Print this pageA New Method to Determine the Source-Reservoir Association of Tight Oil in Jiuquan Basin, NW China
Baiying Li1,2, Zhenxue Jiang1,2, Zhuo Li1,2, Qun Luo1,2, and Hexin Huang1,2
1State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing, China
2Unconventional Nature Gas Institute, China University of Petroleum, Beijing, China
Tight oil is becoming one of the most important unconventional hydrocarbon resources recent years, and drawing great attention from petroleum geologists around the world. However, the types of source-reservoir association of tight oil play in the Jiuquan Basin are still poorly understood. A new method, which primarily considers the scale, types and association of the source rocks and the reservoir rocks to determine the source-reservoir association of tight oil play is reported in this paper. Applying the method, the most favorable source-reservoir association of tight oil play in the Qingxi Sag, Jiuquan basin, has been determined.
1. Characteristics of the favorable source units
Based on the cognition of favorable thickness of the Bakken Shale, the most favorable thickness of the source of tight oil play is determined to be 30m, and/or interbeded with thin mudstone and shale in thickness of 10m. the source rocks in Xiagou Formation, primarily mudstone, shale and argillaceous dolemite, are buried deeper than 3700m, with the maturity between 0.6%~1.2% and the organic matter types of II-I. The most favorable source units are determined to have the TOC values more than 1.0%.
2. Characteristics of the favorable reservoir units
Based on the statistics data of favorable thickness of the Qingxi Sag, the most favorable reservoir thickness of tight oil play is determined to be 30m, and/or interbeded with 30% mudstone and shale in thickness. Due to the extremely short distance of migration of tight oil play, the decision of the most favorable reservoir units are either reservoir immediately adjacent to the source rock vertically, with the lithology of argillaceous dolomite, siltstone, medium-fine sandstone and the conglomerate or the source rocks with fractures well developed. Logging trace and nature fracture observed image logs can be used to delineate the fractures.
3. Classification of source-reservoir association
Five different types of source-reservoir association can be determined, specifically, the “up-source down-reservoir” association with the source units overlay the reservoir units, the “up-reservoir down-source” association with the reservoir units overlay the source units , the “sandwich” association with the reservoir units interbedded within the source units, the “reservoir hold source” association with the source units interbedded within the reservoir units, the “united” association with the fracture well developed as the source units and the “source – reservoir interaction” with the thin source and reservoir units deposited alternatively.
Considering the effective hydrocarbon explusion thickness, the drive force of overpressure, the porosity and permeability of reservoirs, the content of clay and brittle mineral, the source-reservoir association of the Qingxi sag can be classified with three types, namely the “up-source down-reservoir”, the “up-reservoir down-source” and the “source and rock intergration” association. We inferred the “source and rock intergration” is the most favorable association in the studied area, with the depth between 4200 and 4300 m. This new scientific method has improved the theory of petroleum geology and is of great importance in tight oil exploration.
AAPG Datapages/Search and Discovery Article #90180©AAPG/SEPM/China University of Petroleum/PetroChina-RIPED Joint Research Conference, Beijing, China, September 23-28, 2013