+ MODEL Available online at www.sciencedirect.com ScienceDirect Natural Gas Industry B xx (2017) 1e7 www.elsevier.com/locate/ngib Research Article Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin* Zhang Guangrong a,b,*, Ran Qi b, Liao Qi b, Yu Yi b, Zhang Xuan b, Chen Kang b, Cao Hong c, Zeng Ming b, Wen Long b, Lai Qiang b b a Chengdu University of Technology, Chengdu, Sichuan 610059, China Exploration and Development Research Institute of PetroChina Southwest Oil & Gas Field Company, Chengdu, Sichuan 610051, China c PetroChina Research Institute of Petroleum Exploration and Development, Beijing 100083, China Received 10 March 2016; accepted June 2016 Abstract The dolomite reservoirs of the Lower Cambrian Longwangmiao Fm in the GaoshitieMoxi area, Sichuan Basin, are deeply buried (generally 4400e4900 m), with high heterogeneity, making reservoir prediction difficult In this regard, key seismic exploration technologies were developed through researches Firstly, through in-depth analysis on the existing geologic, drilling, seismic data and available research findings, basic surface and subsurface structures and geologic conditions within the study area were clarified Secondly, digital seismic data acquisition technologies with wide azimuth, wide frequency band and minor bins were adopted to ensure even distribution of coverage of target formations through optimization of the 3D seismic geometry In this way, high-accuracy 3D seismic data can be acquired through shallow, middle and deep formations Thirdly, well-control seismic data processing technologies were applied to enhance the signal-to-noise ratio (SNR) of seismic data for deep formations Fourthly, a seismic response model was established specifically for the Longwangmiao Fm reservoir Quantitative prediction of the reservoir was performed through pre-stack geo-statistics In this way, plan distribution of reservoir thicknesses was mapped Fifthly, core tests and logging data analysis were conducted to determine gas-sensitive elastic parameters, which were then used in pre-stack hydrocarbon detection to eliminate the multiple solutions in seismic data interpretation It is concluded that application of the abovementioned key technologies effectively promote the discovery of largescale marine carbonate gas reservoirs of the Longwangmiao Fm © 2017 Sichuan Petroleum Administration Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Keywords: Sichuan Basin; GaoshitieMoxi area; Early Cambrian; Longwangmiao Fm gas reservoir; 3D seismic; Well-control seismic exploration; Gas-bearing sensitivity parameter; Reservoir prediction * Project supported by the National Key S&T Special Project “Development of large oil and gas fields and CBM” (No.: 2011ZX05004-005, 2016ZX05004005), PetroChina Key S&T Special Project “Field experiment of exploration and development technology of deep marine carbonate in the Sichuan Basin” (No.: 2014E-3208), and PetroChina S&T Research Project “Evaluation and research of carbonate gas reservoir development of Sinian in the Anyue Gas Field” * Corresponding author Chengdu University of Technology, Chengdu, Sichuan 610059, China E-mail address: 635447923@qq.com (Zhang GR.) Peer review under responsibility of Sichuan Petroleum Administration The Sichuan Basin is a major gas-producing area in China, with the Carboniferous, the Lower Triassic Feixianguan Fm, the Upper Permian Changxing Fm, and the Upper Triassic Xujiahe Fm as its major gas reservoirs, and the Sinian and the Lower Paleozoic as its important field for further gas exploration [1] Located in the core of the LeshaneLongnuăsi paleouplift, GaoshitieMoxi area is a long-term inherited uplift, and a favorable gas-bearing area in the Lower PaleozoiceSinian The granular beach facies formation in the Lower Cambrian Longwangmiao Fm is widely distributed in a zonal pattern in the paleo-uplift, which is favorable for reservoir formation [2] On September 28, 2012, Well Moxi revealed a test gas http://dx.doi.org/10.1016/j.ngib.2016.06.004 2352-8540/© 2017 Sichuan Petroleum Administration Production and hosting by Elsevier B.V This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/) Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 production of 190 Â 104 m3/d in the Longwangmiao Fm, recording another breakthrough after gas obtained in Well Gaoshi in Sinian in the Sichuan Basin This further verified the good gas-bearing potential in the Sinian and the Lower Paleozoic in the LeshaneLongnuăsi paleo-uplift But, Well M2 in the Longwangmiao Fm didn't show any industrial capacity of gas, with a reservoir thickness of only 4.5 m, which proved that there is reservoir heterogeneity in the Longwangmiao Fm The Longwangmiao Fm in Moxi area is deeply buried (generally 4400e4900 m), making reservoir prediction difficult In this regard, through in-depth analysis on the existing geologic, drilling and logging data, reasonable seismic data interpretation was made In this way, main reservoir features and distribution rules were clarified, seismic reservoir prediction technology was deepened, favorable well locations were discovered and ultimately good exploration effects were achieved Reservoir characteristics 1.1 Geological setting Built on the basis of clastic rock continental shelf or mixed continental shelf (gentle slope) deposits