Case Histories of Step Rate Tests in Injection Wells

Abstract

ABSTRACT Knowledge of the formation parting pressure (FPP) is important for efficient operation and surveillance of waterflood projects and CO2 floods. Knowing this information will assist in optimizing recovery by reducing injection rates in wells to control cycling (i.e. prevent fluids from going through uncontrolled fractures or high permeability zones) or by Increasing injection rates to maximize injection efficiency and increase oil production. A step rate injectivity test (SRIT) is one of the best methods available to determine formation parting pressure, also known as the fracture pressure. Previous step rate tests at Salt Creek have been unsuccessful due to procedural problems resulting in inconclusive results. This paper outlines the procedures, pitfalls, and field problems encountered while running successful step rate injectivity tests in the Salt Creek Field Unit. Findings obtained from running these tests include: frac gradient is highly dependent on average reservoir pressure; a correlation exists between average reservoir pressure and frac gradient for a particular field; bottom hole injection pressure measurements are extremely important on high rate injection wells; and theoretical formation parting pressure predictions are important in designing test procedures. We also present results of conducting a decreasing-rate-sequence SRIT. This is the first presentation of such data. The experience and lessons learned from running these step rate tests can be successfully applied to other carbonate reservoirs.