Rate transient analysis of gas/water two-phase reservoirs - a density-based approach

Open Access
Author:
Feng, Yao
Graduate Program:
Energy and Mineral Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 29, 2016
Committee Members:
  • Luis F Ayala H, Thesis Advisor
Keywords:
  • rate transient analysis
  • gas/water
  • two phase
  • density-based
  • production data analysis
Abstract:
As natural gas becomes an important energy source, a number of studies have attempted to solve gas problems numerically or analytically. From the introduction of real gas pseudo-pressure (Al-Hussainy et al. 1966) to the dimensionless type curve proposed by Fetkovich (1980), continuous progress is made along with more questions raised. In 2014, Zhang and Ayala proposed a density-based rescaled exponential model for dry gas produced under constant bottomhole pressure during boundary dominated flow, and improved it for variable-pressure/variable-rate cases and gas reserve prediction. This study extended their model from dry gas reservoirs to gas and water two-phase reservoirs, involving constant bottomhole pressure scenarios, variable bottomhole pressure cases and reserve prediction. Fluid densities and the density form of material balance equation are used in this method. Factors such as saturation and relative permeability are regarded as the key of this problem, while fluid miscibility, capillary pressure and water influx are not considered. Model outcomes are compared with CMG numerical simulations, and sensitivity analyses of initial water saturation, irreducible water saturation and drainage radius are done to test the model's adaptation and limitation. The model is proven to be feasible but limited to reservoirs with low water saturation to avoid the impact caused by the simplification of diffusivity equations. The transformation of the model inversely predicts original gas in place and original water in place with reservoir and fluid properties provided.