Directional drilling technology for coalbed methane wells

(China United Coalbed Methane Co., Ltd. Beijing 1000 1 1)

Abstract: The difference between coalbed methane reservoir characteristics and conventional natural gas reservoirs determines the particularity of coalbed methane drilling, completion and reservoir protection technology. On the basis of continuous test and summary, a set of directional well drilling technology and well quality control measures suitable for coalbed methane development are developed, which meets the needs of industrialization and commercial development of coalbed methane to reduce drilling and production costs and has reference significance for economical and efficient development of coalbed methane.

Keywords: CBM directional well drilling technology, wellbore quality

Drilling technology of coalbed methane directional well

Yan Bo Zhang Li Qing Shao Yong

(China United Coalbed Methane Co., Ltd., Beijing, 1000 1 1, China)

Abstract: There are many differences between coalbed methane reservoir and conventional natural gas. These differences determine the particularity of coalbed methane in drilling, completion and reservoir protection. On the basis of continuous test and summary, this paper studies the drilling technology and quality control technology system of coalbed methane directional wells. This meets the requirements of reducing drilling and production costs in the industrialization and commercialization of coalbed methane. This is of reference significance for the economic and efficient development of coalbed methane.

Keywords: coalbed methane; Directional well; Drilling technology; Well quality

Fund Project: National Science and Technology Major Project "Demonstration Project of Coalbed Methane Vertical Well Development in Southern Qinshui Basin, Shanxi Province" (No.:2009ZX05060)

About the author: Hou Yanbo, born in 1983, male, born in Qian 'an, Hebei Province, with a master's degree, graduated from China University of Mining and Technology (Beijing) in 2009 with a major in geological engineering, and now Zhonglian CBM Co., Ltd. is engaged in CBM exploration and development. E-mail: hybjerry@ 163.com

The south block of Shizhuang is located at the west foot of Taihang Mountain in the south of Qinshui Basin, and is administratively subordinate to Qinshui County and Gaoping City in Jincheng City, Shanxi Province. The area is 260 kilometers north of Taiyuan, the capital of Shanxi Province, and 60 kilometers southeast of Jincheng City. The total area of the block is about 388km2, and the resource abundance of No.3 coal seam is 65438+69 million m3/km2. More than 400 CBM wells have been successfully developed in this block, and the average gas production of a single well is >:1000m3/d. Because of the overlapping mountains, criss-crossing gullies and dense forests in this area, considering the aspects of protecting the environment, reducing the difficulty of land acquisition and pre-drilling construction, 2-4 cluster wells with directional wells are deployed in areas with complex local topography and dense forest land to develop CBM. Cluster well can also effectively reduce the construction cost of surface gathering and transportation and the daily post-mining production management cost, which is a drilling technology suitable for large-scale development of coalbed methane in this area.

1 geological survey

The thickness of Quaternary loess in the southern block of Shizhuang is about 30m. The bedrock strata drilled in the developed No.3 coal seam are Liujiagou Formation, Shiqianfeng Formation, Shangshihe Formation, Xiashihezi Formation, Shanxi Formation and Taiyuan Formation from top to bottom. The drilling principle is 50m below the floor of No.3 coal seam. See table 1 for details. Generally speaking, the geological conditions in this area are simple and the buried depth of coal reservoirs is moderate.

Table 1 Summary of Stratigraphic Characteristics of South Shizhuang Block

2 Architectural design

Take TS04C cluster well group as an example. The well group consists of four directional wells, with the well gate direction of 86, the magnetic declination of-2.9 and the wellhead spacing of 5m, which are arranged in a straight line. In the design, anti-collision measures should be fully considered, and the drilling sequence should be arranged reasonably, so that the design direction of each well is radially distributed and the borehole trajectory is not staggered. See figure 1 and figure 2 for the specific design.

Completion technology: the diameter of the first spudding is φ3 1 1. 15mm, after drilling, the stable bedrock is 10m, and the surface casing with φ244.5mm×8.94mm is run. Cementing cement needs to be returned to the ground, with the second spudding diameter of φ2 15.9mm and the drilling depth of 65433.

Figure 1 TS04C Horizontal Projection of Well Cluster

Fig. 2 Trajectory data of TS04-4D borehole

3 drilling equipment and tools

3. 1 equipment

Drilling rig: TSJ-2000；; GZ2000GZ2600. Drilling tower: A-shaped, with load ≥700KN. Mud pump: 3NB-350; 3n b-500； 3NB-800 diesel engine with displacement of 20 ~ 30L/s and power: 12V 135, 8V 190, 12V 190.

3.2 Drilling tools and others

φ 127mm drill pipe, φ 159mm nonmagnetic drill collar, φ 159mm drill collar, φ165mm (1.25/1.5) single bending screw, φ 2.

