Investigating the horizontal well performance under the combination of micro-fractures and dynamic capillary pressure in tight oil reservoirs

Abstract

Micro-fractures and capillary pressure are two typical characters of tight oil reservoirs. In ongoing productivity evaluation methods, micro-fractures tend to be ignored and the effect of capillary pressure is treated as a static issue. However, recent literatures show that micro-fractures play an important role in enhancing flow capacity of tight oil reservoirs. In addition, with a constant saturation change in wetting phase, capillary pressure varies in a dynamic form. That is, its value strongly tied to the changes in the saturation. Thus, in tight oil reservoirs, considering the effects of micro-fractures in productivity prediction is a key issue, and dynamic capillary pressure is a vital parameter of fluid flow in a two-phase reservoir system. In this study, to investigate the contribution of micro-fractures on well productivity and the effect of dynamic capillary pressure on oil-water phase flow in tight oil reservoirs, a semi-analytical model is introduced and solved considering interference between each hydraulic fracture. History matching against actual field data shows that the proposed model works well. According to the results, considering micro-fractures and dynamic capillary pressure is important in the establishment of mathematical model for predicting well productivity, if these issues are not attached much importance, the results will have great deviation from actual production data. It is also found that micro-fractures have critical influences on well productivity. In early production period, as the oil production is high, water saturation changes faster than it in later period and the effect of dynamic capillary pressure is much clear.