Lithologic Reservoirs ›› 2026, Vol. 38 ›› Issue (5): 71-82.doi: 10.12108/yxyqc.20260507

• PETROLEUM EXPLORATION • Previous Articles     Next Articles

Sedimentary characteristics and favorable reservoirs distribution of the first member of Leikoupo Formation in Middle Triassic， central Sichuan Basin

QING Chun1(), WU Xueyan2(), TANG Song1, LIU Bowen1, GAN Wenjie1, YU Yan1, LIANG Xinyu1, LIAO Yue1   

  1. 1 Central Sichuan Oil and Gas District， PetroChina Southwest Oil & Gasfield Company， Suining 629000， Sichuan， China
    2 School of Geoscience and Technology， Southwest Petroleum University， Chengdu 610500， China
  • Received:2026-03-30 Revised:2026-04-29 Online:2026-09-01 Published:2026-09-04
  • Contact: WU Xueyan E-mail:qingchun@petrochina.com.cn;15913269101@163.com

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Abstract:

Based on core observation， thin section identification， and logging facies analysis， a sedimentary facies classification scheme for the first member of Leikoupo Formation（Lei 1 Member）in Middle Triassic of central Sichuan Basin was established. Through cross-well profiles correlation， the distribution and evolution of sedimentary facies are systermatically analyzed. From dual perspectives of conventional and unconventional oil and gas fields， favorable reservoir zones were delineated. The results show that：（1） Lei 1 Member in central Sichuan Basin mainly develops evaporative platform and restricted platform，which can be further divided into three subfacies （evaporative tidal flat， restricted tidal flat， and intra-platform shoal） and six microfacies （gypsum flat， gypsiferous dolomite flat， dolomite flat， limestone flat， argillaceous dolomite flat， and grain shoal）. （2） Sedimentary evolution of the study area was jointly controlled by paleostructure, paleogeomorphology， and sea level changes， exhi-biting the staged sedimentary evolution sequence of “shoal and flat developed in the early stage， and evaporation enhanced in the late stage”. During the deposition of Lei 11 submember， the basin was characterized by a topography of “high west and low east” with a relatively high sea level， developing dolomite flats and grain shoals in a restricted platform setting. During the deposition of Lei 12 submember， the climate turned arid and sea level fell， leading to widespread gypsiferous dolomite flats， increased terrestrial argillaceous material input. The depositional system evolved into an evaporite‑dominated saline system， constituting a regressive sequence. （3） Reservoir characteristics in the study area show obvious stratification differences. Lei 11 submember is dominated by facies‑ controlled conventional reservoirs of grain shoals and dolomite flats， with reser-voir lithologies consisting of grain dolostone and crystalline dolostone， which were transformed into high‑quality reservoirs through penecontemporaneous exposure， early karstification， and dolomitization. Lei 12 submember features “source‑reservoir integrated” unconventional argillaceous dolomite reservoirs， with the top and bottom sealed by gypsum layers， forming a closed hydrocarbon accumulation system. （4） Moxi area is the most favorable zone for grain shoal facies. The west and south parts of central Sichuan Basin are favorable for dolomite flat facies， and Pengyang area is the “sweet spot” for unconventional exploration of argillaceous dolomite flats.

Key words: sedimentary facies, grain shoal facies, unconventional oil and gas, “sweet spot” prediction, restri-cted platform facies, logging facies, the first member of Leikoupo Formation, Middle Triassic, central Sichuan Basin

CLC Number: 

  • TE121.3

Fig. 1

Structural location of central Sichuan Basin （a） and comprehensive stratigraphic column of Middle Triassic Leikoupo Formation （b）"

Fig. 2

Macroscopic and microscopic photos of main rock types of the first member of Leikoupo Formation in Middle Triassic of central Sichuan Basin"

Fig. 3

Types and characteristics of logging facies of the first member of Leikoupo Formation in Middle Triassic of central Sichuan Basin"

Table 1

Classification of sedimentary facies types of the first member of Leikoupo Formation in Middle Triassic of central Sichuan Basin"

沉积体系 相 亚相 微相 主要岩性
碳酸盐岩
台地		 蒸发
台地		 蒸发
潮坪		 膏云坪 膏质白云岩、膏岩与白云岩、
泥质白云岩互层
膏坪 膏岩、云质膏岩
局限
台地		 局限
潮坪		 云坪 泥—粉晶白云岩、结晶白云岩
灰坪 泥—粉晶灰岩
台内滩 泥云坪 泥质白云岩、含泥白云岩
颗粒滩 砂屑白云岩、鲕粒白云岩

Fig. 4

Comparison of sedimentary cross-sections of Lei 11 submember of Triassic in NE-SE direction of central Sichuan Basin"

Fig. 5

Comparison of sedimentary cross-sections of Lei 11 submember of Triassic in west-south part of central Sichuan Basin"

Fig. 6

Comparison of sedimentary cross-sections of Lei 12 submember of Triassic in NE-SE direction of central Sichuan Basin"

Fig. 7

Comparison of sedimentary cross-sections of Lei 12 submember of Middle Triassic in west-south part of central Sichuan Basin"

Fig. 8

Plane distribution of sedimentary facies of Lei 11 submember of Middle Triassic in central Sichuan Basin"

Fig. 9

Plane distribution of sedimentary facies of Lei 12 submember of Middle Triassic in central Sichuan Basin"

Fig. 10

Sedimentary models of the first member of Lei-koupo Formation in Middle Triassic in central Sichuan Basin"

Fig. 11

Reservoir physical properties characteristics of Lei 1¹ submember of Middle Triassic in central Sichuan Basin"

Fig. 12

Prediction of favorable reservoir zones of the first member of Leikoupo Formation in Middle Triassic of central Sichuan Basin"

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