of the Canglangpu Fm, the Longwangmiao Fm is controlled by paleogeomorphology with a feature of being high in the west and low in the east It presents as a carbonate platform deposit thin in the west and thick in the east It is in conformity with its overlying and underlying strata, with formation thickness of 70e110 m Lithologically, it is composed of grain dolomite, dolarenite, oolite dolomite and argillaceous dolomite interbedded with a small amount of sandstone Its electrical property is characterized by low GR value, presenting lowamplitude box shape Its resistivity is middleehigh, presenting peak shape 1.2 Physical properties According to the statistic on physical properties from coring test, the porosity of small plunger sample analysis of reservoir section is 2.00e18.48%, and the total average porosity is 4.28% The porosity of full-diameter sample analysis of reservoir section is 2.01e10.92%, and the total average porosity is 4.81% The correlation result shows that the full-diameter core porosity of reservoir section (averagely 4.81%) is obviously larger than small sample porosity (averagely 4.28%) Due to the development of reservoir dissolution pores, the full-diameter core samples can better represent the reservoir, with porosity closer to the real porosity of the reservoir Therefore, the analysis result of full-diameter property can better reflect the physical property of the Longwangmiao Fm According to the result of full-diameter sample analysis, the samples with porosity of 2.0e4.0% account for 37.8% of the total, those with porosity of 4.0e6.0% account for 41.73%, and those with porosity more than 6.0% account for 20.47% Thus, the porosity mainly ranges between 4.0% and 6.0% 1.3 Logging responses of reservoir Well M11 in Moxi area obtained a test gas production of 108.04 Â 104 m3/d in the well section 4684e4712 m, and 109.49 Â 104 m3/d in the well section 4723e4734 m in the Longwangmiao Fm Due to the influence of pyrite stripe in well section 4681.5e4683.6 m and at well depth of 4688.2 m, the resistivity decreases in spininess Due to the influence of fractures in well section 4703e4715 m, the resistivity obviously reduces, and the geological logging shows circulation loss According to the correlation result of logging data of multiple industrial gas wells in the study area, the conventional logging responses of the Longwangmiao Fm reservoir is usually presented as low GR, low density, high neutron and high DT values The resistivity varies with physical property and fluid, and the dual lateral resistivity normally shows positive variance in gas layer sections Particularly, the low density and high DT values will certainly lead to the obvious change of reflection energy of reservoir seismic wave and wave group features High-precision seismic imaging technology for deep low-relief carbonate reservoir 2.1 Seismic data acquisition In order to simultaneously meet the requirements of gas exploration in Cambrian and Sinian and for the convenience of 3D seismic merged processing and reservoir prediction in the late stage, it is suggested that the scheme of overall deployment and separated implementation be adopted for 3D seismic data acquisition in the GeoshitieMoxi area The 428 XL exploration tool was used for separately acquiring 3D seismic data of areas Orthogonal observation system was used, with basically similar acquisition parameters Field operation parameters were optimized for target formation of Cambrian, with digital seismic acquisition technology of wide azimuth, wide frequency band and minor bins [3] Besides the 3D area in the east of Moxi area, the azimuths used are all 37.94 , all with minor bins, large offset and multi-trace recording In all areas of 3D seismic survey, wide-azimuth acquisition was adopted with an aspect ratio more than 0.67, which is a rare large-area wide-azimuth acquisition in onshore China currently, and provides high-quality basic data for merged seismic data processing The seismic data acquired by high-precision 3D seismic acquisition has a frequency band of 6e125 Hz, and dominantly of 10e70 Hz in target formation, with active waveform of seismic reflection and high SNR 2.2 Difficulties in seismic data processing and technological solution As the single-shot data is influenced by surface and topographic conditions in Moxi area, there are three difficulties in pre-stack processing First, the surface relief requires static Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 correction to a certain extent Second, the Lower Paleozoic in the target formation has relatively low SNR, and noise interference is mainly presented as multiples, surface wave, industrial interference, traces with dominating noise and abnormal amplitude, etc Third, the main frequency of target formation is relatively low with a narrow frequency band To address the above difficulties, the following techniques and solutions are adopted (1) Accurate tomographic static correction technology combined with surface structure data is adopted to inverse the surface structure model, in order to address the static correction caused by lateral change of surface, and to accurately depict the subsurface structure to guarantee the authenticity of structural form and improve the imaging effect of the data [4] (2) Multiple methods