Assessment of Efficiency of EOR/IOR Technologies Using Rate Transient Analysis

Oil industry knows dozens of hundreds of different EOR/IOR methods to improve reservoir recovery efficiency. Among today's priorities are assessment of various EOR/IOR and bottomhole treatment technologies and selection of the most effective ones that will meet the specific reservoir conditions. For assessment of stimulation efficiency, different techniques can be used: decline curve analysis (DCA), production rates analysis before and after stimulation, analysis of reservoir properties in the near-wellbore zone and in the reservoir using pressure build-up (PUB) curves. Each technique has advantages and disadvantages. Thus, comparison of production performance ignores bottomhole pressure changes before and after stimulation, pressure buildup curves are not infrequently of a rather low quality, DCA is based on empirical relationships liable to misinterpretation because of subjective estimate. Devoid of these drawbacks is the rate transient analysis (RTA). The advantage of this method is that it makes allowance for change of production rates always occurring following stimulation. This is achieved through use of diffusion equations. Practice has shown that RTA provides a comparative analysis of production rates and cumulative oil production through time, porosity and permeability before and after stimulation, being, thus, a comprehensive tool for efficiency evaluation. Variation in oil production is the most reliable parameter, because it accounts for changes in bottomhole pressure and water cut before and after stimulation. To determine this parameter, an algorithm based on the pressure drop change is offered. RTA allows production forecast by two scenarios, the scenario involving stimulation, and the scenario without any production enhancement operations with a view to assess cumulative incremental production. In conclusion, it can be said that rate/pressure transient analysis allows assessment of efficiency of a large variety of EOR/IOR projects and a long-term production forecast. The offered approach may serve a good alternative to the decline curve analysis and comparison of production rates and PUB curves before and after stimulation.