Many strategies have been evaluated and applied by CNPC in the Sulige Gas Field that typically features in low permeability, low pressure, low quality and low productivity. Cluster well technique was supposed to be most appropriate to deal with the “four-low” reservoir related problems, especially in the vulnerable ecologic environment of desert area. The early pilot test, however, severely restricted its extension in larger scale due to the longer operation cycle and higher drilling cost compared to vertical wells. The Sulige development team was driven to re-design and optimize the cluster drilling project, with the principal objectives to further improve the rate of penetration and reduce the unit gas development cost. This paper will focus on the optimized cluster drilling concept that has been successfully applied in recent two years within Sulige, which is the largest gas field in China to date.

A “Cluster” usually consists of a reference “Mother” well and several “Daughter” wells from a single pad location. In Sulige, the “Daughters” are mostly directional ones and sometimes with auxiliary horizontal ones. Based on the optimized wellbore configuration, controlled trajectory and improved PDC bits, bottom hole assemblies and circulation fluids, a complete set of cluster well technique in a safe and faster drilling mode have been formed. Its application has resulted in an average ROP improvement of more than 36% and a dramatic increase of short- and long-term well economics, compared with previous cluster wells. The mature “Cluster” pattern triggers its complete extension in Sulige and promotes its trial applications in the Hailaer-Tamtsag Basin and Sichuan Basin.

This paper will present the optimized measures of cluster drilling and operational results within the Sulige field, and will discuss the cluster well design challenges, relevant drilling operations and subsequent post well evaluation. Recommendations on the helicoid hydraulic motor, directional wellbore profile and drilling fluid will also be presented.

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