Based on the productivity equation of coalbed methane (CBM) well, considering the impact of coal reservoir reformability on gas well productivity, the main production layer optimization index in the “three-step metho...Based on the productivity equation of coalbed methane (CBM) well, considering the impact of coal reservoir reformability on gas well productivity, the main production layer optimization index in the “three-step method” of optimal combination of production layers is corrected, and then the CBM production layer potential index is introduced to evaluate favorable areas for commingled multi-coal seam production. Through analysis of the key parameters of coal reservoirs affecting the CBM productivity index, a development unit division method for areas with multi-coal seams is established, and a quantitative grading index system is proposed. On this basis, the evaluation process of CBM development favorable area is developed: the mature 3-D modeling technology is used to characterize the reservoir physical properties of multi-coal seams in full-scale;the production layer potential index of each grid is calculated, and the production layer potential index contour under single-layer or commingled multi-layer production are plotted;according to the distribution of the contour of production layer potential index, the quantitative index of CBM development unit is adopted to outline the grade I, II, III coal reservoir distribution areas, and thus to pick out the favorable development areas. The practical application in the Yuwang block of Laochang in Yunnan proved that the favorable area evaluation process proposed can effectively overcome the defects of selecting favorable development areas only relying on evaluation results of a major coal seam pay, and enhance the accuracy of the evaluation results, meeting the requirements of selecting favorable areas for multi-coal seam commingled CBM production.展开更多
The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade...The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade into CBM reservoir easily,resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure.In order to reveal the damage mechanisms of slurry to this type of coal reservoirs,we analyzed the physical and chemical properties and potential damage modes of coal rocks.Then,the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope(SEM),and the percentage of slurry and fractures in coal core volume was calculated.In this way,a method to quantitatively evaluate the damage of slurry to coal reservoirs was established.And the following research results were obtained.First,under the effect of differential pressure,slurry and its filtrate invade into coal reservoirs along the fractures.The invasion degree varies with the development degree of fractures and pores.The more developed the fractures and pores,the higher the invasion degree.Second,the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely,so CBM flowing channels are blocked severely.Consequently,the permeability of coal core samples decreases and the compressive strength of coal rocks increase,leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects.Third,the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks.In conclusion,this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development.展开更多
基金Supported by the National Natural Science Foundation of China(No.41772155)the National Science and Technology Major Project of China(No.2016ZX05044-002)the Fundamental Research Funds for the Central Universities of China(No.2015XKZD07)
文摘Based on the productivity equation of coalbed methane (CBM) well, considering the impact of coal reservoir reformability on gas well productivity, the main production layer optimization index in the “three-step method” of optimal combination of production layers is corrected, and then the CBM production layer potential index is introduced to evaluate favorable areas for commingled multi-coal seam production. Through analysis of the key parameters of coal reservoirs affecting the CBM productivity index, a development unit division method for areas with multi-coal seams is established, and a quantitative grading index system is proposed. On this basis, the evaluation process of CBM development favorable area is developed: the mature 3-D modeling technology is used to characterize the reservoir physical properties of multi-coal seams in full-scale;the production layer potential index of each grid is calculated, and the production layer potential index contour under single-layer or commingled multi-layer production are plotted;according to the distribution of the contour of production layer potential index, the quantitative index of CBM development unit is adopted to outline the grade I, II, III coal reservoir distribution areas, and thus to pick out the favorable development areas. The practical application in the Yuwang block of Laochang in Yunnan proved that the favorable area evaluation process proposed can effectively overcome the defects of selecting favorable development areas only relying on evaluation results of a major coal seam pay, and enhance the accuracy of the evaluation results, meeting the requirements of selecting favorable areas for multi-coal seam commingled CBM production.
基金supported by the National Major Science&Technology Project“Development of large oil/gas fields and CBM”(No.:2016ZX05044)the Program for Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China(No.:IRT_14R58)。
文摘The coalbed methane(CBM)reservoirs in the areas of eastern Yunnan and western Guizhou are characterized by developed cleats and fractures and low fracturing pressures,so cementing slurry(“slurry”for short)can invade into CBM reservoir easily,resulting in reservoir damage and abnormal increase of reservoir transformation fracturing pressure.In order to reveal the damage mechanisms of slurry to this type of coal reservoirs,we analyzed the physical and chemical properties and potential damage modes of coal rocks.Then,the development situations of fractures and pores before and after the coal core samples were internally contaminated and the invasion and plugging situations of slurry in fractures and pores were analyzed intuitively by means of CT scanning and scanning electron microscope(SEM),and the percentage of slurry and fractures in coal core volume was calculated.In this way,a method to quantitatively evaluate the damage of slurry to coal reservoirs was established.And the following research results were obtained.First,under the effect of differential pressure,slurry and its filtrate invade into coal reservoirs along the fractures.The invasion degree varies with the development degree of fractures and pores.The more developed the fractures and pores,the higher the invasion degree.Second,the cement products formed after the slurry in the reservoirs gets cemented and solidified fill the fractures and pores tightly and cover the surface of coal core samples densely,so CBM flowing channels are blocked severely.Consequently,the permeability of coal core samples decreases and the compressive strength of coal rocks increase,leading to the abnormal increase of subsequent fracturing pressure and impacting the fracturing stimulation effects.Third,the effect of slurry filtrate on the alkali sensitivity and velocity sensitivity of coal rocks is much less than the damage degree of slurry invasion to coal rocks.In conclusion,this newly developed quantitative evaluation method for the damage of slurry to coal reservoirs is of guiding significance to improving the cement job quality of coal reservoirs and ensuring the efficient CBM development.
