A new method to calculate shale gas content based on gas reservoir characterization-A case study of Wells JY 1 and PY 1 in Sichuan Basin and its surrounding areas

Li Donghui; Nie Haikuan

doi:10.11743/ogg20190616

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A new method to calculate shale gas content based on gas reservoir characterization-A case study of Wells JY 1 and PY 1 in Sichuan Basin and its surrounding areas
Vol. 40, Issue 6, Pages: 1324-1332(2019)
Online First：28 December 2019，

Published：2019
DOI： 10.11743/ogg20190616
稿件说明：

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DOI：

Li Donghui, Nie Haikuan. A new method to calculate shale gas content based on gas reservoir characterization-A case study of Wells JY 1 and PY 1 in Sichuan Basin and its surrounding areas[J]. 2019, 40(6): 1324-1332. DOI： 10.11743/ogg20190616.

摘要

损失气含量是页岩气含气量的重要组成部分，是页岩气总气量的确定、页岩气资源量和储量计算的重要参数。基于煤层气岩心解吸测试中采用的损失气计算方法——USBM方法及其改进方法不能真实反映页岩气藏损失气含量。综合考虑页岩气藏特征、储层类型及特征、孔隙结构、孔喉大小、气藏压力、取心时间、解吸气含量和解吸时间等因素，重点考虑了钻遇岩心时的瞬间散失气量和解吸速率，提出了一种页岩损失气含量和含气量的计算方法。以超压页岩气藏JY1井和常压页岩气藏PY1井为例，采用该方法计算JY1井下部优质页岩层段的总含气量为6.87~9.02 m

/t，平均7.47 m

/t，上部页岩层段的总含气量为3.25~3.82 m

/t，平均3.64 m

/t；PY1井下部优质页岩层段的总含气量为3.18~4.29 m

/t，平均3.83 m

/t；上部页岩层段的总含气量为1.67~2.28 m

/t，平均1.94 m

/t。明显高于常用算法计算的总含气量数值。采用理论计算法和依据焦石坝页岩气井生产特征计算法两种方法对本文提出的页岩含气量计算方法进行了验证，吻合度较好。研究成果为页岩气藏、尤其是超高压页岩气藏含气量、储量计算和产能评价提供理论依据和计算方法支撑。

Abstract

Lost gas content is an integral part of the total shale gas content

and also a significant parameter for determination of total shale gas volume and evaluation of shale gas in place and reserves.However

the USBM method

the existing calculation method of lost gas content based on core desorption test of coal-bed methane

along with its modified methods

cannot truly reflect the loss of gas content in shale gas reservoirs.Focusing on the instantaneous lost gas content and desorption rate during the core-drilling

we proposed a new method to calculate the lost gas content and the total shale gas content after performing a series of analyses

including characteristics of shale gas reservoirs

reservoir types

pore structure

pore throat size

gas reservoir pressure

coring time

desorbed gas content

and desorption time.The Well JY1 in the shale gas reservoir of overpressure and Well PY1 in the gas reservoir of normal pressure were taken as examples in the study.In applying the new method to Well JY1

we figured out the total gas content of the high-quality lower shale interval

varying from 6.87 m

/t to 9.02 m

/t with an average of 7.47 m

and the total gas content of the upper shale interval

varying from 3.25 m

/t to 3.82 m

/t with an ave-rage of 3.64 m

/t; while in the Well PY1

the total gas content of the high-quality shale intervals ranges from 3.18 m

/t to 4.29 m

/t with an average of 3.83 m

and the total gas content of the upper shale layers ranges from 1.67 m

/t to 2.28 m

/t with an average of 1.94 m

/t.Obviously

these values above are significantly higher than those calculated by using conventional methods.The new method proposed above has been verified by both the theoretical calculation method and performance-based calculation method with the shale gas production wells in Jiaoshiba area as examples.For shale gas reservoirs

especially the overpressured shale gas reservoirs

the new method highlighted in the study serves to provide not only a great theoretical support but also a practical way to calculate shale gas content and reserves

so as to evaluate the reservoir productivity.