Oil & Gas Geology ›› 2025, Vol. 46 ›› Issue (1): 273-287.doi: 10.11743/ogg20250119

• Methods and Technologies • Previous Articles     Next Articles

Main factors controlling the efficient production of horizontal wells for deep coal-rock gas in the eastern and central Ordos Basin

Shixiang FEI1,2(), Yuehua CUI1,2(), Xiaofeng LI1,2, Shujie WANG1,2, Ye WANG1,2, Zhengtao ZHANG1,2, Peilong MENG1,2, Xiaopeng ZHENG1,2, Yundong XU1,2, Jianwen GAO1,2, Wenqin LUO1,2, Tingting JIANG1,2   

  1. 1.National Engineering Laboratory for Exploration and Development of Low Permeability Oil & Gas Fields,Xi’an,Shaanxi 710018,China
    2.Research Institute of Exploration and Development,Changqing Oilfield Company,PetroChina,Xi’an,Shaanxi 710018,China
  • Received:2024-09-05 Revised:2024-11-03 Online:2025-02-28 Published:2025-03-03
  • Contact: Yuehua CUI E-mail:fshix_cq@petrochina.com.cn;cyh168_cq@petrochina.com.cn

Abstract:

Abundant deep coal-rock gas in the Ordos Basin boasts enormous potential for exploration and development. The geological characteristics of deep coal-rock gas exhibit substantial regional changes, and reservoir simulation tests under various process conditions have revealed notable differences in the productivity of coal-rock gas wells. This study aims to investigate the main factors controlling the coal-rock gas productivity of horizontal wells. Using the dynamic and static data from deep coal-rock gas in the pilot test area and employing the analytical approach of geology-engineering integration, we depict the geological features of coals in detail and thoroughly assess the production indices of producing wells. Furthermore, geological and engineering assessments are carried out using methods such as Pearson correlation analysis, hierarchical clustering, and machine learning. The results indicate that under similar regional geological features such as coal structure and thermal maturity, coal thickness and gas-bearing property, two geological factors, significantly affect the productivity of coal-rock gas wells. Meanwhile, the total length of coals encountered during drilling (L), total drill-in liquid volume (W), proppant volume (S), and proppant intensity (Sq) among engineering factors exhibit positive correlations with the productivity of coal-rock gas wells. Notably, engineering factors show more pronounced correlations with the first-year daily gas production compared to geological factors, and the composite geology-engineering factors display more significant correlations than individual factors. Increasing well-controlled drainage volume and stimulated reservoir volume (SRV) contributes to the high productivity of coal-rock gas wells. Assuming target coal thicknesses measuring 6 ~ 10 m and an average proppant intensity of 5.5 t/m, a lateral length of 1 000 ~ 1 500 m is required to achieve a single-well estimated ultimate recovery (EUR) of 5 000 × 104 m3. A new method for predicting the single-well productivity of deep coal-rock gas, based on geological and engineering parameters, is developed using intelligent algorithms such as deep neural networks, support vector machines (SVMs), and random forest models. This method achieves a coincidence rate of up to 91 % according to blind well verification with 22 wells involved.

Key words: machine learning, geological characteristics, productivity prediction, horizontal well development, deep coal-rock gas, Ordos Basin

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