Salym Petroleum Development (SPD), a 50/50 joint venture of Shell and Gazprom Neft companies, collaborates closely with Shell Global Solutions (SGS) on the realization of new technologies in the Salym group of oil fields. SPD is renowned in the West Siberian oil and gas industry to be a leading incubator of innovative technologies. Beside a large scale “Game Changer” project in the area of Enhanced Oil Recovery, SPD is working on a number of smaller initiatives that strive to reduce the cost basis and to improve efficiencies in the domain of conventional operations: one of these projects is the trialing of Self Healing Pipe Dope (SHPD) technology in water injector wells.
The SHPD technology was developed by SGS in Rijswijk (Netherlands) and is currently implemented and tested for durability in the Salym oil fields. The basic idea of SHPD is to use a special swelling elastomer (instead of the standard thread greasing compound) in low grade API “type” tubing as an alternative to expensive premium tubing connections.
At present, 280 water injector wells are working at Salym oilfields; 20+ new water injectors are added to the well stock every year. These injector wells are operated at working pressures of approx. 170 bar that under normal circumstances calls for the use of premium tubing connections.
Premium connections (unlike API type threaded connections) provide excellent sealing characteristics under high working pressures, however, these tubulars come at a considerable higher cost. Special “make-up” services are required during the installation and employing 3rd party contractor services for tubing running-inhole operations incurs additional costs and add to the logistics and running-in-hole time; and, experienced hoist crews are a critical success factor under these circumstances.
SHPD is a 3-component compound that can provide good sealing characteristics when used in low grade API threads, and, within limits, even when applied to damaged threads. The main idea is to prevent and stop leakage in tubing connections by activating the self-expanding and self-sealing mechanism of the compound in the presence of foreign water.
Research was done in Rijswijk several years ago on subject swellable elastomers that could be applied as a liquid and that could open a whole range of new applications. One of the applications identified was to use the elastomer as the thread compound for increasing the sealing properties of oilfield tubular connections. The main challenge was to select the right ingredients and to define the correct mixture in order to create a thin and swellable layer according to given parameters. The materials should be readily available, non-toxic, and, easy-to-apply under oilfield conditions. Also, materials should provide sufficient and sustainable sealing capabilities under ambient borehole conditions. After several tests the correct composition of the components was found.
Like for regular swellable elastomers the principle of the swelling mechanism is based on the principles of osmosis. A special component is blended into the elastomer’s matrix that absorbs water in order to establish an osmotic balance. This process causes the elastomers matrix to expand in volume, i.e. what we commonly refer to as swelling. When a tubing connection leaks, water passes by the SHPD that is trapped between the thread rounds and causes it to swell and to seal off the leak path.
Lab tests have proven that SHPD has the capacity to seal a wide range of connection types and even damaged and expanded connections seal within a short period. The picture above shows standard 9-5/8” size oilfield pipe that is completed with a standard API Buttress type connection and treated with SHPD. The connection was found leaking after the initial make-up under ambient pressure conditions.
After applying internal pressure in several steps the sealing capacity of the connection improved because of the swelling of the SHPD between the thread rounds and the leakage stopped. Eventually, the pipe body failed while the threaded connection was firmly resisting the differential pressures. All components of the SHPD compound can be acquired easily and often locally or delivered to any location. The cost of the chemical components is relatively low and when adding up all the cost items to prepare the pipe the total cost for API type tubing treated with SHPD is typically around 35% less than the cost of tubing completed with premium connections.
In field applications the tubing is pre-prepared in a machine shop before they can be used in wells. It is necessary that SHPD is applied to all couplings (that form the box end) and then the connection is pressure tested to 100 bar 24 hours after they have been madeup.
Usually, all connections pass the pressure test; however, if some of the connections still leak it is only necessary to wait for some more time until the dope expands and the leak path closes. Laboratory tests showed that threaded tubing connections can be made leak proof to differential pressures of up to 700 bar when applying SHPD. Currently, the use of SHPD is limited to 90°C and new tests are underway that could make the application suitable in High-Temperature wells. When all preparation works are completed the tubulars are preserved and sent to the storage area. The storage location has to be kept dry and SHPD treated pipe should not be stored for more than 1 year.
For running-in-hole operations the pre-prepared tubing joints are trucked to well location and final preparations are made for the installation, i.e. SHPD is applied to the tubing pin ends. The technology of preparing dope and applying onto tubing joints is simple and it takes only 10 minutes to educate the hoist team to apply the correct procedures. The time for running in-hole pipe completed with SHPD is comparable to the time required for standard operations when using untreated tubing. When all tubing are run-in-hole the string is pressure tested after a 24 hours waiting period.
The results of the SHPD trials in SPD are quite encouraging: to date, 13 water injectors in SPD were completed with 3-1/2” NUE + SHPD and the total number of installations will increase to 18 by the end of the year. On average, the wells were in operation for 5 months and the longest for more than 1 year. Until now, all wells have proven tubing integrity with no abnormal pressures in the annulus, except for one well that was eventually repaired and the root cause of abnormal annulus pressure however was never In field applications the tubing is pre-prepared in a machine shop before they can be used in wells. It is concluded. Bottom line is that statistical data collected to date suggest that SHPD is very much competitive with premium tubing connections.
The database of applications is still increasing and the confidence in the innovative SHPD technology is growing. The use of SHPD is likely to become a standard operating practice in SPD. Company’s specialists consider substituting tubing expensive premium connections with this technology in all future water injector wells. SHPD will significantly reduce the initial completion and well repair costs in SPD.Back to