新世纪以来非常规油气获战略突破，致密油气作为典型代表，是常规油气资源的重要接替能源。致密油气主要赋存于致密砂岩和致密碳酸盐岩储层中。然而，致密砂岩和致密碳酸盐岩中的多尺度-多维度渗流通道（孔、洞、缝）、多种类型流体（油、水、气）以及多类渗流特征（滑移、扩散、吸附），使得致密油气运移不再是单一尺度、线性理论所能描述的。因此建立一套描述致密油气运移的多尺度渗流模型是致密油气研究的关键。本文针对致密砂岩和致密碳酸盐岩，建立了三个多尺度渗流计算模型，搭建了致密油气渗流计算平台。具体研究工作从以下三个方面开展。

识别孔隙孔喉。首先，基于数学形态学理论提出了划分孔隙-孔喉的方法。根据孔隙和孔喉的特征，运用形态学方法将岩石三维图像中不规则的孔隙空间划分为新型孔隙-孔喉系统。该系统的优势在于孔隙和孔喉的识别计算无参数调试，可完备表征岩石的孔隙孔喉空间结构。其次，提出了该系统的并行算法，研究分析了算法的可靠性和计算效率，为后续多尺度渗流计算模型奠定了基础。

致密砂岩的油气渗流模型。针对致密油，引入微链接表征纳米尺度微孔，在实测渗透率约束下，建立了多尺度油水两相渗流模型。该模型考虑了致密砂岩的多尺度孔隙结构，以及微纳孔喉引起的液体滑移效应。通过他人的实验结果验证了模型的可靠性；与现行计算模型比较，在相同计算精度下，该模型计算效率提高了一个量级。针对致密气，引入孔隙簇等效模型表征纳米孔的气体传输，提出了三维的变径微通道，有机地串联起岩石的微-纳结构，形成了致密气的多尺度渗流计算模型，并通过实验数据证明了模型的可靠性。初步形成了致密砂岩的渗流计算平台。

致密碳酸盐岩的油渗流模型。针对致密碳酸盐岩中微-纳孔、洞、缝共存的特点，提出中轴线-最大球（AB）算法和中轴面算法相结合抽提孔-缝混合网络，并在图像基质内引入小尺度随机孔隙网络表征纳米孔。进一步在实测渗透率的约束下，有机地串联起纳米孔-微米孔以及纳米孔-裂缝，形成了多尺度混合油水两相渗流模型。和现有模型相比，该模型完备考虑了致密碳酸盐岩的微-纳孔、洞、缝的空间结构，以及微纳孔喉引起的液体滑移效应和裂缝内液体的流动效应。通过实验结果验证了模型的可靠性，研究分析了裂缝对油水两相渗流的影响。本文建立的三个致密油气多尺度渗流计算模型计算效率高，计算结果准确，形成了致密油气渗流计算平台，为致密油气研究提供一种新的方法。

Since the new century, unconventional oil and gas have achieved strategic breakthroughs. Tight oil and gas, as the typical representative, are an important alternative energy for conventional oil and gas resources. Tight oil and gas mainly occur in tight sandstone and tight carbonate reservoirs. However, the multiscale and multi-dimensional seepage channels (pores, vugs, fractures), multiple types of fluids (oil, water, gas), and multiple types of seepage features (slip, diffusion, adsorption) in tight sandstone and tight carbonate make the migration of tight oil and gas no longer described by the single-scale and the linear theory. Therefore, establishing a set of multiscale seepage models to describe the migration of tight oil and gas is the key to tight oil and gas research. In this paper, three multiscale seepage calculation models are established for tight sandstone and tight carbonate, and a tight oil and gas seepage calculation platform is built. The specific work is carried out from the following three aspects.

Identifying pores and throats. Firstly, a method for dividing pores and throats is proposed based on the mathematical morphology theory. According to the features of pores and throats, the irregular pore space in the three-dimensional rock image is divided into a novel pore-throat system via the morphological methods. The advantage of this system is that there is no parameters adjustment for the identification and calculation of pores and throats, and it can fully characterize the spatial structure of pores and throats of rocks. Secondly, a parallel algorithm of the system is proposed. The reliability and computational efficiency of the algorithm are studied and analyzed, which lays a foundation for the subsequent multiscale seepage calculation models.

Oil and gas seepage models of tight sandstone. For tight oil, micro-links are introduced to represent the nano-scale micropores, and a multiscale oil and water two-phase seepage model is established under the constraint of measured permeability. This model considers the multiscale pore structure of tight sandstone and the liquid slip effect caused by the micro-nano throats. The reliability of this model is verified by the experimental results of others. Compared with the existing calculation models, the computational efficiency of this model is improved by one order of magnitude under the same calculation accuracy. For tight gas, the equivalent model of pore cluster is introduced to represent the gas transmission in nano pores. And the three-dimensional microchannel with variable diameter is proposed to organically connect the micro-nano structures of the rock to form a multiscale seepage calculation model for tight gas. The reliability of this model is verified by the experimental data. A seepage calculation platform for tight sandstone is preliminarily formed.

Oil seepage model of tight carbonate. Aiming at the coexistence of micro-nano pores, vugs, and fractures in tight carbonate, a medial axis-maximal ball (AB) algorithm and a medial surface algorithm are combined to extract the pore-fracture hybrid network, and a small-scale stochastic pore network is introduced into the image matrix to represent the nano pores. Under the constraint of measured permeability, nano pores-micro pores and nano pores-fractures are organically connected to form a multiscale hybrid oil and water two-phase seepage model. Compared with the existing models, this model fully considers the spatial structures of micro-nano pores, vugs and fractures of tight carbonate, as well as the liquid slip effect caused by the micro-nano throats and the liquid flow effect in the fracture. The reliability of this model is verified by experimental results, and the effect of fractures on oil and water two-phase flow is studied and analyzed. The three tight oil and gas seepage calculation models established in this paper have high computational efficiency and accurate calculation results, which form a tight oil and gas seepage calculation platform and provide a new method for tight oil and gas research.