Characteristics and exploration potential of porous reservoirs in 4th to 5th members of Lower Triassic Jialingjiang Formation in southwestern Sichuan Basin

Abstract

The main body of Lower Triassic Jialingjiang Formation in the Sichuan Basin is a set of cratonic platform facies deposits. It is characterized by shallow burial depth, thin reservoir thickness and good gas-bearing property in the southwest. Some small- and medium-scale gas reservoirs such as Maliuchang, Moxi and Chishui were discovered in the early stage. In the southwestern Sichuan exploration zone of SINOPEC, a gas production of 2.32×104 m3/d has been discovered in the 4th member of Jialingjiang Formation in well JS 1 in Jingyan area, and a gas production of 5.58×104 m3/d has been discovered in the 5th member of Jialingjiang Formation in well JH 1 in Weiyuan area in recent years. In order to further clarify the distribution of pore-type reservoirs in the Jialingjiang Formation in the southwestern Sichuan Basin and favorable target areas for further exploration, the pore-type reservoirs of the 4th and 5th members of Jialingjiang Formation were evaluated in this study based on the analyses of regional geological characteristics, drilling core cuttings, casting thin sections and experiments. The pore-type reservoirs are found to be mainly distributed in the 1st section of the 4th/5th member of Jialingjiang Formation. Both limestones and dolomites were developed. Vertically, (grey) dolomitic flat and granular beach superimposed in multiple periods. The main rock types of the reservoirs are crystalline dolomite, granular dolomite and granular limestone. The pore structure of high-quality reservoirs is characterized by large pores with medium throat, large pores with fine throat, and medium pores with fine throat. Favorable sedimentary microfacies such as dolomitic flat and granular beach controlled the distribution of reservoirs. Quasi-contemporaneous dissolution was the key to the formation of high-quality pore-type reservoirs. Fluid charging in the Indosinian and mid-late Yanshanian resisted the destruction of pores caused by later diagenetic compaction and cementation. The areas of Jingyan, Rongxian-Yibin and Weiyuan on the western margin of Luzhou paleo-uplift are favorable targets for future exploration.

Keywords

• reservoir characteristics
• oil and gas reservoir
• exploration target
• jialingjiang formation
• lower triassic
• southwestern sichuan basin