Research and Application of New Methods to Oil-Gas Geochemical Exploration

692VoL.74No3ACTA GEOLOGICA SINICASept. 2000Research and application of New Methods toOil-Gas Geochemical ExplorationChEn Yuanrong and JIA GI1gGuilin Research Institute of Geology for Mineral resources,2 Fuxing Rd, Guilin 541004, GuangxiAbstract Based on the results of researches and applications for many years, it has been discovered that newmethods and techniques for geochemical exploration of oil and gas such as AC, altered carbonate, Hg in absorptionphase, Ks, Fe, 8C, fluorescence in two and three dimensions, and N, and O, in heat release can give full play inthe following five fields: (1)optimization of the favourable target or hollow zones and structural zones in a region; (2)evaluation of oil traps and delineation of prospective oil and gas areas; (3)prediction of deep-seated oil-bearing horzons; (4)evaluation of the genesis of oil and gas geochemical anomalies and determination of the types of oil and gasaccumulations; (5) forecast of the burial depths of oil and gas poolsKey words: geochemical exploration for oil and gas, new method, field of application1 Introductiontion phase, Ks and Fel+ among hollow zones andstructural zones in regional cross sections some aOil-gas geochemical exploration, as a non-seismic vantageous target or hollow zones and structural zonesexploration technique, has aroused great interest to can be selectedpetroleum geologists for its advantages of rapidness, For example, the Linqing depression, located westeffectiveness and economy, and has been arranged in of the Shengli oil field with an area of 18,000 kmrthe procedure of regional oil and gas reconnaissance consists of 18 second-order structural units(6 holloand exploration by many countries Ci et al., 1994; units, 9 structural zones and 3 raised units, see Fig. 1)Zhao Yongjun, 1994). After having studied its appli- Since 1958, many geologic and seismic surveys andcations to more than sixty districts of thirteen petrolilmore than 30 exploratory wells have been finished inerous basins ( Du et al., 1998; Zhao Changyi et al., that region by Shengli Petroleum Administrative Bl1998: Zhao Wenzhi et al., 1999; Zhou Jingao et al., reau. But, a great breakthrough has not been made1999), it was discovered that new geochemical because of the complexity of tectonics, the variabilitymethods such as AC and Hg in absorption phase, Ks, and small size of trap structures and reservoirs. So, weFe+, 8C, fluorescence in two and three dimensions, decided to carry out a regional oil-gas geeand n2 and O, in heat release can give full play to the exploration in that region in 1993. The results arefollowing fields of oil and gas explorationshown in Tables I and 2. The comprehensive evaluation is based on the geochemical and geologic indic a2 Optimization of Advantageous Target or tors. values of the former are obtained by normaliza-Hollow Zones and structural Zones in a tion of the variation characters of the component aver-Regionage content, variance, anomaly percentage and average contrast: those of the latter are based on the areaIn some poorly studied basins or large depressions, of the hollow zones, thickness of the dark-colouredfter comparisons with the average content, deviation, mudstones and maximum burial depths of the majorpercent anomaly and average contrast of different source rocks. It is clear from the tables that(1) basedindicators of hydrocarbons, AC and Hg in the absoon geochemicH出中国煤化工 six hollowNMHGVol. 74 No. 3ACTA GEOLOGICA SINICASept, 2000693Ningjin Countye ShangheLuxi uplZouping CountyX First-order faultSecond-order fault G Area of studyknOwn oil fieldL Regional sectionFig. 1. Structural sketch map of the Linqing-Yangxin area of Shandong province in ChinaO Bixuedian structural zone; 2 Denan-Kongzhuang hollow zone; 6 Huanglukou structural zone: Encheng structural zone; G Wunan-Linginlow zone; Yaozhan-Suji hollow zone; Xiaozhuang structural zone: 6 Dachengzhuang structural zone: Xujiayingzi structural zone; XiajinGuanxian hollow zone; 11 Guanxian structural zone; 12 Gaotang-Tangyi buried hill zone: 13 Tangyi structural zone: 14 Shenzhuang-Liangshuizhen hollowzone, 15 Jiangdian structural zone: 16 Yucheng-Yangguantun hollow zone: 17 Anren structural zoneunits of the Linqing depression, the Wunan-Linqing Therefore, this district is believed to be the best areaand Xiajin-Guanxian hollow zones have higher scores, for oil and gas accumulation in the linqing depressionthe next is the Yucheng-Yangguantun hollow zone.