Abstract
The NE field is located in Barmer Basin, Rajasthan, India. The field is on production with two wells since March 2015 and is currently producing about 1100 bopd. Both the wells are completed with progressive cavity pumps (PCPs). Production is being carried through a small production facility (QPF). The presence of pumps in the well makes the acquisition of pressure build up (PBU) data complex. However, gathering a PBU was considered an important part of gauging reservoir performance. This paper details how an echo-meter was used in one of the wells for acquiring Pressure Build Up data. The echo-meter was used to measure dynamic fluid levels in the casing-tubing annulus; these were used to estimate reservoir pressure and other properties in a cost effective manner. The paper discusses a systematic approach in echo-meter based well test design, execution challenges and the PTA of the acquired data.
The well was flowing with a drawdown of about 100 psi and the liquid level in the annulus was about 100m from the top. The direct collection of PBU data would have required a work-over to remove the pump to place the gauge. This would need to be repeated to retrieve the gauge. A novel & cost effective approach was required to acquire pressure build up data. An alternate option was acquiring the pressure data indirectly by measuring the continuous dynamic level in the annulus using an echo-meter. Although this option had its own challenges, it was economically justified. The required number of echo-meter shots and frequency of the shots was selected based on well test design. The test design provided guidance on the pressure build up rate required for damaged (skin) and non-damaged conditions, permitting us to identify the pressure build up duration and the optimum frequency of the echometer shots. One challenge was concern over annulus liquid level rise in the wellbore. This was addressed prior to the build-up by injecting nitrogen into the annulus to reduce the liquid level in the annulus. This mitigated the possibility of liquid level rise in the annulus to the wellhead.
The quality of the pressure data acquired through echometer shots was good enough for carrying out pressure transient analysis. The pressure derivative plot was constructed and information on skin & permeability was obtained. Radial flow signature was clearly observed. The average reservoir pressure value as well as the permeability agreed with expectations. The impact of uncertainties on the final interpretation was evaluated and found to be in acceptable range.
In current oil price environment and in marginal fields like NE, where there is always a constraint on economics, this low cost technique can be a vital tool for effective reservoir management.
