New Progress in High-Precision and High-Resolution Seismic Exploration Technique in Coal Industry of

Vol. 74 No. 2ACTA GEOLOGICA SINICAJune 2000New Progress in High-Precision and High-Resolution SeismicExploration Technique in Coal Industry of ChinaNi BinChina National Administration of Coal Geology, Beijing 100024Abstract In the past twenty years, the proportion of coal in primary-energy consumption in China is generally between71.3% and 76.5%. The output of coal was 1.374 billion tons in 1996, and 1.21 tons in 1998, which ranked first in the worldNow coal is mined mainly with mechanization in China, which is planned toreach 80%o in major State-owned coal mines in2000 according to the planning of the government(Li et al., 1998; Tang Dejin, 1998)Compared with the USA and Australia, China has more complex coal geological structures. Based on high-resolutionseismic technique in coal exploration, a new seismic technique with high-precision and high-resolution(2-D and 3-D)hasbeen developed for theof detecting small geological structures in coal mine construction and production to meet theleeds of large-scale popularization of mechanized coal mining in China. The technique is low in cost and requires a relativelyshort period of exploration, with high precision and wide-range applications. In the middle of the 1980s, it began to be used-mining coal exploration on a trial basis, and entered the peak of exploration in the 1990s, which has made significant proress in providing high-precision geological results forthe construction and production of coal industry in China, and is stillin the ascendantThis paper discusses some new progress and the exploration capability and application range of the techniqueKey words: coal, high-precision seismicexploration technique, progress1 IntroductionTherefore, it is important for coal geologists to workhard to improve the precision of pre mining geologicalChina. rich in coal resources is one of the countrieexploration and solve issues such as the small geologicalcoal as the main energy in the world. Coal coversstructures hindering the development in new ly-builtin the production and consumption of primary energy. minesThe development trend of coal production is high-Since the 1990s, a high-precision and high-resolutionproductivity and high-effic iency with mechanization of 2-D and 3-D seismic exploration technique has beenmining as its core. This puts forward high requirementdeveloped and improved, which aims to provide servi-for the coal resource conditions and the precision of ces for mine construction and production in large-scaleological exploration results (Li et al., 1998; Tang, coal mines in the eastern and central areas of China(tan1998).and Fang, 1998). It has been popularized and used inIn China, coal mainly occurs in the Carboniferous- over two hundred coal mines of more than ten provincesPermian and Jurassic, and partly in the Triassic and Ter- and regions. It has changed to a large degree the passivetiary. According to the classification of world coal re-sed by complex geological structures in thesources, it basic ally belongs to the third type with com- construction and production of coal mines. Since theplex structures, irregular coal seams, and difficult to be states of small structures can be determined accuratelymined, which causes many difficulties to construction of with the seismic exploration in the mining area, e.gmines and mining. In the past, as affected by the preci- determination of the distribution of caved pillars, thesigns and prowashing-out zone of coal seams and erosion area ofduction plans changed frequently, ineffic ient digging igneous rocks, the mines' design can be optimized andscale was high with big losses of coal resources, high the mining face laid out more reasonably, which canfrequency of accidents, low effic iency and poor benefitsavoid wasteYH中国煤化工 of unknownCNMHG312Vol. 74 NoACTA GEOLOGICA SINICAJune 2000geological conditions, thereby greatly reduc ing ineffH geological structures and problems. In particular, withcient digging, improving production efficiency and lothe flourishing 3-D seismic exploration, continuous 3-Dering the cost. It is estimated that during the period of data bodies can be obtained, with which we shall be able1991-1997 alone more than RMB 5 billion yuan of to identify various fine geological structures accuratelydirect economic benefits were obtained by undertaking and actively. This has played a significant role ofsupplementary seismic exploration in 68 newly-built geological safegurading for high-produc ing and higlmines. In addition. enormous economic and social bene.efficient minesfits have been gained by avoiding serious accidents ofwater bursting, reasonably adjusting water-proof coal 2.2 Main contents of the techniquepillars, liberating a large amount of coal resourcer and The high-precision and high-resolution seismic explora-safeguarding the production safety, since the seismic tion technique is a complete sys tematic project, whichexploration helped determine the karst fracture deveinvolves seismic data acquisition, processing and interopment areapretation and other aspects. Its key link is to improve theuifers and aquifuges, water diversion faults etcsignal-to-noise ratio for high-frequency signals. In theThis paper gives some brief examples to introduce the past ten-odd years, the dominant frequency of coal seisnew progress of seismic exploration technique in coal mic reflected wave has been improved from about 40 Hzindustry of Chinato 60-100 Hz, and the frequency bandwidth widenedfrom 80 Hz to over 200 Hz, which improves the longi-2 The Technique of High-Resolution Seismic tudinal resolution by three times so that 