| Since entering the 21 st century, a series of important igneous rock oil and gas reservoirs have made great progress and breakthrough, such as Xushen gas field and Changshen gas field of Songliao Basin, Kelameili Gasfield of Junggar Basin, etc. Oil and gas reservoir exploration of igneous rock has been gradually trended to maturing stage, which become a hot spot in the study of deep oil and gas exploration and development. The eastern sag of Liaohe basin has been carried out oil and gas exploration on igneous rock for more than 20 years, in recent years, there has observed better oil and gas shows in igneous rock of dozens of exploratory wells, which has formed the industrial scale of igneous rock oil and gas production capacity, and has good exploration prospect. Igneous rock oil and gas reservoir has become the important exploration and development area of Liaohe basin. Compared with other basins, volcanic strata sequence of Liaohe basin is affected by multiphase magmatic activities, which has the characteristics of multiple series of strata, wider distribution, frequent interbedding with sedimentary rock, etc. Liaohe basin is influenced by long term of Tan-Lu fault zone activities, which has many later tectonic movements, the igneous rock body generally have broken, fracture is developed widely, while fracture not only can be used as a good space for oil and gas reservoir, and also the important channel for the oil and gas migration, therefore, the recognition and prediction of fracture has become the important basis for igneous rock reservoir evaluation and well placement in research area. However, due to affected by multi-layer reflection effect of the overlying igneous rock series of strata, seismic data of target strata has poor quality, and low signal noise ratio(SNR), the resolution of the traditional fracture prediction method is relatively lower, therefore, it needs to find a way to improve the resolution of fracture prediction method.This paper, with reservoir fracture as the core, using geological, well logging method for comprehensive evaluation of igneous rocks fracture in the research area, establishes the corresponding relation of fracture development degree and oil-gas possibility of reservoir. It adopts seismic discrete frequency amplitude technology to predict igneous rock fracture, and uses core-imaging logging to measure the fracture development degree and test results, and compared with conventional seismic attributes fracture prediction results, the fracture prediction method proposed in this paper has feasibility. The fracture prediction results in this paper have been used for well deployment of igneous rock exploration.The specific research process, method and results are as follows 1. Geologic-logging comprehensive assessment of igneous rock fractureThe comprehensive geologic-logging assessment and quantitative characterization of igneous rock fracture are the basic work in the study of fracture, method in this paper can be divided into direct description and indirect prediction. Direct description method includes core fracture description and image logging fracture description, description includes fracture genetic type, fracture development degree, fracture occurrence, fracture effectiveness; and indirect method is through the correlation analysis of the test result of oil test conclusion, oil-bearing occurrence, well logging interpretation, and the maximum of total hydrocarbon oil to determine oil-gas possibility of reservoir, thus establish the corresponding relation of fracture development degree and oil-gas possibility reservoir.(1)Core fracture descriptionIt conducts quantitative characterization and comprehensive assessment on 225 pieces of igneous rock core fracture of 23 Wells, including fracture genetic type, fracture development degree, fracture occurrence, and fracture effectiveness.Fracture genetic type: structural fracture as primary, a small amount of shrinkage fracture observed in diabase, a small amount of explosive fracture observed in trachyte, and respectively accounted for 95.1%, 3.1% and 1.8%;Fracture development degree: diabase best fracture development degree and the basalt class times, poor trachyte, fracture surface porosity were 1.459%, 1.446%, 1.333%, and at the same time, according to the results of the core fracture quantitative description to establish core fracture development degree evaluation standard, divide the core development degree of each well development, the development, development of three levels.Fracture occurrence: three kinds of lithology are given priority to high Angle fracture, oblique fracture is the second, horizontal fracture development is the least, and relatively accounted for 61.0%, 32.4%, 6.6% of the total;Fracture effectiveness: trachyte fracture effectiveness is relatively better, diabase fracture effectiveness is the second, basalt fissure effectiveness is relatively poor, no filling fracture percentage respectively are 70.8%, 67.5%, 62.8%.(2)Imaging-logging fracture descriptionAccording to the FMI imaging logging response, it describes fracture development degree and fracture occurrence of 37 m well section, 8 sections of igneous rock of 6 Wells in the research area, and compared with development degree of core fracture.Fracture development degree: imaging logging fracture linear density range is 0.80 ~ 1.60 piece/m, which is in conformity with the development degree assessment results of core fracture, and according to the imaging-logging fracture linear density, it predicts the fracture development degree of well section without core.Fracture occurrence: with vertical fracture and high Angle fracture as priority, and it is in conformity with core fracture occurrence.