Field A considered in this paper is an oil field characterized by low permeability and large vertical variability of formation properties. Injection and production take place in commingled multi-layer zones of Field A. Wells are hydraulically fractured across the entire stack of the producing layers. In the injection wells, the bottomhole pressure is higher than the formation fracturing pressures causing continuing growth of fracture length.
This paper discusses 60 multi-rate injection tests to determine the injection profiles in Field A. The tests consisted of continuous measurements of the bottomhole pressures for several constant injection rates. Measurements were made for three different injection periods with pressures below and above the formation fracturing pressure. Each injection period lasted until steady-state conditions were established. Layer injection rates were determined from stabilized injection profiles obtained by spinner surveys before the tests. Layer properties were determined by matching the constant injecting rates and layer pressures for multiple injection periods.
Test results demonstrated that well performances in Field A could not be described by known solutions for a constant fracture length. The non-linear relationship between the steady-state pressure and injection rate indicated that continuous change in fracture geometry had to be taken into account. These tests were useful to determine individual layer injectivities, current formation pressures and fracture opening pressures of each layer.
Based on the results, it is concluded that multi-layer, multi-rate injection tests are useful to monitor layer pressure distributions and effectively produce multi-layer fields. The Simultaneous Separate Injection (SSI) technology used in these tests provides the ability to control layer injection rates and maintain uniform production from multiple layers. The SSI technology also allows injecting controlled volumes simultaneously into several layers through one injection well. Comparison of the tests using the SSI technology and adjusted valves demonstrates redistribution of injection rates from a higher- permeability layer to a lower-permeability layer.