Pressure build up and drawdown analysis applied to D. S. T. shut-in and flow periods is reviewed.
A description of D. S. T. periods and their influence on pressure behavoir is made.
The flow equation in dimensionless form is presented. A development in SI Units of parameter calculation formulas is made, as follows: Initial Reservoir Pressure, Transmissibility, Flow capacity, Permeability, Damage Ratio, Skin Factor, Radius of Investigation and Potentiometric Surface.
Use of D. S. T. in calculation of productivity index and open flow deliverability is discussed.
Type curve matching techniques for afterflow part of build up in D. S. T. is explained.
Reservoir management begins at the exploration stage; therefore all the documentation obtained at this time will help in the decision making process when completion and production time come.
A definition of the reservoir and knowledge of its parameters is important, and that is the reason why drill stem tests are performed.
A drill stem test is a short production test early in the life of a well; the basic principle is the isolation of the formation with packers, either conventional or inflatable, then the use of a multi-flow evaluatorl allows to produce to the drill string during the flow periods and close downhole during the shut-in periods to get a draw-clown and a buildup respectively.
The analysis of these flows (draw-down) and shut-ins (build-up) permit the calculation of reservoir parameters such as initial reservoir pressure, permeability, skin, damage ratio, radius of investigation, potentiometric surface, and estimations of productivity index in liquid wells or absolute open flow potential in gas wells.
The formulas used for the above calculations have been dealt with in the literature 1,2,3,8.
The implementation of the 51 (metric) units in Canada makes it necessary for the development of equations directly in this system.
The purpose of this paper is to develop equations for parameter calculations from data obtained in a D. S. T. in SI units, and the analysis by type curve when the use of conventional methods is not possible.
The location of the different pressure gauges in the drill string is presented in figure 1, and the first step in a successful interpretation of the drill stall test is the study of the different charts, to make sure that a mechanically successful test was obtained. A check list would include:
Good flows and shut-ins were achieved.
No plugging occurred.
Recorders functioned satisfactorily
Clocks ran adequately
No leaks or communications around the packer were experienced.
If the chart analysis is satisfactory, further calculations will check. if reported data is in agreement with pressure data from the charts.
The hydrostatic pressure can be calculated be the equation: Equation (Available in full paper)
From the final flowing pressure and if a liquid test is being analysed the recovery can be calculated as
Equation (Available in full paper)