4 drilling technology

4. 1 mud technology

Firstly, low solid drilling fluid was prepared with bentonite powder, soda ash, caustic soda, a small amount of potassium polyacrylamide KPAM and sodium carboxymethyl cellulose CMC. Soda ash and caustic soda mainly improve the hydration dispersed phase energy of clay, reduce water loss, increase viscosity and adjust the PH value of mud. CMC filtrate reducer improves the aggregation stability of clay particles, helps to maintain the content of fine particles in drilling fluid, forms a dense filter cake, reduces the filtrate loss, inhibits the expansion of water-sensitive formations such as mudstone, and can effectively consolidate the borehole wall. In addition, CMC filtrate reducer can increase the rock carrying capacity of drilling fluid, reduce the sand content, effectively control the harmful solid content, reduce the probability of repeated rock breaking, prolong the service life of drilling tools such as drill bits and screws, and improve drilling efficiency. KPAM has the functions of controlling formation mud making, reducing water loss, improving flow pattern and increasing lubricity. It can stabilize the borehole wall, reduce the filtration of drilling fluid and improve the ROP. When drilling to the target coal seam, the drilling fluid should be changed to clean water until drilling is finished. If drilling encounters a leakage layer or a formation prone to leakage, the mud performance can be properly adjusted on the premise of protecting the reservoir, and treatment agents such as plugging agent can be added as appropriate to ensure the smooth completion of the project.

Properties of drilling fluid in coal seam section: density 1.02 ~ 1.05g/cm3, viscosity 22 ~ 25s, pH 7.5 ~ 8.5, sand content.

4.2 Surface Drilling Technology

BHA: φ 311.15mm tri-cone bit +φ 159mm drill collar +φ 127mm drill pipe.

The first section is a Quaternary loess layer, containing a small amount of pebbles, with loose structure and easy leakage and collapse. During drilling, it is mainly to ensure no leakage and adjust the mud properly. At the beginning of drilling, slowly drill and lift it to ensure that it does not collapse and is not straight, and control the pump pressure and displacement to prevent the loess layer from leaking.

In the first spudding, φ3 1 1. 15mm roller bit was used for drilling with WOB WOB 30～50kn and pump pressure of 2MPa. After the first spudding penetrates the bedrock 10m, the drilling is finished, and the φ244.5mm×8.94mmJ55 surface casing is run, with the casing collar flush with the ground, and the cement with the density of 1.80g/cm3 is used to cement the well and return it to the ground.

4.3 Drilling Technology in Vertical Interval

BHA: φ 215.9mm bit+φ159mm drill collar+φ127mm drill pipe.

The strata in the vertical interval of the second spudding are mainly sandstone and mudstone with good drillability. Conventional tower drilling tool structure is adopted. In order to prevent the drilling parameters of well deviation, the principle of light pressure lifting is still adopted, and the well deviation is measured every 30 meters, so as to track and monitor the changes of well deviation and azimuth as soon as possible to prevent collision and reduce the construction risk.

4.4 Directional interval drilling technology

BHA: φ2 15.9mm bit+φ165mm (1.25/1.5) single-bend screw +φ 159mm nonmagnetic drill collar+φ159mm.

When the second spudding reaches the well depth of about 100 m, directional deflection will be started. In case of directional deflection, the turntable should be locked, and the directional deflection should be carried out by using a single bending screw or a straight screw plus bending joint. The inclinometers shall calibrate the compass regularly to ensure accurate data acquisition. Drill 1 to two single inclinometers at a time, and the interval between inclinometers drilled into the interval shall be ≤20m. At the initial stage of orientation, well deviation and orientation should be well controlled to prevent tool face dislocation and difficulty in control. When drilling in anti-collision interval and directional deviated well interval, the drilling team should intensively measure points, calculate and draw drawings, and closely grasp and predict the changes of borehole trajectory; Salvage sand samples frequently to observe whether cement cuttings appear; Carefully analyze the phenomenon of jumping. Drilling parameters: WOB 50 ~ 60kn, pump pressure 3 ~ 4 MPa, screw motor speed 200 ~ 300 r/min. During drilling, the drilling parameters are adjusted in real time according to the borehole trajectory, and the azimuth is controlled stably when the azimuth error increases.

Considering the particularity, stability and continuity of coalbed methane well drainage, the productivity construction unit has higher requirements for borehole trajectory, especially for the inclined section of directional wells. The smoother the borehole trajectory, the smaller the curvature, and the smaller the eccentric wear loss between the pumping system and the formation, which is more conducive to the continuous and stable drainage and production of the production device. Therefore, it is required that the slope of the whipping section is ≤ 4/30m, and the total angle change rate of three continuous measuring points in the whipping and twisting sections is ≤ 5/25m.

4.5 Drilling Technology for Stable Inclined Section

BHA: φ2 15.9mm bit +φ2 14mm stabilizer +φ 159mm nonmagnetic drill collar +φ 159mm drill collar ×6 drill pipes +φ 127mm.

