Method of determining reservoir pressure

摘要

A new approach is disclosed for measuring the pressure of tight gas reservoirs, using information obtain from continuous injection prior to hydraulic fracture stimulation. The technique can be obtained utilizing either bottom-hole or surface pressure gauges and properly instrumented surface injection pumps. The analysis is completed by plotting injection and rate data in a specialized form from terms arranged in Darcy's radial flow equation to obtain a curve or trend. The key component to proper application of this technique is to obtain both baseline and one or more calibration data sets. These calibration data sets are obtained by either increasing or decreasing the injection pressure and/or rate from the baseline data. Initial reservoir pressure is assumed, but the calibration data indicates if the guess was too high or low. Accurate estimates of reservoir pressure may be obtained in a few iterations.

主权项

1. A method of determining reservoir pressure from a reservoir:
(a) injecting, by a PUMP, a fluid into a well drilled into the reservoir; (b) measuring, by one or more sensors, one or more parameters indicative of reservoir pressure over a period time to form a baseline dataset, wherein the one or more parameters include at least bottom hole pressure and volumetric flow rate; (c) inducing, via the PUMP, a change in an injection rate or injection pressure of the fluid; (d) measuring, by the one or more sensors, the one or more parameters indicative of reservoir pressure for at least a second period of time to form a calibration dataset; (e) estimating, by the one or more processors, a reservoir pressure value, wherein estimating further comprises plotting the baseline dataset and the calibration datasets based upon the following equation:ln⁡(rerw)=2⁢π⁢⁢khμ⁢Pbh-Presq-S where q is the volumetric flow rate, μ is the dynamic viscosity, Pbh is measured bottom hole pressure, Pres is the reservoir pressure, re is the radius of invasion, rw is the wellbore radius, h is perforation height, k is reservoir permeability, and S is a skin factor; (f) plotting, by the one or more processors, fluid injection volume versus a ratio of pressure change to flow rate for the baseline dataset and the calibration datasets to form a baseline curve and calibration curve based upon the reservoir pressure value; (g) comparing, by the one or more processors, the baseline curve and the calibration curve to determine if the reservoir pressure value is correct; and (h) if the baseline curve and the calibration curve are not aligned, then repeating (e) through (g) until the baseline curve and the calibration curve are aligned.