Real-Time Evaluation of Pressure Transients: Advances in Reservoir Monitoring

Abstract

Reservoir engineers operating in mature fields across the world struggle to get necessary reservoir data to make their exploitation plans more realistic. Pressure transients are the most effective way to understand the dynamic behavior of the reservoir. Loss of production and cost of acquiring data versus the benefits has always been a classical management dilemma. With the advent of digital oilfield technology, the pressure and hence the deterioration in well deliverability can be continuously and cost effectively monitored. This paper illustrates how real-time data can be used to make decisions on when to invest in pressure transient tests, and when a test is run, how to minimize the downtime. The case studies presented here are for wells on electrical submersible pumps in various types of reservoirs across Latin America.The paper briefly discusses the three pillars of digital oilfield; technology, processes and people and how they work together to achieve continuous reservoir and production optimization. Reservoir analysis for wells on electrical submersible pumps (ESP) is challenging due to the restrictions imposed by the downhole equipment. Our work presented here focuses on developing workflows and interpretation techniques for this unique environment.Having sensors downhole provides operators with an opportunity to get pressure drawdown and buildup data when the ESP starts and stops. For the wells we monitor, 10% of these unscheduled events provided much coveted reservoir information without having to stop the production intentionally. For the scheduled pressure transient events, the data acquisition rates were actively changed to ensure sufficient high quality data. Also, the length of the test was decided in real time to make sure that the test was long enough to meet the objectives but not too long to increase the cost without additional benefits. Thus with real-time technology we were able to overcome the shortcomings of traditional well testing and address the concerns of both engineers and the management. Case studies are presented where production enhancement opportunities were uncovered as a result of scheduled and unscheduled events on wells producing with ESPs. The results show that more than 70% of wells can benefit from stimulation, potentially increasing production up to 300%. To make proactive decisions and act on the recommendations generated from these production enhancement opportunities is still a challenge that needs to be addressed.For fields with large numbers of ESP wells, a time snap of reservoir properties could be periodically obtained to track changes in pressure, skin and permeability for real time optimization.