South Timberlier Area, Gulf of Mexico
The subject well had experienced a Sustained Casing Pressure (SCP) problem for several years in the
13-3/8″ x 9-5/8″ annulus. Diagnostics indicated that the pressure source was most likely a zone at the 13-3/8″ casing shoe, traveling to the surface via a microannular channel. When bled to zero, the pressure would increase to 1015 psi within 3 hours. A sustained flow of approximately 1.6 gallons per hour was recorded.
Seal-Tite® International injected approximately 30 gallons of customized sealant, filling the microannulus to an estimated depth of over 4000 ft. Once the sealant was allowed to cure, the annulus was bled off and the pressure
response recorded. The pressure held at 0 psi for several days, and then began building at approximately 60 psi per day until the original pressure of 1300 psi was reached.
A second sealant treatment of 25 gallons was then pumped into the microannulus and displaced with nitrogen.
After one week the nitrogen pressure was bled off and the annulus pressure observed. After a period of 43 days, the annulus pressure has fluctuated between 75 psi and 300 psi, apparently in relation to thermal effects.
Background:
The subject well was completed in November, 1991 with a TD of 14,310′ MD. The casing program consisted of 30″ drive pipe, 20″ surface, 13-3/8″ & 9-5/8″ intermediate, and 7 ” production. The casing string characteristics are listed below:
| Casing String | Shoe Depth | Burst | Collapse | Cement Info |
|---|---|---|---|---|
| 30” | 254 ft | – | – | Drive Pipe |
| 20” | 1,010 ft | – | – | Details unknown – reported to surface |
| 13 3/8″, 68#/ft N80 Butt | 4,499 ft | 5,020 psi | 1,950 psi | Details unknown – reported to surface |
| 9 5/8″, 47 #/ft S95 Butt | 11,371 ft | 8,150 psi | 5,080 psi | Details unknown – reported to surface |
| 7″ 32#/ft P-110 LT&C | 14,200 ft | 11,640 psi | 10,760 psi | Details unknown – reported to surface |
In August, 2002 the Operator contacted Seal-Tite® International to evaluate and possibly repair the subject leak Seal-Tite® specializes in repairing leaks in various systems for the oil and gas industry. Recently they collaborated with Cementing Solutions Inc., a recognized industry expert in oilfield cement systems, to develop sealants and methodologies specifically for microannular problems.
Leak Analysis:
On site diagnostics conducted by Seal-Tite® technicians indicated a stabilized fluid feed-in rate of 100 ml/min, and the ability to pump into the microannulus at 2 liters/hour at 1200 psi, increasing to 17 liters/hour at 2500 psi. Analysis of the pressure diagnostics for all strings indicates that the pressure source for the subject annulus is most likely a reservoir close to the 13-3/8″ shoe, traveling up the annulus via a “microannulus channel”. The observed pressure is very similar to the pressure expected in a reservoir at that depth.
Work Summary:
In October, 2002 a Seal-Tite® technician was mobilized to the platform. The procedure involved bleeding the annulus to zero and then slowly atomizing a customized blend of sealant into the annulus. Injection continued over the space of six days, interspersed by bleed-off periods to begin sealant activation. A total of 30 gallons of sealant was successfully injected into the annular area, at a maximum injection pressure of 2500 psi. Nitrogen pressure was left on the annulus to allow the sealant to cure.
After 3 days the pressure was released and the casing vented for one hour. A 7 day chart was placed on the casing to monitor the pressure increase. Over the course of 27 days the casing pressure slowly built back up to 1300 psi. This corresponds to the initial buildup rate of 3 hours, for a reduction of 99.5%.
In November 2002 a technician was mobilized to perform a second sealant application. The annulus pressure was again bled to zero. Additional sealant was then injected into the annulus and allowed to cure. The pressure was bled off and monitored. After 43 days the casing pressure of 75-300 psi has been observed to fluctuate according to thermal effects, which is expected due to a fluid packed annulus. No sustained feed-in has been recorded.
Conclusion:
The procedures developed and implemented by Seal-Tite® International have effectively sealed the microannulus channel in the subject wellbore.
High Island Area, Gulf of Mexico
The subject well had experienced a Sustained Casing Pressure (SCP) problem for several years in the
10-3/4” x 7-5/8″ annulus. Diagnostics indicated that the pressure source was most likely a zone at the 10-3/4” casing shoe, traveling to the surface via a microannular channel. When bled to zero, the pressure would increase to 1300 psi within 45 minutes, for an equivalent calculated rate of 7.6 MCF/day.
Seal-Tite® International developed and injected approximately 15 gallons of customized sealant, filling the microannulus to an estimated depth of over 1200 ft. Once the sealant was allowed to cure, the annulus was bled off and the pressure response recorded. The initial feed in rate was calculated to be only 0.042 MCF/Day, a reduction of 99.4%. A second sealant treatment of 20 gallons was then applied and the casing again bled to zero.
