Fault characteristics and their control on oil and gas accumulation in the southwestern Ordos Basin

3D seismic data recently acquired from the Ordos Basin shows three sets of regularly distributed fault systems,which overrides previous understanding that no faults were developed in this basin.Seismic interpretation suggests that the faults in the southwestern Ordos Basin have three basic characteristics,namely extreme micro-scale,distinct vertical stratification,and regularity of planar distribution.These NS-,NW-,and NE-trending fault systems developed in the Meso-Neoproterozoic e Lower Ordovician strata.Of these,the NS-trending fault system mainly consists of consequent and antithetic faults which show clear syndepositional deformation.The fault systems in the Carboniferous e Middle-Lower Triassic strata are not clear on seismic reflection profiles.The NW-and NE-trending fault systems are developed in the Upper Triassic e Middle Jurassic strata.Of these,the NW-trending fault system appears as a negative flower structure in sectional view and in an en echelon pattern in plan-view;they show transtensional deformation.A NE-trending fault system that developed in the Lower Cretaceous e Cenozoic strata shows a Y-shaped structural style and tension-shear properties.A comprehensive analysis of the regional stress fields at different geologic times is essential to determine the development,distribution direction,and intensity of the activity of fault systems in the Ordos Basin.Current exploration suggests three aspects in which the faults within the Ordos Basin are crucial to oil and gas accumulation.Firstly,these faults serve as vertical barriers that cause the formation of two sets of relatively independent petroleum systems in the Paleozoic and Mesozoic strata respectively;this is the basis for the‘upper oil and lower gas’distribution pattern.Secondly,the vertical communication of these faults is favorable for oil and gas migration,thus contributing to the typical characteristics of multiple oil and gas fields within the basin,i.e.oil and gas reservoirs with multiple superimposed strata.Finally,these faults and their associated fractures improve the permeability of Mesozoic tight reservoirs,providing favorable conditions for oil enrichment in areas around the fault systems.

Study of formation boundary and dip attribute extraction based on edge detection technology

In the seismic profile interpretation process,as the seismic data are big and the small geological features are difficult to identify,improvement of the efficiency is needed. In this study,structure tensor method in computer image edge detection processing is applied into the 2D seismic profile. Coherent attribute is used to extract formation edge. At the same time,extracting the eigenvalues and eigenvectors to calculate the seismic geometric properties which include dip and apparent dip,automatic identification is achieved. Testing the Gaussian kernel function with synthetic models and comparing the coherent attribute and dip attribute extraction results before and after,the conclusion that Gaussian filter can remove the random noise is obtained.

Estimation of aboveground biomass of arboreal species in the semi-arid region of Brazil using SAR(synthetic aperture radar)images

The Caatinga biome is an important ecosystem in the semi-arid region of Brazil.It has significantly degraded due to human activities and is currently a region undergoing desertification.Thus,monitoring the variation in the Caatinga biome has become essential for its sustainable development.However,traditional methods for estimating aboveground biomass(AGB)are time-consuming and destructive.Remote sensing,such as optical and radar imaging,can estimate and correlate with vegetation.Nevertheless,radar imaging is still a novelty to be applied in estimating the AGB of this biome,which is an area with little research.Therefore,this study aimed to use Sentinel-1 images to estimate the AGB of the Caatinga biome in Sergipe State(northeastern Brazil)and to verify its influencing factors.Nineteen sample plots(30 m×30 m)were selected,and the stems of individuals with a circumference at breast height(1.3 m above the ground)equal to or greater than 6.0 cm were measured,and the AGB through an allometric equation was estimated.The Sentinel-1 images from 3 different periods(green,intermediate,and dry periods)were used to consider the phenological conditions of the Caatinga biome.All the pre-processing and extraction of attributes(co-polarized VV(vertical transmit and vertical receive),cross-polarized VH(vertical transmit and horizontal receive),and band ratio VH/VV backscatter,radar vegetation index,dual polarization synthetic aperture radar(SAR)vegetation index(DPSVI),entropy(H),and alpha angle(α))were performed with Sentinel’s Application Platform.These attributes were used to estimate the AGB through simple and multiple linear regressions and evaluated by the coefficients of determination(R2),correlation(r),and root mean squared error(RMSE).The results showed that the attributes individually had little ability to estimate the AGB of the Caatinga biome in the three periods.Combined with multiple regression,we found that the intermediate period presented the equation with the best results among the observed and estimated variables(R^(2)=0.73;r=0.85;RMSE=8.33 Mg/hm^(2)),followed by the greenness period(R2=0.72;r=0.85;RMSE=8.40 Mg/hm^(2)).The attributes contributing to these equations were VH/VV,DPSVI,H,α,and co-polarized VV for the green period and cross-polarized VH for the intermediate period.The study showed that the Sentinel-1 images could be used to estimate the AGB of the Caatinga biome in the green and intermediate phenological periods since the SAR attributes highly correlated with the estimated variable(i.e.,AGB)through multiple linear equations.