Because the third-level wellbore profile is directly widened, in principle, it is not allowed to lower the top angle in the inclined section. In order to avoid the out-of-control phenomenon of directional well trajectory, process control should be paid attention to in drilling construction. Stabilizing the inclined interval requires uniform drilling transportation and drilling speed to ensure uniform drilling tool load and smooth operation. When drilling through the coal seam, the stabilizer should be removed as much as possible. Although the hole inclination below the coal seam section will be slightly reduced by 2 ~ 3, it can effectively prevent the serious collapse of the hole diameter of the coal seam section, avoid the probability of accidents such as buried drilling and reduce the risk of drilling construction.

According to the requirement that the azimuth error of target closure is less than 5, and the radius of target area is 20m, the core of drilling technology in stable deviation section is to strictly control borehole trajectory and azimuth drift, and timely adjust drilling parameters and BHA according to the survey of borehole deviation to ensure the well to hit the target smoothly. The main measures are to adjust the placement position of stabilizer, change the outside diameter of stabilizer, adjust the length of drill collar and WOB, and achieve the effect of stabilizing well deviation and azimuth. In practical application, the double-support pendulum drilling tool has the best control effect on borehole trajectory. Double-support pendulum drilling tool can effectively reduce the local dog leg problem and make the trajectory smoother. Although it increases the difficulty of drilling, it lays a good foundation for later completion and casing running. Drilling parameters: WOB 80 ~ 120kn, pump pressure 3MPa. After drilling, run φ 139.7mm×7.72mmJ55 production casing. By running a short casing of about 3m between the casing shoe and the back pressure valve, the length of the drainage bag can be effectively increased, and the number of casing centralizers can be increased in the inclined section and other well sections with large dogleg. Cementing with cement with the density of 1.65g/cm3, and the cement slurry returns to 200m above the target coal seam.

5. New drilling technology of coalbed methane directional well

At present, in order to improve drilling efficiency, drilling construction units generally adopt the composite drilling technology of combining screw drilling tools with rotary table. Through the cooperation of rotary table and screw hydraulic motor, the drilling times are reduced and the mechanical speed is increased. In addition, if it is necessary to adjust the well deviation and twist direction, it can be adjusted at any time according to the well trajectory to control the drilling trajectory in time and efficiently. If it is combined with PDC to form a four-in-one drilling tool structure, it can complete the second drilling to completion in one drilling, which can obviously shorten the drilling cycle and shorten the wellbore. BHA: φ2 15.9mmPDC bit +φ 165mm. 1.25 single-bend screw +φ 159mm drill collar× 3m+φ 210mm stabilizer+φ10mm stabilizer. Drilling parameters: WOB 50 ~ 60 KN, pump pressure 3 ~ 4 MPa, screw motor speed 200 ~ 300 r/min.

Because CBM wells have higher and higher requirements for directional well trajectory and drilling efficiency, MWD technology and composite drilling technology can be introduced to better and more conveniently control well trajectory and improve drilling efficiency. Low-cost drilling technology is the development trend of coalbed methane resources in China at present, and copying logging-while-drilling equipment and technology developed by conventional oil and gas fields will have a great impact on drilling cost. However, with the large-scale development of coalbed methane and the increasingly high requirements for drilling engineering, MWD and LWD technologies suitable for the current situation of coalbed methane development in China will appear in the near future, with very broad development prospects.

6 conclusion

(1) Using cluster well drilling technology to develop coalbed methane resources can save land resources, protect the environment, effectively reduce the cost of surface gathering and transportation projects and later production and operation, and have remarkable economic effects.

(2) The well profile of the three-stage direct stabilization system is reliable and reasonable, which is most beneficial to well trajectory control and drilling construction, and is suitable for the production of coalbed methane.

(3) Combining with the actual situation of formation and borehole trajectory, reasonably optimizing the drilling parameters of different intervals, and process control is the key of directional drilling technology. Only by closely monitoring the well trajectory and combining with efficient drilling technology can we ensure that each well can hit the target smoothly with the optimal well trajectory.

(4) The use of the four-in-one drilling tool structure has a strong ability to stabilize the well deviation and azimuth, reducing the tripping times. Combined with MWD, the risk of out-of-control wellbore trajectory can be reduced and drilling efficiency can be effectively improved.

refer to

Lu Guizhou. 20 10. hole trajectory control of directional wells [J]. Shaanxi Coal, 1: 85 ~ 86

Wu. 2006. Application of directional drilling technology with screw drill in coalbed methane drilling [J]. Prospecting engineering (geotechnical drilling and excavation engineering), 1 1: 48 ~ 49.

Xi Hongxi, Liu Qiang, Liu Xingguang. 2005. Application of cluster well drilling technology in northern Shaanxi Oilfield [J]. Development of scientific and technological information and economy, 15 (7): 293 ~ 294