After 69 days the annulus pressure had built up to 825 psi. This corresponds to a calculated inflow rate of 0.023 MCF/day, a 99.9% reduction in the original inflow rate.
Background:
The subject well was completed in July 1978 with a TD of 8,316′. The casing program consisted of 26″ drive pipe, 16″ surface, 10-3/4″ intermediate, and 7-5/8″ production. The casing string characteristics are listed below:
| Casing String | Shoe Depth | Burst | Collapse | Cement Info |
|---|---|---|---|---|
| 26” | 655 ft | – | – | Drive Pipe |
| 16″, 65#/ft H40 Butt | 1,022 ft | 1,640 psi | 670 psi | 850 sxs + 230 sxs grout |
| 10-3/4″, 45.5 #/ft K55 Butt | 4,500 ft | 3,580 psi | 2,090 psi | 2359 sxs |
| 7-5/8″ 26.4#/ft N80 LT&C | 8,316 ft | 6,020 psi | 3,400 psi | 2365 sxs, cement to surface |
The first significant casing pressure on the 10-3/4″ x 7-5/8″ annulus was reported in 1988, with a reported pressure of 1665 psi. Standard “bleed and build” diagnostics indicated that the pressure would bleed to zero within 2 hours with an effluent of only gas. Within 12 hours the pressure would build back up to 1400 psi, eventually building to 1665 psi or 47% of burst pressure. Standard diagnostics performed in subsequent years indicated a very similar pattern.
In April, 2002 the Operator contacted Seal-Tite® International to evaluate and possibly repair the subject leak Seal-Tite® specializes in repairing leaks in various systems for the oil and gas industry. Recently they collaborated with Cementing Solutions Inc., a recognized industry expert in oilfield cement systems, to develop sealants and methodologies specifically for microannular problems.
Leak Analysis:
Drilling records indicate that the 7-5/8″ casing string was cemented with full returns to the surface. This is supported by a rapid (5 minutes or less) pressure bleedoff of the 10-3/4″ x 7-5/8″ annulus observing only gas as the effluent. Analysis of the pressure diagnostics for all strings indicates that the pressure source for the 10-3/4″ x 7-5/8″ annulus is most likely a stray gas reservoir close to the 10-3/4″ shoe, traveling up the annulus via a “microannulus channel”. The observed pressure is very similar to the pressure expected in a reservoir at that depth.
It is unlikely that the pressure response is from a casing leak, as the adjacent casing annuli exhibit pressure substantially lower than is observed on the subject annulus. In addition pressure diagnostics indicated that bleeding or injecting into the adjacent annuli had no effect on the study annulus.
In October of 2000 an injection test was performed in which approximately 8 gallons of fluid were injected into the microannulus over a space of 24 hours. Previous testing has indicated a typical microannulus to have a thickness of 0.005″ to 0.10″. Therefore in terms of microannular volume this could be equivalent to a length of over 1000 ft.
These injection diagnostics were repeated in June of 2002 with similar results. With these results in hand, a procedure and work plan was developed.
Work Summary:
In July, 2002 a Seal-Tite® technician was mobilized to the platform. The procedure involved bleeding the annulus to zero and then slowly atomizing a customized blend of sealant into the annulus. Injection continued over the space of three days, interspersed by bleed-off periods to begin sealant activation. A total of 57 liters (15 gallons) of sealant were successfully injected into the annular area, at a maximum injection pressure of 2500 psi. Nitrogen pressure was left on the annulus to allow the sealant to cure.
After 2-1/2 days the pressure was released and the casing vented for one hour. A 7 day chart was placed on the casing to monitor the pressure increase. Over the course of 37 days the casing pressure slowly built back up to 1550 psi. This corresponds to a flowrate of 45 SCF/day. This is a significant decrease (99.5%) as compared to the original buildup of 1550 psi over 24 hours (a calculated flowrate of 7650 SCF/day).
In November 2002 a technician was mobilized to perform a second sealant application. The annulus pressure was again bled to zero through a 0.120 choke nipple and the data carefully recorded. Analysis of the data (See Table 3) indicated a total bleed of 1559 SCF, which corresponds to a buildup rate of 42 SCF/Day. This compares well with the earlier calculated value of 45 SCF/day.
Additional sealant was then injected into the annulus and allowed to cure. The pressure was bled off and monitored. After 69 days, the pressure had slowly built up to a total of 825 psi and appeared to be stabilizing. This buildup rate was significantly lower than the previous buildup rate of 1550 psi in 37 days. The calculated inflow based on this buildup is 160 SCF, for a corresponding gas inflow rate of 2.3 SCF/day. Relative to the initial inflow rate of 7648 SCF/day, this is a 99.9% reduction.
Conclusion:
The procedures developed and implemented by Seal-Tite® International have effectively sealed the microannulus channel in the subject wellbore.