Fluid flow in porous media is the key issue in the development of oil and gas reservoirs. The traditional fluid flow mechanics of porous media, which are based on the single-scale continuum hypothesis and Darcy’s law, play an important role in the development of oil and gas reservoirs. With the increasing exploration and development of fractured vuggy carbonate and unconventional oil and gas reservoirs, there are different voids with different spatial scales, including pores, fractures, and cavities. And the scale difference is up to 10 orders of magnitude, which impacts the fluid flow in real reservoirs. Usually, there are three different scales for a reservoir rock, i.e., the pore scale, the mesoscopic scale, and the macroscopic scale. Different methods are used to discover and obtain different fluid flow mechanisms at different scales. However, connecting these mechanisms at different scales is critical for getting a systematic macroscopic fluid flow theory. As a result, upscaling theory and multiscale methods are very important for real petroleum reservoirs. It just likes to string together each pearl of different scales to form a perfect necklace. This paper reviewed the recent research progress of multiscale methods for oil and gas flow in porous media. Some remarks were made, including pore-scale flow, macroscopic unconventional oil and gas flow, large-scale fractured vuggy carbonate oil and gas flow, and upscaling theory and multiscale methods.

The analysis of interwell connectivity plays an important role in the formulation of oilfield development plans and the description of residual oil distribution. In fact, sandstone reservoirs in China's onshore oilfields generally have the characteristics of thin and many layers, so multi-layer joint production is usually adopted. It remains a challenge to ensure the accuracy of splitting and dynamic connectivity in each layer of the injection-production wells with limited field data. The three-dimensional well pattern of multi-layer reservoir and the relationship between injection-production wells can be equivalent to a directional heterogeneous graph. In this paper, an improved graph neural network is proposed to construct an interacting process mimics the real interwell flow regularity. In detail, this method is used to split injection and production rates by combining permeability, porosity and effective thickness, and to invert the dynamic connectivity in each layer of the injection-production wells by attention mechanism. Based on the material balance and physical information, the overall connectivity from the injection wells, through the water injection layers to the production layers and the output of final production wells is established. Meanwhile, the change of well pattern caused by perforation, plugging and switching of wells at different times is achieved by updated graph structure in spatial and temporal ways. The effectiveness of the method is verified by a combination of reservoir numerical simulation examples and field example. The method corresponds to the actual situation of the reservoir, has wide adaptability and low cost, has good practical value, and provides a reference for adjusting the injection-production relationship of the reservoir and the development of the remaining oil.

Matrix acidizing is one of the most practical stimulation technologies for carbonate reservoirs, which effectively improve the region permeability near the wellbore. In addition to solid matrix, vugs are also very common in carbonate reservoirs. However, a few studies have been addressed with existence of vugs on carbonate acidizing process. In this work, a two-scale model is developed using dual domain method and discrete vugs model to study effect of vugs on acidizing process. Darcy equation is employed in solid matrix region. Navier Stokes equation is adopted for free flow region in vugs. The two regions are coupled by modified Beavers-Joseph-Saffman boundary condition. Numerical cases are conducted to present the effect of vug characteristics on acid-rock reaction process. The results show that acid solution has the largest effective reducing distance and the smallest breakthrough volume in circular vugs. Dominant wormhole is created when acid injection direction is parallel or vertical to the azimuth angle of vugs. Increasing amount of vugs in horizontal effectively reduces the flow distance and breakthrough volume of acid solution. Vugs with random distribution increases effective flow distance and breakthrough volume of acid solution compared to vugs with orderly distribution.