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火成岩储层及其研究方法
长期以来,在石油、天然气勘探开发中,与沉积岩相关的油气圈闭一直是勘探开发研究的重点,而沉积盆地中的与火山岩相关的油气圈闭却一直没有引起足够的重视. 近年来,随着油气勘探的不断发展,在美国、阿根廷、墨西哥、俄罗斯、印度尼西亚以及我国东部、新疆北部等地与火山岩相关的油气藏相继被大量发现,与火山岩相关的油气藏已经成为了新的油气储量增长点,因此,与火山岩相关的油气藏已引起了石油地质学界的越来越广泛的关注.
火山岩是地球深部物质在一定的物化条件下部分熔融后上升到地表或近地表冷凝后而成的岩石,是板块运动的产物,在盆地的各个阶段都有火山作用的活动,其和盆地的演化,圈闭的形成以及油气的生成、运移等有着密切的联系。作为地球深部物质向上运动的产物,岩浆具有高温(700-12000C)、粘稠、富含挥发组分（CO2, CH4,NH3,H2,HCl,HF,H2S,SO2,P2O5和H2O等）和Ni、Co、Cu、Mn、Zn、Ti和V等矿物质的特点,其不论是侵入到地壳深部地层或近地表地层，还是喷发出或溢出到地表，都会对周缘地层岩石的储集性能、岩石中的有机质成熟度及烃类的分布、演化产生重大的影响，可形成一系列与火成岩相关的油气藏，此外，火成岩本身的原生孔隙、受后期后生作用改造形成的次生孔隙等会使部分火成岩具有良好的储渗性能，形成以火成岩为储层的油气藏。火成岩油气藏具有初始产量高但递减快，分布广但规模较小、储层岩相、岩性变化快，储集类型和成藏条件复杂等特点,这些都对与火成岩相关的油气藏的勘探开发研究造成了一定的困难。近年来，随着对火成岩油气藏勘探工作的不断开展和深入，火成岩对与其接触的地层岩石的储集性能、岩石中的有机质成熟度及烃类的分布、演化的影响、火成岩储层的类型、储集性能、储层潜力及其分布规律、与火成岩相关圈闭的成藏模式、类型、特点、分布规律等逐渐被了解，与火成岩相关的油气藏研究的研究方法也日趋成熟。本文总结了火成岩相关油气藏的储层类型以及火山岩储层的相关研究方法。
1、火成岩储层的储集空间类型及其演化
按照火成岩储集空间的形成机理，其可分为原生储集空间和次生储集空间。原生储集空间主要有岩浆侵位时冷却结晶或喷出地表迅速冷却时所形成的晶内/晶间孔隙、粒间孔隙、气孔、矿物炸裂纹、解理缝隙和冷却收缩裂缝等；次生空隙主要包括断裂改造、构造抬升、风化淋滤、蚀变溶蚀或深埋溶蚀、交代作用形成的次生溶蚀空隙、构造裂缝、风化裂缝、晶间/晶内/粒间孔隙等。
火山岩储集空间的形成和演化可经过以下几个阶段:
（1）原生储集孔隙形成阶段。侵入岩冷却结晶形成各种晶间/晶内/粒间空隙或火山物质喷溢至地表形成气孔、冷凝收缩缝和火山角砾间孔隙等。
（2）浅埋阶段和/或抬升剥蚀阶段遭受的风化淋滤作用。由于大气降水的淋滤溶蚀,产生大量溶蚀孔、洞、缝。
（3）遭受构造断裂阶段。构造应力作用的结果,使火成岩体发育了较大规模的断层,与断层伴生的是产生大量构造裂缝。
（4）深埋阶段各种酸性流体的溶蚀作用。这些酸性流体包括在油气侵位过程中有机质脱羧产生的大量有机酸溶液和由矿物间的相互作用产生的无机酸溶液。在这些流体的作用下,火山岩中的部分物质发生溶解,形成一些深部溶蚀孔、洞、缝,同时另外一些化学物质可能发生沉淀充填孔隙。
（5） 随着油气成熟,在断层或不整合面等输导层的作用下,油气运移到火山岩储层中去,从而进入油气成藏阶段。
2、火成岩储层的类型及其评价
从火成岩的成因角度，火成岩储层可分为两大类：侵入岩型储层和火山岩型储层。侵入岩型储层再根据其相应的岩石分类方案分为超基性岩型、基性岩型、中性岩型、酸性岩型或橄榄岩、辉长岩、闪长岩、花岗岩及其过渡类型；火山岩储层可根据其成因分为火山熔岩型、火山碎屑岩型和火山碎屑沉积岩型（应属沉积岩范畴），或根据其岩相分为火山通道相、侵出相、喷溢相、爆发相、爆发沉积相、沉火山岩相。火山熔岩型再根据其SiO2含量分为苦橄岩型、玄武岩型、安山岩型、流纹岩型及其中间的过渡类型。目前在各油田比较常用的分类方法是按火成岩岩性进行分类。
