Compared with conventional resources, unconventional oil and gas reservoirs mainly have the following geological characteristics: ultra-tight rocks with a relatively low porosity and ultra-low permeability, multiscale pore spaces, high heterogeneity, low abundance of reserves, etc. In order to achieve the intensive and efficient development of unconventional reservoirs, horizontal-drilling and massive hydraulic-fracturing technologies are usually applied to create an “artificial oil and gas reservoir” with interconnected multiscale fracture networks. From the perspective of efficient development, this paper elaborates four engineering scientific problems in the development of unconventional reservoirs: (1) the problem of geological modeling (including initial modeling and secondary modeling after compaction) considering stress fields and multiscale pore spaces; (2) the problem of numerical simulation of fracture propagation in unconventional reservoirs; (3) the problem of production numerical simulation of unconventional reservoirs and the massive numerical computation that is involved; (4) optimization design of the positions of horizontal wells and hydraulic fractures in the “well factory” development pattern. Considering the research features of the Center of Multiphase Flow in Porous Media (CMFPM) of China University of Petroleum (East China), this paper states the background and development trends of the above four problems, and puts forward the optimization design method for engineering parameters of the “well factory” development pattern based on geological modeling and numerical simulation of unconventional reservoirs. This may be of great significance to the scientific and efficient development of unconventional reservoirs.