The Characteristics Of Carbonate Reservoirs In Lower Paleozoic Of Gucheng Low Uplift, Tarim Basin

There are huge potential resources and excellent prospects in the vast areas of East Tarim Basin, and the carbonate in lower Paleozoic is the most realistic exploration domain in this region, which has been accepted by nearly all the explorers. After many years of exploration in Tadong area, some achievements have been gotten, indicating a pretty good exploration prospect. The geological researches, especially those on reservoir characteristics are restricted by a low level of exploration and a large-spaced 2D seismic net.In this study, the newly acquired seismic data and the data acquired from drilling of Well Gucheng4 are used, sedimentary facies distribution along Gucheng platform margin, faults and traps in Gucheng 3D area, single well sedimentary facies of Well Gucheng4, and the sedimentary evolution of Gucheng Slope-break, and are employed in the primary reservoir prediction of mid-lower Ordovician and upper Cambrian to make clear the distribution of different types of reservoirs in different formations of this region and provide preparation for further explorations.Based on this study, karst reservoirs are classified into 3 types, and develop in 3 different periods. The karst reservoirs of Yingshan formation, Ordovician develop most, and mainly develop on the top of Yingshan formation and Penglaiba formation, and in the mid-lower part of Yingshan formation. They are the most important target layer in carbonate exploration domain all around the whole basin. According to the Gucheng 3D seismic data, it is predicted that the advantaged reservoir area of karst on the top of Yingshan formation, mid-lower Ordovician is about 109 km2 within the area fully covered by 3D seismic, and the related gas reserve is up to 30-40 billion m3; the advantaged reservoir area of fractures and vugs under the top karst reservoirs in Yingshan formation is about 169.3 km2, and the gas reserve in the whole 3D seismic region is up to 80-100 billion m3, so this type of reservoir is the most important target layer at present.4 periods of overlapping dolomite reservoirs in upper Cambrian forming in the shoals of platform margin originally develop in the east part of the 3D seismic region, with a width of 7-12 km in east-west direction, and an area of 300 km2. However, they are buried too deep to be explored for the time being.