In order to optimise well completions and production in naturally fractured reservoirs and to predict the effectiveness of enhanced oil recovery schemes, it is important to locate and describe the insitu fractures. A combination of log measurements and core data were employed to locate and orient the fractures and assess their overall contribution to reservoir performance in a Devonian reef complex. These techniques include the imaging of the wellbore with the Formation MicroScanner Log (FMS)* and the Borehole Televiewer (BHTV). The image data were compared to detailed core analysis, where available, and were used to determine the length, orientation and probability of fractures as a function of porosity. The Array-Sonic* tool was also run to help identify fractured zones using full waveform data and to quantify producibility from Stoneley wave data in comparison to flowmeter production logs.From the comparison of the images with core, the utility of the FMS and BHTV Logs were established in identifying fractures and fracture sets as well as determining the orientation and vertical extent of the fractures. In addition, the response of FMS images to different porosity types was confirmed by core ~ata. Comparison of the Array-Sonic data and the flowmeter production log data established the usefulness of the Stoneley wave attenuation as a means of identifying permeable zones.The study results permit better definition of tool response to porosity types and fractures, and reveals the influence of fractures on the overall production of the reef complex. These results have implications on the initial and secondary production techniques of this and other carbonate reservoirs.
A Layer Pulse Test was designed, implemented and analyzed in a pinnacle reef in Alberta. Two Repeat Formation Tester (RFT)* surveys were performed in the observation well at a pre-designed interval. The second RFT survey was performed after the pulsed well was put back on production. The design was based on an older, history-matched model of the reef. A geological and stratigraphic interpretation was performed to update the geological and the numerical model. Subsequently, a three-dimensional, three-phase, single equation numerical simulator was used to model the inter-well area and a history match was obtained to the pressure shift in the two RFT surveys. The vertical pressure profiles from the RFT surveys identified barriers to vertical flow while the geological interpretation and the history match to the pressure shift provided a quantitative distribution of horizontal and vertical permeabilities in the inter-well area. Introduction Pulse testing requires generating a series of pressure disturbances by intermittently shutting-in or running-on a producer or an injector. These pressure pulses are then recorded as superimposed pressure waves over the background pressure-time behavior, for that reservoir, at the observation well. For a single layer homogeneous reservoir the measured pressure pulse can be interpreted using analytical methods. This interpretation, among other parameters, should result in inter-well permeability. The pressure amplitude and time-lag of the pressure pulses are dependent on inter-well permeability, fluid viscosity, total compressibility and porosity. They are also dependent on the interwell distance and the injection/production rate of the pulsed well. For a multi-layer reservoir the analysis of pressure pulses is not that straight-forward. In such a situation the pressure amplitude and time-lag are also a function of the vertical permeability between the layers. Moreover to monitor a complete pressure wave for even a single pulse at every layer in the observation well is not operationally possible today. One way to overcome these hurdles is to catch two or more pressure points on every wave. The number of different waves will depend on the layering of that reservoir. A wireline formation tester (RFT) is an ideal tool to measure pressure points, layer by layer, at pre-designed time intervals. In a layered reservoir with interlayer communication and commingled flow in the pulsed well, the shift in the RFT measured pressure points is not interpretable using convenient analytical models. To interpret the pressure shifts in the RFT profiles an elegant, three-dimensional, three-phase, single equation numerical simulator has been formulated. The numerical simulator, RFTSIM, assumes that the saturation distribution during the course of the Layer Pulse Test remains constant. RFTSIM requires a history match to the shift in the RFT measured vertical pressure profiles. This history match quantifies the horizontal and vertical permeability distribution and ascertains barriers to flow. These barriers could be partial or sealing, they could be a result of a fault system or just a reservoir structural boundary. The Layer Pulse Test was first introduced by Dakel and since then several tests have been carried out, mostly in the North Sea. Two other North Sea tests reported were by Lasseter and Bunn. Lasseter used RFTSIM to interpret a two-layer pulse test, thereby obtaining the vertical and horizontal permeability in the inter-well area and the fault block geometry. Bunn designed, implemented and analyzed a Layer Pulse Test from the Cormorant Field in the North Sea and obtained the transmissibility of the partially sealing layer between two lithological layers. This paper will describe the design, measurement and the interpretation of a Layer Pulse Test conducted in a pinnacle reef in Alberta. (This Layer Pulse Test was the first one to be conducted in North America.) DESIGN OF THE LAYER PULSE TEST A history-matched, two-dimensional radial model of the reef was available. P. 543^
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