Did you know that drillers, reservoir engineers and production engineers face a lot of problems in the process of extracting crude oil to be ready for use in our day-to-day activities? This article seeks to discuss a few.
Sand Production Problem
The forces that hold the particles of reservoir rock together may be weak, thereby causing movement of fines. Sand production can be a very serious problem when it occurs in an oil and gas well. Some reservoirs naturally produce sand whilst others will only do so if certain conditions exist. This can result in the following problems; casing collapse, plugging and erosion of downhole and surface equipment, sand disposal problems, formation damage, loss of production etc.
1 - 10Ibs/1000bbls or 1MMScf may be produced in a well but in heavy oil, amounts could be very large. How much sand is tolerable depends on the well location - offshore/onshore, fluid type (oil/gas), well type (subsea/ platform/ onshore) facilities for separation handling/ disposal.
Sand production can be predicted using cores and log analysis, laboratory and theoretical modeling as well as field observation. Sand can be controlled by mechanical method (sieves or gravel packing), chemical method (epoxy or resins), and natural method (optimum production rate). Furthermore, there are various ways of controlling sand production. Sand control type thus depends on the following factors as; sand production, effect on oil deliverability, well integrity and surface facilities. When these methods failed, there is need for sand cleaning by fluid circulation through coiled tubing.
Corrosion is caused by increased quantity of water being in contact surface facilities in the presence of air. Corrosion attacks casing, flowlines, tanks, etc. The worst type of corrosion is caused by entry of oxygen into the producing system, usually during maintenance and workovers. The method adopted to control or mitigate corrosion include: the use of inhibitors, use of protective coatings, selection of appropriate materials, cathodic protection technique and adequate corrosion monitoring and inspection.
Sour Crude Production
There are basically two types of crude oil which are sweet and sour crude. A crude oil is said to be sour if it contains excess amount of hydrogen sulfide (H2S). Production of sour crude is a well problem in that it create severe health problems as well as corrosion and failure of equipment, couplings and tools. The effect of these crude can be reduced using improved steel alloys for surface and sub-surface equipment.
A large number of mechanical failures of different types can cause loss of production as well as increasing costs in well operations. Some of the more common failures include: primary cement failure, casing, tubing and packer leaks, failure of artificial lift equipment and wellbore communication in multiple completions. Casing cement formation bond failures are frequently caused by applying fracture pressure on well during a matrix acid job. To differentiate between casing leaks and normal water encroachment, water analysis is done. Also, temperature surveys and other production logs are very helpful in locating casing leaks. With packer and packer-bridge plug combinations, the precise location of the leaks can be made or obtained.
Liquid Loading of Gas Wells
When gases are produced, they carry liquid water and/or condensate in mist form. As the gas flow velocity drops due to depletion of reservoir pressure, the carrying of the liquid by the gas also decreases. With continuous drop of gas velocity to a critical level, this will lead to liquid accumulation in the wellbore. This accumulation will increase the bottom hole pressure resulting in reduction of gas production rate and can eventually lead to production ceasing.
Diagnosing liquid loading is usually difficult but the symptoms to look for include: onset of liquid slugs at the surface of the well, increasing differential pressure between the tubing and casing with time, sharp drop in production decline curve. However, measures can be taken to mitigate liquid-loading problem include foaming the liquid water, using smaller tubing or creating a lower wellhead pressure, gas lift methods or pumping the liquid out of the well, heating the wellbore to prevent condensation and downhole injection of water into an underlying disposal zone is another option.