(3)Set up corresponding relation of fracture development degree and oil-gas possibility of reservoirThrough the result correlation analysis of oil test conclusion(industrial oil/gas reservoir, low oil yield /gas/water/gas-oil reservoir, dry reservoir), logging interpretation, oil/gas reservoir, poor oil/gas/water reservoir, dry reservoir), the maximum value of total hydrocarbon, oil-bearing occurrence(oil stain/oil spots, fluorescence, non-fluorescence) on 39 wells, 70 well sections in research area, it determines the oil-gas possibility of reservoir, and compared with core- imaging logging fracture development degree, sets up the corresponding relation of fracture development degree and oil-gas possibility of reservoir.Fracture developed/better developing well sections have the possibility of industrial oil/gas reservoir, that is oil-gas possibility of reservoir is relatively better; poor developed well section is more likely to be dry reservoir, and the oil-gas possibility of reservoir is relatively poor, so in the study of fracture prediction, put the fracture developed/better developing zone as the favorable exploration area, try to avoid the poor fracture development zone.2. Igneous rock fracture seismic predictionIn view of the the quality of seismic data of target reservoir is poor in research area, low dominant frequency(12~20Hz) and low signal noise ratio(SNR), and the resolution of traditional method for fracture prediction is relatively lower, this paper puts forward discrete frequency amplitude technology for fracture prediction.Discrete frequency is a seismic imaging method based on spectrum analysis, and its basic principle is Fourier transform. By discrete frequency can convert the seismic data of full spectrum band from time domain to frequency domain, and extracts a narrow bandwidth of seismic data volume, this narrow band data volume is the discrete frequency data volume. To extract amplitude attribute of discrete frequency data volume on target reservoir, can get the discrete frequency amplitude attribute.Due to the existence of fracture zone may usually leads to the decrease of the frequency of seismic wave, and the extracted discrete frequency amplitude attribute may well reflect the change of single frequency(dominant frequency) of seismic data volume energy. On the premise of lithology relatively uniform, the attenuation of dominant frequency energy can be considered to be caused by the fracture, and the lower of the discrete frequency amplitude represents the fracture development is better. Therefore, the relative full frequency of seismic data, the single frequency of seismic data is more sensitive to discontinuity of seismic axis, which can identify the small fracture that is difficult to be found by full frequency of seismic data, so as to improve the resolution of the fracture prediction.Discrete frequency amplitude attribute is expanded by identifying the discontinuity of seismic event, while the discontinuity of seismic axis may be affected by lithology, heterogeneity, fracture and other factors. Therefore, before fracture prediction, it needs to carry on lithological inversion of three types of igneous rock in research area to eliminate the influence of lithology on the result of fracture prediction. Then, it uses discrete frequency amplitude properties for fracture prediction of lithology, stage of igneous rock in the research area. Compared the fracture prediction results with other conventional seismic attributes(coherence, curvature, ants volume), it can identify the small fracture that is difficult to be found by full frequency of seismic data, so as to improve the resolution of the fracture prediction and result is completely consistent to the comparison of core- imaging logging fracture development degree, and the coincident rate with the test results is higher, thus further verifies the feasibility of discrete frequency amplitude technology for fracture prediction. Finally, it conducts well deployment based on the predicted results, and has 2 deployment Wells(ho34 well and x44 well), where x44 Well is located at target reservoir(S3I-II diabase rock) oil testing conclusion is industrial oil reservoir, and the X fracture development degree of target reservoir coring section is also in conformity with the predicted results; and oil testing conclusion of ho34 well is not out, but the logging interpretation of target reservoir is oil reservoir(the 3rd member of Shahejie Formation S3q3 trachyte).3. The distribution rule of igneous rock fracture development zoneUsing discrete frequency amplitude properties for fracture prediction of lithology, stage of igneous rock in the research area, and from the perspective of structure, lithology and lithofacies, summarize the distribution rule of igneous rock fracture development zone.(1)The distribution rule of volcanic rock fracture development zoneHongxing-Xiaolongwan Region develops two forms of diabase intrusive bodies, one form is dish structure, another is plate structure. Three diabase bodies of the 1st member of Shahejie Formation, S3I-I and S3I-IV diabase bodies of the 1st member of Shahejie Formation are plate intrusion, plate form fracture develops along the fault zone, the fracture development degree declines as it is away from the fault zone, and reaches the maximum development at about 2 km; S3I-II and S3I-III diabase bodies intrusive form is dish structure, the edge of dish structure intrusive body, and area near fault zone, general depth center fracture develop better. At the same time, the core fracture is given priority to structural fracture, which indicates that the diabase fracture in this area is mainly formed by later reconstruction.(2)The distribution rule of diabase fracture development zoneS3q3 trachyte and S3q4 basalt has the same distribution rule of fracture development zone. When the heterogeneity of the rock itself and its upper igneous rock is relatively larger, the seismic facies are relatively clutter, seismic event is discontinuous, at this point, the discrete frequency amplitude attribute not only reflects the fracture development zone, and also reflects the stronger heterogeneity of rock bodies; when the rock bodies has good layered property, and seismic event is relatively continuous, and it reflects effective fracture development zone information at this time. S3q5 development effusive facies of basalt, the top is sedimentary rock, lithology is relatively uniform, reflection interface is stronger, seismic event is relatively continuous, at this point, it basically reflects the effective fracture development zone information.The distribution rule of S3q3 trachyte, S3q4 and S3q5 basalt fracture development zone: fracture near the fault zone is developed relatively better, fracture far away from the fault zone is relatively developed poor. |
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