ASSESSMENT OF RESERVE ESTIMATION TOOLS FOR LOW PERMEABILITY RESERVOIRS FLOWING UNDER EARLY TRANSIENT FLOW REGIME

Open Access
Author:
Husain, Taha Murtuza
Graduate Program:
Petroleum and Natural Gas Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
July 28, 2011
Committee Members:
  • Dr Luis Ayala, Thesis Advisor
  • Luis Ayala, Thesis Advisor
Keywords:
  • Reserve Estimation
  • Power Law Loss Ratio
  • Arps
  • Flow Regimes
Abstract:
Growing energy demand has led to the focus being shifted to unconventional reservoirs. One such reservoir type is shale gas. The introduction of hydraulic fracturing has helped make production from shale gas reservoirs economical. But there are a number of difficulties in accounting the reserves for a shale gas reservoir. The low permeability of shale increases the time taken for the pressure transient to hit the external boundary. Thus an understanding of the decline trend during the early transient period would help improve the forecast. Newer analytical tools available for decline curve analysis help improve forecast by obtaining a better match for decline trends observed during early transient period. The forecast made using production data of a reservoir producing under early transient period leads to an over estimated value of reserves. The first step in this work is directed towards understanding the trend exhibited by decline rate (D) and decline exponent (b) during early transient period and it was observed that these values were not constant during this period. Production data was generated analytically by solving respective flow equations in Laplace space. Then the inversion from Laplace space to real space is done by Stefhest algorithm. Using this data a study of the trends for decline exponent (b) for radial and linear flow was conducted and the same was done for dual porosity system. Various decline curve analytical tools were analyzed which include Arp’s, Power Law Loss Ratio and Stretched Exponential. It was found that modified power law loss ratio and power law loss ratio have a reliable forecast for reservoirs flowing under radial and linear flow conditions, while stretched exponential has a more reliable forecast in case of a dual porosity system.