China Petroleum Exploration ›› 2019, Vol. 24 ›› Issue (2): 203-209.DOI: 10.3969/j.issn.1672-7703.2019.02.008

• PETROLEUM GEOLOGY • Previous Articles     Next Articles

Geology-engineering integration for low-permeability and thin marginal reservoirs: a case study on Zanazour oilfield, Pre-Caspian Basin

Zhang Hewen1, Cui Mingyue1, Zhang Baorui2, He Anle1, Yan Jun1, Liang Chong1, Guo Shuanggen2, Jia Hongge2, Ma Liang3   

  1. 1 PetroChina Research Institute of Petroleum Exploration & Development;
    2 CNPC(Aktobe) Oil and Gas Company;
    3 Yilong Hengye Petroleum Engineering Technology Co., Ltd
  • Received:2018-09-06 Revised:2019-02-28 Online:2019-03-15 Published:2019-03-15
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Abstract: After developing for more than 20 years, the main part of the Zanazour oilfield in the pre-Caspian Basin, has demonstrated high recovery efficiency and low reservoir pressure. However, the marginal reservoirs with low permeability and thin pay remain a challenge for effective development, with only low productivity by conventional vertical wells. To develop these low-permeability and thin reservoirs, a horizontal well geology-engineering integration technology system was proposed, and a series of research and field test were carried out. This technology system organically integrates drilling and completion, staged fracturing and oil production engineer with consideration to geologic and reservoir characteristics. It is manifested in six aspects. First, the lowest effective porosity is reduced from 8% to 4%-5% considering the influence of horizontal well staged fracturing on production. Second, preferable target layers are selected and horizontal section orientation is determined depending on stress distribution, orientation of induced fractures, and thickness and distribution of pay zones comprehensively. Third, rotary geosteering and LWD techniques are combined to increase the drill-in rate of thin layers (1.4-6.1 m) from 20.7% to 72%. Fourth, multiple measures are taken to improve the cementing quality in horizontal section and the resistance to impact by perforation and fracturing operations. Fifth, the staged fracturing design and parameters are optimized in accordance with the principle of "one design for on stage" by considering the heterogeneity of horizontal section. Sixth, gas lift and liquid nitrogen assisting flowback techniques are adopted for low-pressure reservoirs. The technology system has been successfully applied in development wells (e.g. H8) in marginal reservoirs. Well H8's post-fracturing production is 11 times of the adjacent well. So far, field test has been completed in 8 wells, revealing a cumulative oil production added by 11×104t. Thus, the geology-engineering integration technology system represented by staged fracture is proved efficient for low-permeability and thin marginal reservoirs.

 

Key words: integration, marginal reservoir, staged fracturing, horizontal well

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