Pressure drawdown test

It is common practice to record the bottom hole pressure firstly during a flowing period (pressure drawdown test), and then during a shut-in period (pressure build-up test). During the flowing period, the FBHP is drawn down from the initial pressure, and when the well is subsequently shut in, the bottom hole pressure builds up. 

The reservoir boundaries are normally determined by the constant rate pressure drawdown test. A plane boundary at a distance l from the well would have the same effect on the pressure as the presence of a second well producing at the same rate and at a distance 21 from the first well in a reservoir of infinite size. An analytical solution can be found through superposition for the bottom-hole pressure pw, p(r = rW9 t), in which the effect of the boundary is represented by the effect of the second (image) well (49) ... 

Pressure Drawdown Tests. This series of experiments were designed to determine the effect of pressure reduction on the stability of certified gas composition between a maximum filling pressure of 300 psig and atmospheric pressure. Two sets of cylinders filled with a 10-component gas blend, similar in composition to our NBS primary standard, will be analyzed before and after each 50-psig pressure reduction at different gas withdrawal rates. The results of these tests will indicate the optimum rate of gas withdrawal as well as the residual cylinder pressure for the GC calibration gas. 

Extensional Viscosity. AH three types of extensional viscosity can be measured (101,103) uniaxial, biaxial, and pure shear. Only a few commercial instmments are available, however, and most measurements are made with improvised equipment. Extensional viscosity of polymer melts can be estimated from converging flow (entrance pressure) or from a melt strength drawdown test (208). 

In the JAPEX/JNOC/GSC program, small-scale field production tests were conducted by using pressure-drawdown experiments. Data measured in response to depressurization are pressure, temperature, gas flow, and water flow. During our study, these data were not available to us. 

At each setting of the outlet pressure, the steady-state pressure profile and the production rate were measured. Therefore, for each oil, 10—12 flow experiments were conducted. End-point average gas saturations (5 ) were estimated after the flow test at the highest pressure drawdown and are presented in Table II. 

The influence of shear stress and pressure drawdown on solids production has been demonstrated in large-scale laboratory tests (38). Short bursts of solids, from perforation clean-up, and productivity improvement occurred after each increase in effective stress or drawdown. 

Initialization procedures. Well test field procedures fall into two varieties, namely, pressure drawdown and pressure buildup. Very often, an initially quiescent, pressurized reservoir of uniform pressure (typically equal to the farfield pressure Pr in an aquifer-driven flow) is opened to a lower well pressure P and allowed to produce. The pressure in the neighborhood of the... 

Further calibrations with respect to cross fault communication within hydraulic compartment II was obtained by re-entering well 7-2 2 years after the initial production test to assess formation pressure recovery relative to the initial drawdown and to perform further testing. The data acquired gave indications of partial pressure communication across intensity zones and small scale (10-20 m throw) faults in the vicinity of the well. 

Parabolic equations describe transient compressible effects, including modeling well test buildup and drawdown. These also require boundary conditions as described previously in addition, they must be solved together with initial conditions. For example, how active is the reservoir at the outset Do transients dominate the physics Or is it flowing at steady state Perhaps it is static, held at constant uniform pressure Boundary conditions may be related to skin resistance and storage in wells and flowlines. We will formulate these auxiliary constraints generally and offer exact solutions later. 

Reservoir coimectivity is important to sweep efficiency in all phases of production. How efficiently a formation s pore spaces are coimected is determined through tracer analysis, where chemical or radioactive tracers are introduced at injection and monitored at production wells. The idea is simple the more tracers obtained at a producer, the better the connectivity between the injectors and it. In reservoir simulation, the oilfield s permeability and porosity distributions are determined, often by trial and error, and more than likely nonuniquely, by history matching with production and well test data. In singlephase flow reservoirs, steady-state production profiles are completely determined by the pressure equation and Darcy s law, neither of which depends on porosity. In well testing, pressure buildup and drawdown depend on porosity and compressibility, factors that do not directly enter in steady-state production. Empirical tracer tests provide further information porosity, inferred from tracer travel times, enters in steady flows where compressibility is unimportant. These three flow tests therefore provide good independent check points that are essential to good reservoir description. 

When transient effects are present, as in well test pressure buildup or drawdown, the effects of compressibility and porosity enter. The governing equation for constant properties takes the form... 

Numerical stability. Nothing strikes greater fear in simulation than instabilities. Numerical instabilities manifest themselves through unrealistic oscillations in pressure buildup or drawdown curves, wiggly spatial pressure distributions that lead to infinities and overflow. How can they be avoided One useful tool is the von Neumann stability test, after John von Neumann, the computer pioneer who advanced finite difference methods in the 1950s. Numerical analysts employ these tests to evaluate candidate algorithms before code development begins. Consider the heat equation u = u, for u = u(x,t). We... 

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