不同岩性的火成岩在一定的条件下均可以做储层，如辽河盆地驾掌寺地区的辉绿岩作储层的油气藏，苏北闵桥地区的玄武岩作储层的油气藏，松辽盆地南部安山岩作储层的油气藏，松辽盆地流纹岩、英安岩、流纹质熔结凝灰岩、火山角砾岩作储层的油气藏等。火成岩储集层的储集物性主要取决于火山岩的岩性、岩相、储集空间、物性等几项指标。一般说来，火山岩的储集物性要优于侵入岩的；酸性火山岩的储集物性要优于中性岩的，基性岩的相对较差；处于火山斜坡位置的爆发空落相、火山碎屑流相、溢流相是储集物性较好的相带，流纹岩、熔结凝灰岩、流纹质火山角砾岩、英安岩等酸性火山岩具有较好的储集物性。
3、火成岩储层的研究内容和方法
松辽盆地、准噶尔盆地、渤海湾盆地等地的火成岩油气藏勘探实践表明，火成岩储层的储渗性能和火成岩的岩性、岩相密切相关。一般说来流纹岩、英安岩、流纹质、英安质熔结凝灰岩、流纹质、英安质火山角砾岩等酸性火山岩的储渗性能较好，火山斜坡位置的爆发相、溢流相上部是有利储层发育的有利位置，因此，研究火成岩的分布、识别其岩性、岩相、分析其储渗性能等就成了火成岩油气藏勘探的基本内容。然而，近年来的火成岩勘探实践表明，火成岩储层一般都埋藏比较深，在纵向上、横向上变化快，岩性、岩相变化快，成藏条件、成藏模式比较复杂，这给勘探造成了一定的困难，利用传统的研究方法或单一的地球物理勘探方法来研究火成岩满足不了现今火成岩勘探的需求。
笔者通过对近年来火成岩油气藏勘探实践的总结，归纳了目前油气勘探中火成岩的主要研究方法与手段。
相对沉积岩而言，火成岩具有地震波速度高、地震波吸收能量大、密度高、磁化率高、电阻率大的特点，不同火成岩的地球物理特征存在差异，这为利用重、磁、电、震和地球物理测井等地球物理勘探方法来综合研究火成岩相关的油气藏提供了地球物理依据。另外，火成岩的喷发方式、岩性、岩相组合等与构造密切相关，利用传统的火成岩研究方法，结合地球物理勘探来研究火山岩可减少地球物理勘探研究的多解性。而近年来的勘探实践也表明，综合勘探的方法是在现今条件下研究火成岩的有效手段。
利用综合方法研究火成岩的具体步骤如下:
1) 首先，通过分析地表出露的火山岩或者分析钻井的连井剖面，了解火成岩的大致发育情况，包括火山岩的时代、喷发的大致旋回和期次，主要的岩性、岩相组合特征、大致火山机构类型等；
2) 分析火成岩及其围岩的物性特征，包括密度、磁化率、电阻率、声波时差、波阻抗等，这是地球物理勘探的基础；
3) 分析各钻井钻遇的火成岩及围岩与各重磁电震地球物理异常的对应关系，建立它们的内在联系，建立一套解释依据；
4) 利用磁力异常圈定火成岩的分布范围。相对其它地球物理方法而言，火成岩对磁力反应最灵敏，因此可利用磁力异常大致圈定火成岩的分布范围。
5) 根据重力、磁力、电法、地震资料，利用解释依据，初步解释火成岩的岩性、岩相；
6) 利用地震资料，结合重磁电资料，在纵横向上对火成岩的岩性、岩相、分布等进行近一步研究；
7) 分析断裂和火成岩发育特征的关系；
8) 根据钻井、露头资料，综合解释的火成岩的岩性、岩相成果，以及断裂和火成岩的关系等，分析火成岩的成因、构造环境、演化特征、时空分布规律等，并以此近一步指导重磁电震资料的解释；
9) 利用重磁电震联合反演软件，综合解释、完善相关成果；
10) 根据解释的岩性、岩相、与构造的关系以及其它石油地质条件，优选有利勘探目标。
此外，还可借助火成岩岩石学、矿物学、岩相学、地球化学和年代学等来辅助研究。
4、结论
松辽盆地、准噶尔盆地、渤海湾盆地等地的火成岩油气藏勘探成果表明，火成岩油气藏已经成为了新的油气储量增长点, 火成岩相关油气藏的勘探日益引起了石油地质学界月来越广泛的关注。.
