Critical Cementing Application on a Snubbing Unit to Isolate Well in Kuwait
Authors: Al-Mohailan Mohannad , Nellayappan Karthikeyan , Patil Dipak , Al-Qadhi Fahad , Sounderajjan Mahesh , Kunchur Basavaraj , Hussain Khaddar 
Published: March 2019

In deep wells in Kuwait, completions are fairly standardized which after flow testing are handed over to assets. In course of time, well interventions were done due to one or more of the following reasons - water shut off, addition of zone, plugged perforations, tubing check or production logging. In course of these Rigless interventions over a period of two decades wells have accumulated with fish primarily coiled tubing or wire line fish with some wells being partially plugged. In view of this, a snubbing unit with targeted capabilities to fish inside tubing was deployed.

Earlier, the well could not be killed either by bull heading or with heavy mud circulated by coiled tubing. Thus, the well was identified as a candidate to mobilize a snubbing unit to clean out and place a cement plug. The Snubbing operations itself was being performed for the first time under a regular contract.

The operations include a complete cleaning of all the bridges suspected from about 4200 ft to the deepest depth possible as per the availability of the work string tubulars. It was identified from previous records, this is likely to be an off bottom kill with mud and may not effectively prevent the gas seepage. Thus a detailed planning for a critical cement plug to be placed inside the liner to isolate the open hole from below was made.

Extensive laboratory testing and job modeling was conducted to ensure proper placement of the cement slurry in a challenging HP/HT environment. A 16.5 ppg Gas Block Slurry with low Fluid Loss and favorable rheological propertieswas utilized. Additionally, an alternative, customized engineered designed spacer was used to prevent the formation of a filter cake.

The cement plug was placed with only 1.5″ ID workstring in a 5″ liner while taking due care to prevent cement back into the 31/2″ completion tubing above. Besides, care had to be taken to factor in a sufficiently long thickening time to enable pull out work string safely. The well was successfully secured and isolated and will now allow the utilization of a work over rig to recomplete the well.

The use of a Snubbing Unit has been proven effective to isolate the gas zone and ensure zero pressure on surface to enable mobilization of Workover rig. The paper discusses the challenges in design, planning and operations of placing a 8 bbl plug to stem the gas which made the well unapproachable for the last 3 years.

In 2010, a deep well in North Kuwait was facing continuous complications with gas cuts during completion operations. In order to secure the objectives of the well the open hole section was cemented and was stimulated in LM zone with no success in flow at surface. Additionally, heavy mud was pumped to control the gas influx, resulting in barite settlement but the well reflected pressure of 4000 psi. In order to subdue, attempts have been made to kill the well with CT and heavy mud which failed as CT could not be run to the deepest depth due to high circulating pressures.