| Wuxia area is located in the Northwest of Junggar basin. The geological structure consists of fracture zone and bruchfalten zone which concerned with thrust fractures. In geographic location, the south boundary of Wuxia area are Ailike lake buried fault and well Ma2fault, the north boundary of Wuxia is Wulanlinge fault. In recent years, several wells had obtained high productivity oil within Permian formation. All of the discovered reserves display the favorable prospective exploration of Wuxia area. Consequently, Wuxia area is one of the most important oil/gas exploration replaceable field in northwest of Xinjiang Oilfied Company.The generalized sequence of geology in Wuxia area is as follows:Cretaceous Period of Tugulu group, Jurassic Period (Qigu formation, Xishanyao formation, Sangonghe formation, Badaowan formation), Triassic Period (Baijiantan formation, Kelamayi formation, Baikouquan formation), Permian Period (Wuerhe formation, Xiazijie formation, Fengcheng formation, Jiamuhe formation). The average rate of penetration over Triassic Period was8.94metre per hour, suggesting the well drillability of upper formation. Once drilled into Permian Period formation, especially the target zone Fengcheng formation, the rate of penetration decreased to1.19metre per hour. The dense and abrasive rock in Fengcheng formation brought extremely difficulties for drill bits and increasing speed technology selection. Consequently, the long drilling period and high drilling cost slowed down the exploration and development progress of Wuxia area extremely.Analyzing the drilling and geological datas of completed wells, the difficulties which limited drilling speed promoted were as follows:high strata dip angle and a large of faults limited rate of penetration improved, hard formation with abrasive rock and low drillability, the variable lithology with anisotropic in vertical and horizontal strata, the bits selection encountered large problems, the low pore pressure and abundant fractures in P1f3formation always result in severe lose circulation, the salt rock in P1f2formation contaminated drilling mud, the abnormal high pore pressure occurred in P1f1formation brought out well control risks and subsurface drilling accident.To promote the drilling speed and solve the long drilling period of deep Permian Period formation in Wuxia area, the study combined on-site data analysis, laboratory rock mechanical testing with mathematical statistics methods. The study contains Permian period formation anti-drilling characteristics parameters calculation, bits selection and drilling method optimization, the main research content and result are as follows:(1) By analyzing completed drilling data, the Fengcheng formation in Permian period was defined as the main difficulty of drilling speed promoted section. The study tested rock drillability, compressive strength, hardness, plasticity coefficient and acoustic velocity in the laboratory. The test results were processed by mathematical statistics method. Finally, the study build Permian period formation rock anti-drilling characteristics such as compressive strength, drillability and plasticity coefficient calculation model by using logging acoustic velocity.(2) Completed the correlation analysis between rock drillability and mechanical parameters. The research result reveals that the compressive strength and hardness had great effect on rock drillability, the plasticity coefficient had little effect on drillability. However, rock drillability was effected by these three factor synthetically. The study build the relationship between drillability and hardness to caculate rock hardness. On the basis of the model, the study completed rock anti-drilling parameters calculation of Fengcheng formation for three wells.(3) The study used drillability selection method, on-site bit performance analysis method and gray correlation analysis method to optimize bit selection for Fengcheng formation in Permian period of Wuxia area. The suitable bit types were selected on the basis of research. Compared the research result of these three bits selection methods, the selected bits types were coincident. It proves that the drillability caculation model is perfect, which can meet the on-site application demand considerably.(4) The study comparing and analyzing the rock breaking mechanism and characteristics to define the applicability of different drilling method. Through cost composition analyse of different drilling method, the study build the drilling method optimization selection model. By using the drilling and geological datas of completed wells, the study finished commercial estimation of different drilling method and select undcrbalanced drilling technology as the optimization drilling method.(5) Take the research issue into on-site application, the footage and rate of penetration of selected bit type were promoted considerably. The drill bits teeth broken and cone lose accident were decreased greatly. Compared with the same section and the same drill bit in offset well, the bit rate of penetration was promoted by5～15%. However, the ROP of Fengcheng formation in Permian period was not improved successfully. Compared with conventional rotary table drilling, PDM (positive displacement motor), Turbine, hydraulic impulse rotary drilling tool, hydraulic power joint and UBD (underbalanced drilling) can promote rate of penetration and decrease drilling cost of Fengcheng formation respectively. Considering the economical of increasing speed and drilling cost, the UBD method was the optimization drilling method of Fengcheng formation. The ROP of UBD drilling section was increased2-4times than conventional mud drilling. However, the borehole stability and fluid production limited the UBD applied in the total Fengcheng formation. Consequently, the increasing drilling speed goal in Fengcheng formation was not realized. |
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