Research On Drilling Key Technology Of Coalbed Methane Cluster Well In Liupanshui Karst Stratum

Coalbed methane belongs to clean energy and is an important support for China’s energy development in the future.Liupanshui coalfield is one of the three key target areas for coal bed methane exploration and test development.The cluster wells are used for coalbed methane development with the average of 4~7 two-dimensional directional Wells in each well field.However,the karst landform in this area is widespread.It is prone to leakage,which presents a great challenge to drilling operation specifically in three aspects.First of all,the surface is rich in caves and often accompanied by water.The conventional water-based drilling fluid is faced with the problem of cavernous leakage.The air drilling is at risk of the well slanting and sticking.Secondly,the formation fractures in the central Feixianguan formation are often characterized by the drilling fluid loss of return.In the end,it is difficult to direct drilling in the missing strata.At the same time,the leakage and orientation are mutually affected.On the basis of the previous research results,this paper uses the methods of theoretical analysis,calculation,numerical simulation,experience summary and field test to study the technology of preventing well deflection and sticking for shallow ground air hammer drilling,the drilling fluid loss of return for Feixianguan formation and the directional drilling technology for leakage formation.The specific contents are as follows.Through the comparison of packed hole assembly and pendulum drill assembly,the pendulum drill assembly with double stabilizer is selected and designed.A long steel pipe wrapped with kelp is used to seal off the water formation to solve the problem of pneumatic drill balling-up sticking.The upper centralizer is turned into a backstroke device to solve the problem of sand bridge sticking.ANSYS Fluent finite element software is used to simulate the optimal velocity of pneumatic drill.On this basis,the optimal displacement is calculated.This paper analyzes the mechanism of the malignant leakage in Feixiguan formation,and puts forward the practical method of determining the location,pressure and opening degree of the leak.A formula for sealing material is designed.The process of "bridging + cement" is optimized by means of mixing dry bridging agent,adding polypropylene fiber and calculating the depth of the drill pipe.Through the analysis of the relationship between the sliding directional drilling and the leakage,it is considered that reducing the number of directional frequency and time,improving the orientation efficiency and drilling through the leakage layer as soon as possible,is the priority direction.By using the composite rotary drilling as far as possible,quick-adjusting the angle of inclination or azimuth and improving the accuracy of the reference value of the reverse twist angle,the directional drilling technology of the leakage formation is optimized.Based on the analysis of drilling data,the track changing rule under this process is summed up.Passing on the field application of six directional wells in one cluster well,these technologies have achieved good results,improved drilling efficiency and shortened the well construction period of coalbed methane cluster wells.It will provide theoretical support and field application experience for coalbed methane development oriented drilling engineering in Liupanshui coalfield and similar formation in the future.