| Chentuokou depression is a negative-second-order tectonic units in Jianghan basin. Xinggouzui formation is an important layer for exploration target and has a good exploration prospect because of its low degree of prospecting and rich residual resource. According to the third-time resource assessment, the resource of Chentuokou depression is 1013×104 t. By doing research such as provenance direction and sedimentary environments of Chentuokou depression, we point out the potential direction to guide the rolling exploration and development, which has a great significance on the "adding reserves and increasing production".Using theories and methods such as sequence stratigraphy, sedimentology, logging geology, seismic theory, sequence stratigraphy of Ⅱ and Ⅲ oil groups from the lower segment of Xingouzui formation is divided. Then log facies and seismic facies is identified in the sequence stratigraphic framework. And combining with related information such as the provenance analysis and lithofacies characteristics, types of sedimentary facies and distribution of sedimentary system is studied. Main understanding is as follows:1、By using the geology, logging, seismic data comprehensively, Xingouzui formation is a second-order sequence. The top and bottom surfaces are T8 and T9 reflection surfaces, which are obvious unconformity contacts. On the basis of summarizing the sequence interface at all levels, Xingouzui formation is divided into four third-order sequences (SQXS SQXX1 SQXX2 and SQXX3), which are separated by T8, T81, T811, T82 and T9 interfaces. Surfaces of the third-order sequence can be identified on the seismic sections for its cuttings and on laps on the margin of basin and conformity on the center of the depression.. Those surfaces difficult to find can be seen on well logging curves. The curves of the bottom of sequence boundary are box, block or mutation of base value. Characteristics of SQXX3 on seismic section are thickness, medium amplitude, medium continuously. Characteristics of SQXX2 on seismic section are thinner thickness, strong amplitude, medium continuously. Sequence can be divided into LST,TST and HST by recognizing IMS and MFS. IFS and MFS of SQXX3 are the top and bottom surfaces of clay-interlayer which can be traced in the whole basin. IFS and MFS of SQXX2 are the top and bottom surfaces of stable argillaceous sediments in a region. By analyzing the changes of lake levels.it can be seen that the trend of sedimentary base-level change is rise slowly.2、The direction of provenance is analyzed with the heavy mineral analysis method(single heavy mineral and combined heavy mineral group methods) and sandstone dispersion system method(sandstone thickness and sand mudstone ratio) in this paper. Due to the a little data in the study area, it can be found that the direction of provenance comes from the north-west ancient han river(the direction of Xingou-laoxin area),which controls the deposits of northern area in Chentuokou depression. It can be found that, from northwest to southeast, the contents of heavy mineral increase, thickness of sandstone is reduced ,thickness of mudstone increases and sandstone mudstone ratio is reduced.3、According to the well logging curves in our religion and core analysis, electrofacies models of different sedimentary environments are summed. There are main two eletrofacies to be identified (delta logging facies and lake logging facies).Delta sedimentary facies include two subfacies:delta front and front delta. Eletrofacies can be seen as follows:underwater distributary channel logging facies model (bell), underwater distributary bay logging facies model (micro tooth or smooth rectilinear or finger), estuary dam logging facies model (funnel), sand sheet logging facies model (finger), predelta mud logging facies model (bell).Lacustrine facies include coastal-shallow lake facies and shallow lake facies. Eletrofacies can be seen as follows: dolomitic flats logging facies model(micro tooth bell), mudflat logging facies model(tooth flat), shore sand logging facies model(finger).4、According to the principle of seismic stratigraphy and in combination with the characteristics seismic reflection events of Ⅱ and Ⅲ oil groups, five kinds of typical seismic facies are divided from the external morphology and internal structure and seismic reflection to reflect the depositional geological characteristics:parallel sheeted seismic facies, subparallel sheeted seismic facies, wedge seismic facies, mounded seismic facies and filling seismic facies.These seismic facies respond to different sedimentary environments respectively. Parallel sheeted seismic facies and the subparallel sheeted seismic facies reflect the depositional environment with weak hydrodynamic power. Wedge seismic facies reflects rapid-deposition of sand and mud of sedimentary environment. Filling seismic facies reflects the sedimentary of delta front, delta and shallow lake. Mounded seismic facies reflects delta sedimentary environment.5、Types of sedimentary facies and the distribution of sedimentary systems of Ⅱ oil group and Ⅲ oil formation is analyzed with the lithofacies features (color, rock types, granularity and so on) logging facies, seismic facies and provenance analysis. Delta-lake sedimentary system is developed during the Ⅱ oil group and Ⅲ oil formation. Sedimentary subfacies are delta front and front delta. Microfacies are underwater distributary channel, underwater tributary bay, mouth bar, sheet sand and predelta mud. Lake facies includes coastal lake facies and shallow lake subfacies. Microfacies includes beach sand, mud flat, cloud mudflat, mud plaster flat, shallow lake mud plaster mass mud, cream mudflat, mudflat and so on.During the sedimentary period of Xingouzui formation, the ancient climate changes from subtropical semiarid-arid climate to humid climate gradually. Longitudinally, Ⅲ oil group is given priority to delta front subfacies and become to Ⅱ oil group upwards gradually, which is a predominantly shore and shallow lake. It reflects that the water becomes darker, which is an expansion process of lake basin. |
PDF Full Text Request