By: Cascade

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In July, , we hosted our first webinar in a series covering drilling fundamentals, the various technologies and their applications. There were plenty of great questions posed in this first webinar in our drilling series, so if you missed it, we thought we&#;d take the opportunity to answer a few of the most salient ones.

WHAT IS THE BEST DRILLING METHOD FOR CLAY?

There isn&#;t a single best method. The various methods each have strengths and weaknesses as they run into clay. For example, air rotary struggles as the clay balls up and becomes hard to lift up. Also, when clays get wet they can swell, so you really have to be careful if you&#;re drilling with fluid or mud rotary. The depths to which you are drilling also changes equation. Take for example the, the corcoran clay in Central CA, that at 700-800 ft can cause problems. While you cannot hollow stem auger to that depth, if you are only putting in a 75 foot well, auger is really good at getting through the clay.. Air methods definitely have challenges as well. It is difficult for sonic because clay attenuates a lot of energy, much like hitting rock with a hammer as opposed to a pile of playdough.  

WHAT IS THE BEST METHOD FOR SOIL SAMPLING AT 36 FEET IN CLAY IN THE PAN HANDLE?

Hollow stem auger or direct push.

IS SONIC VIABLE FOR DRILLING LONG LENGTHS OF BEDROCK?

Yes, but it depends on what is meant by &#;long.&#; Hundreds of feet is going to be hard on the tooling: you will go through a lot of core barrels, wear out tools and put stress and strain on the rig. It is capable of doing it, but it also depends on the competence of the rock. Sonic works great in siltstone, clay stone or weathered rock. Pure granite is going to be different and so definitely depends on how long you are talking about. At 20 &#; 30 feet, the headache of switching over doesn&#;t offset the difficulty of penetration, but it is worth considering other methods if you&#;re dealing with hundreds of feet.

IS SONIC THE BEST METHOD FOR ACHIEVING AN UNDISTURBED SAMPLE? WITH A SHELBY TUBE FOR GEOTECH, DO THE VIBRATIONS AND ROTATION DISTURB THE SAMPLE?

You can&#;t measure something without changing it, and there is no drilling method that doesn&#;t disturb a sample. However, from the geotechnical perspective, Shelby tubes pushed with auger or rotary wash are pretty undisturbed. The sonic method of penetration liquefies the particles in the immediate vicinity of the bit interface so it&#;s disturbing the soil as it is going down. If you stop and push a Shelby tube once you get away from that bit interface, you should have an undisturbed sample at some point, but it is hard to know exactly how far the extent of the disturbance goes. The amount of disturbance is generally on the scale of inches or fractions of an inch. If you need to get through a shallow material that&#;s impenetrable to auger or rotary wash methods, Sonic at least gets you to where you need to be in order to push a sample. Afterall, it&#;s better to have some data than no data.

IN REGARDS TO ROTO SONIC, WHEN YOU OVERRIDE CASING, WHERE DO THE CUTTINGS GO?  AND HOW MUCH WATER IS REQUIRED?

When you override the casing, like a 4 inch diameter to a 6 inch outside casing, that couple inches of material between the two has to go somewhere. The short answer is that is get displaced into borehole wall. If you are circulating water when running the outside casing, commonly known as washing over the casing, it can cause cuttings to return back out of the hole. Drillers typically have a pan at the surface to catch the returns coming back up.  So, not all cuttings are getting shoved into the formation. As for how much water to use  - that varies a lot on geology and driller experience.

IN MUD ROTARY, HOW IS THE CORE SAMPLE COLLECTED?  

Generally you do not use mud rotary for core sampling. You can take a split spoon sample by tripping out the tri cone bit and drill pipe, running in a split spoon barre and then driving a discrete soil sample. If you need to collect a core, there is a coring system called 94 mm wireline using wireline coring for unconsolidated material. You run the wireline in the mud hole with the drilling fluid to advance the core system. If you want a continuous core with mud rotary, wireline coring would be the best recommendation.

For more Casing Drilling Systeminformation, please contact us. We will provide professional answers.

