Method of Water Influx Identification and Prediction for a Fractured-Vuggy Carbonate Reservoir

Abstract Naturally fractured-vuggy carbonate reservoirs in China have some distinctive characteristics, which reservoir is a discontinuum and isolated developed. And these reservoir usually have strong aquifer support. So one of the most important things for these reservoirs is to avoid too early water breakthrough, because water breakthrough explicitly reduce oil productivity and recovery. Therefore, how to identify aquifer influx in advance are important in order to guide well production rate optimization and improve reservoir performance. This paper proposes four diagnostic curves to identify aquifer influx phase for producers with aquifer support, which are mainly based on well daily production and pressure data. And whole production period of a producer can be classified into 3 phases based on the curves: no aquifer influx phase, early aquifer influx phase, and middle-late aquifer influx phase. The methods are validated by reservoir simulation and well performance data. Then aquifer influx phases of all wells in a fractured-caved carbonate reservoir are classified, and a correlation for well oil cumulative production prediction is established. This new method has been applied to K fractured-vuggy carbonate reservoir in China. The mid-depth of K reservoir is 6000m, and current oil recovery is only around 7% of OOIP with primary depletion and more than 100 producers. Around one third of producers have been water flooded, most of which water cut increased from 0% to more than 60% within only one month. The four proposed diagnostic curves for aquifer influx identification are tubing pressure drop vs. cumulative oil production curve, flowing material balance curve, Blasingame type curve, and dimensionless expansion production ratio curve. And how to use diagnostic curves to identify aquifer influx are detailed illustrated based on the reservoir simulation data and actual well production data. Then production phases of all wells are identified and classified. Furthermore, based on performance of water flooded wells, correlation between oil cumulative production and dimensionless expansion production ratio are established, which are used for well performance prediction. This paper offers a new method and a case study of aquifer influx identification and prediction for aquifer drive carbonate reservoirs. It also provides a methodology and reference case for other similar oil fields.