Analytical Model in Elliptical Flow Period of Tight Sand Gas Well Considering Stress Sensitivity

  • CAI Zhenhua ,
  • LIAO Xinwei ,
  • SHANG Baobing ,
  • AN Lei
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  • 1. CNOOC EnerTech-Drilling & Production Co., Tianjin 300452, China;
    2. College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China;
    3. Tianjin Branch of CNOOC Ltd., Tianjin 300452, China;
    4. Sinopec International Exploration and Development Company, Beijing 100083, China

Received date: 2014-06-03

  Revised date: 2014-06-19

  Online published: 2014-11-15

Abstract

The flow phases of fractured gas well in a conventional reservoir usually cover a linear flow period and a radial flow period. The elliptical flow period is usually regarded as a transition phase and thus ignored. The tight gas is the most realistic unconventional gas in China. Tight gas reservoirs are featured with low permeability and strong stress sensitivity. The pressure transmits slowly and every flow period is fairly extended. The elliptical flow phase at a tight gas well keeps a quit long time, even lasts for a couple of years. Therefore, the elliptical flow stage can't be ignored. When it comes to well test analysis, the conventional model is usually hard to match the double log curve in the field. To describe the flow phases more accurately, a flow model in elliptical coordinates is built through conformal transformation. The stress sensitivity coefficient is utilized in the model to consider the stress- sensitivity of tight gas reservoirs. After perturbation transforming and variable separation, the controlling equation is transformed into the Mathieu equation. Then it can be solved with a corresponding method. It's found that the stress sensitivity makes a higher pseudo-BHP drop and an end of derivative curve up warp. This model can simulate the flow period of tight sand gas well more accurately, and is significant to well testing of tight gas reservoir.

Cite this article

CAI Zhenhua , LIAO Xinwei , SHANG Baobing , AN Lei . Analytical Model in Elliptical Flow Period of Tight Sand Gas Well Considering Stress Sensitivity[J]. Science & Technology Review, 2014 , 32(31) : 50 -54 . DOI: 10.3981/j.issn.1000-7857.2014.31.006

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