The essence of most drilling operations in our industry is to open the maximum length of reservoir formation with the minimum damage to the rock surface. This should allow maximum efficient flow of the desired reservoir fluids into the wellbore and to the surface. The proper completion of a well will ensure that production is not denied or restricted, and enough care is taken to ensure that all the investment made in drilling the well is safeguarded. The term “completion” covers a gamut of activities related to stopping the movement of wellbore material into the well, the running of tubing and attachments needed to flow the reservoir fluids to the
surface safely, the installation of subsurface equipment to increase production, and to provide well protection. One short article will not be adequate to do justice to this very important element of providing energy for the world.
My first experience with well completions was in the Niger delta where the producing formation is friable sandstone, which is prone to dislodgement when production commences. We used a mixture of sand consolidation chemicals to “glue” the sand matrix through perforations in the production casing. The process required preparation of chemicals at the surface properly tailored to the prevailing temperature and pumped into the selected part of the pay zone. The placement had to be very accurate, as any unconsolidated part of the open reservoir could play havoc with production and surface equipment after the well was brought into production. These wells were relatively simple, as they were vertical and shallow.
Since the first wells were brought into production, a number of completion innovations have been introduced that have permitted the safe and profitable production of oil and gas. Some of them are now routinely used and their process of evolution is now buried in history. Today’s wells are in general much deeper and more complex and therefore have benefitted from innovation to ensure maximum inflow per length of reservoir. Operators carefully choose the form of completion that best suits the formation—including gravel packs, open hole, and multizone, to name a few.
If a reservoir has been cased off, it is necessary to make holes through pipe to allow fluid flow. The early use of guns to make perforations was enhanced by borrowing techniques from the munitions industry. Early perforations were made using small guns lowered into the well and set off from the surface, releasing small bullets that penetrated the casing and cement. The need to have deeper penetration led to research and development of more advanced shaped charges. We looked toward the battlefield tanks for how to design better penetrating guns, bearing in mind the very demanding bottomhole conditions of high pressure and high temperature. These guns need to be precise and leave their carriers undamaged. But oilfield perforators had even more stringent constraints. They had to be able to focus their penetrating jets on the target, in this case, multiple casing/cement sheaths and hard rock formations, with precise orientation and without collateral damage to the perforating gun carrier. And they had to operate under environmental conditions not found on even the harshest battlefield—temperatures of more than 400°F and 25,000 psi.
Shell UK Exploration and Production enlisted the help of QinetiQ, a leading defense technology and security company, and Jet Research Center (JRC), Halliburton’s perforating design and manufacturing subsidiary, to help improve the perforations in its Penguin field in the UK North Sea. The partnership of QinetiQ and JRC brought the best of the defense technology together with oilfield experience to give Shell the slim, ultrahigh-performance jet perforator it wanted to complete the difficult Penguin wells with maximum penetration (Ghiselin 2005).
Sand-Exclusion Completion
Sand-exclusion completions are used in an area that contains a large amount of loose sand. These completions are not only designed to allow for the flow of natural gas and oil into the well, but also to prevent sand from entering the well at the same time. Sand inside the well hole can cause many complications, including erosion of casing and other equipment. The most common method of keeping sand out of the well hole are screening or filtering systems. This includes analyzing the sand encountered in the reservoir and installing a screen or filter to keep sand particles out. This filtering may be done by hanging a type of screen inside the casing or by adding a layer of specially sized gravel outside the casing. Both types of sand barriers can be used in openhole and perforated completions.
A good example of sand control innovation that comes from outside the industry is a new patented system of protecting well completion components from sand erosion by Maersk Oil. Sand erosion has been a problem for the oil industry for decades. The major challenge is proppant flowback that leads to numerous downhole and production problems. Maersk Oil partnered with ESK Ceramics, a ceramics company that supplies material to a variety of industries including cosmetics, automobiles, and ballistics vehicle armor, to help solve this problem. The collaboration produced a ceramic screen, called PetroCeram, which is harder than metallic materials, and shows no indications of abrasion under reservoir conditions (KogsBoll and Wagner 2011).
There are too many innovative technologies in this discipline to discuss in just one column. I will continue the discussion on completions in my next column with intelligent completions. Until then, I suggest you get the latest technical content on completions and many other topics from SPE events on www.speondemand.com and view the new online knowledge sharing site www.petrowiki.org.
References
- Ghiselin, Dick. 2005. New Jet Perforator Dominates. http://www.epmag.com/
- KogsBoll, Hans-Henrik, and Wagner, Sabine. 2011. Ceramic Screens Control Proppant Flowback in Fracture-Stimulated Offshore Wells. http://www.worldoil.com/August-2011-Ceramic-screens-control-proppant-flowback-in-fracture-stimulated-offshore-wells.html
