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Downhole pressure

DH5R

The upper part of DH5 was drilled to 182m in 2011. In 2012 the well was drilled to the target depth of 701 m with BQ 
string. DH5R was used for observation during injection tests in DH7a. 

An injection test was carried out in well DH5R before the P&A operation began. The well was closed in after the tests 
and observed for 35 days before re-opening for plugging. The pressure in the well was recorded to be slightly higher 
than observed in the previous injection test. 

It was decided the bottom cement plug in DH5R could be placed by “bullheading”,  1500 liters of G cement slurry was 
pumped at a pressure of 96 bar decreasing to 76 bars into the well and the formation. The well was reopened after 42 
hours after cementing and several core samples retrieved. None of which were sufficiently hard enough to qualify as 
a satisfactory plugging job.

A second attempt was made to plug the well, this time 2200 litres G cement slurry was mixed and ready to be pumped 
down the WL46 string. The pumping operation started. From the outset cement became visible on the surface at the 
return and the pump pressure was low (around 10 bars). It became clear something was wrong. The cement operation 
was immediately stopped and evaluated. A crack was found in the WL46 string near to the surface. The temperature 
of the cement slurry in the well had increased; the setting and curing process of the cement had begun. 

Routine tests were carried out to determine circulation within the WL46 string as this would determine the success 
of the administration of the cement to the bottom of the well. These tests came back negative. The operation to plug 
DH5R had to be temporarily aborted.

The next steps – DH5R

The P&A operation in well DH5R faced problems. The WL46 string used to administer the cement during the plugging 
operation was found to be the cause. When pulling the equipment out of the well it was not possible to retrieve some 
items that were damaged. Metal, debris and some cement is identified as possible challenges to a future plugging 
operation.  

The well is now secured with a pressure tight blind cap. When this cap is removed in 2015 it will tell us if the well is dead 
or not. If there is no pressure the bottom cement plug has successfully been plugged off from the formation and the 
gas. Future P&A operations to DH5R will be concluded once the status of the well is identified.

The down-hole sensor was retrieved 35 days after the test. The upper part of the wire to the down- hole sensor was 
dry which indicate that the fluid level in the well had started to sink. 

After the 35 days the tested temperature was back to 24, 1 °C approximately its initial temperature from the start of 
testing. The temperature had a slow increasing trend where by the pressure had a decreasing trend. 

Once the injection test was finalized in well DH5R the equipment was removed and the well was closed and secured 
due to the presences of gas. 

(See summary of injection and falloff data by Larsen)

Surface pressure

The surface pressure decrease to 0 bar as seen in the surface press graph (blue line) with a stable and continuous 
trend over 2, 5 days. The following 10 days of the shut in period the pressure recorded some irregularities up to 0, 5 
bars. A common cause for this would be gas bubbles that are rising to surface. Day 13 of the shut in period the pres-
sure starts to increase slowly; believed to be due to the gas.