Process and installation for drilling holes in the earth's crust under freezing conditions

摘要

Process for drilling a hole in the earth's crust in which the bottom of the drill hole is frozen in front of or near the drill bit by a cold driling liquid in which liquid particles that have been frozen to solid parts or have been solidified have been taken up whether or not by addition. In this way the bottom of the drill hole is always so hard -- also upon drilling in soft or plastic formations, such as clays, -- that use can be made of diamond drill bits or other drill bits normally used for hard formations, in order that the number of times a drill bit is to be replaced can be strongly reduced. The purpose of adding ice is to make it possible for a sufficient amount of frigories per unit of time to be introduced into the drill hole, so that at greater depths the temperatures at the drill bit are decreased to such a degree that here, too, use can be made of drill bits for hard formations here described. P PBy preference, the drilling liquid is a mud consisting of an eutectic salt water solution with plastering properties, to which ice of the same composition has been added.PPThe pressure in the drilling liquid in the bottom of the drill hole is somewhat lower than the pressure of the liquid in the drilled formation, so that during the drilling the drilling liquid cannot penetrate into the layer, but a slight influx of water from permeable rocks can take place, as a result of which all drilled layers, both permeable and non-permeable ones, will be frozen. The lower pressure on the bottom of the drill hole is achieved by injecting a gas, in the cirulating drilling liquid to reduce its (mass) density. Regulation of the pressure in question may take place with the aid of a throttling element which controls the over-pressure required at the top of the annular circuit between the drilling string and the drill hole wall.PPThe invention further relates to an installation for realizing the process according to the invention. This installation is mainly characterized by means included in the drilling liquid system at the ground level to cool drilling liquid and change it partly to ice, by means to add a gas to the drilling liquid, and by means to control the over-pressure at the top of the annular circuit between the drilling string and the drill hole wall.PPThe process according to the invention may be applied in any production process for recovering energy, such as production of oil or natural gas, thermal energy and thermal energy from coal formations and oil shales or oil sands.