Analysis of interval pressure transient tests conducted by wireline formation testers in oil reservoirs with a connected water aquifer system

Interval Pressure Transient Test (IPTT) is one of the commonly used formation testing methods in the industry to estimate some of the unknown parameters that have vital importance in the characterization of the reservoir. The parameters such as vertical and horizontal permeability can be estimated by applying classical straight line analysis if classical radial and spherical flow regimes are observed. Nevertheless, these estimations may not be accurate when there is a transition zone such as oil reservoirs with connected water aquifer systems. In this case, regression analysis should be performed to estimate the unknown parameters. In this study, basically, parameter estimation is performed in an oil reservoir with connected water aquifer system having a transition zone through the method of history matching using the IPT test data. Before estimating the parameters, two different reservoir models for an oil-water system having a single well in radial coordinates are created by using commercial simulator software CMG-IMEX. One of these models includes a transition zone between oil and water phases while there is a sharp interface for the other. Several IPT tests are run at different depths and in different zones for these two models and water cut ratios are measured in addition to packer and probe pressure data. The vertical and horizontal permeability values are estimated at first from packer-probe pressure data by using a gradient based approach based on maximum likelihood estimation for both models. Then, the same parameters are estimated only for the reservoir model having a transition zone by using CMOST which is an optimization and history matching tool of CMG. Furthermore, relative permeability and capillary pressure curves are estimated from the Modified Brooks-Corey model parameters by using CMOST based on the water cut data obtained from IPT tests performed in the transition zone. Lastly, relative permeability and capillary pressure curves as well as horizontal and vertical permeability are estimated at the same time by using all IPT test data including both packer-probe pressure and water cut measurements in CMOST software. The results show that accurate estimation of horizontal and vertical permeability values of the model where the capillary pressure is zero is possible with gradient based approach whilst having a transition zone gives moderately acceptable results for the same approach. On the other hand, estimated horizontal permeability value and anisotropy ratio is slightly better when CMOST is used in parameter estimation for the model where a transition zone exists. Moreover, relative permeability and capillary pressure curves are estimated accurately when water cut measurements are used in addition to packer-probe pressure data.