火成岩储层的类型众多，分类方法不一，如可按岩相划分或按岩性划分，目前按火成岩的岩性划分得到了石油地质学界的较广泛的认同。火成岩储层的储集空间可分为原生储集空间和次生储集空间，其中后期构造作用形成的裂缝和风化作用形成的孔隙是火成岩储层的主要储渗空间。
一般说来，火山斜坡位置的爆发空落相、火山碎屑流相、溢流相的上部的酸性岩如流文岩、英安岩、酸性的熔结凝灰岩、火山角砾岩等的储渗性能较好，是勘探的有利目标。
综合利用重力、磁力、电法、地震、测井等地球物理方法，结合火成岩地质学等来综合研究火成岩是解决油气勘探中的火成岩问题的有效方法。
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陈岩,1998.克拉玛依油田一区石炭系火山岩油藏剖析[J].新疆石油地质,1988 ,9(1):17-31
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高印军,郭春东,余忠等.综合解释技术在孔南地区火成岩油藏研究中的应用[J].石油勘探与开发,2000 27(3):81-83.
段志斌,火成岩油藏油气来源及火山活动对油气影响的探讨.石油技术, 1990.(3):36-43.
熊寿生,卢培德,火山喷溢—喷流活动与半无机成因天然气的形成和类型.石油实验地质, 1996.18(1):13-26.
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野人把这篇附到这来啦，^_^
Comprehensive Application of Geophysical Techniques to Igneous Rock Study
Comprehensive Application of Geophysical Techniques to Igneous Rock Study
Summary
Presently, the igneous reservoir has become a new exploration target for hydrocarbon reserves and increased more and more attention from worldwide petroleum and geology experts. The concept of comprehensive application of different geophysical techniques can provide a new and effective approach for igneous reservoir detection and delimitation since it advocates the principle of solving problem by combining multi-technique and comprehensive interpretation.
Comprehensive application of gravity and magnetic data, electric data and seismic data provides a platform for jointed data processing and interpretation, consequently, reduces the interpretation ambiguity, and enhances the ability for special geological body study such as igneous rock distribution and lithology identification. The concept made the research on igneous rock in several large basins in west China extremely successful
Key words: comprehensive geophysical techniques，igneous rock，oil and gas reservoir
Introduction
With the development of hydrocarbon exploration, the exploration on tectonic reservoir, clasolite reservoir and carbonate reservoir become more difficult and of higher risk. In resent years, many igneous rock-related hydrocarbon reservoirs were discovered such as in Pohaibay Basin, Songliao Basin, Junggar Basin and Tarim Basin of China, and in foreign countries such as U.S.A, Argentina, Mexico and Russia. Igneous-related reservoir has become a new target for hydrocarbon reserves. So, more and more attention has been focused on study of igneous-related reservoir.
Igneous reservoirs widely exist, the lithofacies and lithology of reservoir beds changes frequently and their accumulation pattern and development environment are complex (Du Xianyue etc., 1998).All these make the exploration upon this kind of reservoir more difficult. Igneous rock was featured by high density, high susceptibility, high resistivity, low sonic differential time, high seismic-wave velocity and high absorption rate of seismic wave energy. All the features or natures are the geophysical bases of comprehensive application of different kinds of geophysical techniques, such as gravity and magnetic technique, electrical technique, seismic technique and logging technique, for igneous-related reservoir study.
Case study
Exploration challenge
The survey area is located at a large basin in the west of China. All survey work there indicated that only medium-to-acid igneous rock can be the effective reservoir beds as carboniferous basement. April 2004, well DX10 on anticline DX1 produce high hydrocarbon output with gas output of 15.25×108m3/d and condensate 3.47t/d. The drilling result discovered the potential of hydrocarbon accumulation in acid carboniferous igneous rock. But the subsequently drilled well D101 adjacent to well DX10 met no the similar acid igneous horizon and failed. All these verified that igneous rock distribution and its lithology is complex. Further more, seismic reflection data regarding horizons below Permian are bad. To accurately identify lithofacies and lithology and improve the success rate of igneous reservoir exploration, high precision gravity and magnetic survey (500×500m) and artificial source electrical survey were deployed in the area.
Geophysical natures
Basic igneous rock has higher density than acid one. Compared with normal clasolite, some carboniferous rock such as diabase and balsalt has higher density, whereas some other such as andicite, dacite and tuff has lower density. Generally, susceptibility of normal clasolite is lower than 50×10-5SI. Andesite and dacite have the average susceptibility about 200×10-5SI, whereas diabase and basalt has higher susceptibility and the average susceptibility of diabase may be higher than 800×10-5SI. The carboniferous rocks with decreasing susceptibility are sequenced by: medium-to-basic rock, volcanic breccia, andesite, dacite, tuff, sand gravel and mud rock.
