Advanced production decline analysis of tight gas wells with variable fracture conductivity
SUN Hedong1, OUYANG Weiping2,3, ZHANG Mian2,3, TANG Haifa4, CHEN Changxiao5, MA Xu6, FU Zhongxin2,3
1. PetroChina Research Institute of Petroleum Exploration & Development, Langfang 065007, China;
2. Changqing Downhole Technology Company, CNPC Chuanqing Drilling Engineering Co., Ltd., Xi’an 710018, China;
3. National Engineering Laboratory for Exploration and Development of Low-Permeability Oil and Gas Fields, Xi’an 710018, China;
4. PetroChina Research Institute of Petroleum Exploration & Development, Bejing, 100083, China;
5. PetroChina Coalbed Methane Company Limited (Xinzhou Branch), Baode 041000, China;
6. Changqing Headquarters of CNPC Chuanqing Drilling Engineering Company Limited, Xi’an 710018, China;
Abstract:Considering the characteristics that the fracture conductivity of fracture formed by hydraulic fracturing varies across space and time, a new mathematical model was established for seepage flow in tight gas fractured vertical wells which takes into account the effects of dual variable fracture conductivity and stress sensitivity. The Blasingame decline curves of the model were obtained using the mixed finite element method. On this basis, the effects of conductivity varying with fracture space and time dual and stress sensitivity on Blasingame curve were analyzed. The study shows that the space variable conductivity mainly reduces decline curve value at the early stage; the time variable conductivity can result in drops of the production and the production integral curves, leading to a S-shaped curve; dual variable conductivity is the superposition of the effects given by the two variable conductivities; both time and space variable conductivities cannot delay the time with which the formation fluid flow reaches the quasi-steady state. The stress sensitivity reduces the curve value gradually rather than sharply, delaying the time the flow reaching the quasi-steady state. Ignoring the effects of variable conductivity and stress sensitivity will not affect the estimation on well controlled dynamic reserves. However, it can result in large errors in the interpretation of fractures and reservoir parameters. Practical advanced production decline analyses of a tight gas fractured well in the Sulige gas field showed that the new model is more effective and reliable than the conventional model, and thus it can be widely applied in wells with the same characteristics in other gas fields.
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