The Research Of Affective Facts Of Production And. Enrichment Of Cbm In Linfen Block

The exploration and production of coal bed methane, Petro China has set it as the primary business during the 12 th Five-Year Plan and listed it as the long term development. It has made productivity job and forerunner testing in Qinshui, Hancheng, Sanjiao, Baode. In addition, it has also conducted some work of exploration and evaluation in blocks of mining rights registered. After more than one decade of CBM exploration in Linfen and forerunner testing of CBM, it has resulted in CBM production and built foundation for the next step of scale development.It researched herein Linfen block located in the east of Erdos Basin based on the theory of development geology of CBM, coal petrography, fluid mechanics in porous medium, lithomechanics and the basic data of geology, well logs, fracture and production, combined theory analisis, simple examination and production test to work out three main elements for CBM concentration. It utilized gray co-analysis method to optimize the best condition of well and formulate the standard production model of Linfen Block. It analyzed the influence of downhole operation upon succession production and focused on the research of coal fine occurring, the mechanism, character and elements of pipe eccentric wear. It worked out the measures of providing against coal fine and eccentric wear of Linfen Block based on production optimization, well washing art, technology and equipment optimization and pipe string structure optimization. It extends the period of pump examination and gains good result.The main achievements are following:Based on the geological data, it summarized the main control factor of CBM enrichment; and figure out the CBM enriched zone in Linfen. And summarized geologocal affecting facts. It optimized prospecting wells by using the methods of single-fact analysis and grey correlation analysis.In the three factors of controlling CBM reservoir development, the basic is generating and reserve conditions, and the key is conservation. The maturity of coal is high in Linfen with good generation condition. As a result, the key element is conservation condition. It worked out the main controlling factors for CBM abundance and potential block based on structure, deposition, hydrology geology. Linfen Block locates in the south of Erdos Basin. It is a large west-east monocline structure. A NE-SW pressure fault lays through whole block and make it complex and form interphase col-pump structure. Main coal beds developed in the block and coal body structure is protogenetic structure coal and fragment coal. In the vicinity of faults, crumpled coal and mylonitic coal developed. Two different hydrology units exist in the block from east to west. The watershed between the two units is Xueguan reverse fault which penetrates through the block. The hydrology unit in the east includes water supplying area, radial-flow area and water escaping area. In the west of the fault, it is not obvious for the character of water supplying. The controlling elements for CBM enriching are faults, surrounding rocks and hydrology in Linfen. Other elements, such as coal rank, structure evolution, structure style, geometry of coal bed(the layout structure in 3D), have less affection for CBM enriching. Based on the thickness of coal bed, buried depth and reservoir pressure, it worked out the potential block is Xiaohuigong-Yaoqu-Caojing and Puxian-MIngzhu-Sange. The secondary block locates in the surrounding area of the north and south area.Accroding to the depth of coal bed, abundance of CBM, coal body structure and crush of top and bottom, the pressure ratio of critical resolution and reservoir bed and hydrology condition, the evaluation standard is set up for CBM enriching. Main static elements for CBM productivity are coal bed thickness, content of coal bed, the buried depth of coal bed, coal body structure, hydrology condition, pressure of coal bed, resolution pressure of coal bed. Researching the data of exploration 76 wells and seismic, to make a choice with single element. It gets rid of those wells with low potential production which is: buried depth deeper than 1400 m, the thickness of coal bed thinner than 1m, gas content per ton less than 4m3,locating in water supplying and radial-flowing area. 14 wells are got rid of. Then to evaluate the left 62 wells with the method of gray correlation and choose 7 main elements, In the last, to optimize the most potential block for developing CBM based on the sequence of correction data of 62 wells.Researching the data of fracturing and special log, it summarized the charactor of crustal stress of main coal bed. The main direction of the biggest main stress is NEE. it indicates that the pressure of coal bed, fracture pressure, closure pressure, the biggest horizontal stress, vertical main stress, the smallest main stress increase in linear with the buried depth