10 m-thick thinExplorationlayers and small faults with throws larger than 3 m canbe resolved. The CDP grid has been densified to 5-102.1 General situation of developmentmx5-10 m by using 3-D seismic exploration. With suchBased on the progress of modern science and technique, a high sampling rate in combination of the highseismic prospecting technique has developed rapidlprecision one-step migration, the hteral resolution wasNow, a complete digitalized high-tech system has beerimproved by several tens of times on the basis of 2-Dformed in field acquisition, seismic data processing and seismic so that small structures with extension lengthinteractive automatic interpretation, which results in the larger than 10 m can be identified. The technique of coalimprovement of precision of seismic resultshigh-resolution seismic exploration mainly contains theIn the 1980s, a comprehensive exploration method follow ing pointsion of seismic exploration and drillingData acquisitionmeans was firstly studied and used in eastern China(1) Seismographs have developed from the convenwhich achieved good results such as reducing the num-ional 14-bit a/d conversion ifp modeber of drill holes, shortening the exploration period, A/D conversion 2-A mode, which greatly improvessaving the funds and improving the precision for pro- the precision of A/D conversion and widens the dyjects of preliminary survey and detailed survey. The namic rangetechnique of high-resolution seismic exploration has(2)Densification of sampling, with the time samplerbeen promoted with the popularization of comprehen- interval improved to 0.5-1 ms, and the spatial samplingsive explorationinterval generally 5 mx125 m for 2-D seismic andDuring the 1990s, with the development of compre- 5-10 mx5-10 m for 3-Dnsive mechanized coal mining, the high-resolution(3)Different induction modes of drilling, vibrators etcd high-precision seismic exploration technique en- are chosen in the light of local conditions to inducetered the fields of coal mine construction and production. seismic signals with rich high-frequency componentst present, with the seismic exploration technique we and high signal-to-noise ratiosare able to identify small faults with throws larger than(4)Large-area combination of multiple low-frequency10 m(2-D)and 3-5 m(3-D), and small folds of corre- geophones is replaced by small combination of smallsponding amplitudes as well as many other special number of high-amount of中国煤化工CNMHGHigh-Precision and High-Resolution Seismic Exploration in Coal Industr313explosives with low explosion velocity is replaced with lakes, shallow sea areas, desert areas, the gobi desertsmall amount of explosives with high explosion velocityand cobble areasto raise the frequency of field data acquisitionIt is used mainly to accomplish the following geologData processingcal tasks(5) The following methods are adopted in the proc(1) Determination of faults with buried depths withinessing: reasonable compensation, high-precision static s, 1000 m, throws larger than 10 m, planar oscillation aappropriate prestack and poststack deconvolution, DMo rors less than 30-50 m(2-D); faults with throws largerstacking in the area with big dip and complex structurethan 3-5 m and planar oscillation errors less than 15-30good measures for noise removal, high-precision migram(3-D)tion etc. so as to improve the resolution of time section2)Determination of folds with buried depths within1000 m, coal seam undulation larger than 10 m(2-D),(6) Enhancing the pre-stack processing, making full and larger than 5 m (3-D); the interpretation errors foruse of frequency division measures, building a high- bottom depths of main mineable coal seams smaller thanprecision velocity field, proper coordination of models, 2%(2-D)and 1%(3-D)use of known borehole data for longitudinal labelin(3) Prediction of bifurcation, merging, washout andand lateral constraintsmissing zones in main mineable coal seamsData interpretation(4)Delineation of the range of the burning area of7)2-D seismic exploration is used to interpret the main mineable coal seamsstructures. coal seams and strata with the intensive re(5) Determination of the outcrop position in mainflection data on regular survey lines and grids(with the mineable coal seams with planar oscillation errorsline spacing depending on the exploration stage and smaller than 50 m(2-D)and 20 m(3-D)geological task), whereas 3-D seismic exploration is(6)Classification of the karst fracture developmenused to make more accurate and direct interpretation ofone of ordovician limestonethe structures, strata, coal seams and any other special7) Determination of the influence of mageological phenomena with especially intensive 3-D on mineable coal seams, range of the coking zone anddata bodiesdistribution of the(8)Methods such as labelling the horizon with VSPformation, and 3-D spatial homing of 2-D seismic data 3 Case Studiesetc are adopted to improve the precision of 2-D seismicdata interpretationThe huainan mining area(9)The workstation interactive interpretation methodIt is located in central anhui province of easterncan be applied to 3-D seismic data. For example, use of China During 1989-1996, high-precision 2-D and 3-Dsynthetic seismograms and logging sections for labelling mining area explorations were carried out in 23 sectionsthe geological horizons, longitudinal and lateral sectionsof 7 mines with an area of 264 km among which 3-Dfor identifying and picking up the breaking points, exploration was done in 1l mining areas in 4 mines withmaking full use of the high resolution of isochronical an area of 21 kmtime slices to analyze and interpret small faults, and297 faults were discovered in the 2-D exploration area,extraction of lithological parameters by using the data of among which 169 faults were newly found, and 2amplitude, velocity, flattening slices and other special faults with the original geological reports modified.processed sections to do the lithological interpretationOnly 36 faults were found identical with the originaldetailed geological survey reports2.3 Exploration capability and application rangeIn the 3-D exploration area, 311 faults were found inAt present, the high-precision and high-resolution se]- two main mineable coal seams, among which 15. 