(2) Petroleum geologists were greatly interested and carIn the Xiakou area which has known oil and gas fields, ried out, regional geochemical reconnaissance in thatall indicators of hydrocarbons or non-hydrocarbons district during 1994 to 1995. Consequently, three largehave higher scores, but the indicators of hydrocarbons prospects were delineated, which are located in thehave higher scores and those of non-hydrocarbons Baimahu area in the northwest part of the Xujiayingzihave lower scores in the area of oil reservoirs of the structural zone and around Linqing City in the centralWells De-1 and Jia-2. This means that the score of west part. In recent years, the exploration departmenthydrocarbons indicator should be taken as thwas arranging detailed three-dimensional seismicfactor in evaluating the favourable structural zones in prospecting in these prospect areas, and there is thethat region. (3)Among the structural zones, those with hope to make great a breakthrough for oil and gashigher scores of hydrocarbons indicators are: the exploration in the Linqing depressionGaotang-Tangyi buried-hill zone, the East Guanxianfault structural zone, and the Encheng, Xujiayingzi 3 Evaluation of Oil Traps and Determina-and Bixuedian structural zones. But spatially, the bettion of Prospective Oil and Gas areaster hollow zones and structural zones that are borderng on each other and can constitute a favourable This work has been conducted extensively both atsource-reservoir caprock association are the Wunan- home and abroad. But because of the differences inLinqing hollow zone and Xujiayingzi structural zone. the indicators,中国煤化工CNMHGVolACTA GEOLOGICA SINICATable 1 Comprehensive evaluation results of different hollow zones of the linqing depressionGeochemical indicatorGeologic indicatorSynthetic scoreHNHH+NHBasic valueScoreunan-Linqing81.04Xiajin-GuanxianDenan- KongzhuangYaozhan- Suji63.3429.8546.6038.7433.0371770.881Notes: H-hydrocarbons score, NH-non-hydrocarbons score.Table 2 Comprehensive evaluation results of second-order structural units of the linqing depres-Name of second-order structural unitsH+NH69.6846.4326.527295Bixuedian42.0529,427147East GuanXian fault47.81Chengzhuang30.8124.645545Gaotang-Tangyi buried hill49.1573.1Guantao rise38.2367.4l378584.71Oil pool of Well De-21465.17Notes: H-hydrocarbons score, NH-non-hydrocarbons scoreand evaluation procedures used by different countries of wells to testify those geochemical prospective areasor research teams, and their different understanding to and a large gas-field has been discovered in baithe genesis of the anomalies and the relationship be- mamiai, which has natural gas reserves of 338x10'mtween different indicators, the evaluation effects are in deep level and 245.01x10'min shallow layers invariedn area of 80 kmAfter many years of practice, we believe that theoil-gas-bearing structures, traps and prospective areas 4 Predication of Deep-seated Oil-bearingcan be determined on the basis of synthetic anomaly Horizonspatterns of different types of oil and gas pools and byanalyzing the anomalous characteristics of different Researches in this field are few. After studies of manyindicators, the linear correlation among hydrocarbon years, we have found that it is possible to prognosticomponents, the upward and downward relationship cate deep-seated oil-bearing horizons based on ana-between hydrocarbons and AC(derived carbonate) lyzing the characteristics of different components orand by comparing the anomaly patternsindicators (including concentrations and various ratiosFor instance, in the Baimamiao region of Sichuan of vertical sections of drill holes and comparing thebasin, some good geochemical anomalies of oil andnomal patgas have been discovered by geochemical explorationFor example, we consider that there are gas-bearinAfter evaluation of these anomalies by using the formations both in the Penglaizhen Formation in theabove-mentioned method, we believed these anomaly- upper part of the hole and in the Shaximiao Formationes were caused