Numerous waterflooding projects are under way throughout the world for increased recovery. Water injection tests of oil zones are frequently undertaken during the planning phase of waterfloods. Analysis of the bottomhole pressure data recorded during these tests not only provides similar information to that obtained from production tests concerning the well and the reservoir characteristics but also allows the mobility ratio between the injected and resident fluids to be determined.
Conventionally, pressure fall-off test data is analyzed using semilog plot of bottomhole pressure versus time. This paper is the extension of the Tiab's Direct Synthesis Technique10–15 to pressure injection and Fall-off tests in water injection wells.
Direct synthesis is a transient pressure analysis technique10–15, which uses log-log plot of pressure and pressure derivative vs. time. Thus, different straight line portions indicating different flow regions are directly analyzed. Direct synthesis is very useful in conditions of short and early time pressure data missing tests. It also verifies the results since it uses more than one equation for the estimation of reservoir parameters such as permeability, wellbore storage coefficient, and skin factor.
Finally, field examples of pressure falloff analysis are presented to illustrate use the direct synthesis and results are compared with those from type curves and conventional semilog analysis.
Traditionally water flood schemes have been implemented later in the life of the field following primary depletion. Now, such schemes are often considered during the initial development of a field. The economic viability of many fields depends upon successful implementation of water injection at early stage. Injection tests are, therefore, performed on appraisal wells drilled prior to the decision to develop the field. These tests are designed to assess both the efficiency of the filtration equipment and the injection characteristics of the formation. Operational and the cost considerations dictate that the maximum possible information be derived from these tests, which may be few hours of duration.
Analysis of the pressure Falloff and injectivity tests has been discussed at considerable length in the literature. The pressure buildup during injection period, however, has received relatively little attention. The main reason is that falloff tests match to the pressure buildup test in production wells, which is easy to analyze. Furthermore, the injectivity test is mathematically difficult to handle due to moving boundary, the flood front.