-
地层孔隙压力,指的是地层孔缝空间内流体(油、气、水)所具有的压力。准确识别高压成因、精确预测孔隙压力是合理设计套管程序、确定钻井液密度、调整生产工艺等的基础[1]。莺歌海盆地斜坡带天然气资源丰富,是南海西部天然气勘探主力战场与开发接替区之一[2]。该区发育的黄流组二段(黄二段)属于优质储层,其地层压力系数在2.15以上,地层温度在180 ℃以上。虽然在前期探索中,莺琼盆地异常压力预测取得了一些成果[3-4],但由于不同层段的成因机制复杂,表现出多源多机制的特点,针对全井段使用单一预测方法,孔隙压力预测精度低,明显不适用于莺歌海盆地斜坡带。且在钻进时频繁出现井涌、井漏等复杂情况,严重制约该区域的油气开采。笔者基于莺歌海盆地斜坡带已钻井的地质、测录井等资料,开展了研究区域异常高压成因的研究与分析,提出分层段、分机制地进行全井段孔隙压力预测的方法,提高多源多机制成因下的孔隙压力预测精度,进而指导莺歌海盆地斜坡带钻探工程实际。
-
20世纪60年代以来,国内外在利用测井资料确定地层孔隙压力方面进行了大量研究,在理论基础和计算精度方面都有了较大提高,使地层孔隙压力预测技术由过去的经验、半经验阶段走上了科学化阶段。具有代表性的方法[1]见表1。针对不同的高压成因层段,选用适用的预测模型是精确预测地层孔隙压力的前提。其次,在保证精度的条件下,对测井资料的需求也是需要考虑的因素之一。
表 1 有代表性的基于测井资料的地层孔隙压力预测方法
Table 1. Representative formation pore pressure prediction methods based on well logging data
模型 适用高压机制类型 测井参数 应用情况 Eaton 欠压实作用 声波测井 各地区应用广泛 Alixant & Desbrandes 欠压实作用 自然伽马、深电阻率 在北海、墨西哥湾、地中海等应用效果较好 Ward 欠压实作用、流体膨胀 自然伽马、深电阻率、密度测井、声波测井 预测欠压实情况精度较高,但预测流体膨胀精度较低 Bowers 加载曲线 加载型成因 声波测井 在北海、墨西哥湾应用效果很好 卸载曲线 卸载型成因 -
莺一段和莺二段上部层段异常高压成因为欠压实作用,此类机制孔隙压力最常用的计算模型为Eaton法[15],且该方法对测井资料需求较少,计算简便。其计算方法为
$$ {p_{\text{p}}} = {p_{\text{o}}} - ({p_{\text{o}}} - {p_{\text{h}}}){\left ( {{{\Delta {t_{\text{n}}}}}/{{\Delta t}}} \right)^n} $$ (1) 式中,pp为地层孔隙压力,MPa;po为上覆岩层压力,MPa;ph为静水压力,MPa;Δtn为计算点正常趋势线上的声波时差,μs/ft;Δt为计算点实测声波时差,μs/ft;n为Eaton指数,与地区和地质年代有关。
-
莺二段下部地层异常高压成因为“欠压实作用为主,流体膨胀为辅”,属于加载型,该类机制符合Bowers加载曲线[7],结合有效应力定理式(3)能准确预测孔隙压力。Bowers加载曲线表达形式为
$$ v = 1524 + A\sigma _{{\text{ev}}}^B $$ (2) $$ {p_{\text{p}}} = {p_{\text{o}}} - {\sigma _{{\text{ev}}}} $$ (3) 式中,v为声波速度,m/s;σev为有效应力,MPa;A、B为相关系数,可由邻井的泥岩声波速度和有效应力数据回归得到。
-
黄一段异常高压成因为“流体膨胀为主、欠压实作用为辅”,Bowers卸载曲线[7]结合有效应力定理,能很好预测这类机制下的异常孔隙压力。Bowers卸载曲线表达形式为
$$ v = 1524 + A{\left[ {{\sigma _{{\text{ev}}}}{{\left ( {\frac{{{\sigma _{{\text{ev}}}}}}{{{\sigma _{{\text{max}}}}}}} \right)}^{1/U}}} \right]^B} $$ (4) 式中,σmax为地层卸载开始时最大有效应力,MPa;U为模型回归系数。
-
黄二段成因复杂,多源多机制特征明显,上述模型均不适用于这类地层。因此,提出了多变量孔隙压力预测新模型。
-
借鉴Bowers法的思路,综合考虑地层岩性、物性、有效应力等参数对声波速度的影响,建立相对应的声波速度模型,并基于有效应力定理建立多变量地层孔隙压力检测新模型。
目前国内外主要基于Han的室内实验数据[16]拟合声波速度的求取模型,主要有Eberhart-Philips模型(式5)[17]和Sayers模型(式6)[18]。
$$ v = {a_0} + {a_1}\varphi + {a_2}\sqrt {{V_{{\text{sh}}}}} + {a_3}\left ( {{\sigma _{{\text{ev}}}} - {{\text{e}}^{{a_4}{\sigma _{{\text{ev}}}}}}} \right) $$ (5) $$ v = {b_0} + {b_1}\varphi + {b_2}{V_{{\text{sh}}}} + {b_3}\sigma _{{\text{ev}}}^{{b_4}} $$ (6) 式中,
$ \varphi $ 为孔隙度,小数;Vsh为泥质含量,小数;a0、a1、a2、a3、a4、b0、b1、b2、b3、b4为常量参数,无量纲。Eberhart-Philips模型和Sayers模型都以泥质含量表示岩石的岩性。事实上,相同泥质含量的砂泥岩其矿物组分、颗粒粒径、胶结物类型等都不一定相同,这些因素对于声波的传播也会有一定的影响。而密度在一定程度上可以反映上述因素的影响[1, 19],且补偿密度测井作为常规的测井手段之一,相关数据比较容易获取。因此,可引入密度项,弥补上述两个声波速度模型的缺陷。
-
基于现场测井数据,分析孔隙度、有效应力、泥质含量、密度与声波速度的关系,建立声波速度模型。为了更准确判断各因素与声波速度之间的相对关系,各因素应来源于不同的测井资料:声波速度来源于声波测井数据,泥质含量来源于自然伽马测井数据,密度来源于补偿密度测井数据,而孔隙度则来源于补偿中子测井。