4%mic technique can be widely used not only in the plains were faults with throw s larger than 10 m, 36% withwith good conditions but also in various areas with throws ranging 5 to 10 m, and 48% with throw s lesscomplex conditions, such as hills, mountain areas, rivers,than 5 m whic中国煤化 aults areCNMHG314Vol. 74 NoACTA GEOLOGICA SINICAJune 2000Table 1 Correlation of main faults observedin the wells with those determined by 3-DFig. I shows faults F, F2, F3seismic interpretationand Fu on the adjacent surveyObserved on the faceCorrelationName ofmeeting the faultThrowThrow53-644 ConclusionPansan 1552(3)700-1012Pansan 1552(3)700-100670High-precision and high-reso-Pansan 1221(3)eeeelution seismic exploration hasachieved excellent results inPansan 1221(3)0-12Pansan 1221 (3)FS50-124 m erorSamecoal industry of China, whichXieqiao 11218Samemainly depends on the progressIn China, coal not only hasmedium-sized to small faults in the mining area. Downenormous usable reserves, but also, differ ing from othehole verification of the control of 3-D exploration on theenergies, is a basic raw material for power generationstructures is shown in Tableheating, industrial power, steel making, gas synthetizaThe Datun mining areation, liquid fuels and chemical products necessary forThis area is located in the northestem part of Jiangshuindustry. Today, the newest developments in coal mininProvince in eastern China. During 1993-1998, exploramethods and mining equipment have been used andtions were carried out in 14 mining areas of the Yaoqiao,popularized successfully. Proceeding from the actualDatun, Xuzhuang, Longdong mines with an area of 14.8 situation in China. coal will continue to bemaInkm for 2-d and 13.2 km- for 3-d exploration.energy in China for a long time. Now, there are overa 3-D exploration was completed in the Xifu mining1500 mining areas and over 3000 faces by State-ownedarea of longdong coal mine with an area of 1. 8 kmkey coal mines as well as over 3000 mining areas andThe coal seams in the area occur in the Carboniferous- more than 5000 faces by State-owned localaveraging 5 18 m, well developed in the whole area with prospect of application to coal mine: 3i@ Coal minesPermian There are two main mineable coal seams noTherefore, it may be considered that7 and No. 21. The No.7 coal seam is 2.70-6.07 m thicka simple structure favourable for comprehensive miningthod in geophysical exploration has certainThe No. 21 mineable coal seam is stable. 1. 12-1. 55conditions for application. The key to success dependsthick with an average of 1.3 m, and at an average ds- on a detailed analysis and knowledge of the actualtance of 180 m from the above no. 7 coal seam In thegeological issues by the usersfield acquisition a time sampling rate of 0.25 ms and aFrom the point of further development, the target ofcombination reception by serial connections of three 100coal seismic exploration is not only to detect smallHz geophones were used. The small faults were inter-geologic structures, but also to explore coal seams, roofspreted by us ing the 3-D fuzzy probability testing resultand floors of the coal seams, gedeostress anomalies waterthe 3-D correlative data body interpretation result, theprevention and control, gas-accumulated zones etchorizon flattening planar result map and the surface slice Therefore, efforts must be made to further improve theinterpretation result. 14 faults were discovered in the resolution to develop a high-precision and high-area, including seven smallfaults with throws <3 mTable 2 Faults discovered in the area(Table 2). Four of themThrow of faultTotalhave been proved by tun>10m5-10m>3mheling with an accuracy ofNumber of faults100%(Table 3)and the Table 3 Faults verified by tunnelingothers are to be verified by Name of faulttunneling in the futureMethod usedSeismic TunnelThrow of fault5-10m94mMU中国煤化工m22mCNMHGHigh-Precision and High-Resolution Seismic Exploration in Coal Industrand the seismic data with111131drilling and logging data. Itcan be predicted that coalreach a more splendidperiod of development,and play a more importantrole in coal industry ofChina in the coming 21stManuscript receivededited by Zhu Xilingand zhou jianChenspect on mechanization of coalmining in the "Ninth Five- YearTang Dejin, 1998. Devel n Inof coal mining mechanizatioChina. China CoaL, 24(1)14-16Tan Jianyi, and Fang Zheng,Seismic Exploration in the CoalMine. Beijing: Press of Coaland He Zonglian, 1999. Controlof palaeoclimatic change olLate palaeozoic coal accumula-of the North China plaActa Geologica Sinica, 73(2)131-139(in ChinEngabstract)Zhong Rong and fu zemin1998. The relationship betweenthe distribution of thick coalbelts and the late carboniferous-Early Early Permian marinetransgression-regression in theFig. 1. Display of the faults on adjacent survey linesNorth China platform. ActaGeologica Sinica(Eng. ed. )72(1):114120resolution seismic technique, to expand uses of waveabout the authortechnicand combine more closely the structuralexploration with lithological and coal seam exploratioNi Bin Senior geologist and vice-director of ChinaNational Administration of Coal geolog中国煤化工CNMHG