are combined to perform pre-stack noise attenuation in multi-field and step by step, and amplitude or frequency difference is used to suppress abnormal interference Coherent noise is suppressed depending on the velocity of interference wave and frequency difference, in order to reduce the loss of effective signal energy [5] By attenuating the lowfrequency surface wave and abnormal energy on prestack data and the random noise on post-stack data, SNR is improved (3) Using the well-control seismic data processing technology, together with VSP data, the Q model is determined, and the absorption attenuation of strata is compensated, effectively broadening the frequency band of seismic data Anisotropic pre-stack time migration technology is used to enhance the details of migration imaging, and improve the quality of large-offset data, making more information involved in overlay, in order to guarantee the imaging precision of seismic data in Cambrian and thereby to correctly reflect the reservoir changes in detail 2.3 Well-control seismic data processing technology Well-control seismic data processing technology is to make the best of drilling, logging and VSP data of the existing wells to perform a combined analysis and processing of well data and surface seismic data, making the selection of processing parameters more precise and reasonable during the seismic data processing [6,7] The well data obtained by VSP method is used to provide constraints of key parameters for seismic data processing, serving as calibration basis in the workflow of well-seismic 3D processing In the seismic survey of Moxi area, the VSP data of Wells M11, M1 and M6 are all available, thus making the application of well-control seismic data processing technology very suitable [8,9] The well-control processing result shows that the target formation of Cambrian is presented as a accurately-depicted low-relief structural form, distinct fault contact relation and obvious wave group features [10,11] Thus, high-SNR, high-resolution and high-fidelity data are provided for high-precision structural interpretation and reservoir prediction 2.4 Anisotropic pre-stack time migration technology Normalization should be done to the data before migration to make the distribution of offset and fold more uniform The shot point and receiver point should both be calibrated to the floating surface to conduct the migration on the floating surface, and then they should be stacked to the final datum after migration The key parameters for pre-stack time migration are offset group interval of 100 m, migration aperture of 9000 m and dip of 45 The anisotropic pre-stack time migration is obviously superior to post-stack time migration in terms of the imaging of target formation and reflection with steep dip and fault depiction After merged processing, the target formation has an effective bandwidth of 6e70 Hz, and main frequency of 35e40 Hz The Cambrian formation is presented as clear wave group features and obviously improved SNR Besides, the seismic data of each 3D area has consistent waveform features, such as frequency, phase and amplitude Therefore, the requirement of seamless splice for merged 3D seismic data processing is met, providing reliable and high-quality basic seismic data for further structural interpretation and reservoir research Seismic interpretation and reservoir seismic response 3.1 Fine seismic interpretation Seismic and geological horizon calibration results indicate that the bottom of the Longwangmiao Fm in GeoshitieMoxi area is mainly a stable trough reflection The analysis of stratigraphic lithology and velocity structure reveals that there is micrite dolomite in the bottom of the Longwangmiao Fm and siltstone on the top of the underlying Canglangpu Fm This lithology difference leads to a large velocity variance in the overlying and underlying strata of bottom Longwangmiao Fm There is a strong negative reflection from high velocity to low velocity Seismic reflection shows relatively continuous and stable strong trough reflection in the whole area, which can act as an important marker for contrast and tracking The lithology of the Longwangmiao Fm is dolomite and that of the Gaotai Fm of Cambrian in its overlying strata is siltstone But, the development of reservoir in middle and upper of Longwangmiao Fm in Moxi area led to little difference in formation velocity in the overlying and underlying strata of top Longwangmiao Fm, thus resulting in small reflection coefficient and weak peak or trough The full 3D visualization seismic interpretation technology and integrated point-line-plane full 3D interpretation mode are used to conduct fine interpretation in GaoshitieMoxi area Variable velocity mapping technology is used for timeedepth conversion The subsequent 24 wells verified that the absolute error in top Longwangmiao Fm is 4.8e14.4 m and relative error is 0.06e0.33%, far less than the industrial standard of 3D seismic data structural interpretation This indicates that the Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 seismic interpretation result is reliable and that timeedepth conversion has high precision 3.2 Reservoir seismic response Based on fine calibration for all reservoirs of wells through synthetic seismogram, and with reference to seismic reflection