Oil & Gas Geology ›› 2024, Vol. 45 ›› Issue (3): 801-815.doi: 10.11743/ogg20240316

• Petroleum Geology • Previous Articles     Next Articles

Stepwise identification of favorable facies belts and reservoir sweet spots of deep intermediate-basic volcanic rocks in the Songliao Basin

Ning LI1,2(), Ruilei LI2, He MIAO2, Kaifang CAO2, Jun TIAN2   

  1. 1.College of Earth Sciences,Jilin University,Changchun,Jilin 130061,China
    2.Exploration and Development Research Institute,Northeast Oil & Gas Branch,SINOPEC,Changchun,Jilin 130062,China
  • Received:2024-01-12 Revised:2024-05-20 Online:2024-07-01 Published:2024-07-01

Abstract:

Intermediate-basic volcanic rocks are extensively distributed in the deep Lower Cretaceous Huoshiling Formation of the Songliao Basin. However, their intricate lithologies and lithofacies, as well as the strong lateral heterogeneity of their reservoirs, complicate the prediction of reservoir sweet spots, restricting the exploration and exploitation of hydrocarbon resources. Focusing on the Chaganhua area, we investigate the lithofacies and reservoir characteristics of deep intermediate-basic volcanic rocks in the Songliao Basin and develop a methodology for identifying volcanic conduits, favorable lithofacies and lithologies, and reservoir sweet spots within the volcanic rocks. The key findings are as follows. (1) Three facies with six subfacies are primarily identified in the volcanic rocks. High-quality reservoirs predominantly comprise coarse- and fine-grained tuffs and tuffaceous sandstones. Reservoirs of the volcanic explosive facies are the most extensive in the proximal-middle facies belts. The distribution of tuffs with favorable lithologies is governed by the facies belts. Furthermore, the reservoir sweet spots of the volcanic rocks are primarily governed by their physical and gas-bearing properties. (2) For various volcanic eruptive phases, volcanic conduits are identified based on fracture density, along with the superimposed profiles of ant tracking and seismic data. This helps determine the proximal volcanic facies belts. Then, in combination with the thickness of volcanic edifices and the energy half-time attribute, the boundaries between middle-distance and distal volcanic facies belts are identified, facilitating the qualitative characterization of areas containing reservoir sweet spots. (3) To minimize the multiplicity of solutions in the quantitative prediction of intermediate-basic volcanic reservoirs using seismic data inversion, we preferentially employ low wave impedance, low density, and low Lame constant to characterize tuffs, reservoirs with high porosity as indicated by nuclear magnetic resonance (NMR), and gas layers, respectively. Accordingly, based on the porosity data volumes derived from pre-stack density inversion, we eliminate the interference from the sedimentary tuffs, low-porosity layers, and non-gas layers sequentially, obtaining reliable predictions of the spatial distribution of reservoir sweet spots. It is verified that the predicted results align with the distribution pattern of favorable facies belts and agree with interpretations of drilled gas layers. The qualitative identification and stepwise quantitative characterization of the spatial distribution of reservoir sweet spots based on favorable facies belts, have been successfully applied to well emplacement, yielding encouraging outcomes. Therefore, this methodology is highly applicable in the seismic prediction of sweet spot distribution in deep volcanic rocks.

Key words: stepwise identification, volcanic conduit, favorable facies belt, reservoir sweet spot, intermediate-basic volcanic rock, Songliao Basin

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