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Chapter 7 WELL Testing STUDENT COPYBuildup test Drawdown test Multiple rate flow test Analysis of well testing data Skin factor
Formation Evaluation (CGE674)
Universiti Teknologi MARA
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CHAPTER 7 WELL TESTING
- Commonly used in petroleum industry include
Test Information obtained Drawdown test Pressure profile, reservoir behavior, permeability, skin, fracture length, reservoir limit and shape Buildup test Reservoir behavior, permeability, fracture length, skin, reservoir pressure, boundaries DST Reservoir behavior, permeability, skin, fracture, reservoir limit, boundaries Falloff test Mobility in various banks, skin, reservoir pressure, fracture length, location of front, boundaries. Interference and pulse tests
Communication between wells, reservoir type behavior, porosity, interwell permeability, vertical permeability Layered reservoir tests Horizontal permeability, vertical permeability, skin, average layer pressure, outer boundary Step-rate tests Formation parting pressure, permeability, skin
- Single well test: flowrate is changed and the pressure response is recorded in the same well. Example: drawdown, buildup, injectivity, falloff and step-rate test.
- Multiple well test: flowarte is changed in one well and the pressure response is measured in
another wells.
Figure 1: Concept of drawdown and buildup test
a. Pressure drawdown
- A series of bottom hole pressure measurements made during a period of flow at constant producing rate.
- Usually the well is shut in prior to the flow test for a period of time sufficient to allow the pressure to equalize throughout the formation, i., reach static pressure.
- To: Obtain average permeability, k, of the reservoir rock within the drainage area of the well. Assess the degree of damage of stimulation induced in the vicinity of the wellbore through drilling and completion practices. Determine the pore volume Detect reservoir inhomogeneities within the drainage area of the well
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Figure 2: Idealized drawdown test b. Pressure buildup
- Pressure buildup analysis describes the buildup in wellbore pressure with time after a well has been shut in.
- Because the buildup in wellbore pressure will generally follow some definite trend, it has been possible to determine: The static reservoir pressure without waiting weeks or months for the pressure in the entire to stabilize
c. Effect of variable flowrates
- Every flowrate change in a well will result in a pressure response which is independent of the pressure responses caused by the other previous rate changes.
- Accordingly, the total pressure drop that has occurred at any time is the summation of pressure changes caused separately by each net flowrate change.
- Consider the case of a shut-in well, i Q = 0, that was then allowed to produce at a series of constant rates for the different time periods. As in figure below;
Figure 4: Production and pressure history of a well
- To calculate the total pressure drop at the sand face at time t 4 , the composite solution is obtained by adding the individual constant-rate solution at the specified rate-time sequence
Where;
Example 1
Figure 4 shows the rate history of a well that is producing under transient flow conditions for 15 hours. Given the following data; Pi = 5000 psia Ø = 15% Ct = 20x10-6 psi- h = 20 ft μo = 2 cp s = 0 Bo = 1 bbl/STB rw = 0 ft k = 40 md Calculate the sand face pressure after 15 hours.
The additional pressure drops at well 1 due to the production from wells 2 and 3 are;
The total pressure drop at well 1;
Example 2
Assume that the three wells as shown in Figure 5 are producing under transient flow condition for 15 hours. The following additional data is available; Qo1 = 100 STB/day r 1 = 400 ft Qo2 = 160 STB/day r 2 = 700 ft Qo3 = 200 STB/day μo = 2 cp Pi = 4500 psia Bo = 1 bbl/STB Swell,1 = -0 Ct = 20x10-6 psi- h = 20 ft Ø = 15% k = 40 md rw = 0 ft If the 3 wells are producing at a constant flowrate calculate the sand face flowing pressure at well 1.
Chapter 7 WELL Testing STUDENT COPYBuildup test Drawdown test Multiple rate flow test Analysis of well testing data Skin factor
Course: Formation Evaluation (CGE674)
University: Universiti Teknologi MARA
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