Abstract
Steamflooding is an effective and commonly-used thermal recovery technique for the development of heavy oil reservoirs. In the Pai-601 block of Chunfeng Oilfield where the viscosity is over 50000 mPa.s with the layer thickness only ranging from 4 to 10 m, traditional thermal recovery technology using vertical well cannot produce preferable performance for the thin net pay; thus a horizontal well steamflooding pilot is implemented. However, steam breakthrough takes place frequently in this field, leading to ineffective steam circulation and seriously weakening the development. Therefore, numerical simulation and field production dynamic analysis are applied to understand the characteristics of steam breakthrough, and to provide an efficient avenue for the treatment. The validity of the numerical simulation results is verified by the field tests.
On the basis of the reservoir geologic features as well as the well trajectory information, the reasons for steam breakthrough are analyzed, which manifest the human factors such as the well spacing and target point play important roles in the steam breakthrough except the geological factors, and careful attentions should be paid for the well design. Then, the breakthrough channels under various situations are characterized by numerical simulation technique, and the effects of different geologic and development factors on the steam breakthrough are also analyzed, like steam injection rate, reservoir heterogeneity, and etc. The result shows that the locations of steam breakthrough in Pai-601 can be mainly classified into three kinds: the lateral unimodal type, the middle unimodal type and the bimodal type, and the conditions for each kind are also presented. To further improve the development performance, the nitrogen foam is injected to impede the steam breakthrough. Simulation study shows that it’s significantly efficient for the improvement of oil production rate. This technology will provide guidance for the treatment of steam breakthrough in heavy oil reservoirs.
Introduction
Heavy oil plays an important role in worldwide oil & gas resources. Due to the high viscosity and low mobility of heavy oil, the conventional development schemes are no longer extremely efficient and special treatments are necessary. Generally, there are several heavy oil production technologies such as huff and puff, steamflooding, in-situ combustion, and Steam Assisted Gravity Drainage (SAGD). At present, the steamflooding is the one of the most effective and commonly-used recovery technique for the development of heavy oil reservoirs. However, with the development of the oilfield, the steam breakthrough may occur because of the reservoir geologic features or development factors. This leads to ineffective steam circulation and low heat efficiency so as to weaken the oil recovery seriously. Therefore, studying the development of steamflooding and the solution to breakthrough in heavy oil reservoirs is very important.
Horizontal well steamflooding is widely applied in the exploitation of heavy oil reservoirs (Andy, 2006; Tankersley, 2002). In comparison with vertical well, horizontal well increases the heating volume as well as well drainage area, which is more suitable for thin layer reservoirs. However, because of the reservoir heterogeneity and some development factors, the steam profile is inhomogeneous and this will cause steam breakthrough, leading to a low heat efficiency and oil recovery (Chen, 1998; Feng, 2012). Therefore, several profile control technologies are developed to impede the steam breakthrough, among which the nitrogen foam has attracted more attention (Yuan, 2004). This technology application in Gudao Oilfield indicates the creation of plug in the breakthrough channels and promotion of heating efficiency (Cao Z.Q., 2006). However, research on breakthrough channels mainly focuses on qualitative analysis in oilfield, and studies on nitrogen foam mainly concentrate on physical modeling experiments and application in oilfield (Zhang, 2012; Cao, 2012).
