| LuoYang-YiChuan depression (LuoYi Depression) is located in the northeastmargin of Qinling-Dabie orogenic belt and the southwestern margin of the North Chinaplate, central eastern China, its tectonic system changes is related with the Qinling-Dabie orogenic belt, the Taihang orogen and Tanlu fault closely. Due to the hub statusof "North-South division, East-West connection" and a large number of oil and gasaccumulation geological unit in the margin, LuoYi Depression win the attention ofmany domestic and international geological experts and oil and gas exploration experts.This area is a small inherited-developing Mesozoic-Cenozoic intermountain compositerift lying in the North China platform, showing the overall NW trending near a "T"shape, which from east to west is about120km, south-north is20-80km, and the area isabout5800km2. As the LuoYi depression was in phase of the northern margin of theNorth China plate and Yangtze plate, which is the converge part of a variety of stressproduced by the tectonic movement between the Taihang orogenic belt and the eastQinling-Dabie orogenic belt, and resulted in multi-stage tectonic and uneventransformation of later period, and in the depression, Triassic strata, as the explorationtarget, is subjected to varying degrees of erosion, So it is quite difficult to study itstectonic evolution history, thus affecting the process of oil and gas exploration in theregion.Therefore, the further use of the new, old seismic geological data to study thecharacteristics of its structure and tectonic evolution systematically, to restore itserosion thickness and the paleotectonic face of main Triassic period, to analyze thehydrocarbon geological response relations between the tectonic movement and sourcerocks, or fracture-fold, or accumulation of oil and gas, and to research the relationsbetween oil and gas generation and evolution, has important theoretical guiding significance for the favorable exploration region optimization and oil and gasexploration as soon as possible.1. Regional tectonic and stratigraphic-structural layer dividing(1)Regional tectonicIn light of the characteristics of the gravity and magnetic field and regionalMohosurface in and around the area, combined with the reanalysis of the regionalgeophysical profile and the characteristics of Shangdan-Mianlue ophiolite beltdevelopment and distribution, it comea to summarize the regional tectonic features ofthe western Henan and adjacent areas in system, and divide the tectonic evolution ofthe Qinling orogenic belt into five stages, such as ancient Qinling ocean basin-NorthChina-Yangtze plate prototype and the largest expansion of the ancient Qinling Ocean,and so on.(2)Stratigraphic-Structural layer dividingBased on the Previous research, and the recent drilling, outcrop geology,paleontology, seismic interpretation results, this is essay studies out and perfects theformation system in LuoYi Depression, identifies11unconformities and divides theLuoYi Depression into six structural layers, newly discovers and confirms theunconformity, angular unconformity between the upper Paleozoic and Triassic orparallel unconformity, of great significance to the oil and gas exploration in the region.On account of the regional unconformity identification and the construction layerdivision and perfection, it preliminarily finds out the vertical and horizontaldistribution of the upper Paleozoic strata and above, especially the Triassic.2. Tectonic units and fracture-fold analysis(1)Tectonic units dividingAccording to the latest research results and the newly worked-out bottom-Triassicstructure map, this essay details the regional tectonic units division, and divide theLuoYi Depression into the fundamental tectonic pattern of three noses, five sages, onethrust belt, that are nine third-grade structure unites——five sages successively areYiMa sag, YiYang sag, LuoYang sag, North YiChuan sag, South YiChuan sag fromnorthwest to southeast, three noses successively are XunCun-YaLing nose belt,Xinan-Longmen nose belt, Zhaizhen nose belt, the thrust belt is YiMa-YiYang-YiChuan thrust belt.(2)Fracture-fold analysis①Fracture characteristicsThe regional pressure-shear strike-slip in the Indosinian-Yanshanian period formed four classes thrust faults and a part of normal fault of control sag fracture,control belt fracture, control source fracture and control reservoir fracture, the hedgingthrust faults were dominating, which mainly were northwest-northwest westward andnortheast eastward-near east charactering of flying geese combination, the normalfaults of northeast-near eastward, active lately and with the role of "cut" or"transform", were auxiliary, Northeast-nearly east faults are not well develop becauseof the limitation of the former, but has "cut" or later reformation to the former.