increasing of coal bed. Manometric modular focus in the range of 0.7~1.1, and the average value is 0.9, and also increasing with the depth increasing. The local stress is σv>σhmax>σhmin when buried depth of Coal bed is less than 1070 m, within 1070~1200m,the crustal stress of coal bed changes to σhmax≈σv≈σhmin, the state of coal bed changes from stretching to compressing, λ increases gradually. The crustal stress of coal bed changes to σhmax≈σv>σhmin, when the buried depth is bigger than 1200 m. The smallest main stress is bigger than 20 MPa, the coal bed is in a state of compressing, λ comes to 1.2. Based on geology of CBM production and production data, it divided the period of CBM production and the production curves according to the character of water and gas production. Researching bottom pressure and variation rules of water and gas production, it divides the production of CBM into four periods: dewatering decreasing pressure, fluctuating production, steady production and exhaustion. Utilizing dimensionless gas production/dimensionless water production as the main element for dividing the period of CBM production, it found that, in Linfen Block for CBM wells, dimensionless productivity is about 0.3 after the period of removing water for decreasing pressure, dimensionless productivity is about 0.6 after the period of unstable gas production, dimensionless productivity is about 0.8 after the period of stable gas production. According to the data analysis for CBM wells production, it divided CBM wells in Linfen into five styles: gas and water increasing, gas increasing with water decreasing, water decreasing, water stable and water increasing. It made the evaluation for CBM production and the grade for the productivity for Linfen Block. According to production time, gas production and bottom hole pressure, it divided the gas wells into high production well, media production well and low production well. The low production wells in Linfen is 79.3%. At the moment, the bottom hole pressure is high(the average value of low production is 4 MPa, high production well is 2 MPa), so it is of high potential for production.3. According to the character of CBM developing in Linfen, it analyzed three items: developed well style, reservoir modified and production technology. There are 4 well styles in Linfen: multi-wells, multi-branch horizontal well, U-shape horizontal well and L-shape horizontal well. The average gas production for the 4 styles is: L-shape horizontal well>U-shape horizontal well> multi-wells> multi-branch horizontal well. It has strong relation between coal bed fracture and fracture liquid, in the present, the sequence for the 4 fracture is: active water fracture>clear liquid fracture>guar gum fracture>nitrogen foam fracture. it is inclusive of two parts for production technology: borehole and surface. It is simple for surface equipment, equipment of borehole is complex, it is inclusive of two styles: sand producing, coal dust pump stuck and sucker rod break or pipe leak due to eccentric wearing of pipe abd rod.Based on the test analysis, it summarized the character of ingredient and particle degree in Linfen block. Coal dust dispersant test indicated that it is good for coal dust to be excluded from the pipe by adding suitable amount of coal dust dispersant. The speed of water producing is bearing on coal dust producing. When the speed is low, coal particle is relative small and bigger particle sinks at the bottom. With speed increasing, the particle becomes bigger up to 80μm. The speed of water producing affects coal dust producing. It is positive correlation between the speed and coal dust producing when the speed is low. The amount of coal dust producing no longer increases and becomes stable with the speed increasing when the speed is up to 3m3/d. The amount producing becomes stable with the speed increasing. The concentration of coal dust becomes low with dispersant adding at the same speed.According to the site of eccentric wear, it worked out the technology of preventing eccentric wear by the analysis for well track, pole and pipe combination and the character of liquid produced. Multi-well is the main style in Linfen Block. Comparing with other style, more eccentric occurs. It creates more eccentric wear due to coal dust and high Cl-、slight amount of H2 S. It extends the period of well fix after taking the measures of optimizing pipe design, replacing usual pipe with paint pipe, coat pipe, replacing usual caps with anti-eccentric wear caps.4. The optimization of CBM production model for Linfen. It recognized that the main developed model in Linfen is U-shape horizontal well and L-shape horizontal well with multi-wells in part. The fracture fluid is clean fracturing fluid and slick water. In order to keep success production after initial period, it may adapt to put water to settle the problem of high coal dust inside the pipe, then to increase CBM production of single well.