key seismic exploration technology for the longwangmiao fm gas reservoir in gaoshiti moxi area sichuan basin

Research ArticleKey seismic exploration technology for the Longwangmiao Fm gas reservoir Zhang Guangronga,b,* , Ran Qib, Liao Qib, Yu Yib, Zhang Xuanb, Chen Kangb, Cao Hongc, Zeng Mingb,

Research Article

Key seismic exploration technology for the Longwangmiao Fm gas reservoir

Zhang Guangronga,b,* , Ran Qib, Liao Qib, Yu Yib, Zhang Xuanb, Chen Kangb, Cao Hongc,

Zeng Mingb, Wen Longb, Lai Qiangb

a Chengdu University of Technology, Chengdu, Sichuan 610059, China

b 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 6 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 pre-diction 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 above-mentioned 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; Gaoshiti eMoxi area; Early Cambrian; Longwangmiao Fm gas reservoir; 3D seismic; Well-control seismic exploration; Gas-bearing sensitivity parameter; Reservoir prediction

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 explo-ration[1] Located in the core of the LeshaneLongnu¨si paleo-uplift, 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 8 revealed a test gas

* Project supported by the National Key S &T Special Project “Development

of large oil and gas fields and CBM ” (No.: 2011ZX05004-005,

2016ZX05004-005), 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.

ScienceDirect

Natural Gas Industry B xx (2017) 1 e7

www.elsevier.com/locate/ngib

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/ ).

production of 190  104 m3/d in the Longwangmiao Fm,

recording another breakthrough after gas obtained in Well

Gaoshi 1 in Sinian in the Sichuan Basin This further verified

the good gas-bearing potential in the Sinian and the Lower

Paleozoic in the LeshaneLongnu¨si 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

diffi-cult 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

pre-diction technology was deepened, favorable well locations

were discovered and ultimately good exploration effects were

achieved

1 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

paleo-geomorphology 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

inter-bedded with a small amount of sandstone Its electrical

property is characterized by low GR value, presenting

low-amplitude box shape Its resistivity is middleehigh,

present-ing peak shape

1.2 Physical properties

According to the statistic on physical properties from

cor-ing 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

(aver-agely 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

Long-wangmiao 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  104 m3/d in the well section 4684e4712 m, and 109.49 104m3/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 obvi-ously 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 conven-tional 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

2 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 deploy-ment and separated impledeploy-mentation 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 5 areas Orthogonal observation system was used, with basically similar acquisition parameters Field operation pa-rameters 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 5 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 domi-nantly 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 topo-graphic conditions in Moxi area, there are three difficulties in pre-stack processing First, the surface relief requires static

correction to a certain extent Second, the Lower Paleozoic in

the target formation has relatively low SNR, and noise

inter-ference is mainly presented as multiples, surface wave,

in-dustrial 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

in-verse 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

im-aging 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

low-frequency surface wave and abnormal energy on

pre-stack data and the random noise on post-pre-stack data,

SNR is improved

(3) Using the well-control seismic data processing

technol-ogy, 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

appli-cation 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 sur-face, 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

3 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 Long-wangmiao Fm in Moxi area led to little difference in formation velocity in the overlying and underlying strata of top Long-wangmiao 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

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

Reser-voir 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

4 Reservoir prediction

4.1 Qualitative reservoir prediction

Reflection strength gradient is a seismic attribute

Funda-mentally, 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

con-stant, its gradient is close to 0 If the reflection strength

in-creases 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

ten-dency 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

win-dow is selected Here, 25 ms moving winwin-dow is selected

ac-cording 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 Long-wangmiao Fm Generally, the LongLong-wangmiao 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 observa-tion 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 li-thology 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 pre-stack geostatistical inversion is a method which combines stochastic simulation theory with seismic inversion It employs Bayesian inference based Markov ChaineMonte Carlo algo-rithm 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 high-resolution logging data and low-high-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 1 Planar map of reflection strength gradient of the Longwangmiao Fm in Gaoshiti eMoxi area.

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 3 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

low-impedance reservoir, and cold light blueeblueeblack color

indicates relatively high-impedance non-reservoir The

Long-wangmiao 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 pre-diction 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 2 Contrast between the sections of deterministic inversion and pre-stack geostatistical inversion.

Fig 3 Wave impedance section crossing wells from pre-stack geostatistical inversion of the Longwangmiao Fm.

Fig 4 Planar map of seismic prediction of reservoir thickness in the Long-wangmiao Fm in Gaoshiti eMoxi area.

5 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

gas-bearing sensitivity parameters, and used pre-stack inversion

technology for hydrocarbon detection, achieving the

gas-bearing potential prediction of thin reservoirs of granular

beach

5.1 Petrophysical analysis

Basic elastic parameters of tight carbonate in the

Long-wangmiao Fm under dry and water saturation conditions were

obtained through core ultrasonic wave measurement and

ma-trix 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

morpho-logic parameters and weight of rocks was measured, thereby

volume and density of rock were calculated The basic

phys-ical 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

calcu-lated 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 Long-wangmiao 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 fea-tures 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 experi-mental sample indicates thatlr 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

re-quirements of pre-stack inversion, the angle gather in this area

is classified into 5 parts of stacked data.Fig 5shows pre-stack hydrocarbon detection section crossing wells Wells M009-x1 and M101 are not involved in constraint.Fig 5shows that the Longwangmiao Fm of Wells M009-x1 and M101 is dominated

by a yellowered abnormal strip, suggesting a good gas-bearing potential in these two wells The subsequent test result shows that Well M009-x1 obtained a test gas production

of 263.47 104m3/d at well section of 4748.5e4998.5 m, and Well M101 obtained a test gas production of 85.90 104

m3/

d at well section of 4596.0e4645.0 m Based on the verifi-cation of 24 wells, the overall hydrocarbon detection has a

Fig 5 Pre-stack hydrocarbon detection section crossing wells of the Longwangmiao Fm.

coincidence ratio of 82% The detection section is well

coin-cident with the planar prediction result, and can better reflect

the horizontal and vertical changing features of reservoir

gas-bearing potential

6 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

pro-cessing 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

high-frequency band of seismic data, and the method of

expanding effective frequency bandwidth can

remark-ably improve the bandwidth and main frequency of

seismic signal It is an effective method for

high-resolution 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

technol-ogy 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

Long-wangmiao 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 LeshaneLongnu¨si paleo-uplift 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

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