A New Analytical Model to Predict Oil Production for Cyclic Steam Stimulation of Horizontal Wells

摘要

For cyclic steam stimulation (CSS) process of horizontal wells, previous studies mainly focused on the shape of heating zone and few scholars took heat losses from upper and lower reservoir rocks into consideration. However, it is hard to accurately describe the shape of heating zone accounting for steam override and boundary shielding effect. And on-site production cares more about the heating volume and efficiency which determine the cumulative oil production rate. As a result, the object of this paper is to propose an accurate and computationally efficient method for calculating heating volume and oil production rate. In order to precisely describe the heating zone, a scaling factor, M0, is introduced to coordinate the maximum and minimum heating volume. The maximum heating volume is calculated by assuming there is no heat loss from upper and lower reservoir rocks while the minimum heating volume is demonstrated by assuming the heat losses from an equivalent vertical well. Besides, time-dependent average temperature, pressure and saturation are included to demonstrate steam override effect. Instead of using conductivity equation, frictional pressure loss from toe to heel is solved by an iteration scheme. Results of this model are compared with results simulated from commercial software Computer Modeling Group, STARS. Daily oil production rate exhibits good agreement between the proposed model and STARS. Different thermal conductivities and diffusivities of sandstone, shale rock and limestone are considered to expand the application of this model. Moreover, different values of M0 are calculated for further validation. This thermal model can be an effective predictor for planning heavy oil field development.