐岩缝洞储层岩心压力衰竭过程主要是一个油相由多孔状、单孔状和油膜状向网络状转变的过程,最终网络状油增加,多孔状、单孔状和油膜状油减少;利于凝析油析出的储层构造由强到弱排序依次为多缝洞横向叠置型储层、单缝洞型储层、多缝洞垂向叠置型储层;在压力衰竭过程中,随着凝析油增多,油相会向岩石壁面靠近,当凝析油开始产出,油相会远离岩石壁面,随着油相的产出,油相减少,凝析油在表面张力的作用下向岩石壁面靠近。

Gas Condensate Occurrence During the Pressure Depletion of Fracture-vuggy Carbonate Condensate Gas Reservoir

Different fracture-vug types are of great influence to the precipitation and occurrence of gas condensate during depletion-drive development. In order to study the precipitation mechanisms and micro states of gas condensate during pressure depletion of fracture-vuggy carbonate condensate gas reservoir, condensate gas pressure depletion experiment and collaborative computed tomography (CT) scanning are carried out to three kinds of fracture-vuggy carbonate reservoirs - single fracture-vuggy, vertical multifracture-vuggy and horizontal multifracture-vuggy reservoir. The scanning images at different depletion pressure are segmented into oil, gas and rock skeleton to obtain 3-D pore network model by artificial intelligence algorithm. Quantitative and location representation of gas condensate occurrence at different development stages are achieved through image processing and computational analysis. Studies show that pressure depletion of carbonate fracture-vuggy reservoir is a gas condensate transforming process from multi-porous, single porous and membrane states to network states. And the amount of the former three decreases and the later one increases in the end. The sequence of the reservoir structure that is conductive to gas condensate production is horizontal multifracture-vuggy, single fracture-vuggy, and vertical multifracture-vuggy reservoir. During the process of pressure depletion, the gas condensate gets close to the rock wall as it is getting more. With the production of the gas condensate, it goes away from the rock wall. But with the further decrease of the gas condensate in the pore resulting from gas condensate production, it will get close to the pore wall again by surface tension.