图8为声波速度与不同影响因素的拟合结果。声波速度-孔隙度采用 “线性+指数”的组合形式拟合程度(相关系数为0.518)更高(图8a)。声波速度-有效应力的拟合形式,不管是幂函数还是“线性+指数”,拟合程度都非常高,相关系数均达到0.75以上,说明有效应力很大程度上能反映声波速度(图8b)。声波速度-泥质含量无论是采用线性还是幂函数(0.5次幂),其拟合结果都不是很好,相关系数只有0.332和0.312(图8c),这进一步说明单纯以泥质含量来表示岩性对声波速度的影响是不合适的。而声波速度-密度采用线性函数、指数函数和幂函数拟合的程度都差不多,相关系数均在0.57左右(图8d)。
-
综合Han、Eberhart-Philips和Sayers等人的研究成果和现场测井数据分析结果,考虑各因素与声波速度拟合的相关程度和模型精简程度,建立新的声波速度模型。孔隙度项取“线性+指数”的组合形式,密度项取线性形式,泥质含量项取线性形式,有效应力项取幂函数形式。
$$ v = {c_0} + {c_1}(\varphi + {{\text{e}}^{{c_2}\varphi }}) + {c_3}\rho + {c_4}{V_{{\text{sh}}}} + {c_5}\sigma _{{\text{ev}}}^{{c_6}} $$ (7) 式中,c0、c1、c2、c3、c4、c5、c6为模型参数,无量纲。
Method for predicting pore pressure of whole well interval in slope zone in Yinggehai Basin
-
摘要: 为探索多源多机制孔隙压力预测方法,精准预测莺歌海盆地斜坡带全井段的孔隙压力,综合考虑区域沉积构造演化过程、测井数据的响应特征,明确了各层段异常高压成因;针对常规高压机制地层,优选了不同层段的孔隙压力预测模型;对复杂成因地层开展了孔隙压力精确预测新方法的研究。研究表明,莺一段—莺二段上部层段异常高压成因为 “欠压实作用”,可使用Eaton法预测孔隙压力;莺二段下部层段异常高压成因为 “欠压实作用为主、流体膨胀为辅”,可利用Bowers加载法预测孔隙压力;黄一段异常高压成因为 “流体膨胀为主、欠压实作用为辅”,可使用Bowers卸载法预测孔隙压力;黄二段异常高压成因复杂,为“超压传递+流体膨胀为主、欠压实作用为辅”的组合模式,针对此特殊成因,提出了多变量孔隙压力预测新模型。将预测结果与实测孔隙压力数据进行了对比,全井段预测精度达97%,能满足工程需求。研究结果可为莺歌海盆地斜坡带钻井设计和施工提供依据和指导。Abstract: In order to explore the method for predicting pore pressure with multiple sources and multiple mechanisms, and to accurately predict the pore pressure of the whole well interval in the slope zone of the Yinggehai Basin, by comprehensively considering the evolution process of regional sedimentary structure and the response characteristics of logging data, the cause of abnormally high pressure in each interval was clarified. For formations with conventional high-pressure mechanisms, the models for predicting pore pressure in different intervals were optimally screened. For formations with complex genesis, a new method for accurately predicting pore pressure was studied. The research shows that the abnormally high pressure in the upper intervals of the Ying 1-Ying 2 member is caused by under-compaction, where the pore pressure can be predicted by the Eaton method. The cause of the abnormal high pressure in the lower intervals of the Ying 2 member is that, under-compaction primarily, supplemented with fluid expansion, where the pore pressure can be predicted with the Bowers loading method. The cause of the abnormal high pressure in the Huang 1 member is that, fluid expansion primarily and supplemented with under compaction, where the pore pressure can be predicted with the Bowers unloading method. The causes of the abnormal high pressure in the Huang 2 member are complex, which is a combined pattern composed