Characteristics of In-Situ Stress Field in Heterogeneous Ultra-Heavy Oil Reservoir of Fengcheng Oilfield

doi:10.7657/XJPG20200213

Abstract

Abstract:

The heterogeneous ultra-heavy oil reservoir in the Fengcheng oilfield is characterized by shallow-burial, strong heterogeneity and developed interlayers, which are the main obstacles for the steam chamber development during SAGD. In order to form flowing channels by hydraulic fracturing, the paper analyzes sedimentary characteristics, in-situ stress field distribution and the influences of interlayers on in-situ stress field and establishes a 3D stress field model for the reservoir with the burial depth of 282~332 m based on the results of rock mechanics experiment, logging data interpretation and stress test. The comparison of the simulation results with mini-fracturing test shows that the established 3D stress field model accords with the actual lateral formation pressure coefficient and the ratio of the max. horizontal principal stress to vertical principal stress, which can better reflect the features of lithology interfaces and stresses in the reservoir. The ultra-heavy oil reservoir is dominated by vertical principal stress which is in favor of guiding vertical fractures. The sudden stress changes at lithology interfaces result in the min. horizontal principle stress of sandstone being lower than that of mudstone interlayer. The mudstone interlayer has relatively high breakdown pressure, Young modulus and min. horizontal principle stress, and the fracture propagation capacity of the mudstone interlayer is lower than that of oil sand interval. The positions within interlayers or below interlayers should be selected for perforation during fracturing design, by which fracture height can be controlled, sand plugging can be avoided and reservoir seepage can be improved.

Key words: Fengcheng oilfield, ultra-heavy oil reservoir, heterogeneous reservoir, 3D model, mudstone interlayer, principal stress distribution, fracture pressure

CLC Number:

TE112.23

WU Han, LIN Botao, PAN Jingjun, CHEN Sen. Characteristics of In-Situ Stress Field in Heterogeneous Ultra-Heavy Oil Reservoir of Fengcheng Oilfield[J]. Xinjiang Petroleum Geology, 2020, 41(2): 217-222.

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