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Accurate casing ID key to cement drill outs

Nov. 25, 1996

Table 1 [6448 bytes] Table 2 [6418 bytes] BP EXPLORATION CO. (COLOMBIA) INC. (BPXC) DETERMINED THAT measuring casing string IDs improved its success for bumping 133/8-in. and 95/8-in. cement plugs, thus minimizing cement drill-out time. In 24 cement jobs with casing ID measurements, BPXC says only two plugs failed to bump. This 92% success rate compares to only 40% success prior to measuring IDs. BPXC found that measured IDs were larger than published values for both 133/8-in. and 95/8-in.

BP EXPLORATION CO. (COLOMBIA) INC. (BPXC) DETERMINED THAT measuring casing string IDs improved its success for bumping 133/8-in. and 95/8-in. cement plugs, thus minimizing cement drill-out time.

In 24 cement jobs with casing ID measurements, BPXC says only two plugs failed to bump. This 92% success rate compares to only 40% success prior to measuring IDs.

BPXC found that measured IDs were larger than published values for both 133/8-in. and 95/8-in. casing. Typically, BPXC calculated 30 bbl more in displacement volume from the measured IDs.

According to BPXC, this additional volume is the principal reason why plug-bumping success was poor prior to measuring casing ID. Tables 1 and 2 summarize the IDs measured during 24 cement jobs.

BPXC measures casing ID during its routine casing inspection program. It uses an internal digital micrometer to check about 10% of the joints. Accuracy is in the range of 0.001 in. The micrometer is calibrated initially against a known measurement.

BPXC takes eight radially distributed measurements at both ends of the casing, about 1-2 ft from the joint ends. All points are then averaged.

Also, BPXC recalculated rig pump efficiencies after each job based on the known displacement and the top plug location. For the 24 jobs, it calculated an average rig pump efficiency of 96.3 %.