Prosty sposób przybliżonego określania przepuszczalności horyzontu gazowego na podstawie danych okresu przypływu i bilansu masy gazu

The routine procedure for evaluation of the permeability and skin of the gas zone consists in flowing the gas well until the bottomhole pressure is nearly stabilized. The pressure values must be recorded versus time of flow, initial reservoir pressure must be known and the constant flow rate should be maintained during the flow test. The permeability and skin are calculated using the straight line approximation of bottomhole pressures versus logarithm of flowing time, and the permeability is calculated using the slope of this line. The standard method for calculation of permeability and skin is known for decades and will not be discussed here. This paper proposes somewhat different technique for calculation of permeability which is based on mathematical model of gas flow in porous rocks given by Szpunar (2001). The total volume of gas produced during the flow period is used for calculation of permeability instead of using the flow rate which is never known precisely. The reliability of the calculated results is checked by comparing the total mass of gas produced during the flow test (evaluated at standard conditions of temperature and pressure) with the mass of gas evacuated from the reservoir predicted by the mathematical model. The article provides calculation examples. Because no data from domestic oil industry was available, the method was tested using the data from technical literature. The discrepancies between the results of both methods are within the acceptable range of a few percent.