I-BOSS Helps Client Drill through Depleted Zones with Overbalances Up to 3,500 psi

Historically, wells drilled in this field presented hole stability problems, such as sloughing, that typically start in the 12 ¼ in interval and increased in the 8 ½ in production interval. In the past, increasing mud density had been the favored way to solve this type of hole instability; however, depletion of producing formations has become more common, and with it the risk of lost circulation has increased when the mud density was increased. A frequent occurrence now is planting of BHAs and the necessity to drill sidetracks. In the case here, the client was running over budget because of problems in the 12 ¼ in interval, and it was critical that the 8 ½ inch interval be drilled trouble-free.

The Solution

The input data required to design a hoop-stress-enhancement wellbore strengthening operation with the OPTI-STRESS* software were not available. The formation was sandstone and was being drilled at a low ROP. Of the available options, the most desirable alternative appeared to be pumping 40 ppb pills of OPTISEAL IV on every connection (stand). Related recommendations included (a) running VIRTUAL HYDRAULICS* software on every shift to maintain good control of the ECD, and (b) delay raising mud density if sloughing was observed to give the OPTISEAL IV treatment some time to work.

The Results

Drilling was started with 10.8 ppg mud and the mud density was increased to 11.1 ppg when sloughing over the shakers was observed at 13,027 ft MD, and a 50 bbl 40-ppb OPTISEAL IV pill was pumped. Very little of this pill was seen at shakers, so it was decided to pump another one. This time, some of it came back. From here on, pills were pumped every connection, and the well was drilled to TD with no further sloughing observed.

The hole was then wiper-tripped twice though a few tight spots (20 – 25K over-pull), then the liner at TD was run and cemented. The client is very satisfied with the results and gave a score of 10 in the customer satisfaction survey.

The Details

Two 50 bbl pills of 40 ppb OPTISEAL IV product at 13,027 ft MD were pumped to control sloughing. After this, 15 bbl of 40 ppb OPTISEAL IV pills were pumped on every connection. The flow rate was 450 - 470 gpm while drilling at an ROP of 3 - 8 ft/hr. The client raised some concerns of overtreatment due to the low ROP, and this was why the pill volume was reduced to 15 bbl. No signs of sloughing were seen after the two 50 bbl pills pumped at 13,027 feet, although the well inclination of 39.8 deg helped in this regard. From this point on, there was no need to increase the mud density. Total drilling fluid losses to the formation amounted to 589 bbl; historically, this has been a four-digit number.

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If you’d like to know more about the OPTISEAL IV product and the I-BOSS suite of integrated solutions and how it’s performing for our other customers, please call the SLB office nearest you.