features of borehole-side seismic trace and forward modeling analysis, it is considered that there are three types of reservoir seismic response (1) Double-peak seismic reflection Reservoir thickness is large (10e50 m); weak peak is observed in top Longwangmiao Fm; internal strong peak corresponds to the reservoir bottom, and energy of internal peak strengthens with the increase of porosity (Wells M8, M9 and M11) (2) Internal single strong peak Reservoirs developed in the upper; trough is observed in top of Longwangmiao Fm, and internal strong peak approximately corresponds to the reservoir bottom (Well M10) (3) Single strong peak in top Longwangmiao Fm Reservoir is thin (less than 10 m), and no internal strong peak reflection is observed (Wells M1 and M2) Types (1) and (2) above are both features corresponding to the development of the reservoir, while Type (3) corresponds to non-development of the reservoir (small thickness and low porosity) The Longwangmiao Fm in Moxi area is dominated by Types (1) and (2), and Gaoshiti area is dominated by Type (3) The establishment of seismic response mode of the Longwangmiao Fm reservoir provides a basis for selecting seismic attributes [12], and provides an important guidance to further reservoir prediction Reservoir prediction 4.1 Qualitative reservoir prediction Reflection strength gradient is a seismic attribute Fundamentally, amplitude value of each trace is converted into reflection strength, and then the curve relation of reflection strength and reflection time using the least square method in a given time window The slope of this curve is the reflection strength gradient If the reflection strength is basically a constant, its gradient is close to If the reflection strength increases from top to bottom of the analyzed interval, the gradient is positive; otherwise, the gradient is negative When the attribute of reflection strength gradient is extracted, the moving window should not be too large or too small egenerally 20e50 ms is selected according to the thickness of target formation If the moving window is too large, the slope may tend to be 0, and the attribute can only reflect the tendency of overall amplitude in the data (e.g attenuation of residual amplitude) If the moving window is too small, the attribute cannot identify the vertical change of amplitude anomaly Therefore, the amplitude anomaly and the upper and lower normal parts should be included in when moving window is selected Here, 25 ms moving window is selected according to the actual conditions of target formation in the Longwangmiao Fm The reflection strength gradient in GaoshitieMoxi area effectively depicted the horizontal development feature of granular beach reservoir in the Longwangmiao Fm Generally, the Longwangmiao Fm in Moxi area is dominated by warm yellowered color, indicating good reservoir development Gaoshiti area is dominated by cold blueegreen color, indicating relatively poor reservoir (Fig 1) 4.2 Pre-stack quantitative reservoir prediction Seismic inversion is to image (solve) the physical structures and properties of subsurface strata by using seismic observation data and with known geological rules, drilling and logging data as constraints Compared with statistical methods, such as pattern recognition, neural network and amplitude frequency estimation, wave impedance inversion has definite physical meaning, and it is a deterministic method for reservoir lithology and physical properties prediction, and description of reservoir features [13] With the advancement of seismic inversion technology, new computation method and inversion solution continuously emerge Normally, seismic inversion technology can be classified into two types: deterministic inversion and geostatistical inversion The deterministic inversion can distinguish the strata with a thickness of 1/8 wave length in theory due to its vertical resolution limited by seismic frequency band The prestack geostatistical inversion is a method which combines stochastic simulation theory with seismic inversion It employs Bayesian inference based Markov ChaineMonte Carlo algorithm to generate multiple elastic and lithology data volumes of subsurface strata of the same probability This method gives consideration to the horizontal resolution of seismic data and vertical resolution of logging data, and integrates highresolution logging data and low-resolution 3D seismic data, thus reserving both the advantages of horizontal resolution of deterministic inversion and more geological details (Fig 2) With the combination of geostatistics and seismic inversion technology, and a comprehensive application of multiple data sources (seismic, geologic and logging data), high-resolution Fig Planar map of reflection strength gradient of the Longwangmiao Fm in GaoshitieMoxi area Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 Fig Contrast between the sections of deterministic inversion and pre-stack geostatistical inversion Fig Wave impedance section crossing wells from pre-stack geostatistical inversion of the Longwangmiao Fm inversion section with strong predictability can be obtained, providing a basis for uncertainty analysis and risk evaluation 4.3 Analysis of reservoir prediction effect Fig shows the overlaying section of wave impedance derived from