WITH THE SONIC METHOD, WHEN WASHING OVER THE CASING, THE WATER ENTERS BETWEEN THE 4 IN CORE BARREL AND THE 6 INCH CASING AND RETURNS OUT OF THE HOLE OF OUTSIDE 6 IN CASING. FOR ENVIRONMENTAL DRILLING, PLEASE EXPAND ON THE USE OF ADDITIONAL LARGER DIAMETER CASING TO SEAL THE HOLE.

During the webinar we mentioned that the flush threaded casing is able to isolate different aquifers from one another. The best way is by telescoping a smaller diameter casing into the larger casing. For example, say aquifer A is shallow and aquifer B is deep, and you want to make sure those aren&#;t talking to each other during the drilling process. You would drill down to the barrier that separates the two aquifers, set an 8 in diameter casing, then continue to aquifer B with 4in x 6in override, thus telescoping the smaller into the larger.

WHAT TYPES OF DRILLING ARE MOST EFFECTIVE UNDER ARTESIAN CONDITIONS AND FINE SANDS?

Mud rotary is always good because you are able to use the hydrostatic pressure of the mud. You might, however, have to run a different kind of fluid program (usually denser mud maybe with polymers). Sonic is also a good option due to the flush threaded casing. That allows you to hold the head pressure on the formation as you drill. With hollow stem auger, the augers are bolted together and have open joints so they can&#;t hold the head pressure as well. With sonic, once you get past whatever the zone is that has the heave, you are able to cast it off, and then physically isolate it with steel so that it&#;s not continually giving you problems.  

OTHER THAN FLUID DENSITY, WHAT CONSIDERATIONS GO INTO FLUID SELECTION?

There are four parameters to track during mud rotary drilling: density, viscosity, filter cake, and sand content. The filter cake gets measured in two different ways: (1) thickness that is created on the borehole wall, and (2) relative impermeability of the filter cake. This is determined by a Filtrate Loss Test where you take a sample of mud and put it under pressure on filter paper. The amount of water able to get through in terms of volume and again and the thickness of filter cake, tells you what you need to know. Keep an eye out for a Drilling Fluid Fundamentals webinar, because that&#;s an hour long discussion in and of itself.

What Questions To Ask Before Buying A Drilling Rig?

It may be for an established business that might want to upgrade its fleet with new technology or might be a newcomer who wants to open a business and wants to purchase a rig for the first time. Any of the above instances require different rigs, which have a different selection process including particular requirements, horsepower required, which technology is needed etc. We at PRD Rigs are here to solve your problem.

Buyers always get confused between purchasing a new or a used rig. Buyer has a perception that by purchasing a used rig will save them money. Purchasing a new drilling rig just makes the deal as it can fulfil all the requirements needed and all the parts are in new condition, but when looking for a used rig, Owner may have used the rig aggressively which may not be seen in the advertising. A used rig will cost the same as a new rig as it requires some additional work after purchasing. Also, an overlooked factor in buying a used rig why is the owner selling it? This may affect the price. It may be that he is retiring or that he has changed his business or has completed his work with that particular project. The fact is that it&#;ll cost the same either by purchasing a used one or by purchasing a new one.

Other questions to be asked before buying a drilling rig are:

What is the purpose of the drilling?

Before purchasing a drilling rig, you should be very specific with the proposed for the drilling. For example, water well drilling requires different system and soil sampling different.

Where do you want to drill?

This plays a vital role in selecting the power of your rig. There&#;s a lot of difference between drilling on a plain surface and drilling in mountains. Drilling in the mountains requires more horsepower which increases fuel consumption.
We at PRD Rigs have all types of rigs that will just make your deal.

What is maintenance costing?

Before buying a rig you should also see the maintenance cost that depends on the model you select. Also, see the operating cost depending upon the power of the rig and fuel consumption.
At PRD Rigs you&#;ll get low maintenance rigs.

What is your target budget?

Size, capabilities and shipping considerations all need to be taken into account when thinking about how much your business is able to commit and here at PRD Rigs we help you in giving the best products at the best prices.

The company is the world’s best Drilling Accessories Suppliers supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.