Wang, Xin (Key Laboratory of Reservoir Stimulation, CNPC Fracturing&Acidizing Technical Service Center, RIPED, CNPC) | Zhu, Qingzhong (PetroChina Huabei Oilfield Company) | Zheng, Wei (Key Laboratory of Reservoir Stimulation, CNPC Fracturing&Acidizing Technical Service Center, RIPED, CNPC) | Lu, Haibing (Key Laboratory of Reservoir Stimulation, CNPC Fracturing&Acidizing Technical Service Center, RIPED, CNPC)
China has abundant low-rank coalbed methane resources. The research object is the low rank lignite seams in Jiergalangtu Sag in Erlian Basin. The reservoir has low porosity and low permeability, and it has no natural productivity. The coal seams have a burial depth of 200-600 meters, thickness of 40-60 meters, and Ro of 0.32% to 0.47%. Borrowing the idea of well completion experience for the conventional low rank coal seams in the region, open hole cavity completion techniques were adopted in two wells, obtaining an output of only about 150 m3/d. The conventional active water fracturing was also tested in another well, and the output after fracturing was 200-300 m3/d. The effect of stimulation was very poor, which limited commercial exploitation activities in the region. This paper introduces two techniques to improve the effect of stimulation by improving induced fracture extension and supporting capacity in the coal seams, including the hydraulic blasting & grouting caving fracturing technique and the reverse compound fracturing technique, which were applied in two wells. A constant rate of production after fracturing reached 1,500-2,000m3/d, which was well above the lower limit output of economic exploitation in the region of 600m3/d. Exciting results were obtained. The exploration of these techniques is of great significance for low rank coalbed methane stimulation, which can help us to implement effective fracturing stimulation operation in low rank coal seams to obtain the best production effect.
Cheng, Rongchao (CNPC Drilling Research Institute) | Wang, Haige (CNPC Drilling Research Institute) | Zhang, Fucheng (CNPC Drilling Research Institute) | Ge, Yunhua (CNPC Drilling Research Institute) | Chen, Zhixue (CNPC Drilling Research Institute) | Yang, Guo Xin (China U. of Petroleum East)
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.
Sulige Gas Field, located in the north-central part of Ordos Basin and generally covered with grass or sand dunes on the ground surface, belongs to Ordos city of Inner Mongolia Autonomous Region according to China's national administrative division. Its gas-bearing formations are mainly river-island and -channel sandstones from Shihezi Group to Shanxi Group in the Neopaleozoic Permian Period. The reservoir geography principally depends on sand distribution and related physical properties. Its monoclinic and westward-tilt geological structure has no trapping effect. The reservoir permeability is mainly constructed by corroded pores, intercrystal pores and micropores, which hereby creates a typical low-porosity and low-permeability gas field with the bulk porosity and permeability ranging from 5% to 12% and from 0.06×10-3µm2 to 2 ×10-3µm2, respectively (2007, Li Hanyan; 2007, Zhu Xiaomin). Meanwhile, as a nonsaturated dry gas reservoir, its reservoir fluid is mainly composed of methane with a high mass fraction of about 92.5%, and a little content of condensate of about 2.15g/m3~4.93g/m3.