②Fracture-fold combination style and the formation period of fractureBased on outcrop and seismic interpretation results, this essay sums up sevenkinds in four types of fault-fold combination style of compressional tectonic (hedgetype, back flush, imbricate), inversion structures (simple reversal of the negative type),reverse drag structure and strike-slip structure (twisting pressure "flower" strike-slipstructure and transtensional fault-fold strike-slip structure) developing in the region,discusses the fracture of different geological history in the region, and five major faultactivity periods of the mid-late Hercynian North West weak extension rifting, Indoearly weak collision squeeze, late Indosinian subduction and collision extrusion uplift,Yanshanian orogeny and Himalayan period extensional rift since the lateCarboniferous.(3)Regional tectonic deformation characteristics and the mechanics of theformation①Regional tectonic deformation characteristicsAs to two regional seismic-geological sections and three groups combinedseismic-geological profiles prepared, the composite analysis shows that the tectonicdeformation of every formation today in LuoYi Depression is with apparent features ofthe "North-East Zonation, North-West Division", and the tectonic deformation belt candevide into three part, the southwestern margin of thrust nappe intense deformationzone, central secondary deformation bands and northern weak deformation zone.②The mechanics of the fracture formationAccording to the vector superposition analysis of the main regional fracture stressfounded and implemented, the main stress of the region are mainly subjected to twogroups working together to NNE-SSW, the middle and late Hercynian ischaracteristiced by unilateral extrusion-local tension.Tectonic deformationperformance is gradually weakened from south to north, Indosinian is extrusion ofasymmetric bilateral, and Northwest-North East thrust is strong. Yanshanian becomes to a greater intensity of land squeezed orogenic and powerful thrust nappe region, andforces the southern edge of imbricate nappe belt to expand gradually to northeastwave-likely. The region's leading to uneven strike-slip rift in Himalayan period.(4)Trap type and patternIn LuoYi depression,4types and10sub-types traps were confirmed: structuraltrap(incline, fault incline, fault nose, fault-block),lithologic traps (elongate lense,upward pitchout, fracture-vug) and complex trap (structure-fault-unconformity,structure-strata-unconformity). The plane distribution pattern of these traps alongstructure belt, fault, unconformity surface and erosion line were analyzed, and we alsoanalyze the vertical inheritance and overlay relationship in different strata. In this area,the formation of traps was determined by the property heterogeneity of sedimentaryrocks, which was caused by the Songqi paleouplift and northern margin paleoslope thatwere formed by multiple structural movements.3. Construction of erosion thickness and paleostructure feature indifferent period of Triassic(1)Characteristics of strata erosion in different period of TriassicThrough the research of2wellbores,28inlines and17crossline profile, it wasconcluded that upper Triassic bears the largest erosion area and thickness, with themaximum erosion3600m, average of1600-2000m. Total erosion trend is decreased as"Ring-Zoster" from the margin to the center area of the depression.The largest erosionthickness lies in southern YiYang-YiChuan of the southwest thrusting-nappe zone,followed by Songqi area in southeast YiChuan. Uneroed areas were only found inshiling villiage of YiYang and YiMa-MianChi, and these areas spread in anunsymmetrical oval shape in west-east and north-west trending respectively. As for themiddle-lower Triassicthe, errossion features were similar to that of upper Triassic, onlywith the erosion thickness and scope decreasing from shallow to deep.(2)Kinetic charactristics of balance shortening and balance strain indifferent periods of Triassic.①Through17typical profile in this area, it was concluded that in Triassic most ofthe faults have the features of syngenetic fault. Strata rapid shortening period beforeLater Paleozoic to Yanshan period mainly exist in later Triassic ChunShuyao-Tanzhuanperiod, and strata squeezing shortening is basically northeast,secondly northwest.Themain time-space change from northwest to southeast and southwest to northeastappeared the typical "scissors difference feature", which means, from YiMa-YiYang innorthwest to YiChuan in southeast, the early squeezing strain was strong in northwest,and weak in southwest.