This paper proposes specific solutions to the technical difficulties encountered in core drilling construction technology!

The core drilling technical problems frequently encountered in construction include the following:

1. In core drilling production, when diamond bits encounter slippery formations, their penetration rate and rig efficiency decrease markedly, greatly affecting production progress, while the drilling cost per meter also rises correspondingly. Through practice, the engineering and technical personnel of our team, together with the rig crews, have worked out an effective method for dealing with slippery formations, namely the method of feeding sand with brief water cutoff and dry grinding under pressure.

This raises the penetration rate from the original fraction of a meter to 1.5-2 m, and because the reasonable shaping of the bit matrix hardness is strengthened (generally HRC=40-45), the average bit life reaches 30-35 m.

This method is especially suitable for wireline coring drilling; without pulling the drill string, the diamonds in the bit matrix can be exposed, and at the same time the shortcoming of excessively short bit life caused by treating the diamond matrix with strength is avoided.

The specific construction method is as follows:

(1) On site, select hard crushed stone of 3-5 mm (quartz or dense granite fragments, conveniently available on site).

(2) After fishing the inner tube, each time feed 0.3-0.5 kg of crushed rock particles into the drill pipe.

(3) After making up the upper main rod, turn on the large pump and pump the crushed particles to the bottom of the hole.

(4) After running the inner tube, make up the upper main rod again and clamp it tight with the chuck. Without turning on the pump, cut off the water for a short time (2-4 min) and apply pressure with the oil cylinder for dry grinding; during dry grinding, the drill string must be moved back and forth with the oil cylinder, applying pressure while dry grinding, to force the diamonds in the bit matrix to become exposed.

2. "Demulsification" of flushing fluid is also a problem commonly encountered in solid core drilling.

Once the emulsified flushing fluid "demulsifies", in mild cases the rotational resistance of the drilling tools in the hole increases, making drilling impossible, and in severe cases it causes bit burning accidents in the hole. At present, although there are many methods for solving the "demulsification" of emulsion, such as using surfactants without base oil and using composite calcium- and magnesium-resistant lubricants, these methods can achieve certain results but are not entirely satisfactory. For example, surfactants without base oil have poor lubricating effect, and composite calcium- and magnesium-resistant lubricants are difficult to purchase and costly.

By adding laundry detergent to the emulsified flushing fluid, a new type of demulsification-resistant flushing fluid is prepared, which is economical, convenient, and effective. The active substances in the emulsion that provide lubrication—fatty acids, sodium fatty acid esters, sodium naphthenate, etc.—readily adsorb onto rock and ore powders containing divalent metals. For example, calcite, fluorite, apatite, marble, dolomite, hematite, malachite, manganese ore, and cerussite have strong adsorption capacity; when the active substances in the emulsion meet these minerals, strong adsorption occurs, finally forming a mixture of rock powder, emulsifier, and base oil, and the emulsified flushing fluid "demulsifies".

The formations encountered during construction at a certain rig were mainly granite, limestone, and marble, and in one borehole the marble section was 100-250 m long. During two years of construction, severe demulsification in the hole often occurred because saponified oil lubricant was used in the marble section, even requiring diesel oil to wash the hole. Later, the preventive measure of adding laundry detergent to the emulsified flushing fluid was adopted; although the marble section of each hole was more than 200 m long, demulsification never occurred, and the marble section was passed smoothly.

The main function of this measure is to inhibit the formation of oil scale on the surface of the drill pipe and the hole wall during drilling, and it also does not destroy the interfacial lubricating film formed by the emulsified flushing fluid between the drill pipe and the rock. The preparation of emulsified flushing fluid with laundry detergent is extremely simple: add 3-5 kg/m3 of saponified oil to the water, and add 1-1.5 kg of laundry detergent (per shift or every other shift). 

There are two ways to prepare it:

(1) Use a small iron bucket to fully and evenly stir a certain amount of saponified oil and laundry detergent, then pour it into the water supply tank;

(2) Directly pour the measured saponified oil and laundry detergent into the water tank and stir. In the absence of composite calcium- and magnesium-resistant lubricants, adopting this method to pass through the demulsification hole section is both economical and practical.