tion with time. Such tests are quite economical to run and they yield valuable information about the reservoir characteristics and well characteristics. Hence, bottom-hole pressure tests are usually referred (Earlougher, 1977; 1982) to as well tests. Types ofBottom-hole pressure test are:
- Pressure Drawdown
- Pressure Build up
During conventional well tests, fluid is extracted to the surface or injected into the well at controlled rates. A program of flow and shut in periods is used to establish deliverability and completion efficiency of the well. Tests can involve a single well or many wells. Depending on test objectives and operational considerations, a range of well tests can be carried out. The tests usually fall into the following categories (Horne, 1995; Bourdet, 2002):
This test is conducted in a well that has been producing for some time at a constant rate and is then shut in. The build-up down-hole pressure is then recorded for a given time.
Figure 1.2: Build up test
This test is conducted when a well is flowed at a constant rate. The flowing down-hole pressure and the production rate are measured as functions of time and analyzed to estimate the reservoir properties. The major difficulty of the drawdown is the inability to maintain a constant flow rate.
Figure 1.3: Drawdown test
This test is identical to a drawdown test, except that the flow is into the well rather than out of it. Fluid is injected into the well at a constant rate and the injection rate and the down-hole pressure are measured as functions of time.
Figure 1.4: Injection test
This test is analogous to a build-up test and it measures the pressure decline as a function of time subsequent to the shut in of an injection.
Figure 1.5: Falloff test
The combined response can be interpreted in a number of ways to estimate the permeability-thickness and the skin factor.
Unlike the first four tests (drawdown, injection, buildup, falloff) which are tests involving only one well (single well tests), the interference test involves the use of more than one well (multiple well test). During interference tests, pressure changes due to production or injection or shut-in at an active well is monitored at an observation well. Interference tests investigate the reservoir properties and establish pressure connectivity between wells.
Interference tests are primarily used to establish sand continuity between the active and observation wells. In situation where more than one observation well is used, interference test can be used to find maximum and minimum permeability and their directions.
Figure 1.6: Interference test
1.1.3 Uses of Bottom-hole pressure test Derived Information
Results obtained from BHP tests are used for the following purposes:
- Reservoir Surveillance.
- Determination of Stimulation Candidates.
- Gaslift Optimization.
- Input for Reservoir Simulation.
- Material Balance Calculation.
1.2 Statement Of The Problem
During the process of drilling a well, foreign particle may invade into the porous space and plug it, there may be formation of clay dispersion and migration etc. which have great effect on the flow of the reservoir fluid. When this occurred in the wellbore and reservoir, it cannot be known without the help of well testing. Furthermore, for every test conducted, there is an objective to be arrived at but there are challenges of improper design of the test and accurate analysis and interpretation to meet objective.Hence, the need for an effective and accurate tool “Saphir” to determine if there is a damage to the wellbore and impairment to flow.
1.3 Aim And Objectives Of The Study
The importance of well testing in the oil and gas industry cannot be overemphasized just as a doctor trying to treat a patient without carrying out a test to actually diagnose the problem to know the right prescription for the situation. This is also the case of an oil and gas well. Thus, the main aim of this study is to determine well and reservoir properties from a well test data. In order to achieve this aim, the following objectives need to be carried out:
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