The Mechanism And Effect Of Mudstone Interbeds And Fractures On SAGD Development

Steam Assisted Gravity Drainage(SAGD) is an effective method to improve the development of ultra heavy oil reservoir with high oil viscosity and poor utilization. It relies on gravity drainage induced by the density difference between injected steam and heated fluid to produce oil, combined with the effect of heat conduction and heat convection.Based on the reservoir characteristics of Chunhui Haqian 1 oilfield with shallow reservoir depth, high oil viscosity and continuous mudstone interbeds, SAGD method is applied to this oilfield with coupled horizontal wells and discretized wellbore model using reservoir numerical simulation technology. According to production performance and steam chamber expansion, SAGD development can be divided into four stages and each stage can be characterized by different steam chamber expansion areas. Based on the actual logging interpretation results of Haqian 1 reservoir, seventeen distribution patterns of mudstone interbeds have been established using reservoir numerical simulation method, to discuss the effect of mudstone inerbeds on SAGD development. In addition, the relation between SAGD oil recovery and interbed properties has been builded quantitatively with regression analysis method, to predict how SAGD performance varying with interbed properties. The mudstone is liable to produce fracture under high steam temperature conditions, so to estimate at what condition the mudstone can produce fracture, a heat-flow-deformation coupling mathematical model has been established based on thermal repture mechanism of mudstone. Then the finite element software of FEPG is applied to simulate reservoir thermal deformation and stress distribution, to determine at what condition the mudstone can produce fracture and how the fracture is distributed in reservoir. Based on these results, the mechanism of fractures on SAGD development with mudstone interbeds have been discussed from three aspects of incremental oil, improved sweeping efficiency and thermal steam expansion volume, using numerical simulation method and statistical analysis principle. Furthermore, the effect of different mudstone interbeds distribution patterns on SAGD performance and steam chamber expansion has been studied after mudstone interbeds broken, and the results show that: fracture has an active effect on the areas above interbed and meanwhile, it has an inhibited effect on the areas under interbed.In order to determine what reservoirs can be applied to SAGD development with mudstone interbeds, the effect of reservoir parameters on SAGD performance has been discussed. Based on the influencing tendency of different reservoir parameters and interbed parameters on SAGD, the adaptability boundary plates of reservoir parameters have been drawn, combined with dynamically economic evaluation method. And moreover, the adaptability boundaries of reservoir parameters applied to SAGD reservoirs with mudstone interbed and without mudstone interbed have been established, so that it can be convenient to conduct SAGD development economically when oil price has fluctuation.