Preliminary evaluation of hydrocarbon prospects of Cretaceous strata in Xiangfan-Zaoyang sag, Nanxiang basin

Hydrocarbon resource exploration of the Cretaceous strata in Nanxiang basin has been rarely carried out. Through research on mining geology and geochemical oil and gas exploration in the study area, the authors obtained some information of Cretaceous hydrocarbon source rock in Xiangfan-Zaoyang sag: the salt wells in the eastern part of the sag show that in the middle of the upper Cretaceous strata, the hydrocarbon source rock is well developed and characterized by high abundance of organic matter and moderate evolution degree, suggesting certain hydrocarbon-generating capacity. Half of the samples are related to gases of the mature oil, as evidence by methane carbon isotope data from the surface geochemical exploration. The seismic exploration shows that the Cretaceous strata are characterized by wide distribution, great thickness and stable sedimentary environment. The interpretation made by the authors shows that, in an area of 900 km2 of seismic exploration, there exist 23 reliable or relatively reliable traps of the Cretaceous strata, and the area of a trap is generally 4~16km2, with the maximum trap area reaching 200km2 in Xiangfan-Zaoyang depression. Then there are 13 traps from the interpretation of seismic exploration made in the 1990's, possessing totally 189km2 in the Zaoyang depression, and with good precision. According to the data from geological, geophysical and geochemical prospecting, the authors preliminarily evaluated petroleum geological conditions. The data obtained show that the Cretaceous strata are characterized by wide distribution, great thickness, deep burial depth and high evolution degree of the source rock. It is therefore considered that Cretaceous is a new target deserving further investigation.