Detection Of Fracture-caves In The Mid-deep Of Ordovician, East Of 10th Exploration Area In Tahe Oilfield

Tahe oilfield, which is the first major comprehensive marine reservoir mainly contains fracture-caves of Ordovician canbonates of Paleozoic, has a buried deepness of over 5300 meters for its carbonates reservoirs, and the main reservoir space and productivity is closely related to fracture- caves.Based on previous drilling data of east of 10 th exploration area in Tahe oilfield, there exists plenty beads-like seismic response in mid-deep area below uncomformity surface T74 with a range of 80 m to 120 m. Based on practical data, we can know that the beads-like seismic response is related to caves. Due to the display of favorable reservoir in mid-deep area, this thesis focuses on fracture-caves in the mid-deep of Ordovician of east of 10 th exploration area in Tahe oilfield.In order to detect the caves distribution of interest area and potential oil and gas region, this thesis detect the fracture-caves using coherence, curvature, spectral ratio, accumulative energy difference method based on the fundamental results of numerical simulation of caves. Then, absorption analysis was used to detect the features of oil and gas of interest area. Finally, principal component analysis(PCA) was used to fuse multiple attributes into a geological map of fused attribute. Major research results are shown as follows:(1) In view of the geological characteristics, building seismic response models of different kind of caves and analysing the relationships among seismic response to size of caves, shape of caves, velocity model, number of caves, interval of caves. In general, features of beads-like seismic response become more obvious as the scale of cave becomes greater. However, seismic response decreases when the scale of cave is larger than upper limit. In general, seismic response increases with the decrease of velocity, and increases with the frequency of seismic wavelet.(2) Based on coherence, curvature, spectral ratio and accumulative energy difference method, fracture-caves were detected developed near fractures, which are located in the middle, northern and eastern of interest area. Fracture-caves mainly develop in second set of Yingshan Formation between T75-1-T76.(3) Based on the detection results using spectral ratio method and accumulative energy difference method, detection results show that the value of high rate producing well is low, and the value increases with water saturation, resulting highest value for water well.Based on absorption analysis of oil and gas of interest area, value of detection results are relatively low for high producing well and relatively high for water well, corresponding with other detection methods.(4) Based on previous results, PCA was used to fuse multiple attributes into a geological map of fused attribute. Reservoir prediction results show that potential oil and gas exploration area have medium value of fused attribute and medium scale of beads-like response.This thesis focuses on detection of fracture-caves and features of oil and gas using multiple methods based on forward modeling, and fuse multiple attributes using PCA to predict reservoirs, which has made a good effect. In general, this thesis applies a fracture-caves detection method containing model verifying, detection of fracture-caves and reservoir prediction in the 10 th exploration area of Tahe Oilfield. This study plays an important role in precisely descripting the distribution of fracture-caves and feactures of reservoirs in the interest area, and has significant meaning in improving the success rate of drilling and reducing the risk of drilling.