of overpressure transmission+fluid expansion primarily, supplemented with under compaction, and aiming at this special cause, a new multivariable pore pressure prediction model was proposed. Comparing the prediction results with the measured pore pressure data, the prediction accuracy of the whole well interval is up to 97%, which can meet the engineering requirements. The research results can provide a basis and guidance for drilling design and construction in the slope zone of Yinggehai Basin.
-
Key words:
- Yinggehai Basin /
- abnormal high pressure /
- formation pore pressure /
- prediction model
-
表 1 有代表性的基于测井资料的地层孔隙压力预测方法
Table 1. Representative formation pore pressure prediction methods based on well logging data
模型 适用高压机制类型 测井参数 应用情况 Eaton 欠压实作用 声波测井 各地区应用广泛 Alixant & Desbrandes 欠压实作用 自然伽马、深电阻率 在北海、墨西哥湾、地中海等应用效果较好 Ward 欠压实作用、流体膨胀 自然伽马、深电阻率、密度测井、声波测井 预测欠压实情况精度较高,但预测流体膨胀精度较低 Bowers 加载曲线 加载型成因 声波测井 在北海、墨西哥湾应用效果很好 卸载曲线 卸载型成因 -
[1] 樊洪海. 异常地层压力分析方法与应用[M]. 北京: 科学出版社, 2016. FAN Honghai. Analysis methods and applications of abnormal formation pressures[M]. Beijing: Science Press, 2016. [2] 范彩伟. 莺-琼盆地高压成因输导体系特征、识别及其成藏过程[J]. 石油与天然气地质, 2018, 39(2):254-267. doi: 10.11743/ogg20180205 FAN Caiwei. The identification and characteristics of migration system induced by high pressure, and its hydrocarbon accumulation process in the Yingqiong Basin[J]. Oil & Gas Geology, 2018, 39(2): 254-267. doi: 10.11743/ogg20180205 [3] 谢玉洪, 张勇, 黄凯文. 莺琼盆地高温高压钻井技术[M]. 北京: 石油工业出版社, 2016. XIE Yuhong, ZHANG Yong, HUANG Kaiwen. High temperature and pressure drilling technology in Yingqiong Basin[M]. Beijing: Petroleum Industry Press, 2016. [4] 李文拓, 李中, 吴涛, 等. 海上高温高压地层孔隙压力预测方法研究[J]. 重庆科技学院学报(自然科学版), 2020, 22(2):5-9. doi: 10.19406/j.cnki.cqkjxyxbzkb.2020.02.003 LI Wentuo, LI Zhong, WU Tao, et al. Study on pore pressure prediction method in the offshore high temperature and high pressure formation[J]. Journal of Chongqing University of Science and Technology (Natural Sciences Edition), 2020, 22(2): 5-9. doi: 10.19406/j.cnki.cqkjxyxbzkb.2020.02.003 [5] DICKINSON G. Geological aspects of abnormal reservoir pressure in Gulf Coast Louisiana[J]. AAPG Bulletin, 1953, 37(2): 410-432. doi: 10.1306/5CEADC6B-16BB-11D7-8645000102C1865D [6] FERTL W H. Abnormal formation pressures[M]. New York: Elsevier Scientific Publishing Company, 1976: 49-96. [7] BOWERS G L. Pore pressure estimation from velocity data: accounting for overpressure mechanism besides under compaction[J]. SPE Drilling & Completion, 1995, 10(2): 89-95. doi: 10.2118/27488-PA [8] CHILINGAR G V, SEREBRYAKOV V A, ROBERTSON J O. Origin and prediction of abnormal formation pressures[M]. New York: Elsevier, 2002: 21-64. [9] KESARWANI A, MALHOTRA A, AGARAWL V. Pore pressure: Causes, methods of determination and their limitations[C]//10th Biennial International Conference & Exposition, November 2013, Kochi, India. [10] 赵靖舟, 李军, 徐泽阳. 