Abstract
The Machar field is primarily a naturally fractured chalk reservoir; with the subsea wells requiring acid stimulations in order to be economic. This paper describes the design and implementation of an acid stimulation for a new intelligent well completion. The combination of a subsea development, a high rate boat based acid stimulation and a surface operated intelligent completion provided several challenges.
The stimulation challenges arose due to the long reservoir completion and the required use of flow control valves with small tubing within this section. This prevented the traditional use of ball diverters in order to effectively treat the whole reservoir interval. By using the isolation capabilities of the intelligent completion, several intervals were sequentially treated. Within each completion interval, limited entry perforating provided the method of diversion necessary to effectively treat each perforation. In order for this to be successful, the perforations had to be centralised and shot prior to running the completion. Limited entry perforating therefore required physical gun shoot tests and a pump test through the shot holes. The results and conclusions of these tests are included in this paper.
The completion challenges related to the stimulation included assurance of the integrity of the sensitive downhole electronics and hydraulics required to operate the downhole valves and sensors. This assurance was vital as, for the first time with an intelligent completion, the stimulation involved pumping concentrated hydrochloric acid down the well at rates of up to 50 bpm.
Implementation of the stimulation was achieved with the real time multizone downhole pressure and temperature data providing several fascinating opportunities to view downhole mechanisms. Of particular interest is the pressure transient impact of a stimulation on adjacent zones and the cooldown effect on partially trapped annuli. The analysis of this downhole data is presented.
