An Improved Steam Injection Model with the Consideration of Steam Override

Congge He,Longxin Mu,Zifei Fan,Anzhu Xu,Zhongyuan Ji,Baoquan Zeng,Haishui Han

doi:10.2516/ogst/2016026

Abstract

The great difference in density between steam and liquid during wet steam injection always results in steam override, that is, steam gathers on the top of the pay zone. In this article, the equation for steam override coefficient was firstly established based on van Lookeren’s steam override theory and then radius of steam zone and hot fluid zone were derived according to a more realistic temperature distribution and an energy balance in the pay zone. On this basis, the equation for the reservoir heat efficiency with the consideration of steam override was developed. Next, predicted results of the new model were compared with these of another analytical model and CMG STARS (a mature commercial reservoir numerical simulator) to verify the accuracy of the new mathematical model. Finally, based on the validated model, we analyzed the effects of injection rate, steam quality and reservoir thickness on the reservoir heat efficiency. The results show that the new model can be simplified to the classic model (Marx-Langenheim model) under the condition of the steam override being not taken into account, which means the Marx-Langenheim model is corresponding to a special case of this new model. The new model is much closer to the actual situation compared to the Marx-Langenheim model because of considering steam override. Moreover, with the help of the new model, it is found that the reservoir heat efficiency is not much affected by injection rate and steam quality but significantly influenced by reservoir thickness, and to ensure that the reservoir can be heated effectively, the reservoir thickness should not be too small.

Highlights

Under initial reservoir conditions, heavy oil that has viscosity between 50 to 10 000 centipoises plays an important role in crude oil reserve [1,2,3]
To verify the mathematical model formulated in this paper, the computer program is designed based on it and a wet steam injection well W-1 in KMK oilfield, Aktyubinsk, northwest of Kazakhstan is used as an example to calculate the reservoir heat efficiency
This is because the effect of steam override, which is taken into account in our new model but not in the Marx-Langenheim model, increases areas of heated-region top and heated-region bottom directly getting in touch with hot fluid and results in more heat lost to the overburden and underburden

Summary

Introduction

Heavy oil that has viscosity between 50 to 10 000 centipoises plays an important role in crude oil reserve [1,2,3]. When the wet steam is transported from steam generators to the bottomhole of injection wells, much heat is lost. Not all heat carried by wet steam from steam generators can enter and be used to heat the pay zone. As wet steam flows through the surface pipeline system, that distributes wet steam from steam generators to the wellhead of injection wells, a part of heat is lost from the fluid to the surrounding atmosphere through surface pipeline wall and insulation materials [9]. During wet steam flows from the wellhead to the bottomhole of injection wells, a part of heat is lost from the wet steam to surrounding formation [10]. When the wet steam reaches the bottomhole of injection wells and enters the pay zone, heat loss occurs, that is, a part of heat losses to the overburden and underburden [11]

Objectives

Results

Conclusion