SPE 35161 Pressure Transient Data Acquisition and Analysis Using Real Time Electromagnetic Telemetry L.E. Doublet,* Texas A&M U., J.W. Nevans,* Fina Oil & Chemical Company, M.K. Fisher,* ProTechnics Company, R.L. Heine,* Real Time Diagnostics, Inc., and T.A. Blasingame,* Texas A&M U. *SPE Members Copyright 1996, Society of Petroleum Engineers, Inc.
Abstract This paper presents the operational procedures and the results for two pressure buildup tests performed using a wireless telemetry acquisition system (TAS) tool at the North Robertson (Clearfork) Unit (NRU) in Gaines, Co. Tx. Using a single pressure gauge system downhole we obtained real-time telemetry of pressure and temperature data at the surface, as well as a larger sampling of data that were stored in the downhole memory system.
This new wireless telemetry acquisition system was developed to provide real-time pressure and temperature data at the surface by using an electromagnetic signal to transmit these data through the formation strata. The tool is fully programmable so that a wide range of sampling frequencies can be used. The system allows pressure and temperature data to be stored downhole (as in the case of a typical "memory" gauge), or these data can be transmitted to surface data acquisition systems. This provides real-time pressure and temperature data for pressure transient tests, stimulation monitoring. and long-term reservoir surveillance.
Our objective is to demonstrate the use of this technology for pressure buildup tests in low permeability reservoirs. Our goal in utilizing this technology is to reduce the shut-in time requirements for pressure transient tests - which will ultimately result in a more cost-effective reservoir surveillance program as wells can be returned to production (or injection) as quickly as possible.
Once the pressure data were acquired, we performed conventional semilog and log-log analysis, and we simulated test profiles to verify the analyses of the test data. Both surface and downhole pressure data were compared for consistency, and both types of data were analyzed in exactly the same fashion. The results of these analyses were essentially identical. This approach gave consistent estimates of reservoir pressure, permeability, skin factor, and fracture half-length for both of our case histories.
Introduction The accurate acquisition and analysis of pressure transient data is an integral part of the reservoir surveillance process. By analyzing the characteristic shape of the pressure-time profile we can determine the reservoir-well model (i.e., homogeneous or dual-porosity reservoir conditions, hydraulically-fractured or horizontal well behavior, wellbore storage conditions, etc.).
Specifically, we can use pressure transient data to estimate the following:–average reservoir pressure,
–completion efficiency,
–reservoir quality,
–well drainage radius and reservoir shape, and
–flow boundaries or other reservoir heterogeneities.
Unfortunately, in the majority of operating environments the critical issue for most pressure transient tests is the timely return of a well to production or injection. This paper presents one methodology that shows promise in minimizing test time while fulfilling the data acquisition requirements.
When performing pressure transient tests in the low permeability reservoirs of the Permian Basin (such as the NRU), it has been our experience that a test of at least two to three weeks is required for a comprehensive analysis to be possible. The issue is that the low permeability character of these reservoirs, combined with often severe wellbore storage effects, distorts test data and conventional analysis techniques cannot be used until these effects end. One remedy is a downhole shut-in device. but this device can be difficult to install, it requires considerable well preparation, and is quite expensive. Our approach was to minimize the test time by using real-time data for analysis. Conceptually, we can monitor the test and terminate once a valid analysis is obtained - but in our cases we continued data acquisition until the power source in the tool depleted. We did this for two reasons - first, we wanted to acquire as much data as possible; and second, we wanted to establish the practical operating limits of this data acquisition system. To estimate well drainage radius and identify flow boundaries we have found from pressure falloff tests that a total test duration of between five and eight weeks is required. Obviously, it is not economically feasible to shut-in producing wells for this period of time. In the future we may use the TAS tool for long-term surveillance tests, but at present this task is neither operationally nor economically feasible. P. 149