pre-stack geostatistical inversion and seismic waveform crossing Wells from M202 to M16 The warm greeneredeyellowewhite color indicates relatively lowimpedance reservoir, and cold light blueeblueeblack color indicates relatively high-impedance non-reservoir The Longwangmiao Fm reservoir in Wells M202 and M16 is mainly developed in the middleeupper part The location of reservoir usually corresponds to the place where seismic waveform changes, with reservoir top corresponding to the wave trough and reservoir bottom corresponding to the wave peak It means that bright spots on the seismic section correspond to the reservoir bottom on inversion section, which is consistent with the reservoir response mode established earlier In general, the reservoir in Moxi area is distributed continuously in a large area with a large thickness This is consistent with the result of qualitative seismic prediction without well constraints The reservoir thickness is generally 20e60 m, with thicker areas mainly in Well M9eM10 area, Well M8eM204 area and Well M11eM16 area The reservoir changes thinner towards the southwest to Gaoshiti area, with a thickness of 10e20 m (Fig 4) According to the verification of 24 wells, the absolute error range of reservoir thickness of seismic inversion prediction is 4.5e8.6 m, the prediction coincidence ratio of Gaoshiti area is 85% and that of Moxi area is 90%, indicating a reliable seismic inversion result and high-precision reservoir prediction Fig Planar map of seismic prediction of reservoir thickness in the Longwangmiao Fm in GaoshitieMoxi area Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 Pre-stack hydrocarbon detection Based on pre-stack CRP gather data, velocity data and well data (S-wave, P-wave, density and other elastic parameters) and through different approximate expressions for inversion and solution, the pre-stack inversion technology can be used to obtain multiple elastic parameters related to lithology and hydrocarbon-bearing potential, and can further be used to predict reservoir hydrocarbon-bearing potential, in this way multiple solutions of seismic data will be reduced This paper used drilling, logging data and test results of wells in the area to carry out detailed rock physics analysis, obtaining gasbearing sensitivity parameters, and used pre-stack inversion technology for hydrocarbon detection, achieving the gasbearing potential prediction of thin reservoirs of granular beach 5.1 Petrophysical analysis Basic elastic parameters of tight carbonate in the Longwangmiao Fm under dry and water saturation conditions were obtained through core ultrasonic wave measurement and matrix properties were fitted and solved Based on petrophysical parameters under dry conditions, through fluid replacement model of tight medium, the variation of elastic parameters in seismic frequency bands with gas saturation was analyzed Meanwhile, gas layer sensitivity of different parameters was evaluated with reference to logging data The basic morphologic parameters and weight of rocks was measured, thereby volume and density of rock were calculated The basic physical parameters of rock were measured, and P-wave velocity and S-wave velocity of rocks under variable confining pressure were measured Based on volume, density, P-wave velocity and S-wave velocity, other elastic parameters such as Poisson's ratio, bulk modulus, shear modulus and wave impedance were calculated Gas layer detection is primarily based on the principle that after reservoir bears gas, the compressibility of rocks will be strengthened, and relevant changes include the decrease of P-wave velocity, S-wave velocity, bulk modulus and Lame constant, etc will be drop Basically, gas layer sensitivity parameters analysis is based on the idea that the changes of elastic parameters with gas saturation are calculated and the relative differences between gas layer and water layer are compared according to the bulk modulus of dry rocks and based on fluid replacement method [14] As the Longwangmiao Fm has low-porosity, low-permeability gas layers, the improved White model suitable for describing nonuniform plaque saturation (gas and water in pores non-uniformly distributed) is used This model is a theoretical model mostly used and appropriate for describing the changing features of wave velocity in a seismic frequency band under partial saturation status According to the analysis result of changing conditions of gas layer sensitivity parameters when porosities are respectively 2%, 5% and 8%, the product of Lame constant and density (lr) is most sensitive to gas layers This is consistent with the basic physical principle that gas presence leads to simultaneous decrease of rock density and Lame constant Thought bulk modulus and Poisson's ratio also has good identification capacity for gas layers, they are not as good as lr Therefore, the petrophysical analysis of experimental sample indicates that lr is a sensitive parameter for gas layer detection 5.2 Analysis of hydrocarbon detection effect The maximum offset of field 3D seismic survey in GaoshitieMoxi area is about 5741.15 m, and the average burial depth of top Longwangmiao Fm is 4500 m Since general pre-stack hydrocarbon detection technology requires maximum offset to be close to 1.0e1.5 times that of the burial depth