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Investigation on Aplicability of Decline Curve Analysis for Gas Condensate Reservoirs

Sadeghi Boogar, Asghar | 2009

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40054 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Masihi, Mohsen; Gerami, Shahab
  7. Abstract:
  8. Part 1: Techniques of production data analysis for single-phase oil and gas reservoirs have advanced significantly over the past few years. These techniques range from traditional (Arps and Fetkovich) to modern (they account for the variation of operating conditions at the wellbore). Although the production data analysis methods are used generally for single phase reservoirs, the application of these techniques for analysis of production data of a gas condensate reservoir may not yield the reliable answer due to the fact that the flow of fluid in gas condensate reservoirs is not single-phase. This study presents the treatment of the modern methods of production data analysis (single phase flow) to analyze the production data of a gas condensate reservoir (two phase flow). For this purpose a single phase production model consisting of (1): a material balance equation, (2): solution to hydraulic diffusivity equation subjected to constant rate (CR) and constant pressure (CP) boundary conditions, and (3) a material-balance-time function (to convert exponential decline to harmonic decline) is presented. Using a compositional reservoir simulator, long-term production data is generated over a wide range of the gas condensate reservoir parameters. Next, a comparison is made between the simulator results (gas condensate) and the corresponding single-phase gas reservoir model, using a modern production analysis method. The error for each case is analyzed and a correlation for treatment of the single phase analysis method is developed. Our results show that the methodology developed here can be successfully applied for analysis of production data of a gas condensate reservoir. Part 2: Well deliverability is an important issue in forecasting the performance of many gas condensate reservoirs. Condensate accumulation near the wellbore can cause a significant reduction in productivity, even in reservoirs where the fluid is very lean. Generally, the well deliverability is affected by two pressure-drop sources due to depletion and condensate buildup. Recently Rapid spreadsheet tools have developed to evaluate the well performance using material balance equation for depletion and two-phase pseudo pressure integral for well inflow performance. Most of them account for the effects of negative inertia and positive coupling in the calculation of gas relative permeability. This paper introduces a new method for calculation of the well productivity in gas condensate reservoirs. This method uses the concept of two-phase pseudo pressure integral without any need to estimate the radius of two-phase region. The average reservoir pressure is calculated by using a general material balance equation. The only data required for implementing this method is PVT data, relative permeability curves and table of well flowing pressure versus time. The approach is validated by using a single-well fine grid compositional simulation of a hypothetical reservoir model over a typical range of gas condensate reservoir parameters. The results show a reasonable agreement between the fine grid and the proposed approach. The new technique can be encoded on a spreadsheet in order to forecast the gas condensate well performance very rapidly.
  9. Keywords:
  10. Gas Condensate Reservoirs ; Exponential Decline Curve Analysis ; Well Productivity ; Production Data ; Well Performance Methods

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