②Through the balance strain kineti analysis of15combined balance profile,itwas concluded that the dynamic evolution in this area can be divided into5stages:large-scale thrusting-nappe and local extention syngenetic stage in later Haixi Period,rapidly extensive compression-inversion structure formation stage in earlier YinziTriassic,weak compression contemporaneous deformation stage in middle Triassic,unbalanced entire depression and thrust accompanying stage in later Triassic, extensivethrusting-nappe and difference uplift erosion in Yanshan period and unbalancedextensional rift stage.(3)Reconstruction and analysis of paleostructure feature of TriassicThrough the restoration of structural recovery, including eliminating the effect offault, incline, erosion, compression the complication reposition of fault-strata, and theanalysis of the5paleostructure feature from later Haixi Period, it was concluded thatupper Paleozoic was significantly and unbalanced upraised, and inordinately eroded.As a result, a pattern of "three convex, two concave" was formed before the depositionof Triassic. This pattern gave birth to the overthrust of YiYi Fault north-east further,thechanges of structure pattern about "high becomes higher, concave changing shallow"after deposition of Triassic,and "convex becomes low, concave turn to deep" inMiddle-Triassic and the overall depression in large in Late-Triassic. Especially, inChunShuyao period, two deeper depressions were formed in the deep plate of SangLuand Yiyi fault. Meanwhile the3earlier bigger nose-like structures still maintained theunder-water bulge shape,which is the gradually raising nose-structure-belt northwestMianChi-YiMa-Xin'an in the north-west, which is Yiyang-Xuncun Southfaulted-anticline-anticline underwater-uplift in central zone. At the same time,YaLing-YiChuan structural nose was gradually into one in the north-west withYiYang-XunCun nose structures,and it is adjacent across SongShan-QiShan GentleLow-Uplift Underwater via the small sag in the South-East. In Tanzhuan period of laterTriassic, the LuoYi depression evolved into a Mesozoic larger-size deep depressionstage.Two deep depression zones(connected closely and with deep subside) and3under-water low bulges were formed.4. The control action of fault-structure change to hydrocarbonmigration and accumulation in different periods of Triassic(1)Steadily developed faults and under-water paleo-bulges control thestretch and migration of paleo-valley and paleocurrent In earlier-middle Triassic, under the control of Yiyi fault, LuoYi depressionmainly consisted of large delta and shallow lake sedimentary system,and it depositedred-purple red sandshale layer in dry and hot environment.In middle Triassic, largedelta sediment shrinked and shallow lake sediment expended gradually. In laterTriassic,upper triassic sediment under the control of Shanlu fault expended,while deltzone became smaller and tranformed into shallow-deep lake and delt sedimentarysystem in oxygenfree environment, with a set of thicker gray-dark graysnadshalesediment. In YiMa-MianChi of the northwest part, and easternRuyang-zhaizhen western Ruyang-YiYang of the southeast part, the3large deltsedimentary systerms shriked gradually.(2)Stable faulted reservoirs in continuous extrusion environment make theupperTriassic develope the thick high-quality hydrocarbon source rocksSince the late Indosinian continuous extrusion environment makes the area"foreland basin-like" large inherited depression in the Late Triassic. In warm moistancient environments,the study area has an original thickness of about4000-5000m ofthe Upper Triassic the ChunShuyao group-Tanzhuang dark strata deposited. AlthoughSuffered from intense weathering and erosion during the late Indosinian to the LateYanshanian,by late Triassic stable warped lacustrine-delta front facies make the studyarea remained high-quality source rocks with a considerable thickness. Among them,the Upper Triassic ChunShuyao group-Tan Zhuang group remained the distributionarea of3000-4100km2, dark gray mudstone and carbonaceous shale total thickness of800-2200m, organic carbon0.29-5.05%, an average of1.52%. From four aspects ofkerogen macerals, hydrogen carbon and oxygen carbon atomic ratio, hydrocarbonsource rock pyrolysis hydrogen index, chloroform bitumen"A" family compositioncharacteristics,it was confirmed its parent that was type II2-type III, and there were asmall amount of II1type. Ro is0.5-1.3%, Tmax is396-527C, OEP was1with all madethem low mature-mature medium-good source rocks.