Tectono-sedimentary Analysis And Petroleum Geological Significance Of Broken Thrust Uplift Belt In Compressive Basin

Growth Structures plays an important role on control ancient relief, sedimentary processes and sedimentary facies distribution in compressive basin. With the widespread use of3D seismic data, recently subtle tectono-sedimentary analysis of sedimentary basins has attracted much attention. Based on the expatiation of the tectonic development and sediment filling history, the sequence stratigraphic framework of Early Cretaceous in Tarim Basin, this thesis discusses the growth structures pattern, activity, evolution of Yakela Uplift and their controls on sedimentary processes highlighting on sediments entry, transportation pathway, sedimentary facies distribution. Together with the reservoir-cap combination, finally, this paper accesses the favorable traps distribution and presents integrated model of tectonic-sedimentation-hydrocarbon accumulations. The results could not only enrich the theory of tectono-sedimentary analysis of rift basin in eastern China but also be helpful to guide the oil and gas exploration in the Yakela Uplift. The main results in the thesis are as follows:1. On the seismic sections, Yakela Uplift is the basin basement broken uplift, which is formed in tectonic stress transfer from compressional basin of orogen margin. For Tarim Basin in the Early Cretaceous as well as many compressive basins, the shrinkage of basin is often achieved by antithetic fault controlled basement uplift, rather like the foreland basin that formed fold-thrust belt.2. Analysis of fault activity by the fault throw method in Yakela uplift on both sides of Luntai and the Yaha fault which are boundary fault of Yakela uplift. Luntai fault is in the southern margin of Yakela uplift, meanwhile Yaha fault is in the northern margin of Yakela uplift. On the3D seismic sections, Luntai and the Yaha fault were reverse faults in Yageliemu Formation period. The Yaha fault inversed negatively in Shushanhe Formation period, but until the Paleogene, the Luntai fault occurred negatively inversion. The Yaha and Luntai fault have the same tectonic activity, that is strongly in the middle east of Yakela uplift, but weakly in the western. 3. Combined with the analysis of seismic section, logging, drilling, identify the Yakela uplift has the same sedimentary characteristics in the Early Cretaceous.①Stratigraphic inclination angle in the top of Yakela uplift is small, while stratigraphic inclination angle on the both sides is large.②The stratigraphic thickness of statistics have showed striking differences between the top section and the both wings section in the Yakela uplift, that is the stratigraphic thickness of top is thin and the thickness of wings is thick.③Developed unconformity is easy to be found in the top of Yakela uplift; in the wings of the uplift, there is overlap phenomenon.④The same set of stratum lithology changed fining gradually from top to wings.4. Relying on the processing and interpretation of3D seismic data, Early Crataceous tectonic landform in Yakela uplift is restored approximately. Yakela uplift extends along NEE with tectonic characteristics of high-narrow in east part and low-broad in west part. Respectively according to the Luntai thrust fault in the southern margin and Yaha potential fault in the northern margin, Yakela uplift is divided into three secondary geomorphic unit:the central uplift belt, northern slope belt and southern fault ramp belt.5. Based on the study of development and evolution of the marginal fracture in Yakela uplift, synthetically comparing the3D seismic and drilling data, tectonic evolution of synsedimentary uplift in Yakela is divided into two periods:developmental phase and extinction period.(1) In the development period, the regional structure extrusion stress acted so strongly that the formation in Yakela was tilt-lifted and suffered erosion, correspondingly lead to Yageliemu formation sedimentary gap of the central uplift belt, and a set of proximal coarse clastic sediment accumulated both in northern slope belt and southern fault ramp belt. In addition, the regional structure extrusion stress acted increased gradually from west to east, thus the geographic features is East West High low in Yakela uplift.(2) In the extinction period, the regional structure extrusion stress acted so weakening that the Yakela uplift integrally falling even negative inversion locally, and has been overlapping gradually by lateral layer. Sedimentary sequence of this period is developed to fining upward. Furthermore, negative inversion extrusion stress of Yaha fault weakened from west to east, which conduce to some secondary tectonic depressions formed in the western region of Yakela uplift.6. Using method of analysis heavy mineral components and clastic rock components, sediment is identified not the same provenance between periphery of Yakela uplift and the region far away from the uplift, and the sediment source components differences between the east and the west in Yakela uplift. Conglomerate thickness and gravel content is largely used to localize the ancient channels. Such statistics show a high degree of similarity; all maximum are mainly distributed in the marginal fracture in Yakela uplift and the high values zone reflecting the ancient channel basically,while the value reduce slower towards the vertical strike and the value is unsteadily along the strike. According to those features discussed above, development of sediment source along the marginal fracture be showing scattered points distribution, and sediment transportation pathway is thought to perpendicular to the strike of Yakela uplift generally for short distances. At the same time, considering the sediment transportation distance controlled by the geomorphological features in Yakela uplift, the distance of sediment transportation pathway is long relatively in eastern uplift where the discrepancy in elevation is big and the distance is short in western uplift where the discrepancy in elevation is small.7. We described the sedimentary facies type of Yakela uplift and the periphery. Combined with the analysis of outcrop, logging, drilling, core, the sedimentary facies of Yageliemu Formation is mainly fan delta facies, and three subfacies are fan delta plain, fan delta front and front fan delta respectively; the sedimentary facies of Shushanhe Formation is mainly coastal shallow-lake facies, and the subfacies are consist of bar sand body of lakeshore facies and mudstone of shore-shallow lacustrine facies.8. Fault slope break and bending slope break separately identified located in the south and north sides of Yakela uplift. Fault slope break controlled by the Luntai synsedimentary thrust fault in southern margin of uplift and bending slope break controlled by the Yaha reverse regulation fault northern margin of uplift. Combined with the analysis of seismic facies, logging, drilling, in Yageliemu Formation depositional stage, fan delta sediments developed in the downthrow block of lower slope breaks, in Shushanhe Formation depositional stage, bar sand body of lakeshore facies mainly distributed in the upthrown block of upper slope breaks. It can be proved that the slope breaks between the two sides of Yakela uplift constrains sedimentary facies distribution.9. According to statistical data of hundred wells conglomerate, sandstone thickness and gravel content, combined with the comprehensive analysis of3-D seismic section properties, we described the sedimentary facies distribution of Yakela uplift in Yageliemu Formation and Shushanhe Formation:in Yageliemu Formation depositional stage, fan delta sediments developed on both northern slope belt and southern fault ramp belt; coarse clastic sediment in central uplift belt as provenance is eroded. Bar sand body of lakeshore facies mainly distributed on the central uplift belt.10. Combined with reservoir properties, suitable reservoirs within the sand body is predicted in the fan delta deposited on the periphery of Yakela uplift, while the bar sand body is forecasted in lakeshore facies deposited on the top of uplift. Comprehensive utilization of exploration results, tectono-sedimentary Analysis, three types of traps are presented in the study area:The micro-amplitude anticlinal traps in central uplift belt, sandstone up-dip pinch out traps in northern slope belt and fault-lithologic traps in southern fault ramp belt are a variety of primary traps of Early Cretaceous in Yakela uplift. The Yakela uplift tectonic-sedimentation-hydrocarbon accumulation model is presented as followings:the Yakela uplift exerted an important influence both on the sedimentary facies distribution and on suitable reservoir distribution; the marginal fracture penetrating into the deep source rocks by connecting with shallow reservoirs provide the major pathway of hydrocarbon migration; the Yakela uplift and marginal fracture eventually formed beneficial hydrocarbon trap.