A Method to Diagnose Depletion, Skin, , and Drive Mechanism Effects Using Reservoir Monitoring Data

Abstract

Abstract The use of permanent sensors provides a continuous source of downhole pressure measurement throughout the life of the well. Moreover, multiphase flowmeters provide simultaneous flow rate measurements. The significant amount of data produced by these sensors has added a new dimension to traditional well test data interpretation techniques. This new dimension is life -of-well time. During the life of the well, permanent-gauge data and flow rate measurements are affected by several dynamic factors including changes in reservoir pressure, skin, permeability-thickness (kh), and reservoir drive mechanism. A major challenge facing the industry today is how to diagnose and respond to the effect of each of these factors. In other words, it is important to know whether a change in measured downhole pressure or flow rate is caused by depletion, changes in skin, kh, or drive mechanism. This study investigates the effects of the above-mentioned factors in two fields in the Gulf of Mexico area. In addition, experience and lessons learned from numerous wells and fields equipped with permanent sensors have been used to develop a diagnostic method. This method uses key reservoir and well performance indicators to derive techniques to distinguish between the effects of depletion, skin, kh and drive mechanism. Best practices in the collection of flow rate and pressure data with suggestions for near-future improvements are included. Introduction Permanent gauges provide continuous bottomhole pressure data. Production data is also recorded. In reservoir monitoring, these data are usually combined and analyzed to evaluate reservoir depletion, skin, kh, and drive mechanism. In cases where several of these factors impact the well simultaneously, it becomes difficult to distinguish between their effects on the pressure and rate data. Without the clear distinction, it is often difficult to correctly evaluate the well and reservoir performance. Use of the measured high frequency data expands the traditional time scale from the snapshot approach to a process of continuous evaluation and remedial action. This can lead to real-time production and management decision-making. This paper focuses on the application of available techniques1,2,3,6,7,8,9, to diagnose depletion, skin, kh, and drive mechanism effects using reservoir monitoring data. These techniques are explained using simulated examples, and field examples from the Gulf of Mexico area (GOM) to demonstrate some of these effects. Productivity Evaluation of Wells with Permanent Downhole Pressure Gauges As new technology trends introduce a greater use of permanently installed sensors, the previously common approach of taking snapshots for well productivity evaluation is quickly changing to a continuous time scale. The resulting expanded vision during the life of a well brings a totally diffe rent perspective into the well evaluation process. Naturally, a new set of expectations and needs also arises, and a new learning curve is in place. In our experience from one of the GOM cases, the application of permanent downhole gauges ranges from a very practical use in well operation to more detailed analyses for detecting production impairment, for well stimulation decisions, or for continuous production management. Below, we list some of the key considerations needed to maximize the overall use of the available data from downhole gauges. Data Management and Evaluation Tools. Permanently installed sensors generate high-frequency data. The amount of gathered information can be overwhelming. Accordingly, data management becomes a critical aspect defining the workflow required to use these data with suitable evaluation tools and models. Well surveillance tools provide an adequate mechanism to track the evolution and trend of key performance indicators (KPI's) in reservoir or sandface and tubular components.