Single-stage spacer pill additive helps break free stuck drillstring

Using DeepClean™ single-stage spacer pill additive, an operator in Malaysia extracted a differentially stuck drillstring within timeline and financial constraints.

Free differentially stuck drillstring

The operator needed an efficient, cost-effective way to extract a differentially stuck drillstring while handling personnel constraints related to COVID-19 mandates.

Drilling challenges

While drilling a reservoir section, the driller tried to pull out of the hole at 13,871 ft because of a logging-while-drilling tool failure. While pulling out of the hole, the drillstring became stuck at 11,267 ft. With the inability to rotate and move the drillpipe while being able to circulate at 400 galUS/min with 1,650 psi, the drillpipe was differentially stuck. The differential pressure when stuck was 830 psi. The well’s angle was 87°, and for this section, it was a tangent from 95/8-in casing shoe (10,280 ft) until the well’s total depth.

Below is the timeline of the unsuccessful attempts to free the stuck pipe:

Create a high-quality acid-soluble filtercake

SLB selected VERSAPRO™ invert-emulsion reservoir drill-in fluid system to use to drill the reservoir section because it causes minimal damage to the formation and is formulated to create a high-quality acid-soluble filtercake, which was important for the openhole completion planned.

To free the differentially stuck drillstring, 11.1-lbm/galUS DeepClean pill additive was used. The DeepClean pill additive is a combination of powerful solvents, surfactants, and water-wetting agents to break the filtercake and was included in the planning phase as the contingency chemical for the stuck pipe event.

The formulation was adjusted from the one in the program to cater to the barite-free requirement for the reservoir section; hence, the calcium chloride was used to ensure the additives have the same density as the drilling fluid.

Pump pill additive

The operator followed the recommendations to pump the DeepClean pill additive, which took about an hour of operation time. The process is outlined below.

1. Pumped and spotted DeepClean pill additive around the 8.5-in BHA in this order:

a. Pumped 15 bbl of 11.1-lbm/galUS viscous additive.

b. Pumped 25 bbl of 11.1-lbm/galUS DeepClean pill additive (to cover approximately 600 ft in the openhole).

c. Displaced with 210 bbl of 11.1-lbm/galUS VERSAPRO system. d. Worked string while soaking. Torqued up string to 30,000 lbf.ft. Worked string down to block weight to transfer torque down to the sticking point. Freed string after 30 min of soaking. e. Displaced and discharged the DeepClean pill additive at the surface.

2. Pumped and rotated out of the hole to 10,200 ft (inside casing). Observed erratic torque spiking up to 23,000 lbf.ft.

3. Pulled out of the hole to surface on elevator.

Important factors to free drillstring

• Laboratory development and testing of the DeepClean pill additive formulation to find the optimal concentration before it was included in the drilling fluids program.
• Low fluid loss and thin filtercake for VERSAPRO system throughout the drilling. The VERSAPRO system HTHP fluid loss was maintained between 2.6 and 2.8 mL/30min, and the filtercake size was observed by the relatively short soaking time with the DeepClean pill additive before the pipe was set free.

Remove drillstring

The drillstring was removed without damaging the casing and without incurring additional personnel cost—all in a reasonable time period.

DeepClean, SAFE-VIS E, and VERSAPRO are marks of M-I L.L.C., an SLB company.