The Application of Peng Robinson Equation of State to Predict Natural Gas Behaviour in Oil based Drilling Fluid
A major problem associated with the use of oil base drilling fluid is the increased difficulty of detecting gas which enters the borehole and dissolves in the drilling fluid. Previous authors have made computer-simulated comparisons between a water-base and an oil-based drilling fluid for one specific field example. However, a method is needed that will permit field personnel to quickly estimate the amount of dissolved gas that can be associated with an observed pit gain for the field conditions present. . In this paper, methods were presented for estimating the swelling of oil based drilling fluid due to dissolved gas. This involves the determination of the formation volume factors of the fluids (oil-gas-drilling fluid mixture) at given subsurface conditions using Peng-Robinson equation of state and hence the detection of the natural gas intrusion into a given well and subsequent calculation of the pit gains. The results were compared with similar but empirically obtained data. The pressure profile for a well at given conditions have also been made thereby aiding the several predictions that will lead to proper fluid flow control.