Oiliness Assessment for Tight Oil: a Case Study in Huahai Depression, Jiuquan Basin

Chunyan Fan^1,2, Yan Song^1,2, Zhenxue Jiang^1,2, Yuanyin Zhang¹, Qun Luo^1,2, and Nuan Wen^1,2
1State Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum, Beijing, China
²Unconventional Nature Gas Institute, China University of Petroleum, Beijing, China

Although characterized by the relative low porosity (<8%) and permeability (<1mD), the tight clastic sediments extensively distributed but neglected by previous exploration in the lower Cretaceous, Huahai depression, Jiuquan Basin, northwest China, are thought to be available for tight oil development, due to its inspiring genetic conditions including the high TOC value, good organic matter types and maturity. However, it is difficult to delineate the most favorable oiliness for tight oil reasonably since the insufficient evaluation criteria in this area. Based on the detail statistics of the TOC, chloroform bitumen “A” and Rock pyrolysis parameters “S1”, the oiliness for tight oil in this area is classified into three types and separately mapped for further exploration by employing the Triple-Division method (proposed by Lu et al., 2012) in the first time. Particularly, it is found that the sweet points are mainly developed in the depression center in the upper part of lower Cretaceous, where usually renders as abundant sedimentary organic matter and modest tectonic movements even without perfect evolution of hydrocarbon.

The tight clastic sediments extensively distributed in the three layers of lower Cretaceous, Huahai depression, have been proved to be promising by three successful wells in the past five years. And many published researches and exploration experiences show that its high TOC value (>2%), good organic matter types (II and I) and maturity (0.4% ~ 1.3%) are beneficial for tight oil development. It is therefore thought to be an important unconventional exploration and exploitation target, which has been roughly assessed to reserve 5382×104 t oil. However, efficient strategies are always limited by the blurry scenery of source rock quality, especially oiliness, no matter how urgent the ongoing exploration of the Oil Company is.

AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013