Abstract
A new approach to the in-situ determination of permeability, permeability anisotropy and lateral continuity of barriers to vertical fluid flow is introduced. The procedure employs a wireline-conveyed inflatable straddle-packer in conjunction with a vertically displaced pressure monitor probe to conduct vertical interference tests in openhole. The relatively large spacing between the packer interval and monitor probe (approximately 5 ft) results in a larger depth of investigation than is currently available with other wireline-conveyed tools. Multiple interference tests may be conducted during a single trip in the well.
The method of analysis is illustrated with data acquired in an oil well located in a complex, low-permeability, carbonate reservoir that has been under production for almost 40 years and under waterflood for approximately 30 years. As part of a field management program the operator wished to assess the status of pressure maintenance by means of a pressure survey and to measure the permeability anisotropy for use in subsequent numerical simulation work. Analysis of core data indicated that the permeability anisotropy should be low.
Feasibility of the testing procedure was established bearing in mind the restriction that flowrates would have to be limited during the pumping and sampling sequences to keep the test pressure above the bubble point pressure. Computer modelling and automatic parameter estimation techniques were employed to estimate the permeability and permeability anisotropy from the interference test data. Electrical and nuclear logs in conjunction with core photographs provided the means to establish the boundaries of the zones tested and to locate the major lithologic units. For comparison the pressure transients measured in the packer interval were analysed by established well testing methods.
