Float Equipment for 10k psi Pressure Tests
11 May 2010
In the Western Canadian Horn River Basin Shale Gas play we are having problems with leaking shoe tracks on our production casing when we test the casing to 10,000 psi.
The casing string is a tapered string of 5 1/2", P110, 20 ppf and 5 1/2", T95, 23 ppf casing with JFE bear premium connections. We have ran both 3 joint and 5 joint shoe tracks. FTD is 4700m (15,400 ft) and TVD is 2450m (8000 ft) with roughly 1800m (5900 ft) horizontal length. The bottom hole temperature is 140 deg C (285 deg F).
We used a Weatherford latch down top plug capable to 10k psi pressure tests, and we are bumping at calculated volume so we should have cement in the shoe track. After the initial bump, we increase the pressure to 35 MPA (5,000 psi) with no problems. Unfortunately, we cannot go higher with the drilling rig ... but this test confirms the plug has landed (and hopefully latched).
After the drilling rig moves off, we pressure test the casing to 10,000 psi to prove integrity for the upcoming frac jobs (3 weeks after cement job). Unfortunately, roughly 50% of the wells on our last pad have leaked at the shoe track. Both the cement and the plug seem to be failing.
Does anyone have recommendations for a top cement plug capable of 10,000 psi pressure tests in a high temperature environment? Any recommendations on shoe track length in this size and length of hole (is 3 or 5 jts sufficient or should we run more)? Any other idea's on how to get a competent shoe?
Horn River Basin - Shale Gas
801 - 7th AVE SW
Calgary, AB, Canada T2P 3P7
Also, please check the differential pressure rating of your float equipments, many float equipments are not rated to high pressures.
Senior Drilling Engr
Navi Mumbai, India
Base on your info, how do you know that leak is at float shoe?
Your casing type is 5-1/2" P110 20 ppf and T95 23 ppf with near same burst pressure 12,600 psi.
When you pressure up the casing to 10,000 psi (assume water inside 8.33 ppg at 8000 ft TVD) --> total pressure at bottom would be 10,000 psi at surface plus 3465psi Hyd pressure = 13,465 psi. (cement already dry)
My opinion is that the possible leak is not only at float but could also be in the casing, because you applied a pressure higher than the casing burst design (cement already hard, this still not include safety factor.
- when you test the casing, the cement should be still in a fluid state, so there is differential pressure. You can test using cementing unit; as far as I know spec of many cement units can press up to 12,000 psi
We have had a similar problem at EON Ruhrgas on one of our offshore wells in the UK SNS.
Leak-off was observed during pressure testing of the 4-1/2in JFE bear clear run, C95, 15.1# production liner to 10K.
At the time of the leak-off we were not able to fully investigate the leak to confirm where it was. What we concluded was that the shoe track was likely, however upon re-entry into the well, we reached a HUD ca. 200ft above the shoe track indicating that a connection had failed.
Our solution was to place a bridge plug above the HUD and move forward with the Pressure test and Frac.
From our analysis of regional shoe track failures, there was no clear conclusion on cause. We also looked extensively at cement formulations and placement, again and unfortunately with no real conclusions.
Although we were confident with the bridge plug solution, to reduce the risk of a 2nd failure at the 10K pressure we were able to reduce our test requirements on the well through some thorough risk analysis of each stage of the fracture treatment.
A reduced pressure test criteria, along with the availability of contingent bridge plugs to isolate the shoe proved ultimately successful.