页岩储层岩心地应力方向古地磁实验研究
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摘要
由于多裂缝页岩岩心具有完整性较差、磁矩较小等特点,导致利用古地磁实验方法测定水平地应力方向时存在误差。依据在统计意义上岩心黏滞剩磁分量的地理方向与现代地磁场方向相近的原则,研究利用黏滞剩磁进行页岩岩心定向的方法。考虑到高温退磁方法在实验过程中会引发诱导磁成分而影响实验结果的准确性,因此选择利用逐步交变退磁方法分离出岩心剩磁成分中的黏滞剩磁分量,实验结果处理方法采用EnKin主向量法以及主成分分析法,同组多块平行岩心数据采用Fisher平均统计。结合声发射Kaiser效应测试实验,最终计算出水平地应力地理方位角。对取自川南某区块两口页岩气井的73块岩心进行室内古地磁实验测试,针对页岩发育多裂缝、完整性较差、磁矩较小的特点进行误差分析,以此为基础提出相应提高测量精度的对策。将测试结果与先期地震数据以及现场测井数据进行比较,数据结果吻合度较高,由此说明在实验误差校正后,利用交变退磁结合声发射实验测量多裂缝页岩储层地应力方位的可靠性较高。
Due to the poor integrity and small magnetic moment of the fractured shale cores,there will occur errors when determining the orientation of the horizontal in-situ stress by paleomagnetic method. Based on the principle that the geologic direction of the remanent magnetism component on the cores is statistically close to the modern geomagnetic field orientation,a technique called viscous remanent magnetization( VRM) was investigated to determine the shale rock core orientation. In the process of the paleomagnetic experiment,considering that high temperature demagnetization method would lead to the induced magnetic components and affect the accuracy of experimental results,stepwise alternating demagnetization method was used to separate VRM,and furthermore,the experimental data was analysed through EnKin principal normal vector method and principal component analysis,also the Fisher mean statistics method was chosen to handle parallel experiment core data in the same group. Combining the results with acoustic-emission Kaiser effects test data,the azimuth of horizontal in-situ stress was calculated at last. In this paper,a paleomagnetic experiment was introduced on 73 cores obtained from two shale gas wells in Sichuan block,and experimental error was analysed due to the rock properties of fractured shale,and the solutions to improve the accuracy of experiment were proposed. The comparison showed that the experiment results were basically consistent with those from the seismic data and the field logging data,which proved after experiment error corrected,it was effective to measure the in-situ stress orientation in fractured shale formation with the alternating demagnetization plus acoustic emission test.
Due to the poor integrity and small magnetic moment of the fractured shale cores,there will occur errors when determining the orientation of the horizontal in-situ stress by paleomagnetic method. Based on the principle that the geologic direction of the remanent magnetism component on the cores is statistically close to the modern geomagnetic field orientation,a technique called viscous remanent magnetization( VRM) was investigated to determine the shale rock core orientation. In the process of the paleomagnetic experiment,considering that high temperature demagnetization method would lead to the induced magnetic components and affect the accuracy of experimental results,stepwise alternating demagnetization method was used to separate VRM,and furthermore,the experimental data was analysed through EnKin principal normal vector method and principal component analysis,also the Fisher mean statistics method was chosen to handle parallel experiment core data in the same group. Combining the results with acoustic-emission Kaiser effects test data,the azimuth of horizontal in-situ stress was calculated at last. In this paper,a paleomagnetic experiment was introduced on 73 cores obtained from two shale gas wells in Sichuan block,and experimental error was analysed due to the rock properties of fractured shale,and the solutions to improve the accuracy of experiment were proposed. The comparison showed that the experiment results were basically consistent with those from the seismic data and the field logging data,which proved after experiment error corrected,it was effective to measure the in-situ stress orientation in fractured shale formation with the alternating demagnetization plus acoustic emission test.
引文
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[11]杨宇,汪三谷,郭春华,等.川西低渗气藏单井地应力计算方法综合研究[J].天然气工业,2006,26(4):32-34.
[12]金国海,方大钧,吴能友.多剩磁成分的主成分法分离及其应用[J].地球物理学报,1992,35(5):621-625.
[13]Kirschvink J L.The least squares line and plane and the analysis of paleom agnetic data[J].Geophys.Jour.Roy.Astr.Soc.1980,62:699-718.
[14]Fisher R A.Dispersion on a sphere[J].Proc.R.Soc.London,1953,Ser.A 217:295-305.
[15]侯守信,田国荣.古地磁岩芯定向及其在地应力测量上的应用[J].地质力学学报,1999,5(1):90-96.
[16]殷晟.川南地区页岩气水平井井眼轨迹优化设计研究[D].成都:西南石油大学,2014.
[2]李志明.地应力与油气田勘探开发[M].北京:石油工业出版社,1997.
[3]金衍,陈勉,郭凯俊,等.复杂泥页岩地层地应力的确定方法研究[J].岩石力学与工程学报,2006,25(11):2287-2291.
[4]张广清,金衍,陈勉.利用围压下岩石的凯泽效应测定地应力[J].岩石力学与工程学报,2002,21(3):360-363.
[5]Hou B,Chen M,Jin Y,et al.Prediction Method of Insitu Stress in Non-isopachous Ultra-deep Composite Salt-gypsum Formation[C]//paper 176325-MS presented at the SPE/IATMI Asia Pacific Oil&Gas Conference and Exhibition,20-22 October 2015,Nusa,Indonesia.DOI:http://dx.doi.org/10.2118/176325-MS.
[6]Aidona E,Kondopoulou D.Palaeomagnetic and rock magnetic properities of sediment cores from Chalkidiki,Greece[J].Phys.Chem.Earth:A,2001,26(11/12):879-884.
[7]黄宝春,谭承泽.古地磁多磁成分的分离技术[J].地球物理学进展,1994,9(1):125-133.
[8]李学森,吴汉宁,张小浩,等.钻井岩心重定向的古地磁方法及其可靠性研究[J].油气地球物理,2006,4(2):24-32.
[9]卢运虎,陈勉,金衍,等.深层地应力地理方位确定的新方法[J].岩石力学与工程学报,2011,30(2):233-236.
[10]王磊,杨春和,郭印同,等.利用黏滞剩磁进行水平地应力定向的实验研究[J].石油钻探技术,2013,41(4):23-26.
[11]杨宇,汪三谷,郭春华,等.川西低渗气藏单井地应力计算方法综合研究[J].天然气工业,2006,26(4):32-34.
[12]金国海,方大钧,吴能友.多剩磁成分的主成分法分离及其应用[J].地球物理学报,1992,35(5):621-625.
[13]Kirschvink J L.The least squares line and plane and the analysis of paleom agnetic data[J].Geophys.Jour.Roy.Astr.Soc.1980,62:699-718.
[14]Fisher R A.Dispersion on a sphere[J].Proc.R.Soc.London,1953,Ser.A 217:295-305.
[15]侯守信,田国荣.古地磁岩芯定向及其在地应力测量上的应用[J].地质力学学报,1999,5(1):90-96.
[16]殷晟.川南地区页岩气水平井井眼轨迹优化设计研究[D].成都:西南石油大学,2014.