of target formation, the seismic data in this area fully meets the requirements of pre-stack inversion [15] The calculation result indicates that the incident angle of top Longwangmiao Fm is generally around 30 Due to the requirements of pre-stack inversion, the angle gather in this area is classified into parts of stacked data Fig shows pre-stack hydrocarbon detection section crossing wells Wells M009-x1 and M101 are not involved in constraint Fig shows that the Longwangmiao Fm of Wells M009-x1 and M101 is dominated by a yellowered abnormal strip, suggesting a good gasbearing potential in these two wells The subsequent test result shows that Well M009-x1 obtained a test gas production of 263.47 Â 104 m3/d at well section of 4748.5e4998.5 m, and Well M101 obtained a test gas production of 85.90 Â 104 m3/ d at well section of 4596.0e4645.0 m Based on the verification of 24 wells, the overall hydrocarbon detection has a Fig Pre-stack hydrocarbon detection section crossing wells of the Longwangmiao Fm Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004 + MODEL Zhang GR et al / Natural Gas Industry B xx (2017) 1e7 coincidence ratio of 82% The detection section is well coincident with the planar prediction result, and can better reflect the horizontal and vertical changing features of reservoir gasbearing potential Conclusions 1) The 3D wide-azimuth seismic data acquisition is critical for the successful exploration in the Longwangmiao Fm In Moxi area, optimization of 3D seismic geometry was conducted to achieve an even distribution of coverage of target formations in shallow, middle and deep areas Investigation technology of high-precision near surface structures was employed to obtain accurate velocity structure near surface Therefore, acquisition parameters should be selected based on target formations in deep seismic exploration In order to improve data resolution and imaging precision, it is suggested that 3D seismic data acquisition method with wider azimuth, longer spread and wider frequency should be employed to provide high-quality seismic data for pre-stack processing and interpretation, meeting the requirements of oil and gas exploration and development 2) Based on VSP logging data, well-control high-resolution technology was used to improve the SNR in highfrequency band of seismic data, and the method of expanding effective frequency bandwidth can remarkably improve the bandwidth and main frequency of seismic signal It is an effective method for highresolution processing 3) VSP, synthetic seismogram for horizon calibration, variable velocity mapping, reservoir seismic response confirmation based on forward modeling of geological models, and the comprehensive interpretation technology combining seismic attribute with inversion are effective methods for the reservoir prediction of granular beach facies in the Longwangmiao Fm 4) Petrophysical study is a basis for hydrocarbon detection in deep carbonate reservoirs Confirming gas-bearing sensitivity parameters based on coring test and logging analysis can reduce the multiple solutions of seismic data and improve the success ratio of drilling 5) The actual drilling data in deep formations indicate that the development degree of fractures has certain influence on the production of gas reservoirs in the Longwangmiao Fm Fractures can connect pores in carbonate and improve reservoir permeability Thus, research of fracture prediction technology is proposed The above results effectively promote the discovery of large gas fields, and support the targets demonstration and selection of layer-specific well, appraisal well and horizontal well of the Longwangmiao Fm in the whole LeshaneLongnuăsi paleouplift They play an important role both in the confirmation of new effective areas for proven natural gas reserves and in reserves calculation in Moxi area, providing a reference for reserves report and gas-bearing area delineation Currently, the gas reservoir in the Longwangmiao Fm is a super-huge marine facies carbonate reservoir discovered in China with the largest single-body scale Under the background of rapidly-increased gas demand and urgent need of discovery of large high-quality gas reservoirs, the discovery of this gas reservoir has an important implication for promoting the rapid development of natural gas industry and guaranteeing the security of national energy strategy References [1] Huang Jizhong The pros and cons of paleohighs for hydrocarbon reservoiring: a case study of the Sichuan Basin Nat Gas Ind 2009;29(2):12e7 [2] Xu Shiqi, Hong Haitao, Shi Xiaorong Discussion on relationship between LeshaneLongnuăsi Paleo uplift and Lower Paleozoic petroleum potential Nat Gas Explor Dev 2002;25(3):10e5 [3] Song Guiqiao, Yu Shihuan Progress and strategy of the seismic exploration in foothill area Geophys Prospect Pet 2012;51(6):539e47 [4] Wang Shuling Application analysis of constrained tomographic static correction 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seismic fracture characterization technology Geophys Prospect Pet 2012;51(2):193 Please cite this article in press as: Zhang GR, et al., Key seismic exploration technology for the Longwangmiao Fm gas reservoir in GaoshitieMoxi area, Sichuan Basin, Natural Gas Industry B (2017), http://dx.doi.org/10.1016/j.ngib.2016.06.004