Comprehensive Prediction Of Precise Reservoir Fracture And The Application Stduy On The Gas-bearing Detection

With the continuous discovery of unconventional reservoirs and their outstanding resources potential,the relevant research of fracture development and distribution,which having important influence on the hydrocarbon distribution and seepage system,has gradually become a vital part of unconventional reservoir exploration and development.Natural fractures are the main reservoir spaces and migration paths of oil and gas.The existence of fractures improves the permeability of reservoirs,and the fracture-developed degree also determines the distribution of reservoirs.Therefore,the accurate description of fractures' spacial distribution regularity is the key to effective reservoir evaluation.However,due to the complex development mechanism and the irregular distribution,the difficulty of fractures' identification and prediction has greatly increased.This paper takes a carbonate reef-bank facies reservoir in northeastern Sichuan as an example.Starting with making full use of the abundant and effective information contained in pre-stack and post-stack seismic data,my research combines drilling and logging data with geological background and focus on the comprehensive prediction fracture method based on seismic multi-information fusion.And the seismic response characteristics,spacial distribution and development degree of fractures in the target formation are defined.And then,the thickness prediction of reef reservoir and hydrocarbon detection technology based on frequency attenuation attributes are carried out.The obtained achievements can provide technical support for stable production and efficient development of reservoirs in this study area.These results can also provide reference and guidance for the exploration of the other similar hydrocarbon reservoir.The main contents and achievements of this paper are as follows.(1)Aiming at strengthening the seismic response mechanism of fractures,the research on seismic data target processing and seismic response forward modeling technology of fracture development zone are carried out.Based on nonlinear anisotropic diffusion filtering technology and high-resolution processing technology of dynamic deconvolution in cepstrum time-frequency domain,this paper realizes the denoising and high-resolution processing of post-stack seismic data volume,and it lays an important foundation for the research of medium-and small-scale fracture prediction.Through MIVMAS seismic forward simulation,the seismic response characteristics of fracture s are comprehensively analyzed for different types of fault models.The coherence attributes,curvature attributes and ant colony body are selected as the sensitive parameters of seismic response in fracture development zone based on the analysis of different attributes' seismic response characteristics of the fracture belts in drilling cross section.(2)Fracture prediction based on post-stack seismic attribute data volume fusion technology,which combines the weighted coherence,frequency-division coherence,volume curvature and frequency-division ant body,precise depiction of smal-and medium-scale fractures is realized.It is concluded that fractures are mainly developed in large faults and tectonic fold zones,and fractures are also developed in the eastern slope zone,but the overall fracture-developed degree decreased.Attribute fusion technology is used to fuse fracture prediction data volume of different scales into fracture fusion body,which simplifies the process of fracture comprehensive evaluation.(3)A high angle and small-scale fracture prediction technique based on improved prestack P-wave azimuthal anisotropy is presented.Guided by the strike of geological structure,this paper improves the traditional prestack P-wave azimuth anisotropy algorithm and method flow,in order to make full use of azimuthal anisotropy information of the velocity.The improved method is more suitable for steep dip formation,and some errors of fracture prediction method based on post-stack data are solved(such as well L1 and well L4).The coincidence rate of fracture prediction results and the actual drilling statistical result of fractures is about 80%,which verifies the high accuracy of prestack P-wave anisotropic fracture prediction.Based on the ground stress analysis and stress field inversion,the micro-fractures geological analysis technique is developed.By means of structural deformation analysis method,the possibility of micro-fracture system development is predicted by the stress field inversion.It is considered that micro-fracture system mainly develops near the large faults and flexural zones.(4)The results of fracture prediction obtained by different methods are analyzed,and the comprehensive evaluation of fracture at different scales is carried out according to the main controlling factors of fracture development.In this study,the fracture scale is divided into large scale,medium and small scale and micro scale.Based on the analysis of the main controlling factors of fracture development,it is concluded that the fracture development zones of Changxing Formation mainly distribute in the north of the study area and are concentrated in the northwest and southeast.The large faults mainly distribute in the northwest,near the NNE strike.The secondary faults mainly distribute in the marginal zone of reef bank located at southern part of the study area.There are also some secondary faults in the northern area.The medium fault systems mainly develope in the north-central part of the study area and the area near the major faults.The small-scale faults are widely developed in the study area and the regularity of its distribution is not obvious.(5)The reef reservoir thickness based on unsupervised clustering of multifrequency components.In this paper,four methods used to estimate the time thickness of thin bed are discussed and compared.Tthe amplitude of different seismic traces(different time thickness)have different features,and the difference between the curve shapes of the spectrum is obvious enough to differentiate with each other.Based on this observation,I propose the mapping the time thickness of thin bed by clustering the decomposed amplitude spectrum of the seismic traces.The thickness of reef reservoir is qualitatively described and the favorable distribution range of reef reservoir is determined.(6)A package of seismic spectrum characterization-based attenuation attributes to evaluate apparent attenuation effects are proposed.The calculation of each frequency attenuation attribute does not require an absolute Q value.The application of filed data proves that almost all the attributes are well correlated with the actual drilling.Analyzing the relationship between fracture and gas-bearing property,the control effect of fracture on hydrocarbon accumulation can be clarified.It has important guiding significance to find high-yield gas reservoirs.