We studied adsorption characteristics of oil-water system on calcite and dolomite surface with molecular dynamic simulation. To study wettability of calcite/dolomite surfaces, we analyzed equilibrium conformation, relative concentration, radial distribution function and adsorption energy of calcite/dolomite-oil/water system. Then, we proposed a two-step adsorption mechanism. It shows that dolomite-oil/water system is more easily to achieve thermodynamic stability and is more stable; A water film is formed on calcite and dolomite surfaces, which is a double-layer structure; There are interactions among oil molecules, water molecules and the crystal surface; Attraction of dolomite surface to oil and water molecules is stronger than calcite. Finally, we divided the adsorption process into two steps:Water molecules adsorbed on crystal surfaces form a tightly adsorbed layer under van der Waals forces, electrostatic forces and O(CaCO₃,CaMg(CO₃)₂)-H(H₂O) hydrogen bonds. In addition, the remaining water molecules move to the crystal surface form a diffusion layer under the influence of O(H₂O)-H(H₂O) hydrogen bonds. It reveals wettability formation and alteration mechanisms on calcite and dolomite surface, which paves a foundation of further enhance oil reovery.

Based on flow characteristics of horizontal wells in naturally fractured reservoirs,vadose area is divided into two zones: near wellbore zone and far wellbore zone.The far wellbore zone is featured by its continuous homogeneity.In near wellbore zone,a coupling model is established considering fluid flow in fracture and horizaontal well simultaneously.Principles of potential superposition and mirror reflection as well as the concept of infinitesimal line congruence are used in the model.Combining flow characteristics of the far and near wellbore zones,a comprehensive computational method for fractured hoizontal well productivity is presented.A practical case is used to verify this method.Computational result shows that productivity of horizontal well calculated with this method is closer to actual flow rate than theoretical formula.Productivity of horizontal well increases as fracture density rises,but increment of productivity decreases as fracture density increases.