In 1999, an oilfield experiment was initiated to test the application of electrical measurement technologies to permanent reservoir monitoring. The principal objective of the experiment was to demonstrate the feasibility of monitoring water movement between an injection and an observation well. This paper describes the interpretation of the data provided by the resistivity arrays and discusses the data quality and reliability of the measurements.Two wells were drilled into the Mansfield sandstone reservoir in Indiana, U.S.A. The D-8 injector well was located in the center of four development wells. The OB-1 monitoring well was offset 233 ft to the southwest in a location midway between the D-8 injector and the No. 3 production well. The injector was instrumented with a 16-electrode resistivity array that was run on the outside of insulated casing and cemented into the annulus of the well. A similar array was cemented into the annulus of the monitoring well.In March 1999, the D-8 well was perforated and acidized. A surface gauge was used to monitor injection rates and pressures. Initially, injection proceeded at a rate of approximately 20 B/D, increasing to 90 B/D after fracture stimulation. The D-8 array records responses to wellbore operations and injection. It clearly distinguishes the movement of the waterfront in different zones. The OB-1 electrical array clearly indicates early water breakthrough by means of an induced fracture. The data show good signal-to-noise ratio and high reciprocity.The experiment has demonstrated the viability of using permanently installed resistivity arrays to monitor the movement of oil/ water contacts and salinity fronts that are some tens of feet away from the wellbore. Results demonstrate the feasibility of using such arrays to monitor oil/water contact movements remote from injection, monitoring, and production wells.
Summary This paper presents a procedure for interpreting data acquired with permanent downhole pressure sensors in association with surface or downhole rate measurements. The usefulness of this data source in reservoir description and well performance monitoring is illustrated. Unlike previously published examples, the interpretation is based on the analysis on a stream of data acquired over large periods of time, thus utilizing the continuous nature of the measurements. Three field cases are presented using the pressure and rate data in decline-curve analysis for wells with a variable downhole flowing pressure, and through more sophisticated models that are similar to the ones used in well test analysis. Because such interpretation is conducted while continuing production, it is particularly well suited for a well or group of wells under extended testing, which are equipped with downhole gauges and are flowing through surface separation and metering systems. Wells completed with both permanent downhole rate and pressure measurements are also ideal candidates for this type of analysis. Finally, the influence of the pressure sensor long term drift and the rate measurement error on the interpretation results and future forecasts are investigated. Introduction Since the first permanent downhole gauge installations in the early 1960's on land wells, the new technology in cable manufacturing, gauge sensor and electronics has permitted reliable installations also in hot, deep wells and subsea completions. These systems have gained acceptance among operators, and currently several hundred downhole gauges are installed every year. The traditional applications associated with permanent downhole systems can be characterized by four distinctions:single well optimization,reservoir description,safety improvement, andoperating cost reduction. Combining the recent technology development and these applications, the downhole gauge installations can be safe and reliable, as well as good investments. Most of the previous papers on the subject have focused on the hardware involved in permanent downhole pressure gauge installations. Regarding reservoir description, a few examples have been published where data recorded by the permanent downhole gauges have been used in well test transient analysis and multiwell interference tests. However, little has been published on the use of continuous downhole measurement in order to enhance reservoir description when associated with rate data during the pseudosteady state or depletion period of a field or a separate block. Decline curve analysis is one of the most widely used and documented methods for reserve estimation and production forecasting for a field under depletion. Solutions have been published for the case of a well producing at constant downhole flowing pressure. In reality, due to production constraints or change in operating procedures, the downhole flowing pressure seldom remains at a constant level over long periods of time. In the decline curve analysis literature, various methods have been proposed to account for these pressure variations; these include normalization and various types of superposition based on the pressure change observed at the wellhead.
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In 1999 an oilfield experiment was initiated to test the application of electrical measurement technologies to permanent reservoir monitoring. The principal objective of the experiment was to demonstrate the feasibility of monitoring water movement between an injection and observation well. This paper describes the utility of the data provided by the resistivity arrays and discusses data quality and reliability of the measurements. Two wells were drilled into the Mansfield sandstone reservoir in Indiana. The D-8 injector well was located in the center of four development wells. The OB-1 monitoring well was offset 233 ft to the southwest in a location midway between the D-8 injector and the No. 3 production well. The injector was instrumented with a 16-electrode resistivity array that was run on the outside of insulated casing and cemented into the annulus of the well. A similar array was cemented into the annulus of the monitoring well. In March, the D-8 well was perforated and acidized. A surface gauge was used to monitor injection rates and pressures. Initially, injection proceeded at a rate of about 20 B/D, increasing to 100 B/D after fracture stimulation. The D-8 array records responses to perforation, acidization, swabbing, fracturing, and injection. It clearly distinguishes the movement of the waterfront in different zones. The data show good signal-to-noise ratio and high reciprocity. The OB-1 electrical array clearly indicates early water breakthrough via an induced fracture. The arrays show no degradation of signal over the 17-month duration of the experiment. The experiment has demonstrated the viability of using permanently installed resistivity arrays to monitor movement of oil-water contacts that are some tens of feet away from the wellbore. Results demonstrate the feasibility of using such arrays to monitor oil-water contact movements remote from injection, monitoring, and production wells. Introduction The industry drive toward using intelligent wells to improve recovery efficiency will require continuous monitoring and optimization of reservoir drainage. Currently, commercial monitoring is through sensors that measure flow in the wellbore and permanent borehole pressure gauges. These sensors allow for reactive reservoir management: opening or closing production zones as a response to breakthrough of unwanted fluids into the wellbore. Proactive reservoir management is possible if we are able to detect the advance of unwanted fluids in the formation, prior to their breakthrough into the production stream. We have conducted an oilfield experiment to demonstrate that sensors can be deployed and used to monitor fluid movement remote from the wellbore.1 As this was the primary objective of the experiment, emphasis was placed on demonstrating the feasibility and utility of such measurements, rather than on testing a commercially viable deployment scheme.
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