A Study On Flowing Mechanism Of Steam Flooding Of Heavy Oil By Horizontal Well

Thirty five similarity criterions of reservoir and two similarity criterions of horizontal wellbore are obtained by applying integration comparison method and dimensional analysis during steam flooding by horizontal well.According to similarity principle visible scaling physical model and high temperature and high pressure scaling physical model are established.Physical simulation and numerical simulation are conducted by applying scaling physical model,centimeter scaling numerical model and well group numerical model.Row pattern is optimized from the results of oil-steam ratio and recovery.Sweep efficiency is maximum and temperature field between injection wells and production wells is homogeneous on row pattern.Heat loss of wellbore decreases and steam dryness increases gradually as injection time increases.The less heat loss is and the higher dryness retention is,the higher steam injection rate,steam dryness and reservoir permeability are.Steam injection profile along horizontal wellbore shows that heel is high and toe is low.The shape of steam chamber is hammer.And production profile is disequilibrium.Production of heel is higher than that of toe.The main parameters are optimized by the numerical simulation method during steam flooding by horizontal well.The optimized opportunity of converting to steam flooding from steam huff and puff is the sixth cycle or 3-4 MPa.The optimized steam injection rate is 4.0t/h.The optimized steam dryness is 0.7 in the wellhead.The optimized production-injection ratio is 1.2.The optimized well spacing is 100 meter under oil viscosity of Zheng 411 block.Steam overlap can play a role by applying the method of injection on the top and production at the bottom.The heat loss decreases and efficiency of heat utilization increases as reservoir thickness increases.But effect of steam overlap becomes noticeable as reservoir thickness increases.The recommended horizontal section length is below 250 m.Plane zone between injection well and production well can be divided into four zones: Saturated steam zone,condensing hot water zone,hot oil zone and raw oil zone.Steam flooding by horizontal well can be divided into four stages: start-up stage,rapidly increasing production stage,stable and high production stage and low and declining production stage.Production characteristics and displacement mechanisms are different on each stage.On the vertical zone the main mechanism is horizontal displacement,and the auxiliary mechanism is vertical drainage.Shape of steam chamber,reservoir recovery and injection and production profile can be influenced by reservoir heterogeneity.It changes the development characteristics of temperature field.Recovery of heterogenous reservoir is lower than that of homogenous.High temperature during steam flooding decreases viscosity and density of crude oil.Steam distillation and crude oil cracking reaction can occur at high temperature.Aiming at Zheng 411 block reservoir numerical simulation model is established.HDCS huff and puff production history matching of Zheng 411 block is conducted.Steam flooding technology policy by horizontal well of Zheng 411 reservoir is optimized.The following conclusions can be obtained.The optimized horizontal well pattern is inverted nine spot pattern converting to row pattern.The optimized steam injection rate is 4.5t/h by row pattern.The optimized steam dryness is 0.7 in the wellhead.The optimized production-injection ratio is 1.2.