Monitoring Waterflood Operations: Hall's Method Revisited

Abstract

Hall's method is a tool for evaluation of an injecting well performance.It is based on the assumption of radial steady-state flow.Besides time series of historical injection pressures and rates, rigorous implementation of Hall's method requires information about the ambient reservoir pressure.In addition, it is assumed that the influence domain radius is constant during the observation period.Neither of these parameters can be measured directly. This paper discusses a new method called slope analysis.It is based on analysis of the variations of the slope of the plot of the time integral of pressures versus cumulative injection volume.In particular, it produces an estimate of an apparent average reservoir pressure.This method requires only injection pressures and rates data, which are routinely collected in the course of a waterflood.Thus, slope analysis requires no interruption of regular field operations. The method has been verified with numerically generated pressure and rate data, and tested with field data.In both cases it proved to be accurate, efficient, and simple.The estimated ambient reservoir pressure can be used to correct the Hall plot analysis or to map the average reservoir pressure over several patterns or an entire waterflood project.Such maps can then be used to develop an efficient waterflood policy, which will help to arrest subsidence andimprove oil recovery. Introduction Monitoring and control of performance of each individual well is an important component of successful oil recovery operations.The dramatic progress in information technology over the past decade has made it possible to collect and store huge volumes of high-quality production and injection data.These data, if appropriately interpreted, provide new insights into reservoir dynamics across multiple temporal and spatial scales.Therefore, efficient processing and interpretation of the high-frequency field measurements is a task of crucial importance to modern management of oil & gas recovery projects. This paper deals with problems related to monitoring and control of waterflood operations.The necessity of collecting and processing numerous measurements was understood decades ago[1].Recently, ChevronTexaco with participation of the Lawrence Berkeley National Laboratory and the University of California, Berkeley, developed a concept of field-wide surveillance and control of waterflood.This concept is being implemented in the Lost Hills oil field[2]. The work reported here is a part of this effort. Waterflood performance in an entire oilfield sums up from operations at each individual well.The global project objectives are derived from a field-scale analysis, such as inspection of satellite images for surface subsidence and uplift, and calculation of the fluid injection-withdrawal balance.[3]But the subsurface reservoir can only be accessed and controlled through the wells.Therefore, it is critically important to have efficient tools for regular well performance monitoring, and methods for adequate interpretation of this performance for assessment of the reservoir conditions near the wellbore. Traditional transient well tests have been used to evaluate the average near-wellbore formation transmissivity[4].Such tests interrupt regular field operations.Their interpretation is based on analysis of transient effects taking place at time scales which are short relative to those of fluid injection and production.On one hand, unless there is a pipe-like circulation of injected fluid between an injector and the surrounding producers, the injection results in ever-changing reservoir conditions.On the other hand, these changes may be almost imperceptible over a typical observation time interval.Therefore, the field-scale reservoir processes can be called quasi steady-state.In real life operations, short-time fluctuations of the injection pressures and rates at the well are inevitable.Separation of these short-time transient effects and long-time quasi steady-state processes is one of the most important tasks of well performance monitoring and diagnostics,[5–7] crucial to the information-driven oilfields of the future.

Waterflood Surveillance and Control: Incorporating Hall Plot and Slope Analysis

“…18 then p w /Q is a linear function of 1/Q, and the slope of the plot of this function is the reservoir pressure at the perimeter of the injection zone, see Fig. 18.…”

“…Silin et al 18 reviewed some uncertainties associated with this method and proposed to partially resolve them using a novel "slope analysis." The idea of using Hall's method in automatic maintenance of a desired target injection rate is similar to that of using a thermostat for maintaining a constant temperature.…”

“…3, has been corrected using the slope analysis described in Appendix A, see also Ref. 18. After this correction, the Hall plot shows a tiny increase of the slope, which means a decrease of injectivity at the beginning of the data interval.…”

The Development of World-Class High Rates, High Ultimate Recovery Wells in Deepwater Turbidites--Bonga Field, Offshore Nigeria

“…These pressure data combined with the Hall plot 15 gives the single most important information in the evaluation of the success or failure of the fracture waterflood program. These pressure data combined with the Hall plot 15 gives the single most important information in the evaluation of the success or failure of the fracture waterflood program.…”

Identification and Characterization of High-Conductive Layers in Waterfloods

“…Some of the notable contributors include Buell et al (1990), who suggested the use of both bottomhole injection pressure and reservoir pressure instead of the wellhead pressure alone, as used in the conventional Hall plot. Evaluation of the reservoir pressure from a slope-analysis method was offered by Silin et al (2005aSilin et al ( , 2005b. Ideally, the Hall method is suitable for either early injection period or during the post-breakthrough period, because the notion of single-reservoir pressure is entertained.…”