A Production Performance Model of the Cyclic Steam Stimulation Process in Multilayer Heavy Oil Reservoirs

Abstract

Cyclic steam stimulation (CSS) is a typical enhanced oil recovery method for heavy oil reservoirs. In this paper, a new model for the productivity of a CSS well in multilayer heavy oil reservoirs is proposed. First, for the steam volume of each formation layer, it is proposed that the total steam injection volume will be split by the formation factor (Kh) for the commingled steam injection mode. Then, based on the equivalent flow resistance principle, the productivity model can be derived. In this model, the heavy oil reservoir is composed of a cold zone, a hot water zone, and a steam zone. Next, using the energy conservation law, the equivalent heating radius can be calculated with the consideration of the steam overlay. Simultaneously, a correlation between the threshold pressure gradient (TPG) and oil mobility is also applied for the productivity formula in the cold zone and the hot water zone. Afterward, this model is validated by comparing the simulation results with the results of an actual CNOOC CSS well. A good agreement is observed, and the relative error of the cumulative oil production is about 2.20%. The sensitivity analysis results indicate that the effect of the bottom hole pressure is the most significant, followed by the TPG, and the effect of the steam overlay is relatively slight. The formation factor can affect the splitting of the steam volume in each layer; thus, the oil production rate will be impacted. The proposed mathematical model in this paper provides an effective method for the prediction of preliminary productivity of a CSS well in a multilayer heavy oil reservoir.

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“…One approach to the environmentally friendly treatment of sludge is deep thermal decomposition based on the pyrolysis process [42]. Steam treatment or dissolving carbon dioxide CO 2 is known to enhance the physical properties of heavy oil [43,44]. For high-viscosity oil, the degree of viscosity reduction when carbon dioxide is dissolved in it is comparable to the reduction in viscosity when exposed to heat [45].…”

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“…Currently, commonly used methods for viscosity reduction of heavy oil include steam injection through thermal recovery, in situ combustion, and the use of chemical reagents and surface active agents as emulsifiers. , However, in practical applications, these methods still encounter some inevitable issues. In regions like China, where most heavy oil reservoirs are more than 1000 m deep, with some even exceeding 4000 m, thermal recovery methods suffer from serious heat loss. , Additionally, many reservoirs are thin, rendering the thermal method inefficient and unsuitable for viscosity reduction in such cases . On the other hand, chemical viscosity reduction introduces a series of challenges, including expensive costs and difficulties in handling residual oil without impacting the environment. , …”

“…In regions like China, where most heavy oil reservoirs are more than 1000 m deep, with some even exceeding 4000 m, thermal recovery methods suffer from serious heat loss. 12,13 Additionally, many reservoirs are thin, rendering the thermal method inefficient and unsuitable for viscosity reduction in such cases. 14 On the other hand, chemical viscosity reduction introduces a series of challenges, including expensive costs and difficulties in handling residual oil without impacting the environment.…”