Basrah – On the face of it and just listening to Iraqi oil officials describing their new ventures in Rumaila, it would appear as if BP is revolutionizing the way oil is produced in Iraq’s biggest and oldest fields. In reality, much of the work underway aims at reversing the trend of continuous malpractice imposed by years of war and sanctions. This covers all aspects of the production process from the use of submersible pumps and the handling of the resulting water cut; to horizontal drilling; to the use of 3-D seismic and modern well-logging to improve oil recovery rates.
To start with, electric submersible pumps were only used in Upper Shale at depth of 3100 meters where reservoir pressure was very low. “We had no reason to use submersible pumps in Main Pay or in Mishrif since the pressure was good in those reservoirs and the wells were producing,” a veteran SOC official and currently on the Rumaila Operating Division told me during a recent visit to Rumaila.
Iraqi reservoir specialists recognized a long time ago that the use of submersible pumps in high pressure reservoirs would increase production and push the recovery factor further but would result in a high water cut which they did not have the means to handle, nor did they have the necessary investment at hand to treat wet crude. “We used to stop producing the wells once the water cut becomes high, but now for the first time this is not an obstacle,” the official said. Wet crude production facilities were introduced in North and South Rumaila in the late seventies to cater for the expansion scheme at the time, but their capacities could only cater for about 25% of the produced oil. As wet crude production increased as a result of the advance of the water aquifer as well as water injection, the constraints became too many to handle.
Needless to say, a plateau of 2.85 million barrels per day now targeted by BP from the two Rumaila fields was never the goal in the past. Now BP with partner CNPC are pushing ahead with high rate, well-positioned wells in order to provide high production rates, admittedly with high water cut, in order to generate early cash flow. At this rate, the 10% incremental output committed in the service contract signed last year will be reached way ahead of time.
Iraq has been lagging behind its neighbors, let alone the rest of the world, in the introduction of horizontal drilling across the board. The first horizontal well in southern Iraq will be drilled in the Mishrif reservoir in North Rumaila later this year.
With the help of 3-D seismic which will be carried out over those 3 years, itself also a novelty in Iraqi oil fields and a major leap forward, it will be possible to determine for the first time how much trapped oil has been left behind over the past decades. In the absence of 3-D seismic, Iraqi engineers say they had to recur to trial and error in past years.
Such a practice was emphasized by the lack of modern logging techniques. Not a single international logging service company was working in Iraq during the long sanction years between 1990 and 2003, so SOC had to rely on the outdated practices of the Arab Well Logging Co and old – and now obsolete – logging trucks which lacked tools and spare parts. Iraqi engineers had to do with whatever was available to keep producing and even try to push output higher.
The southern dome of Rumaila is a gentle anticline with clean highly permeable sandstone in the Main reservoir. So 3-D seismic was not required to start with, but more importantly it was not available due to wars and sanctions, according to one veteran Iraqi reservoir engineer. “The long production history and the decreasing quality in the reservoir of the northern dome as well as the injection of water inside the oil pool makes 3-D a requirement and 4-D surveys would be advantageous in the coming years to monitor the advance of water front in the southern dome in particular,” he explained.
Well perforation is another area that is being revolutionized in Rumaila. Traditionally, the uni-dimensional zero-phase perforation has been in use for long years and has been sufficient in South Rumaila to produce the wells at a rate exceeding 50,000 b/d. Four-inch guns with four-phase orientation were only used in water injection wells, says the veteran reservoir engineer.
Now for the first time, the multi-dimensional two-phase and four-phase perforation technique is being used allowing for the perforation of wells in several directions at the same time using bullets with a larger diameter to improve and reverse the decline rate in well productivity. Improving the efficiency of perforation is one of the necessary measures to improve recovery rates as well as increase production. Bypassed smaller pockets will now be tapped to recover the last drop of oil. As a result, the three months period it used to take SOC to perforate 20 wells is now cut down to just 15 days.
Some of the techniques used in Rumaila date back to the 1970’s and have not been updated since. For example, based on studies conducted more than 30 years ago, SOC has been injecting water in the Mishrif limestone with particles of less than four microns. At the time, extensive lab experiments showed that using larger size particles in the injection water would clog the tighter reservoir rocks and reduce injectivity. However, studies conducted in similar reservoirs in neighboring countries and successive testing led to the introduction of 10 micron water without the risk of reduced injectivity. Now Iraq is trying to catch up.
“We didn’t conduct any new studies since the 1970’s and we are still using injection water with less than 4 microns. Now, we will do the jump and start using 10 microns water which is easier, cheaper and faster to process” said the Rumaila engineer.
The result of all these remedial steps will impact the ultimate recovery rates at the Rumaila fields. The next three years will show to what extent.