(3)The continuous development of underwater ancient uplift and strike-slipfaults not only control dense sandstone in the region favorable reservoirdistribution, but also creat good condition for the formation and transformationof the structure fractured reservoir.Because of the on going activities, such as Yiyi fault strike-slip fracture with theraw pulse in the Late Triassic, there structrual transfer zones with nose-like underwaterbulges properties exsited along the Strike-Slip fault zone, controll the main zone of theUpper Triassic tight sandstone development of LuoYi depression, and even the geographical distribution and the distribution form of tight sandstone with goodphysical properties of the conditions favorable reservoir strata. Actual drilling to actionproves that sustained activity of the fault created good conditions fo formation andtransformation of various Structure-fractured reservoirs, especially, since Indosinianfracture-folding, so that tight sandstone reservoir and mudstone of upper Triassic ofLuoYi depression obtaine a better transformation in different degrees, and it effectivelyimproved oil and gas reservoir space and reservoir performance.(4)Continuouly developing of fracture-fold controls the development ofdifferent types of traps in the regionResearch shows that the North East and compression in the late Hercyniancompression and uneven uplift denudation laid "three convexes and more concaves"basis of the Triassic trap development, Indosinian further extrusion and the Uplifts anddepression-folding created dood condition for inheritance and diversified developmentof the region traps. Different times of inheritance fracture-folding made the regionpresent "banded (transverse)-stereoscopic pavilion-style (longitudinal)" law ofdistribution. Tectonic framework of different periods controlled distribution ofdifferent trap types.(5)Breaking–tectonism movements plays an important control role onhydrocarbon migration and accumulation in different periods of the region①According to hydrocarbon migration and accumulation of fluid potentialanalysis of Tan zhuang and the ChunShuyao group, we believe that,since thedeposition of TanZhuang group,there are three more obvious oil and gas potentialareas with inherited development under control of the faults and tectonic, and two oiland gas migration "Split groove",So the mature oil and gas generated in UpperTriassic transport along the small nose-shaped beam as "like aggregation state" toancient nose convexes of the MianChi-YiMa, SongQi,YiYang-XunCun. Althoughbecause of the Indosinian-Himalayan fault-fold,the accumulation pattern, small nosetransport beam and convergence zone have been greatly changed, but now UpperTriassic oil and gas accumulation still had there quite obvious "convergence areas"similar with those in late Indosinian.②According to the analysis of well T1UpperTriassic tight sandstone oil and gas characteristics, in the region persistent activity faultwas well T1typical low porosity, low permeability, low pressure, low density, lowabundance, and low productivity which equals "six low" type, Upper Triassicsandstone complex oil and gas reservoir source within short distance migration and accumulation, which played an important role in forming and improving high-speedchannel of favorasle oil and gas migration and accumulation, and mainly presented infollowing four aspects in "pass the source fracture" constitutes the basis for oil and gasmigration and accumulation, the spatial extension of the fracture distance rangedetermines the maximum range and scale of the Upper Triassic hydrocarbon migrationand accumulation, the fracture activity period controled main layer of the oil and gasmigration and accumulation in the region, in Yanshan period, the fault activities mainlydestroyed the oil and gas reservoirs, and oil and gas reservoir adjustment iscomplementary.5. oil and gas exploration area and favorable zone evaluation(1) To sum up all the outcomes above, LuoYi depression was divided intoXunCun–YaLing inheritance development of large structure-composite trapexploration area, YiMa-YiYang-YiChuan north of lithologic trap and stratigraphic trapexploration field, and the middle-Lower Triassic dense sandstone exploration areasthree major oil and gas exploration fields.(2) According to the remnant of the UpperTriassic source rocks and their inherited, transformative and destructive characteristics,hydrocarbon generation center in ancient and modern, paleostructure feature, strengthof tectonic deformation and subdivisions of tectonic units today, and so on, in LuoYidepression today in Triassic oil-gas save unit is mainly divided into a total of4majorcategories, which were inheritance-regenerative, transformation-save type,transformation conservation, transformation-residual type and transformation-destruction type,(3) Comprehensive analysis, the XunCun-YaLing nose-like structuralbelt is the most favorable exploration areas about oil-gas recently, theXin'an-Longmen nose-like structural belt and ZhaiZhen nose-like structure belt arefavorable exploration areas about oil-gas recently.YiMa Sag, YiYang Sag, YiChuanSouth Sag, YiChuan North Sag and LuoYang Sag are favorable exploration areas aboutoil-gas.
|
PDF Full Text Request