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.
Highlights
Introduction published maps and institutional affilHeavy oil is a widespread energy resource throughout the world [1]
The relative error of the cumulative oil production within three cyclic steam stimulation (CSS) cycles is about 2.20%, and the relative error of the cumulative water production within three CSS cycles is about 4.69%. This indicates that our new model can provide an accurate prediction for the productivity of a CSS well in multilayer heavy oil reservoirs
(1) A new production performance model for the cyclic steam stimulation process in multilayer heavy oil reservoirs is established in this paper
Summary
Heavy oil is a widespread energy resource throughout the world [1]. It accounts for more than two-thirds of the global crude oil reserves, mainly distributed in Canada, Russia, Venezuela, China, and Indonesia [1–3]. In China, heavy oil resources are mainly distributed in oilfields of Liaohe, Shengli, Xinjiang, Henan, and the Bohai offshore oilfield [2–4]. Because of its high viscosity in the formation condition [5], the thermal recovery process is usually the primary exploitation method for heavy oil reservoirs [1,2]. WAG (water alternating gas) is another potential exploitation method for the heavy oil recovery process. Considering its characteristics of an operated process system and a high oil production rate at an early stage, cyclic steam stimulation (CSS) is usually considered as the primary development method [6]. Since 2009, a series of pilot tests of the multi-component thermal iations
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