塔中奥陶系生物礁地震识别与预测

THE SEISMIC IDENTIFICATION AND PREDICTION OF THE REEF IN THE ORDOVICIAN OF THE CENTRAL TARIM BASIN

塔中Ⅰ号构造带奥陶系上统发现生物礁以来,生物礁识别与储层预测成为该区油气勘探的重要研究课题。通过钻遇礁体的地震层位标定与追踪,发现在地震剖面上礁体具有多种丘状外部形态、上覆地层有明显超覆减薄现象;礁体内部出现杂乱反射、弱反射、空白反射等地震响应特征,与围岩有明显差异;由于礁体发育特征的差异,台地边缘与台内礁体的地震响应特征各异,台缘发育大型堤礁、台内以小规模点礁为主。在研究塔中奥陶系礁体地震—地质响应特征的基础上,通过编制生物礁发育层段等厚图、生物礁沉积时古地貌图,结合岩相古地理、地震属性、三维可视化技术的分析,识别与预测了塔中62—塔中82井区生物礁体的分布与发育特征,发现上奥陶统礁体垂向上加积、横向上错落叠置连片,发育4～5个旋回,复合厚度达200～300m,宽1～5km,延伸长度为120km,主要沿台地边缘呈条带状展布。在礁体预测的基础上,油气勘探取得重大突破,发现了大型生物礁油气田。

The reef identification and reservoir prediction have become the key research task of the oil and gas exploration in the Central Tarim Basin since the reef was discovered in the upper Ordovician in No.1 structure belt in Tazhong area.The seismic horizon calibration and horizon tracking of the drilled reefs indicate that the reefs express as various mound external shapes in the seismic section,and there are obvious overlapping and thinning phenomena in the overburden layer of the reef;and there are such seismic response properties as littery reflection,weak reflection,and blank reflection in the interior of the reef,which are quite different from that in the surrounding rock.Due to the differences of the reef development features,the seismic response properties of the reef in the platform margin are dissimilar to that within the platform.The large barrier reefs are developed in the platform margin,and small-scale patch reefs are developed within the platform.On the basis of the study for the seismic and geologic response features of the Ordovician reefs in Central Tarim,isopach map of the horizons where the reefs are developed and palaeogeomorphology map of the reef sedimentary phases are drawn,and combined these maps with such techniques as lithofacies palaeogeography,seismic attribute and 3D visualization to recognize and predict the reef distribution and development features in the areas between well 62 and well 82 in Central Tarim.It is indicated that the reefs are aggraded vertically,and are intricate and superposed in the upper Ordovician.There are 4-5 reef cycles with complex thickness of 200-300 m,width of 1-5 km and extending length of 120 km,which behave as strip-shaped distribution along platform margin.On the basis of the reef prediction results,great breakthrough has been made in the oil and gas exploration,and large-size reef oil-and gas-fields have been discovered.This method can be a reference for the reef identification and reservoir prediction in the area similar to Tazhong area.