沉积盆地超压成因研究进展[J]. 石油学报, 2017, 38(9):973-998. doi: 10.7623/syxb201709001 ZHAO Jingzhou, LI Jun, XU Zeyang. Advances in the origin of overpressures in sedimentary basins[J]. Acta Petrolei Sinica, 2017, 38(9): 973-998. doi: 10.7623/syxb201709001 [11] 刘文超, 叶加仁, 雷闯, 等. 琼东南盆地乐东凹陷烃源岩热史及成熟史模拟[J]. 地质科技情报, 2011, 30(6):110-115. doi: 10.3969/j.issn.1000-7849.2011.06.016 LIU Wenchao, YE Jiaren, LEI Chuang, et al. Geothermal and maturation histories modeling of the source rocks in the Ledong sag, Southeast of Qiong Basin[J]. Geological Science and Technology Information, 2011, 30(6): 110-115. doi: 10.3969/j.issn.1000-7849.2011.06.016 [12] 张道军, 王亚辉, 赵鹏肖, 等. 南海北部莺-琼盆地轴向水道沉积特征及成因演化[J]. 中国海上油气, 2015, 27(3):46-53. doi: 10.11935/j.issn.1673-1506.2015.03.007 ZHANG Daojun, WANG Yahui, ZHAO Pengxiao, et al. Sedimentary characteristics and genetic evolution of axial channels in Ying-Qiong basin, northern South China Sea[J]. China Offshore Oil and Gas, 2015, 27(3): 46-53. doi: 10.11935/j.issn.1673-1506.2015.03.007 [13] 赖冬. 莺歌海盆地底辟构造特征及其油气意义: 基于构造物理模拟分析[D]. 成都: 成都理工大学, 2019. LAI Dong. Geometry and kinematics of diapir and its implication in the Yinggehai Basin: Insights from analogue experiments[D]. Chengdu: Chengdu University of Technology. [14] BARKER C. Aquathermal pressuring-role of temperature in development of abnormal-pressure zones[J]. AAPG Bulletin, 1972, 56(10): 2068-2071. doi: 10.1306/819A41B0-16C5-11D7-8645000102C1865D [15] EATON B A. The effect of overburden stress on geopressure prediction from well Logs[J]. Journal of Petroleum Technology, 1972, 24(8): 929-934. doi: 10.2118/3719-PA [16] HAN D H, NUR A, MORGAN D. Effects of porosity and clay content on wave velocities in sandstones[J]. Geophysics, 1986, 51(11): 2093-2107. doi: 10.1190/1.1442062 [17] EBERHART-PHILLIPS E, HAN D H, ZOBACK M D. Empirical relationships among seismic velocity, effective pressure, porosity, and clay content in sandstone[J]. Geophysics, 1989, 54(1): 82-89. doi: 10.1190/1.1442580 [18] SAYERS C M, SMIT T J H, VAN EDEN C, et al. Use of reflection tomography to predict pore pressure in overpressured reservoir sands[C]//SEG Technical Program Expanded Abstracts 2003. 2003: 1362-1365. DOI: 10.1190/1.1817541. [19] 王贵文, 郭荣坤. 测井地质学[M]. 北京: 石油工业出版社, 2000. WANG Guiwen, GUO Rongkun. Well logging Geology[M]. Beijing: Petroleum Industry Press, 2000.