by underground oil-gas accumulation in the lower part after making analysis of the variationand defined the prospective areas of oil and gas. Since of different indicators of Weluan1995, the exploration department has drilled a number basin. The resu…f:a灬…- conclusions中国煤化工CNMHGNew Methods of Oil-Gas Geochemical explorationChen yuanrong and Jia695In the Penglaizhen Group(at depths of 800-1034 m)a mining the genesis of hydrocarbons, it is necessary tocommercial gas flow of 2.410* m per day was d- compare with the classic 8C values of hydrocarbonstained and in the Shaximiao Group (at depths of of different geneses, but it is more important to com2200-2400 m) good commercial gas flow was found. pare with the 8C values of known oil fields in thesame basin or similar regions5 Evaluation of oil-Gas geochemical(3) Three-dimensional fluorescence spectrumAnomaly Genesis and Definition of Oil-Gas analysPool TypesThe three-dimensional fluorescence spectrum analysis is a new technique developed in the 1980s, whi-This work is a key step for oil and gas geochemical ch is used to detect aromatic hydrocarbons. The aro-exploration. Its goal is to sift out the anomaly infor- matic hydrocarbons are one of the main constituentsmation concerned with oil-gas pools, distinguish and of oil. Their contents in oil-gas pools are the secondreject useless interfering anomalies, and make clear highest, only next to those of paraffin alkane andthe distribution of oil and gas and to provide reliable nepthene. Aromatic hydrocarbons and their deriva-geochemical base for oil and gas explorationtions have a large t link, and the three-dimensionalThe following techniques have been usedfluorescence spectrum can detect it easily. The con-(1) Linear correlation analysis of hydrocarbon con- stituents of tested samples can be shown by an iso-gram consisting of Ex (excitation wavelength), EmAs a direct index to indicate oil-gas pools--the(emission wavelength) and fluorescence intensity, orconstituents of hydrocarbon compounds have the described digitally in a qualitative and quantitativeclosest relationship with oil-gas pools. The constitu- way. The finger-print-like maps of three-dimensionalents of hydrocarbon compounds which came from oil- fluorescence are varied because of the difference ingas pools, although quite different in content, have genesis and genetic type of aromatic hydrocarbons ofundergone the same process of geology and evolution different samples. This technique can be used to comhen they accumulated to form an oil-gas pool, mi- pare oil and oil, oil and source rock, oil and coal, oilgrated to the surface and dispersed to the wall rocks. and pollution, and to determine the genesis of geochemical anomalies, According to the research ofship among these constituents an obvious linear cor- Yong Kelan(1992), the following conclusions may berelation. If there are some gases from other sources drawn: a) The main peaks of Ex and Em of crude oil(such as from coal, biological degradation and artif i- vary around 228 nm and 340 nm respectively. Thecial pollution) to enter, the original relationship would main peaks of Ex and Em of the surface samples(soilbe broken, the linear correlation would be weakened, or rock)which are distributed in the range affected byor even lost. Therefore, the genesis of oil-gas geo- underground oil reservoirs are slightly smaller thanchemical anomalies can be determined by using this that of crude oil. The disparity is commonly <10 nmtechniquThe finger-print-like maps are mainly of the Q type,(2) Isotope analysis of methanesometimes the O type. b)For the surface samplesBecause of the isotopic fractionation of carbon, the which are affected by the activity of oil-gas migration8C values are varied for the oil and gas of different the main peaks of Ex and Em are also relatively smalgenetic types and different development periods. Thus but their finger-print-like maps usually show the bthe isotope analysis of methane has been widely used type. c) The finger-print-like maps of coal and itsto determine the genesis of hydrocarbonsconnected samples are of the P type. d) To some indi-It needs to point out that the conditions of sourcevidual polluted districts or samples, the main peaksreservoir-caprocks association and the surface geusually show great deviation, or even scatter everychemical background of different basins are varied, where without any fixed finger-print-like mapsand so are the isotopic composition and isotopic e(4)Analysis of anomaly patternchange reactions of carbon Therefore. when deter-tures of hydro-中国煤化工CNMHG696Vol. 74 No. 3ACTA GEOLOGICA SINICASept. 