1.1.1 Drawdown Testing
Drawdown, the well produced on a fixed choke setting, until the test objective has been reach. A drawdown test is usually initiated from “cold start” or shut in well, but it may be conducted by doubling or more, the current rate. In order to complete drawdown test, data to be valid and there must be a critical flow across choke (roughly 2.2:1 ratio of up-stream to down-stream pressure). At these conditions, there will be adiabatic shockwave across the choke, which will isolate the well, from facilities and other down-stream disturbance.
The best exercise for a draw-down is to do a constant choke test, not necessarily a constant-rate test. Quite often, a well will decline in both rate & pressure on a constant choke setting.…show more content… This mean that the management sees cash flow, reservoir engineer finds the reservoir boundary, size and production engineer evaluates the completion of well. Another advantage of DD over a PBU is in a draw-down test, it is easier to differentiate, whether a boundary or reservoir limit contact during the tests is a fault, start out gas-liquid contact (edge; not bottom or top). Also on the plus side is, draw-down testing evaluates the well or reservoir at production condition. If there is multi-phase flow in the reservoir/ if the rock is extremely compressed or geo pressured; there can be the significant difference between a buildup response and their draw-down response, which case the draw-down will likely be more valid. A final benefit of draw-down testing is that mitigates or calculate the effect of phase re segregation & cross flow between the layer, as long as the flow-rate that is high enough to confirm, that there is not any accumulation of oil or water in the well-bore. A possible problem with draw-down data is that it may be very noisy & therefore it takes longer to analyze than a buildup. This is particularly the case for derivative type curve analysis. However, if MDH Semi log analysis is used for precise and suitable results can be obtained. Quite often buildup and draw-downs are done in succession, especially if the buildup is…show more content… (1996), for the first time. After the discovery of the mentioned three zone, it is possible to develop a comprehensive analysis of effecting parameter near the wellbore using three zones radial combined model. Two-phase pseudo pressure method
This technique was introduced by O’Dell (1967) in 1967 and was improved by Fussell (1973). The stable two phase pseudo pressure technique assumes two separate zones near the well bore as follows,
1. A zone close to the wellbore; the pressure under the dew point & both gas phase and gas condensate are transportable.
2. A zone far away from the well bore; the pressure over the dew point, therefore only gas is movable. This technique ignores the zone in which there is unmoved gas condensate & the gas structure differs. Purpose of this method demands the relative permeability. The contrast between the provided result by this method and simulation output reveals that this technique sufficiently forecasts the flow capacity, however, underestimate the