Is there a standard application of well completion in geothermal drilling in terms of cleaning the drilling mud and stimulation?. In which order, stimulation process should be taken in action, first acidizing or nitrogen or others?
As far as I know edited standard ( eg. DIN,E if published in english!
N,...) there are nothing official! EPA as made some"rules" but no more than that. In geothermal BOP , Mud control, WOB, Cementing, Perfs, Packers, Non-corrosive casing, and safety procedures very high! Iceland has tremendous experience, but I don't know
The high temperatures of geothermal wells means that the drilling fluids have to have a high degree of temperature stability. The flip side of this means that they are often difficult to remove using normal cleanup methods. Water based systems are stable above 400F with sulphonated polymer viscosifiers but they are very hard to break down either chemically or with enzymes. Oil based systems offer similar issues. Since the wells are used for either water injection and production of heated water the clean ups are somewhat different. In the production well the filter-cake left by the fluid can be lifted off with the production and by designing the fluid to be noninvasive and non damaging to the formation you can minimise the impact on production. With the injection wells it is harder. One method is to bypass the damaged zone by casing and perforating.
Once the production hole TD is reached, slotted liners are set (either hung or landed at bottom, frequently the latter). There is essentially a large open-hole section. Often, water (jetted) is used to clean the inside of the slotted liners hopefully to reduce whatever mud (WBM or aerated fluids drilling) is left in the production hole annulus. Thence, cold water injectivity, PTS, and other tests are conducted (lasting typically for 36 hours). The rig is then released. In this heat-up period, a series of PT surveys at regular day intervals are made (e.g., 1 day shut (DS), 3DS, 5DS, 9DS, etc.). The well is then left to thermally recover until it is ready to discharge (~3 months) either naturally or by the proper stimulation technique; sometimes, the well is also stimulated way ahead of thermal recovery using the appropriate stimulation (heating) technique. Acidizing (for skin-damaged wells) is used as a last resort.
What are the effects of lubricants and polymers on non-artesian wells. Is there any tricky solution about drilling mud to remove it after the directional drilling in non-artesian well in order to prevent stucks of the feed zones? Because of the high temperature, lubricants and polymers become gelling, especialy at the feed zones which are filled by mud during drilling to prevent loss and kick.
You will design your lubricants and mud to accommodate high temperatures in order for these to work while drilling. Taking these out after drilling becomes the tricky part. If you have competent formation in-between permeable fractures/faults, it may be possible to jet using water. Porous sections are a different thing altogether. You may later resort to scraping these sections. You may also opt to use aerated fluids or just plain water while drilling provided you have evaluated the risks thoroughly.
SD Scientific Drilling Journal 4 years ago published some proposal of rules!
At this moment I am not able to search for it!
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