2000carbons and their associated elements the characterisics of reservoirs and caprocks and the migration and referencesdiffusion styles of different elements in different types Chen Yuanrong, 1992. Composite geochemical anomaly pat-tern of oil (gas)reservoirs Geology and Prospecting, 28(11):re various. After studies of many years, it is discov38-44(in Chinese)ered that: a) The geochemical patterns for oil-gasDu Deli, Zeng Weijun and Wu Nengyou, 1998. Type and hydrocarbon potentials of Meso-Cenozoic basins in the Southpools where oil is dominant are characterized by thea seanding areas. Geological Review,following Zonation: the Hg anomaly shows a massive44(1): 580-589 (in Chinese with English abstract)shape at the top position (inner zone); anomalies of Li Hanlin, Zhao Yongjun and Zha Ming, 1994. Statistical clashydrocarbons AC, Ks and Fet are distributed at thefication and optimization for indexes of oil and gas surfacperiphery in bay-shaped or ring-like forms. b)Overgeochemical exploration. Geological Review, 40(sup.the lithologic oil-gas pools or those dominated by ga33-45 (in Chinese with English abstract)Yong Kelan, 1992. The application of three-dimensional fltthe anomalies of all indicators (including Hg) are rinrescence spectrum analysis in oil geochemical explorationshaped and distributed at the periphery. c)Over thePetroleum Experiment and Geology, 14(4)(In Chinese)gas accumulations, the anomalies of different indic a- Zhao Changyi, Du Meilin, Shao Longyi et al., 1998. Types oftors often show an"apical ring"pattern, i.e., theseorganic facies and source rock assessment of the coal-anomalies are distributed at the periphery to form ameaure mudstone in the Turpan-Hami basin. Acta Geologiring-shaped zone and also occur in the apical positionSinica(English Edition), 72(2): 169-1Zhao Wenzhi, He Dengfa, Song Yan and Jin Jiuqiang, 1999(5)Prediction of burial depths of oil and gas poolsFundamental characteristics of petroleum geology of majorThis work is very difficult and there are few reportson-land petroleum-bearing basins in China. Geological Reabout it at home and abroad. After tests for years, it isview, 45(3): 232-240 (in Chinese with English abstract)discovered that the special element technique is one of Zhao Yongjun, Li Hanlin and Zha Ming, 1994. Probabilitythe good methods to solve this technical problemdiscriminant and treatment for distorted data of oil/gas sur-The basic procedure is as follows: First, make aface geochemical exploration. Geological Review, 40(sup.8-83 (in Chinese with English abstract)multH-component analysis of the various strata in the Zhou Jingao, Zhao Zongju and Deng Hongying,1999.Tectonicarea. Second, select the constituents or elementsolution of the Hefei basin and analysis of its pertroleumwhich can migrate to the surface, and become specialpotential. Acta Geologica Sinica, 73(1): 15-24(in Chinesefor a reservoir or are obviously higher in content atwith English abstract)one stratum against other strata. third, use a suitablemethod and technique to detect the content of these About the first authorspecial elements in the surface soil. Fourth, forecast Chen Yuanrong Born in 1903, graduated from thethe burial depth of oil-gas pools by analyzing and Department of Geochemistry, Guilin College of Geol-comparing the characteristics of those special ele-ogy in 1983; received his masters degree in geo-lents. For instance, in the baimamiao region of thechemistry from the China University of GeosciencesSichuan basin, H in heat release is the special elementin 1988; presently studying for doctors degree in theof the deep-seated Xujiahe Formation, whereas O, andCentral-South China University of Technology; andN2 in heat release are the special elements of the now serving as a senior geochemist in the ResearchShaximiao Formation at a medium-deep levelInstitute of Geology for Mineral ResourcesManuscript received Jan 2000edited by Zhou Jian and zhu xiling中国煤化工CNMHG