![]()
The practice of using bottomhole pressure measurements to improve oil and gas production and solve problems of reservoir engineering began around 1930. Initially, pressures were calculated using fluid levels; a later method was to inject gas into the tubing until the pressure became constant. The earliest bottomhole pressure measurements were made with one-time-reading pressure bombs and maximum-indicating or maximum-recording pressure gauges that lacked the accuracy, reliability, or durability of present-day technology. The varied uses of bottomhole pressure and temperature measurements have increased in scope during the past two decades as instrumentation technologies have produced more reliable and accurate tools. These advances have made more applications possible, including use in multilayer reservoirs, horizontal wells, interference testing, and drawdown test interpretation. This chapter is focused mainly on the types of measurements made and the tools available. Some information is included on interpretation techniques to connect the data acquisition with its use in characterizing a reservoir and its contents. Detailed explanations of these interpretation techniques can be found in other chapters in this Handbook. Figure 1.1 – Pressure gradients in a well drilled in a virgin reservoir. In a developed reservoir, differential depletion of lithostatic layers with various permeabilities and the movement of fluid contacts can change the pressure profile. Monitoring the static pressures vs. time in developed reservoirs is a crucial tool for reservoir management. Pseudosteady-state flow behavior is observed when a well reaches stabilized production from a limited drainage volume. For constant-rate production under pseudosteady-state conditions, the difference between the flowing wellbore pressure and the average reservoir pressure in the drainage volume is constant, and the pressure drawdown is a linear function of time. The late-time buildup pressure will level off to the average reservoir pressure if the buildup duration is sufficiently long. Pressure depletion occurs with continued pseudosteady-state production. Transient flow is most often modeled with the radial diffusivity equation, which allows modeling pressure vs. time and pressure vs. distance from an observation point (typically, a well). At a sufficiently large time, the pressure disturbance anywhere in the reservoir is proportional to the logarithm of the inverse square of the radius away from the origin of the disturbance.
Site News