Based on statistic resistivity upon electrical logging data of drilled wells meeting igneous rocks in the area, it is indicated that igneous rock is generally of high resistivity, but different kind of igneous rock has different density. Usually, basalt has high resistivity of from 700 to 2000Ω•m, andesite has the relatively low resistivity of 100-300Ω.m, rhyolite and diabase have stable resistivity of 100-200Ω.m and volcanic breccia and volcanic clasolite have relatively high resistivity of several decadesΩ•m. In the area, among all igneous rocks, basalt has highest resitivity, the sub-high are andesite, rhyolite, diabase and volcanic breccia, the lowest is tuff.
Data processing and interpretation procedure
1. To extract gravity and magnetic anomalies, which can be used to study lithology variation of carboniferous basement Firstly, calculate the gravity response of all density layers above carboniferous layer based on seismic and logging data respectively, Then subtract the response of all overburden layers from total field, and perform low-pass filter to the remained field to get rid of regional background response, and consequently the gravity anomaly reflecting carboniferous lithology can be obtained (figure 1).
Induced magnetic anomaly, residual magnetic anomaly, the first vertical derivative of magnetic field and the second vertical derivative of magnetic field can reflect the different features of carboniferous and magnetic bodies in deep basement respectively. Thereinto, compared with residual magnetic anomaly, the second vertical derivative of magnetic field (figure 2) can indicate striped anomaly more clearly and indicate igneous boundary more accurately which are matched well with logging result.
2. To interpret lithology and lithofacies based on correlation analysis
Figure 3 is the correlation analysis map of rock density and susceptibility. From the figure, we can see that there are four main basement lithology zones and the four zones are also clearly indicated in the overlaied map of gravity anomaly map and magnetic anomaly map by four gravity-magnetic anomaly combination zones(figure 4), such as the combination of gravity high and magnetic high in which medium-to-basic rock featured. Based on the anomaly combination, the survey area is divided into four lithology-based zones including clasolite zone, medium-to-acid rock zone, medium-to-basic rock zone, and typical tuff zone.
3. To map igneous boundary based on comprehensive inversion
The primary model can be constructed based on structural information from seismic interpretation and igneous boundary information indicated by high resistivity area on electric profile. Then perform forward calculation of gravity and magnetic anomaly to the model and modify the model iteratively. The final inversion result constrained by several known information can best reflect the true subsurface distribution and can accurately describe the vertical and horizontal boundary of igneous rock.
Comprehensive interpretation result
Based on all the foresaid work, basement lithology and lithofacies are predicted as figure 6. About igneous facies distribution, explosion facies are widely developed and distributed mainly on the heave DN in centre of survey area, clasolite facies is most developed in the area, the area of overflow facies is only inferior to clasolite facies, and intrusion facies, developed least, distribute scatteredly and it mainly includes granite and diabase. Favorable area of igneous basement reservoir is predicted based on the predicted lithology distribution and interpreted structures.
Result analysis
Based on the analysis to the lithology and lithofacies differences upon basement between well DX10 and well D101, the failure of well D101 is interpreted. A newly drilled well DX11 was planned in the predicted tuff zone and the well met tuff at the upper carboniferous formation as the expected. The well verified the prediction to igneous lithology zones based on the comprehensive application of different geophysical techniques.
Conclusions
The comprehensive application of gravity and magnetic technique, electric technique and seismic technique is a powerful and feasible approach to study igneous-related geological problem. Thereinto, magnetic technique is necessary for igneous study, the combination of gravity and magnetic techniques can predict igneous lithology, TMD(Long Offset Transient Electromagnetic method) technique have high vertical and horizontal resolution to igneous rock since its result matches well with drilled well. Seismic data can assist to estimate igneous distribution and identify lithology.
The basic steps to solve the igneous rock-related problem are described as:
1. To analyze the physical property of igneous rock with different lithology and its host.
2. To delimit igneous rock based on magnetic data which is most sensitive to igneous rock.
3. To perform correlativity analysis mainly to magnetic data and gravity data and identify lithology and lithofacies by using known drilling data and seismic data, etc..
4. To construct primary model based on igneous information provided by electric data and perform constrained inversion to map vertical and horizontal boundaries of igneous rock. Presently, the comprehensive application of gravity, magnetic, electric, and seismic data has become a new concept to solve geological problems with the adoption of jointed processing and interpretation techniques for hydrocarbon exploration. |
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发表于 2006-8-28 01:15:39
发表于 2006-8-28 05:17:34
